We may define sterilization as any process that is carried out for eliminating or killing microorganisms, such as spore forms, viruses, bacteria, fungi, excluding prions from the food, equipment, surface, biological or medication culture medium. Sterilization is widely used in the surgical and medical fields. As surgical gloves have direct contact with sterile body tissue and blood stream, sterilization is necessary. Medical and implantable devices also employ sterilization. How the medication or surgical instruments are used in tissues, bone, blood, or skin decides the necessity of sterilization. Parenteral drugs demand high SAL (Sterility Assurance Level). The material being sterilized and sterilization’s purpose directs the method of sterilization that will be used. In order to prevent any mishap, different devices and materials are used, which in turn alters the method of sterilization too. pressured vapor sterilization and dry heat sterilization are the two major methods of sterilization.
Nevertheless, we have seen the advent of alternative surgical methods since 1950s as the technology in medical field has developed. Alternative sterilization methods, such as e-beam sterilization, gamma radiation sterilization, peracetic acid sterilization, gas plasma (H2O2) sterilization, formaldehyde sterilization, and ethylene oxide (EtO) sterilization developed after 1980s as the medical field advanced in the noninventional surgical methods. Methods like aceptic processing, sterilization by filtration, sterilization by ionizing radiation, gas sterilization, dry-heat sterilization, and steam sterilization are the components of pharmacopoeia (such as EP 5, BP, USP 30). Drugs’ sterilization also employs them. Nonetheless, numerous materials use various methods of sterilization. Table 1 depicts the merits and demerits associated with different sterilization methods.
Methods of sterilization are numerous and their efficacy depends on various factors e.g. type of organic protective material against sterilization and its amount in microorganisms, different types and number of the microorganisms, size and number of breaks in the instrument being used while the process is being carried out.
RADIOSTERILIZATION (RADIATION STERILIZATION)
Sterilization which is carried out with the help of gamma rays which is an ionizing radiation is called radiosterilization. These ionizing methods for sterilization were first used in 1895 and then its more frequent use started in the year 1921. The advantage of these radiations is that they can be used in final processing and containers of the drugs with minimal increase in the temperature. SAL of 10-6 is achieved by the reference dose of 25 kGy. Despite having its diverse uses, the radiolytic products formed at the end of the process alter the odor and color of the drug. This is because the process by which these radiations are produced is still unknown. From pharmaceutical perspective, for the drugs which are sensitive to heat, along with different methods of sterilization, radiosterilization is the method of choice. Techniques which are able to determine radio stability of any drug are only chromatographic.
The effects of radiations on the microorganisms and cells depend on dose rate, time of exposure and effects of the wavelength. Treatment of particles either with X-rays or gamma rays does not turn the materials into radioactive materials themselves. Type of particle, material on which the rays are being used and energy of the rays are the factors which may act on turning the material into radioactive. Particles with high energy and high penetration like neutrons can have these radioactive effects. Radiations can either act directly or indirectly on microorganisms. Ionizing the molecule via absorbing radioactive energy frankly is the direct effect. Primary target in this process is water molecule which is produced during the process. Free radicals H3O+ and OH- are the radiolytic products produced. OH- radicals have a known effect of damaging DNA having burly oxidant effects. O2 can also have some effects to the products.
When free radicals combine with the oxygen molecules they may start a chain of reactions and can also produce hydrogen peroxide. Numerous microorganisms die in the first place when they face DNA damage. Sometimes the damage is repaired because one of the filaments of DNA sustains its properties of ionization and exitation. Radiations can also cause formation of dimmers among pyrimidine base pairs. Covalent bonds are formed between thymine and cytosine bases or bacteria in both radiated and non radiated DNA. Presence of little quantity of water is the reason for the resistance of spores of bacteria. Therefore, spores are not damaged by OH- radicals. Formation of the dimmers among pyrimidine bases of a DNA chain is also another effect radiation on microorganisms. Covalent bonds were formed among thymine and cytosine bases in both non irradiated and irradiated chains of DNA. Protoplasm of bacteria have very scant amount of water. This is the main reason of resistance of spores of bacteria. Therefore, very little damage is done to the DNA of bacteria when they live in the form of spores. As compared to the bacteria, viruses aren't that sensitive to radiations. Among viruses some complex viruses are further less sensitive than single chain viruses of simple type. Various factors present throughput during the process of radiation influence the sensitivity of microorganisms. These factors include the pH, oxygen, temperature, ionic balance and water.
One major concern in radiation sterilization of a material is microbiological investigation. The concerns are set in the following order:
a. Prior to sterilization, the bioburden i.e. the microbiological contamination is found out.
b. Probing the microorganism’s radio sensitivity.
c. Terminal products’ complete and pure hold.
d. Biological indicator’s formulation and utilization.
e. Looking at the environment’s hygienic conditions.
Soy bean-casein medium is utilized for sterility test purposes and facultative anaerobic as well as aerobic microorganisms. Moreover, incubation for 14 days is carried out at 30-32°C. For other detailed microorganisms, different types of appropriate medium can be utilized for suitable conditions of incubation. For the purpose of sterilization, chemicals, high pressure, heat, filtration applications or irradiation can be used. Since radiation sterilization has numerous advantages it is used more often as compared to these sterilization methods. Such systems include gamma rays, subatomic particles, electronic beams i.e. e-beam and Ultraviolet (UV) light irradiation.
Gamma radiation sterilization:
Self breaks of Cesium-137 (137Cs) or Cobalt-60 (60Co) make up the gamma rays. This type of sterilization method is very common and high penetrating and is used for disinfecting liquid, solid, gaseous materials homogenous and heterogeneous systems, disposable medical equipment which includes needles, density materials, syringes, cannulas, i.v. sets and cosmetics. Except with acetal, polytetrafluoroethylene (PTFE) and polyvinyl chloride, it can be utilized on various materials and is a batch or on going process. The material’s thickness determines the entire penetration. It is not dependant on heat or chemicals and provides energy saving. According to the rules of protecting radiation, the major source of radioactive should be shielded for purposes of operators’ safety. The continuous releasing gamma rays reveal the needed storage.
Since sterilization is not required, there could be an immediate release soon after the process is completed. One of other advantage is that at the end of sterilization process there would be no residue. In coming sections, detailed discussion would be done on Gamma sterilization procedure.
E-beam sterilization
The most common method for sterilizing medical devices is E-beam sterilization e.g. gamma radiation sterilization. This could be made by using e-beams, which are found with the help of accelerator method and also by isotope method. One of the advantages of these methods is that it requires very little exposition time that depends upon 10MeV of electron with high energy. Effectiveness of sterilization highly depends upon high energy. The time required by accelerator method is about 15 min. On the other hand, the time required for isotope method is at least 24 hours. In isotope method a source with co isotope is normally used. Design specific machines are used for the purpose of producing and increasing the accelerating of elector. The process is continuous and it can also be applied on any kind of materials dependending upon its penetration. Since sterilization test is not required when the process concludes, an immediate release could be done. As compared to X-ray or gamma, it has high dose rate and there is no residue when the process is concluded. These are few of the advantages of E-beam sterilization. Due to the use of high dose rate there would be shorter exposure time as well as there would be a less changes of degradation of polymers. One of the limitations of e-beams is that there is less penetration as compared to X-ray and gamma. E-beam sterilization will be discussed in detail in upcoming sections.
Discuses below are other kind of radiation sterilization techniques other then the two methods mentions above.
X-rays
Bremstrahlung is a type of ionized energy that is used in x-rays. Through this high ionized energy many medical devices and large packages could be sterilized. The x-rays have the potential to sterilize several packages that are of low density, effectively with consistent ratios. However, the process does not involve any use of radio-active or chemical material. Currently the process cannot be used officially for medical devices and drugs.
UV light irradiation
This light is can only be used as germicidal lamp which can be used in the purpose of sterilization of various surfaces and other transparent objects. However it can never be used for sterilizing contaminated areas. Plastics can therefore not be considered as an official method for medical devices and drugs.
Subatomic particles
The particles can either be generated through a radioisotope or a device. It depends what type of particle it is the ability to penetrate mat always vary. It is again not a kind of method that could be officially used for medical devices and drugs.
GAMMA RADIATION STERILIZATION
Gamma radiations can sterilize not only the ingredients of pharmaceutical but the forms of final dosage as well the method of sterilization through gamma radiations was known as the industrial method of sterilization, as declared by USP 30, BP and EP 5. The benefits and the advantages that are gained through the process of gamma radiation could be defined.
1. Penetration
The raw materials or the final products can be easily sterilized when they are in their final packaging. These pharmaceutical ingredients would need terminal sterilization
2. Formulation of the product/package
Like all other packaged products, vials, delivery system of new drugs such as liposome, microspheres or other anti bodies could be easily sterilized successfully and effectively through irradiation. These materials also include syringes and sets of infusion etc. Since, the risk of diffusing the gas into the product or out of it is not involved here as it was there with sterilization along EtO and in multilayer materials, it can be utilized.
3. Easy Validation Process
It is quite simple to validate the process of radiation sterilization as it involves just one variable which is time. Time will vary only when a constant speed is maintained with 60Co source is decomposite. In each situation, in order to control the time span of conveyor as the source turns around time meters are utilized, after determining the required dose and placement of source. Significantly, validation is an easy process as sterilization is compared with vapor or gas and control of many issues has to be maintained.
4. Guarantee After Process
The conformation of the results has been indicated by dosimetry systems which are used throughout the process and after the completion of it. Since, the product’s absorbed dose has been demonstrated by this system, so sterility test is not required. Once sterilization is done, no further process is required before delivering the product to the customer.
5. Decreasing the Endotoxin Level
Through sterilization of gamma radiation this can be attained and it can be applied to toxic hood gases, drogs, drugs, animal feeds. In spite of having various uses, for numerous medical instruments sterilization, gamma radiation sterilization can be very useful. Group (24) can be denoted for these medical instruments. Air filters, test tubes, urine analysing tubes, petri plaques, vaccine vehicles, brushes, masks, rubbers etc are the material which have several medical utilities. Drains, speculums, hermodialyses, air tubes, clips, syringes, adhesive tapes, surgical sets, gloves, sutures, pets etc. are the surgical instruments or that are exposed directly to the patients.
Implants and machine used for short time or for long time for example artherio-venous shunts, periton dialysis sets, aortic valves, peripheralvascular prothesis, dental implants, artificial eyelids, joint prothesis.
E-BEAM RADIATION
E-beam irradiation techniques are getting more popular for sterilization of medical instruments ,they have many benefits like they are safe, without any emission with highly pace dealing out .Although low intensity medical ornaments can be cleaned by e-beam sterilization normally, highly intensity medical devices like vessel bases can be cleaned with high competency constant e-beam .
The capacity to manage the energy levels through and within beams is the logics for adopting of the procedures. Though the first time electronic beam was used in 1950s in sterilization, its common use as sterilization was properly started in 1970s. In 1960s e-beam was initiated to be used in medical packaging as a secure method. From that time these procedures were initially adopted in medical field depending on being companionable with quantity of other material. It can be used for increasing some kind of material. In this system, electrons are concerted and increased as much as higher as of light speed which makes quick reaction on molecules or microorganism on the product or sample that will be cleaned and sterilized. Product which went through e-beam at a particular pace, which helps messenger or card system to get the required electron dosage for sterilization process. Through this way, a connected association can be acquired for product. Thickness and magnitude of the product is dependent on the energy of the electron and their intensity.
The difference between E-beam irradiation and sterilization of gamma radiation is just of less piercing and more dosage ratio in spite of these both are similar in terms of energy ionization. One more distinction among them is the usage of e-beams in production of electricity as it can produce chargeable electrons.
The electrons formed by the accelerator of e-beams are some time uninterrupted but few times they are quiver. The cause behind the desolation of DNA chain is the preoccupation of electron by the product that is a part of e-beam sterilization and also they are behind the changes occurred in chemical and molecular bonds. Product sterilization needs such electrons that have more energy so that they can easily penetrate in product. Packaging material also depend on compactness and size. Second thing that is more considerable is irradiation as it can harm the packaging material due to its high efficiency level. This collapse gives birth to radicals that are made by polymers and name as “chain scissioning”. This takes only seconds to be happened.
The characteristics of e-beams can be gathered in a sequence;
The process of e-beam sterilization is endorsed from FDA and also identified and approved by international standards organizations,
It has an ability to pass from different material of product packaging like foils,
There is no harm on packaging that have sterile seals,
It becomes easy to manage temperature during process of irradiation.
Restrained dose assortment can be attained,
The institution needed for e-beam sterilization are expensive to be built instead of this its process is productive in relating to cost,
This process is high speeded as it take very short time that influence the effectiveness of routine methodology and also can harm shippable and sterilized goods,
-With a quick pace it provide the dosage for the protection of the properties of the product,
-It merely affects the atmosphere. Though it does affect the structuring of slight amount of ozone,
-In order to be on the safer side personnel should wear protective suites to save them from harmful effets of e-beam,
- For the purpose of implementation and procedure validation guidance documents can be brought to use for the process of sterilization (25, 26, 28):
a. Absorbed dose
From the chain cleavage of DNA Microorganisms are departed based upon the impacts between accelerated electrons and breed radicals. The thing that has utmost importance is basically the dose that has been absorbed and the quantity of interaction product and e-beam which will be untainted. It is basically the absorbed energy in joules divided by mass per unit ([J.kg-1] = [Gy]). The small portion of survival of microorganisms is inversely proportional to the dose absorbed. One of the most vital concerns in the e-beam sterilization is the D value that is needed for the reduction of the survival fraction to 1 by 10 and the value of D is basically the value for single microorganism. The amount of dose needed is based upon the targeted reduction level.
b. Acceleration energy
The basic connection between the dose that has been absorbed and the depth mostly depends upon the energy accelerated energy. For serving this purpose, it is very essential to carry out appropriate setting for serving the properties of the product.
c. Necessity of optimum system
The decline in the sterilization efficacy, variation in the strength and color is entirely based upon the additional dose. Another setback of increasing the energy and dose is the considerable rise in cost. It should also be noted that higher energy is generally falling under the parameter of 10 MeV. For the purpose of generating the optimum irradiation system attaining the uniform dose to articles with appropriate e-beam energy is crucial.
As it is delimitated by the Committee for Proprietary Medicinal Products and European Pharmacopoeia, the shape of pharmaceutical dosage that is sterilized in its terminal stage is known as a sterile product. The factors that influence the selection of a sterilization technique includes; the nature of the product, the sterilization dose and microorganisms’ sensitivity to that sterilization technique, and the sensitivity of the product to the radiation and the SAL value that is required (28).
The use of e-beam sterilization in pharmaceutical industry
Those products which have a difficult formulation and wrapping procedures, this process is suitable for them, for the reason that, it seems tough to sustain sterile environment in each phase, and as the conditions are sterile, so the substantiation can not be done easily of these difficult aseptic products. In order to assure and sustain the sterility of pharmaceuticals and medical devices, terminal sterilization can be more beneficial if selected, but there is a disadvantage beside its advantages, that is, to build up huge irradiation institutions, high cost would incurred. In order to sustain protection and usefulness to the FDA’s fulfillment, a time overwhelming and expensive technique is used by the number of pharmaceutical companies, that is, terminal sterilization. In order to reduce the drug debasement, the mechanism that is used to manage the whole bioburden in the product, is the main aspect in the e-beam sterilization of pharmaceuticals. With the e-beam’s elasticity, the little batches are used to benefit the e-beam sterilization, so that the debasement effect on drugs can be reduced. As the formation of chemical changes diminishes, that’s why the right adjustment of dose is required. A lesser sterilization dose is desirable by cleaner raw materials and manufacturing operations. The consumption of e-beam can be extended through the usage of some molecules. In order to decrease the effect of free radicals, antioxidants like ascorbate, or compound which have sulphydral or SH bonds are used, so that their interaction with an active molecular structure of a rug can also be minimized.
A drug being freeze during and after the process of irradiaton increase the chances of recombination, because of freezing of free radicals, and decreases the chances of degradation. Their ability of migration and interaction with other radicals also reduces. By moving oxygen react with nitrogen and argon gas maintains greater stability in product while reducing the oxidative reactions.
Comparison of sterilization methods and their applications
In the comparison for some of the sterilization techniques, in the gamma radiation sterilization the doses for biomedical applications for bulk materials are ranging in between 10-30 kGy. E-beam radiation is used successfully in a variety of materials as a bactericide but the sterilization of polymers only has a disadvantage that irradiations can exert reactions in molecular bonds like chain breaks, photo-oxidation reactions or cross-linkings. Besides the technique of radiation sterilization, EtO sterilization has the most important drawback that in the presence of a residue it causes some cytotoxic reactions blocking the use of EtO of the polymers for the sterilization process and causing degredations in some molecules like hydrolysis in the polymers.
E-beam generators is usually having its single energy ranging in between 3-12 MeV for its operations but in these days better choice for usage of e-beam equipments is in different energies for operations. There are two most important major points in e-beam sterilization, first is that a strict control of the current scan energy and e-beam is required and the other is that the transporting of the product by means of the beam in the conveyor. The process of sterilization can be accommodated by the speed of the conveyor which depends on the beam current, which can be managed by the feedback circuitry which ensures that till the last part of sterilization process keeping the dose constant.
It is very applicative for various types of materials which are used for medical purposes or for packaging. If we consider how different this is from gamma radiation sterilization, the advantage of e-beam sterilization is highlighted with its less degradation effect which relies on how short the exposure time has been in order to link the dose rate. Another advantage of this e-beam sterilization is the dissymmetric release which is also known as the immediate release. The dosage of the radiation makes this achievable. This method was adopted by the FDA and the American National Standard, ANSI/AAMI/ISO 11137-1994 also linked to this issue. It is not an obligation to maintain the sterility but it is however important to follow the instructions properly so that as soon as the product finishes, it can be sent out.
The gamma sterilization and e-beam sterilization are significant processes that are quite useful in the sterilization of pharmaceuticals. The gamma radiation possesses such characteristics as to transform a process of a few minutes to hours. This is dependent on the volume and mass of the product. It is capable of providing the same dose to products that have a relatively small mass. The pharmaceutical formations differ in sterilization methods based on their mechanisms and their functioning processes. The amount of dose given firstly depends on the bioburden, SAL and the level of radio sensitivity that an organism possesses. The normal amount that SAL is set at is 10−6 m.o/ml or g for the pharmaceuticals that can be injected, ophtalmic ointment and ophtalmic drops and is 10-3 for certain products such as the gloves used in the aseptic conditions. Normally for an effectivity (F-value) of n = 8 is used for sterilization of Bacillus pumilus for the standard dose of 25 kGy which is equal to almost eight times that of its D10 (2.2-3 kGy). Due to this factor, the optimum sterilization dose is 25 kGy at the above level of bioburden.
The relative impact of sterilizing oxorubicin-loaded poly (butyl cyanoacrylate) nanoparticles was investigated on e-beam and gamma irradiation. There were made by a method of anionic polymerization. The doses of irradiation were between 10-35 kGy and to see whether the sterilization is successful or unsuccessful, Bacillus pumilus was utilized. Studies in the field of microbiology showed that irradiation dose of 15 kGy was enough for sterilizing techniques of e-beam and gamma radiation for the purpose of sterilizing 100 CFU.g-1 PBCA nanoparticles of bioburden. It was found out that the two chosen techniques of sterilizing resulted well in the dose that was investigated. The firmness of the preparation as well as active ingredient were unaffected by an irradiation dose of 35 kGy. The physiochemical properties of drug loaded as well as empty nanoparticles such as molecular weight, particle size, aggregation stability and polydispersity index were not impacted by the process.
The impact of EtO gas sterilization and e-beam irradiation was studied on the mechanical properties and structure of multiblock copolymer i.e. a biomedical material. A number of doses on the material had been employed to find out the best e-beam irradiation. IR spectroscopy, tensile testing, DSC, gel permeation chromatography and dynamic mechanical thermal analysis were carried out to find out the probable changes that can occur in the mechanical and structural properties of multiblock copolymer. The most suitable sterilization dose is described as 25 kGy after classification had been carried out. It was also discovered that treatment of Eto gas, like e-beam sterilization, did not impact the physiochemical characteristics of polymer and believed it as a substitutive technique of sterilization.
After using the various doses of high energy electrons and gamma radiation, the structure of metoclopramide hydrochloride solid samples were studied. The products’ degredation was classified with several methods such as atmospheric pressure chemical ionization/liquid chromatography/tandem mass spectrometry. No noteworthy difference was found between the metoclopramide hydrochloride’s e-beam and gamma irradiations.
Following the sterilization, the prepared degredation producrs were not significantly different from metoclopramide and in the solid-state was found chemically stable. Macromolecules can be ionized by radiation ionization and depending on the chemical bonds’ decomposition it can affect radiolysis. H3O and OH are the radiolysis products of protein solution and depend upon the existence of water. The indirect impact of irradiation depends on the impact of such radicals macromolecules that make up a huge part of the damage. Despite the radiation of diffusion being very limited, till now the mean frozen form issue is water. A study was carried out for examining the impact of high energy electrons and gamma rays on protein macromolecules. It was found that a large part of the damage to proteins is linked to the primary ionizations to these molecules directly and that in the frozen state proteins are more sensitive to radiation as compared to the liquid state. The measurement of mass active structures can help in identifying survival frozen proteins that from the destroyed ones.
Several studies have also been conducted on the impacts of radiating ionization on animal diets. The impacts of gamma and e-beam rays have been compared on animal diets’ laboratory. A linear accelerator created 10MeV electrons for the laboratory animals’ power diets as well as solid sterilization for e-beam. A resource of 60Co gamma rays was required for sterilizing gamma rays min 20 kGy. Solid diets that had various thicknesses required various sterilizing procedures.
There were two way in which irradiation was given. To diets which have 30 – 45 mm thickness were given one-sided irradiation while dual-sided irradiation was given to diets having thickness ranging form 75 to 90 mm. Through different observation they found that, there was no considerable difference between diet’s nutrition quality when sterilizing was done with the help of gamma radiation or e-beam. Through this it could be said that e-beam sterilization could be an alternative of gamma rays.
There were many studies, but one of them research about the effects on samples of gum Arabic samples if gamma radiation and e-beam was used. At initial stage gum arabic samples were contaminated due to different bacteria like Bacillus cereus, Clostridum perfringens and Enteroccus faecalis. With the help of 10kGy of e-beam or gamma ray a complete process of decontamination was performed. It was observed that material degradation was directly proportional to dose of gum arabic sample. There could be a change in properties due to high doses link decrease in viscosity and darkening of color. By considering SEM results, in sample gamma rays produces more colors and also the crystal size changes. For both, medial and food industry, it was found through sampling that the optimum level for the purpose of sterilization is 5 kGy. Through all the arguments this could be concluded that for the purpose of terminal sterilization e-beam could be used and can also be an alternative of gamma rays.
E-beam irradiation is also used for non-tissue materials such as forming hydrogles for blood vessels and artificial kidneys as well as for tissue materials like bones, aortas and aortic valves. It was reported by a researcher that in tissue materials, a dose of e-beam irradiation is normally in range of 2 Mrad. Without any negative reactions, during different clinical procedures irradiated bones can be used. If we look at from the perspective of sterility and host acceptance, we will find that the usage of e-beam irradiation of tissue material (such as aortic or aorta valves) resulted in optimum conditions. One of the study has also examined the surface characteristics of poly(L-lactide-cocaprolactone) (PLCL) biopolymers, which are basically used in tissue engineering.
Thursday, February 23, 2012
Prehistoric Roads
Introduction
The possessions and variety of the Neolithic and Early Bronze archaeology are present in the South West and most of it has international as well as national segment. Character and quality are determined by survival gap and research histories and reflect actual variation in prehistoric activity nature. Unusual terrains of south west peninsula and the Wessex chalk divide are the main topographies. Media of exchange and different modes are the corresponding resources of these couple of main areas. Dartmoor and Bodmin Moor has relict prehistoric landscapes where outstanding survival of stone monuments is ensured. Artefactual material and uneven range of prehistoric timber trackways have been found in the Somerset Levels within the peats. Although human bone assemblages and rich faunal have been found from the chalk bedrocks and alkaline limestone of Dorset, Wilshire, northern Somerset and Gloucestershire Cotswolds, the intensive study of Early Bronze Age archaeology and Neolithic have occurred. In 1986 The UNESCO World Heritage list was the Stonehenge inscription and landscapes of Avebury. The extensive exploration has led in the dominating synthetic of Wessex and Bronze Age and British Neolithic’s interpretive accounts. (for example, Barrett 1994b; J Thomas 1999).
Sites surviving upstanding on the higher moors and downloads are dominating the image of the well known archaeological resource. The strength of occupation in vales and lower ground is testified by the main concentrations of aerial reconnaissance, lithic material, extensive geophysical survey and relief work shown in the end few areas of the inactive regions.
4.2 Chronologies
4.2.1 The Mesolithic–Neolithic
transition
Sweet Track found in Somerset Levels are one of the most date secured structures in Early Neolithic. The construction dates of Sweet Track (3807/3806 BC) and Post track (3838 BC) have made it clear that the Neolithic artefacts were present at the start of the 4th millennium BC and to some extent the woodland surrounding was managed, gazed, cleared and cultivated (Coles and Coles 1986; Caseldine 1984a). One of the region’s best deposits of Late Mesolithic are also present in the upper fill of the Fir Tree Field shaft on Cranborne Chase. Dated back to the early 4th or 5th millennium and bedded above the rod microliths’ group was a fireplace integrated with Neolithic bowl pottery, domestic cattle bone and a ground flint axehead, which gave rise to radiocarbon dates of 3960–3710 cal BC (OxA-8009), 4050–3800 cal BC (OxA-8010) and 4250–3960 cal BC (OxA-7981, Allen and Green 1998). The first determination, made on short life material will be the nearest age to deposit while the other two, a long lived specie on charcoal and on a diasarticulated animal bone, were termini post quos.
Easy interpretation of the sequence is a fair and rapid transition from one tradition to another. Other than places in Britain, the dates are associated with a reliable source to Mesolithic artefacts that extent to the start of 4th millennium BC (Spikins 2002) as well as certain Neolithic monuments which includes barrows and cairns that were built from c.3800 BC on the fact of radiocarbon measurements on the limited human remains (such as listed by Richards and Hedges 1999, and those added from latest monuments, Bayliss and Whittle 2007).
According to Richards 2004, at this time, dietary change has been rushed, though the results’ interpretation of the analysis of stable isotope remains controversial (Hedges 2004; Lidén et al. 2004; Milner et al. 2004). Within two generations, there is a possibility of the adopting the Neolithic lifeways with intensions of the influential power of new identities, beliefs and practices (Richards 2004; J Thomas 2003).
A process of Neolithic ‘infill’ was developed by major monument complexes in parts of Wessex chalklands which includes areas like Dorchester, Avebury Stonehenge and Cranborne Chase (Whittle 1990; Richards 1990, 263; Barrett et al. 1991, 29; RJC Smith et al. 1997); maybe somewhere near the 4th-5th millennium BC line if the date of 4050-3640 cal BC are reliably taken from Coneybury Anomaly (OxA-1402, Richards 1990). Dense Later Mesolithics are present on the clay-with-flints of Cranborne Chase and are absent from the chalk from which several Early Neolithic monuments were constructed (Barrett et al. 1991, 29–31). In other examples, several practices and significance of places may have crossed the transition to Neolithic. The order at Gloucestershire, Hazleton North starting with a Late Mesolithic flint scatter, is reflected in the repetitive return by the similar social group and sense of place to this locale. A late Mesolithic presence is revealed in the Somerset surface collection surrounding the Devil’s Bed and Bolster long barrow (Lewis 2005) but the nature of relationship is uncertain between construction of monuments and these activities.
Transport
Transporting stone axes and ceramics to long distances is a well known activity in this area. It is said by through the identification of Cornish Heath of charred fragments which are now native in only in the Britain mainland at Hambledon Hill on the Lizard peninsula that some of south-western stone axeheads and gabbroic pottery buried at the place had been directly sent there. The proof is absent for land based trackways with acclaimed long distance routes in the initial prehistoric date i.e. Wilshire Ridgeway which now is known to be Medieval or Roman origin (Fowler 2000). There has been a rise in the probability that people who bought cattle to the causewayed enclosures for slaughtering purposes could have served them as packed animals.
During the 4th millennium BC, a famous means of communication was the route along the long rivers. These routes connected the monument complexes and monuments as shown by the avenue positioning and entrance of enclosures related to the Avon at Durrington Walls and Stonehenge (Parker Pearson et el. 2006). Location of Wessex in between the Irish Seas and the channel alongside rivers that provide possible links not only between the two but also to North Sea via Thames which will make it easy to travel to a huge number of long distance routes. The region is enjoying an advantageous position by going into various communication networks that are in relation to the exchange of low bulk but high quality materials. Phase 3 bluestone settings at Stonehenge provide an example of high bulk materials movement (Cleal et al. 1995). They cannot be derived from the nearby deposits of the glaciers and it seems that the south west Wales brought these bluestones (Scourse 1997), possibly through the Bristol Avon and Bristol channel. Keeping in mind the time period, boats must have been present here however none have been found.
Wetland found in a particular region is a good evidence of non-riverine with in the land transport. Timber track ways were known for Somerset Levels which joins islands with in the fens (Somerset HER; Coles and Coles, 1986). In early fourth millennium BC, Sweet Track and Post Track were early forms of rail and post construction. Trackways like corduroy and hurdle construction were seen in early Bronze Age. (Coles and Coles 1986; Somerset HER)
Sweet Track is a kind of causeway in Somerset Levels which is in England. It’s construction was in 3806 BC and is also clamed as the oldest road of the world. It was ones considered to be the oldest in Northern Europe, but in 2009 trackways were discovered in Belmarsh Prison which was almost 6000 year old. It is now thought that Sweet Track was constructed largely in early structures.
Track starched across Westhay, which was once an island, and Shapwick which is a high ground. This distance is approximately 6600 ft or 2000 meters. Different artifacts were found in this region which includes jadeitie axe head.
These constructions were of wooden poles. These poles were forced into the soil which supported the walkway. The walkway consisted for planks made form oak. Due to the raise in water level they were used only for 10 year. Most of them have been left were they were originally. To maintain the condition of the wood different measures are taken including water pumping. Few for the track are preserved at British Museum.
A track was built in early fourth millennium BC which connected Westhay and Shapwick which was close to River Brue. The site has been marks of ancient lake dwellings. These lake dwellings are similar to once that were found in iron age, Glastonbury Lake Village which is situated near Godney. [2]
Similar track were discovery in the surrounding which have now been uncovered. These tracks were used to connect different settlements situated on peat bog. These settlement includes Abbotts Way, Westhay, Nidons and Honeygore trackways.[3] Sites similar to Meare Pool, provide us with an evidence that the main purpose that these structure served was to help in making traveling easy. Through investigating Meare Pool it can to our knowledge that it was constructed by encroachment of raised pet bogs specifically during the period of Subatlantic climate. And by sampling core helped us indicate that it was filled with detritus mud which was at least 2 meters deep. [4][5]
Two of the Meare Lake Villages which lies in Meare Pool seem to be originated from collection of different structures which erected on the top of dried peat which includes windbreaks, animal folds and tents. Later clay was used to provide raised stands for the movement, occupation and industry. In few areas hearths was built with the help of clay and stones.
Builders:
People who constructed these trackway were Neolithic farmers. Around 3900B.C they have already had colonized their area and it is also suggested that by the time they have started the construction they were well settled and organized. [23] Before human started penetrating the upper lands which was heavily surrounded by wood, only the locals stated clearing these forest for their living and for the space for cultivation. [24] In the time of winter the areas which ever flooded provided the inhabitant with wildfowl and fish. While in summer when the land dries the community who farms uses these grassland for the purpose of grazing sheep and cattle. Summer was rich of wood, reed, and had relatively more bird and wild animals, seeds and fruits. [25] There was a need for reaching other islands in the wetlands where they could find sufficient area to perform different activities like stocking timber and building trackway, most importantly when water is at its lowest level in the end of dry period. [23] The activities which are to be performed for the construction indicates that they were advanced in the skills of woodworking and also suggest that there were some differentiation about the occupation of the workers. [23] it also seem link they have been maintaining the surrounding land for 120 year al least. [23]
Construction:
The track was build in 3806 B.C and was only made of planks made form oak and was supported with the help of crossed pegs of oak, lime and ash. [27] The size of the plank was 40cm wide, 5cm thick and 3meters long. The trees which were cut down to make planks had at least age of 400 years and with a diameter of 1 meter. They were cut, split and felled only with the help of stoned axes, mallets and wooden wedges. [28] With the help of the straightness and length it seems like that were from woodland of coppiced. [29] Longitudinal log rail was up to 7.6 cm in diameter, 6.1m long and was made up of alder and hazel. [27][30] After that, notches were cut down into planks so that they could fit the pegs. Planks were placed in X shapes to form a walkway. [31] At some places second rail was used on top of the previous one to increase the level well above the remaining walkway. [32] Small trees came into use at southern end. Planks were spilt across to utilize its full diameter. Other tree fragments were also found which includes willow, dogwood, poplar, apple, birch and ivy. [1]
The setting of the wetlands indicates that trunks must have come prefabricated and was assembled on the construction site. [27] Presence of chopped branches and wood chips indicates us that some trimming would have been performed locally. [1] About 200,000 kg of timber is used to build a track and according to Coles 10 men could assemble in one day once the required material is on site. [34]
For only 10 year Sweet Track was used because of the rise of water level they may have been engulfed. The objects which were found along the side of the track suggest that the track were used on daily bases by the farmers of the community. Since the time of discovery, it have been seen that different parts of Sweet Track were also build on the routes of earlier track. Post Track was constructed about thirty year before which are about 3838 B.C.
Conservation:
Much of the track is still intact with no major changes in its initial location. It is now situated within the Shapwick Health biological Site of Special Scientific Interest and the National Nature Reserve.38 A huge amount of the track’s length is now being conserved after the successful purchase of the land by National Heritage Memorial Fund. They installed a system which would make the pumping of water and the distribution process much easier, in about a 500 meter land. 39 This process of preserving the wetlands so as to keep a high water table and saturate the land has become a rare practice.41 A piece of land about 500 meters long is owned by the Nature Conservancy Council which is enclosed by a clay bank which helps to prevent drainage into the lower peat fields that surround the land. The water levels are rechecked every now and then.41 The usefulness of this method and the threat to the land can be seen by comparing it to Abbot’s way which is located nearby and has not been treated by this method. Back in 1996, this land was completely deprived on water and was left barren. 42 The Nature Conservancy Council, the Department for Environment, Food and Rural Affairs as well as the Somerset Levels Project are the ones responsible for keeping a check on the level of water in the Shapwick Health Nature Reserve.
Even though, the wood recovered from these pieces of land had become quite soft and of very poor quality, the pieces that were still of better condition were taken out and reserved for analysis later on. 42 This wood could be conserved by a process which involved keeping the wood in tanks which were heated and contained water soluble wax called polyethylene glycol. The water in the wood evaporated slowly and was replaced by wax. This process lasted for approximately 9 months. Through this procedure, the wax cooled down and hardened and the wood was ready to be used.
Early Bronze Age contexts and Developments:
The Early Bronze age in the south west involved traditions like those of megalithic tomb construction. Even though their chronology is not that well recognized and interpreted by people, Ashbee (1982) has sided with the Mesolithic origin which usually belong to the Entrance Graves in the Isles of Scilly and West Cornwall which can also be traced back to the Early Bronze Age. (O’Neil 1952).
Amongst the numerous monuments, about 80 of them are recorded on Scilly, as compared to just nine in the West Penwith. In other parts, the region is populated with dense areas and clusters of round barrows and cairns, which stand there as monuments in the upland areas. The most obvious category of the prehistoric monuments are the 6000 historic monuments in Wessex (Grinsell, 1958), 745 in Somerset (Grinsell, 1969), and about 3500 in Cornwall.
The distribution there is mostly unequal. It may lie in isolation or in big centimeters. Most of the concentrations lie on Mendip around the Priddy Circles, which stretch over 16km and have an already built ceremonial center at the Stonehenge and Avebury. Although the distribution of these monuments is being changed an altered to quite an extent now.
The excavations that took place in these areas have brought up evidence of Cornish barrows which have quite a unique history attached. Also human remains were found which proved to be a small part of the tradition of the barrow. The barrow excavations are still going on and being credited with more and more discoveries like the Crig-a-Mennis (Christie 1960), Davidstow Moor (Christie 1988), Tregulland (Ashbee 1955–1956; 1958), Watch Hill (Miles 1975a), Caerloggas (Miles 1975a), Gaverigan (Nowakowski 1995; 1998; Highgate (Nowakowski 1998), Trenance (Miles 1975a), Chysauster (G Smith 1996) and Stannon (Harris et al. 1984). This list of excavations and discoveries show the various monuments present which range in size and structure and are a unique discovery credited to the barrow excavations.
A diverse and unique mixture of ceremonial practices was discovered with the excavations of the groups residing in the Early Bronze Age barrows. Some of these were Davidstow Moor campaign that took place in the 1940s (Christie, 1988), Colliford (Griffith, 1984) and Stannon. Research has shown that the different sites and landscapes had their own separate roles and rituals that they performed and they were distinct from each other. (Owoc 2001, Nowakowski)
This brings forward the threat of disregarding barrows completely and considering them as mere physical depository remains of the humans. The longevity and complex nature of the barrows and cairns was one of their greatest features and they are credited with the remodeling and restructuring of ancient monuments after many years.
In the first mid of the 20th century there had been number of major burial grounds or digging barrow group which had same complex structures clearly defined in the rounded barrows on the chalk, for example, Crichel Down and Launceston Down (Piggott and Piggott 1944) and after the war taking strong actions in cultivating and military activity such as Shrewton (Green and Rollo-Smith 1984),Amesbury(Ashbee 1985) and Snail Down(N Thomas 2005). Some barrows had simple narrow excavation while others appeared as large mounts such as (Amesbury 71) and (West Overton 6b) with appearance of ring cairns,circles and mound platforms. In the Bronze Age there were wide range of barrow formats with skillfull work including bell,saucer and pond varieties having particular gender associations while before this Age the earlier barrows were small in size but provided some creative linear cemeteries which were used till the 2nd millennium BC,
Circular hilltop enclosures known in Cornwall in the west in Early Bronze Age showed incircle ring cairns and monuments for example at (Bartinney and Caer Ban), menhirs standing single paired and in rows stones were the feature of Cornwall and Isles of Scilly. But in Middle and Late Bronze Age much of its interior were removed in the development.Some were discovered by Antiquarians in the 19th century where deposits of bone chips and ashes were found. At Try Gulval,which shows that it has a long history because of its large menhir attached with stoned lined many deposits of animal and human bone, with trevisker pottery of fragments (Russel and Pool 1964).
Mesolithic material is contained in Neolithic and Early Bronze Age lithics which have 45% of spread out on Dartmoor. However, this may lead to periodic reoccupation on the places where there might be promising chances of recovery. Hiatus is revealed between Mesolithic and ensuing Neolithic and Early Bronze Age gatherings by the lithics occurred from the scatter beneath digging at Batworthy Corner.
North Downs
There have been areas like Downs and most regions in prehistoric times which were covered with thick, intense and deciduous woodland. Regions were mostly covered with woods and it is seen that the human activities initially in the early period of time was the area were granted by the primitive megaliths on the scarp in western Kent. However, there have been areas which were surrounded by the river valleys as parts of Roman and showed habitations. The areas which were exposed at the the upper Downs showed some middle ages and colonization as slow pace and this is considered to be a historic arrangement model of parishes. It is surrounded by the boundaried which takes some area of downland, scarpfoot and chartland. This leaded to a framework of the current network of settlements which were explored in the area.
Downs was seen as an extensive regime filled with stocks and the roads were made for driving purpose and they were developed in order to make feasibility for moving animals to the other summer territory. There were some other tracks as well like North Downs Way and this path was an old path surrounded across the ridge and Pilgrim’s Way and lead to the Canterbury.
There are small villages in North Downs especially in the Kent part and is a rural area with rustic background and has some big settlements like Guildford, Chatham and Dover.
There are some urban developments as well especially in the area where Downs bring about London towards Croydon and Sutton. Moreover, in those urban areas there is a spread of speciesrich grassland valleys.
There are diagonal lined tracks and lanes down a bit and they link the Downs with south Wealden Greensand, the tracks are surrounded by trees and the lanes are contracted and constricted with caricature and are steep sided.
Projection with yew and wayfaring tree and white beam it is observed that the views are restricted and wide-ranging and limited to view from the top.
BOUNDARIES AND EDGES
Boundaries and edges of the countryside and local ecologies should be given attention and significance. It is observed that importance is given to the natural environment in order to retain the natural part of the countryside so, the boundaries and edges are taken into notice and have given especial and vital attention to the natural places as stated by Richard Bradley (2000).
A study conducted in 2003 by Stocker and Everson of Titham valley in Lincolnshire, England, shows that the natural places have long value and life in wetlands and are significant. The boundary of Lindsey an independent state was River Witham in the middle ages. Medieval monasteries were situated at the tactical points along the valley according to a research. Access was provided by the causeways across the river and its widespread riparian wetlands. The period of causeways was old enough in the Middle Ages and there were excavations at Fiskerton of one of them. Precursor of Iron Age and Roman date was shown as mentioned by (Field & Parker Pearson 2003). Votive depositions also occurred at causeways areas particularly on the terminals of the cause ways.
In response to this votive depositions were seen in barrow cemeteries of surrounding area of Bronze Age. However, it has been argued by Stocker and Everson that in the Titham valley there are precise locales and they are supposed as places where boundary could be crossed by one. The boundary can be crossed for a period in surplus of the two millennia in spite of having a wetland landscape as of developing nature. Moreover, the Bronze Age insights lead to some sort of middle Ages practices and values.
MARGINALITY AND LIMINALITY
The sixth point is of getting a knowhow of differentiating between peculiarity and liminality. When wetlands go across that idea is known as liminality. This concept of liminality is considered to be fluid concept disreputably. More precisely, this concept is to be taken as and linked to the means of passageway as projected by Van Gennep( 1908). This basically describes the formal rituals and practices which are accompanied by one transition and tell about one specific place into another. Its main focus is on the rites which are related to the birth, adulthood, marriage and death. The real or symbolic doorsteps are part of these rituals and need to cross representing the luminal zones. The equation of liminality with marginality is often mistaken because the economic and ritual activities are not on the level of landscape and are mutually exclusive. Moreover, few liminal zones were originated in marginal landscapes and this can be explained by an example that threshold went through the newlyweds in the advanced world and are positioned in settlements or in the economic areas. More significantly, it is very important to know and be precise when recognizing the places which are liminal.
Lake dwellings in East Yorkshire are an example of how liminality is not connected to marginality. Giving a second look to the ‘Sfest Furze’ lake dwellings showed that it was a type of a track way going through wetlands in the Bail and Low mere complex and the surroundings were giving an effect like early Bronze Age. The wide mires serve as a boundry between the dead and alive on the east we burial mounds and on the west there are human settlements. At West Furze, a track way crosses these wetlands including a doorway at the east of the short track which symbolizes the space and another symbol are the number of human skills found near the boundary.
(Van de Noort 1995; see also Fletcher & Van de Noort this volume)
We should not undermine the wetland landscapes as taskscapes are, because the significance of wetlands determines how they are perceived. Ingold describes “takscapes” as the tasks undertaken at the particular landscapes, through which landscapes are perceived. What insider’s think about wetland is that it has innumerable resources from fish to fuel and from hay lands to reeds. Raised bogs also come in handy we can use them for grazing, preserving butter and for curing of leather too.
We should not undermine the wetland landscapes as taskscapes are, because the significance of wetlands determines how they are perceived. Ingold describes “takscapes” as the tasks undertaken at the particular landscapes, through which landscapes are perceived. What insider’s think about wetland is that it has innumerable resources from fish to fuel and from hay lands to reeds. Raised bogs also come in handy we can use them for grazing, preserving butter and for curing of leather too.
The possessions and variety of the Neolithic and Early Bronze archaeology are present in the South West and most of it has international as well as national segment. Character and quality are determined by survival gap and research histories and reflect actual variation in prehistoric activity nature. Unusual terrains of south west peninsula and the Wessex chalk divide are the main topographies. Media of exchange and different modes are the corresponding resources of these couple of main areas. Dartmoor and Bodmin Moor has relict prehistoric landscapes where outstanding survival of stone monuments is ensured. Artefactual material and uneven range of prehistoric timber trackways have been found in the Somerset Levels within the peats. Although human bone assemblages and rich faunal have been found from the chalk bedrocks and alkaline limestone of Dorset, Wilshire, northern Somerset and Gloucestershire Cotswolds, the intensive study of Early Bronze Age archaeology and Neolithic have occurred. In 1986 The UNESCO World Heritage list was the Stonehenge inscription and landscapes of Avebury. The extensive exploration has led in the dominating synthetic of Wessex and Bronze Age and British Neolithic’s interpretive accounts. (for example, Barrett 1994b; J Thomas 1999).
Sites surviving upstanding on the higher moors and downloads are dominating the image of the well known archaeological resource. The strength of occupation in vales and lower ground is testified by the main concentrations of aerial reconnaissance, lithic material, extensive geophysical survey and relief work shown in the end few areas of the inactive regions.
4.2 Chronologies
4.2.1 The Mesolithic–Neolithic
transition
Sweet Track found in Somerset Levels are one of the most date secured structures in Early Neolithic. The construction dates of Sweet Track (3807/3806 BC) and Post track (3838 BC) have made it clear that the Neolithic artefacts were present at the start of the 4th millennium BC and to some extent the woodland surrounding was managed, gazed, cleared and cultivated (Coles and Coles 1986; Caseldine 1984a). One of the region’s best deposits of Late Mesolithic are also present in the upper fill of the Fir Tree Field shaft on Cranborne Chase. Dated back to the early 4th or 5th millennium and bedded above the rod microliths’ group was a fireplace integrated with Neolithic bowl pottery, domestic cattle bone and a ground flint axehead, which gave rise to radiocarbon dates of 3960–3710 cal BC (OxA-8009), 4050–3800 cal BC (OxA-8010) and 4250–3960 cal BC (OxA-7981, Allen and Green 1998). The first determination, made on short life material will be the nearest age to deposit while the other two, a long lived specie on charcoal and on a diasarticulated animal bone, were termini post quos.
Easy interpretation of the sequence is a fair and rapid transition from one tradition to another. Other than places in Britain, the dates are associated with a reliable source to Mesolithic artefacts that extent to the start of 4th millennium BC (Spikins 2002) as well as certain Neolithic monuments which includes barrows and cairns that were built from c.3800 BC on the fact of radiocarbon measurements on the limited human remains (such as listed by Richards and Hedges 1999, and those added from latest monuments, Bayliss and Whittle 2007).
According to Richards 2004, at this time, dietary change has been rushed, though the results’ interpretation of the analysis of stable isotope remains controversial (Hedges 2004; Lidén et al. 2004; Milner et al. 2004). Within two generations, there is a possibility of the adopting the Neolithic lifeways with intensions of the influential power of new identities, beliefs and practices (Richards 2004; J Thomas 2003).
A process of Neolithic ‘infill’ was developed by major monument complexes in parts of Wessex chalklands which includes areas like Dorchester, Avebury Stonehenge and Cranborne Chase (Whittle 1990; Richards 1990, 263; Barrett et al. 1991, 29; RJC Smith et al. 1997); maybe somewhere near the 4th-5th millennium BC line if the date of 4050-3640 cal BC are reliably taken from Coneybury Anomaly (OxA-1402, Richards 1990). Dense Later Mesolithics are present on the clay-with-flints of Cranborne Chase and are absent from the chalk from which several Early Neolithic monuments were constructed (Barrett et al. 1991, 29–31). In other examples, several practices and significance of places may have crossed the transition to Neolithic. The order at Gloucestershire, Hazleton North starting with a Late Mesolithic flint scatter, is reflected in the repetitive return by the similar social group and sense of place to this locale. A late Mesolithic presence is revealed in the Somerset surface collection surrounding the Devil’s Bed and Bolster long barrow (Lewis 2005) but the nature of relationship is uncertain between construction of monuments and these activities.
Transport
Transporting stone axes and ceramics to long distances is a well known activity in this area. It is said by through the identification of Cornish Heath of charred fragments which are now native in only in the Britain mainland at Hambledon Hill on the Lizard peninsula that some of south-western stone axeheads and gabbroic pottery buried at the place had been directly sent there. The proof is absent for land based trackways with acclaimed long distance routes in the initial prehistoric date i.e. Wilshire Ridgeway which now is known to be Medieval or Roman origin (Fowler 2000). There has been a rise in the probability that people who bought cattle to the causewayed enclosures for slaughtering purposes could have served them as packed animals.
During the 4th millennium BC, a famous means of communication was the route along the long rivers. These routes connected the monument complexes and monuments as shown by the avenue positioning and entrance of enclosures related to the Avon at Durrington Walls and Stonehenge (Parker Pearson et el. 2006). Location of Wessex in between the Irish Seas and the channel alongside rivers that provide possible links not only between the two but also to North Sea via Thames which will make it easy to travel to a huge number of long distance routes. The region is enjoying an advantageous position by going into various communication networks that are in relation to the exchange of low bulk but high quality materials. Phase 3 bluestone settings at Stonehenge provide an example of high bulk materials movement (Cleal et al. 1995). They cannot be derived from the nearby deposits of the glaciers and it seems that the south west Wales brought these bluestones (Scourse 1997), possibly through the Bristol Avon and Bristol channel. Keeping in mind the time period, boats must have been present here however none have been found.
Wetland found in a particular region is a good evidence of non-riverine with in the land transport. Timber track ways were known for Somerset Levels which joins islands with in the fens (Somerset HER; Coles and Coles, 1986). In early fourth millennium BC, Sweet Track and Post Track were early forms of rail and post construction. Trackways like corduroy and hurdle construction were seen in early Bronze Age. (Coles and Coles 1986; Somerset HER)
Sweet Track is a kind of causeway in Somerset Levels which is in England. It’s construction was in 3806 BC and is also clamed as the oldest road of the world. It was ones considered to be the oldest in Northern Europe, but in 2009 trackways were discovered in Belmarsh Prison which was almost 6000 year old. It is now thought that Sweet Track was constructed largely in early structures.
Track starched across Westhay, which was once an island, and Shapwick which is a high ground. This distance is approximately 6600 ft or 2000 meters. Different artifacts were found in this region which includes jadeitie axe head.
These constructions were of wooden poles. These poles were forced into the soil which supported the walkway. The walkway consisted for planks made form oak. Due to the raise in water level they were used only for 10 year. Most of them have been left were they were originally. To maintain the condition of the wood different measures are taken including water pumping. Few for the track are preserved at British Museum.
A track was built in early fourth millennium BC which connected Westhay and Shapwick which was close to River Brue. The site has been marks of ancient lake dwellings. These lake dwellings are similar to once that were found in iron age, Glastonbury Lake Village which is situated near Godney. [2]
Similar track were discovery in the surrounding which have now been uncovered. These tracks were used to connect different settlements situated on peat bog. These settlement includes Abbotts Way, Westhay, Nidons and Honeygore trackways.[3] Sites similar to Meare Pool, provide us with an evidence that the main purpose that these structure served was to help in making traveling easy. Through investigating Meare Pool it can to our knowledge that it was constructed by encroachment of raised pet bogs specifically during the period of Subatlantic climate. And by sampling core helped us indicate that it was filled with detritus mud which was at least 2 meters deep. [4][5]
Two of the Meare Lake Villages which lies in Meare Pool seem to be originated from collection of different structures which erected on the top of dried peat which includes windbreaks, animal folds and tents. Later clay was used to provide raised stands for the movement, occupation and industry. In few areas hearths was built with the help of clay and stones.
Builders:
People who constructed these trackway were Neolithic farmers. Around 3900B.C they have already had colonized their area and it is also suggested that by the time they have started the construction they were well settled and organized. [23] Before human started penetrating the upper lands which was heavily surrounded by wood, only the locals stated clearing these forest for their living and for the space for cultivation. [24] In the time of winter the areas which ever flooded provided the inhabitant with wildfowl and fish. While in summer when the land dries the community who farms uses these grassland for the purpose of grazing sheep and cattle. Summer was rich of wood, reed, and had relatively more bird and wild animals, seeds and fruits. [25] There was a need for reaching other islands in the wetlands where they could find sufficient area to perform different activities like stocking timber and building trackway, most importantly when water is at its lowest level in the end of dry period. [23] The activities which are to be performed for the construction indicates that they were advanced in the skills of woodworking and also suggest that there were some differentiation about the occupation of the workers. [23] it also seem link they have been maintaining the surrounding land for 120 year al least. [23]
Construction:
The track was build in 3806 B.C and was only made of planks made form oak and was supported with the help of crossed pegs of oak, lime and ash. [27] The size of the plank was 40cm wide, 5cm thick and 3meters long. The trees which were cut down to make planks had at least age of 400 years and with a diameter of 1 meter. They were cut, split and felled only with the help of stoned axes, mallets and wooden wedges. [28] With the help of the straightness and length it seems like that were from woodland of coppiced. [29] Longitudinal log rail was up to 7.6 cm in diameter, 6.1m long and was made up of alder and hazel. [27][30] After that, notches were cut down into planks so that they could fit the pegs. Planks were placed in X shapes to form a walkway. [31] At some places second rail was used on top of the previous one to increase the level well above the remaining walkway. [32] Small trees came into use at southern end. Planks were spilt across to utilize its full diameter. Other tree fragments were also found which includes willow, dogwood, poplar, apple, birch and ivy. [1]
The setting of the wetlands indicates that trunks must have come prefabricated and was assembled on the construction site. [27] Presence of chopped branches and wood chips indicates us that some trimming would have been performed locally. [1] About 200,000 kg of timber is used to build a track and according to Coles 10 men could assemble in one day once the required material is on site. [34]
For only 10 year Sweet Track was used because of the rise of water level they may have been engulfed. The objects which were found along the side of the track suggest that the track were used on daily bases by the farmers of the community. Since the time of discovery, it have been seen that different parts of Sweet Track were also build on the routes of earlier track. Post Track was constructed about thirty year before which are about 3838 B.C.
Conservation:
Much of the track is still intact with no major changes in its initial location. It is now situated within the Shapwick Health biological Site of Special Scientific Interest and the National Nature Reserve.38 A huge amount of the track’s length is now being conserved after the successful purchase of the land by National Heritage Memorial Fund. They installed a system which would make the pumping of water and the distribution process much easier, in about a 500 meter land. 39 This process of preserving the wetlands so as to keep a high water table and saturate the land has become a rare practice.41 A piece of land about 500 meters long is owned by the Nature Conservancy Council which is enclosed by a clay bank which helps to prevent drainage into the lower peat fields that surround the land. The water levels are rechecked every now and then.41 The usefulness of this method and the threat to the land can be seen by comparing it to Abbot’s way which is located nearby and has not been treated by this method. Back in 1996, this land was completely deprived on water and was left barren. 42 The Nature Conservancy Council, the Department for Environment, Food and Rural Affairs as well as the Somerset Levels Project are the ones responsible for keeping a check on the level of water in the Shapwick Health Nature Reserve.
Even though, the wood recovered from these pieces of land had become quite soft and of very poor quality, the pieces that were still of better condition were taken out and reserved for analysis later on. 42 This wood could be conserved by a process which involved keeping the wood in tanks which were heated and contained water soluble wax called polyethylene glycol. The water in the wood evaporated slowly and was replaced by wax. This process lasted for approximately 9 months. Through this procedure, the wax cooled down and hardened and the wood was ready to be used.
Early Bronze Age contexts and Developments:
The Early Bronze age in the south west involved traditions like those of megalithic tomb construction. Even though their chronology is not that well recognized and interpreted by people, Ashbee (1982) has sided with the Mesolithic origin which usually belong to the Entrance Graves in the Isles of Scilly and West Cornwall which can also be traced back to the Early Bronze Age. (O’Neil 1952).
Amongst the numerous monuments, about 80 of them are recorded on Scilly, as compared to just nine in the West Penwith. In other parts, the region is populated with dense areas and clusters of round barrows and cairns, which stand there as monuments in the upland areas. The most obvious category of the prehistoric monuments are the 6000 historic monuments in Wessex (Grinsell, 1958), 745 in Somerset (Grinsell, 1969), and about 3500 in Cornwall.
The distribution there is mostly unequal. It may lie in isolation or in big centimeters. Most of the concentrations lie on Mendip around the Priddy Circles, which stretch over 16km and have an already built ceremonial center at the Stonehenge and Avebury. Although the distribution of these monuments is being changed an altered to quite an extent now.
The excavations that took place in these areas have brought up evidence of Cornish barrows which have quite a unique history attached. Also human remains were found which proved to be a small part of the tradition of the barrow. The barrow excavations are still going on and being credited with more and more discoveries like the Crig-a-Mennis (Christie 1960), Davidstow Moor (Christie 1988), Tregulland (Ashbee 1955–1956; 1958), Watch Hill (Miles 1975a), Caerloggas (Miles 1975a), Gaverigan (Nowakowski 1995; 1998; Highgate (Nowakowski 1998), Trenance (Miles 1975a), Chysauster (G Smith 1996) and Stannon (Harris et al. 1984). This list of excavations and discoveries show the various monuments present which range in size and structure and are a unique discovery credited to the barrow excavations.
A diverse and unique mixture of ceremonial practices was discovered with the excavations of the groups residing in the Early Bronze Age barrows. Some of these were Davidstow Moor campaign that took place in the 1940s (Christie, 1988), Colliford (Griffith, 1984) and Stannon. Research has shown that the different sites and landscapes had their own separate roles and rituals that they performed and they were distinct from each other. (Owoc 2001, Nowakowski)
This brings forward the threat of disregarding barrows completely and considering them as mere physical depository remains of the humans. The longevity and complex nature of the barrows and cairns was one of their greatest features and they are credited with the remodeling and restructuring of ancient monuments after many years.
In the first mid of the 20th century there had been number of major burial grounds or digging barrow group which had same complex structures clearly defined in the rounded barrows on the chalk, for example, Crichel Down and Launceston Down (Piggott and Piggott 1944) and after the war taking strong actions in cultivating and military activity such as Shrewton (Green and Rollo-Smith 1984),Amesbury(Ashbee 1985) and Snail Down(N Thomas 2005). Some barrows had simple narrow excavation while others appeared as large mounts such as (Amesbury 71) and (West Overton 6b) with appearance of ring cairns,circles and mound platforms. In the Bronze Age there were wide range of barrow formats with skillfull work including bell,saucer and pond varieties having particular gender associations while before this Age the earlier barrows were small in size but provided some creative linear cemeteries which were used till the 2nd millennium BC,
Circular hilltop enclosures known in Cornwall in the west in Early Bronze Age showed incircle ring cairns and monuments for example at (Bartinney and Caer Ban), menhirs standing single paired and in rows stones were the feature of Cornwall and Isles of Scilly. But in Middle and Late Bronze Age much of its interior were removed in the development.Some were discovered by Antiquarians in the 19th century where deposits of bone chips and ashes were found. At Try Gulval,which shows that it has a long history because of its large menhir attached with stoned lined many deposits of animal and human bone, with trevisker pottery of fragments (Russel and Pool 1964).
Mesolithic material is contained in Neolithic and Early Bronze Age lithics which have 45% of spread out on Dartmoor. However, this may lead to periodic reoccupation on the places where there might be promising chances of recovery. Hiatus is revealed between Mesolithic and ensuing Neolithic and Early Bronze Age gatherings by the lithics occurred from the scatter beneath digging at Batworthy Corner.
North Downs
There have been areas like Downs and most regions in prehistoric times which were covered with thick, intense and deciduous woodland. Regions were mostly covered with woods and it is seen that the human activities initially in the early period of time was the area were granted by the primitive megaliths on the scarp in western Kent. However, there have been areas which were surrounded by the river valleys as parts of Roman and showed habitations. The areas which were exposed at the the upper Downs showed some middle ages and colonization as slow pace and this is considered to be a historic arrangement model of parishes. It is surrounded by the boundaried which takes some area of downland, scarpfoot and chartland. This leaded to a framework of the current network of settlements which were explored in the area.
Downs was seen as an extensive regime filled with stocks and the roads were made for driving purpose and they were developed in order to make feasibility for moving animals to the other summer territory. There were some other tracks as well like North Downs Way and this path was an old path surrounded across the ridge and Pilgrim’s Way and lead to the Canterbury.
There are small villages in North Downs especially in the Kent part and is a rural area with rustic background and has some big settlements like Guildford, Chatham and Dover.
There are some urban developments as well especially in the area where Downs bring about London towards Croydon and Sutton. Moreover, in those urban areas there is a spread of speciesrich grassland valleys.
There are diagonal lined tracks and lanes down a bit and they link the Downs with south Wealden Greensand, the tracks are surrounded by trees and the lanes are contracted and constricted with caricature and are steep sided.
Projection with yew and wayfaring tree and white beam it is observed that the views are restricted and wide-ranging and limited to view from the top.
BOUNDARIES AND EDGES
Boundaries and edges of the countryside and local ecologies should be given attention and significance. It is observed that importance is given to the natural environment in order to retain the natural part of the countryside so, the boundaries and edges are taken into notice and have given especial and vital attention to the natural places as stated by Richard Bradley (2000).
A study conducted in 2003 by Stocker and Everson of Titham valley in Lincolnshire, England, shows that the natural places have long value and life in wetlands and are significant. The boundary of Lindsey an independent state was River Witham in the middle ages. Medieval monasteries were situated at the tactical points along the valley according to a research. Access was provided by the causeways across the river and its widespread riparian wetlands. The period of causeways was old enough in the Middle Ages and there were excavations at Fiskerton of one of them. Precursor of Iron Age and Roman date was shown as mentioned by (Field & Parker Pearson 2003). Votive depositions also occurred at causeways areas particularly on the terminals of the cause ways.
In response to this votive depositions were seen in barrow cemeteries of surrounding area of Bronze Age. However, it has been argued by Stocker and Everson that in the Titham valley there are precise locales and they are supposed as places where boundary could be crossed by one. The boundary can be crossed for a period in surplus of the two millennia in spite of having a wetland landscape as of developing nature. Moreover, the Bronze Age insights lead to some sort of middle Ages practices and values.
MARGINALITY AND LIMINALITY
The sixth point is of getting a knowhow of differentiating between peculiarity and liminality. When wetlands go across that idea is known as liminality. This concept of liminality is considered to be fluid concept disreputably. More precisely, this concept is to be taken as and linked to the means of passageway as projected by Van Gennep( 1908). This basically describes the formal rituals and practices which are accompanied by one transition and tell about one specific place into another. Its main focus is on the rites which are related to the birth, adulthood, marriage and death. The real or symbolic doorsteps are part of these rituals and need to cross representing the luminal zones. The equation of liminality with marginality is often mistaken because the economic and ritual activities are not on the level of landscape and are mutually exclusive. Moreover, few liminal zones were originated in marginal landscapes and this can be explained by an example that threshold went through the newlyweds in the advanced world and are positioned in settlements or in the economic areas. More significantly, it is very important to know and be precise when recognizing the places which are liminal.
Lake dwellings in East Yorkshire are an example of how liminality is not connected to marginality. Giving a second look to the ‘Sfest Furze’ lake dwellings showed that it was a type of a track way going through wetlands in the Bail and Low mere complex and the surroundings were giving an effect like early Bronze Age. The wide mires serve as a boundry between the dead and alive on the east we burial mounds and on the west there are human settlements. At West Furze, a track way crosses these wetlands including a doorway at the east of the short track which symbolizes the space and another symbol are the number of human skills found near the boundary.
(Van de Noort 1995; see also Fletcher & Van de Noort this volume)
We should not undermine the wetland landscapes as taskscapes are, because the significance of wetlands determines how they are perceived. Ingold describes “takscapes” as the tasks undertaken at the particular landscapes, through which landscapes are perceived. What insider’s think about wetland is that it has innumerable resources from fish to fuel and from hay lands to reeds. Raised bogs also come in handy we can use them for grazing, preserving butter and for curing of leather too.
We should not undermine the wetland landscapes as taskscapes are, because the significance of wetlands determines how they are perceived. Ingold describes “takscapes” as the tasks undertaken at the particular landscapes, through which landscapes are perceived. What insider’s think about wetland is that it has innumerable resources from fish to fuel and from hay lands to reeds. Raised bogs also come in handy we can use them for grazing, preserving butter and for curing of leather too.
STERILIZATION
A contact is necessary between a patient’s mucous membranes or sterile tissue and any surgical tool or medical instrument during all the invasive procedures. Infection is big risk while undertaking such procedures because of the transfer of pathogenic microbes leading to infection. If the reusable medical equipment is not properly sterilized or disinfected, it can cause a breach risk of host barriers. The level of sterilization or disinfection depends upon the needed use of the equipment: non-critical equipment for example stethoscope having contact with intact skin; semi-critical equipment for example endoscopes having contact with mucous membranes; and critical equipment for example surgical tools having contact with the sterile tissue requires low disinfection, high disinfection and sterilization respectively. Sterilization and high-level of disinfection should be done after cleaning. When choosing the process of sterilization or disinfection, advantages and disadvantages of those processes should be considered by the user. Practices of sterilization and disinfection would be improved in the health care facilities if these recommendations are followed as a result of which infections would be reduced.
During 1996, almost 46,500,000 processes of surgery and large number of invasive medical processes took place in the United States. For instance, almost every year 5 million gastrointestinal endoscopies are practiced in United States. Every process such as this uses medical instrument or surgical tool which has contact with the mucous membranes or sterile tissue of the patient. One of the major risks associated with such processes is infection which can begin because of induction of pathogenic microbes. For instance, if the instrument is not properly sterilized or disinfected, it can lead to contaminated instruments through transmission from patient-to-patient such as contaminated bronchoscopes or Mycobacterium tuberculosis.
For ensuring that the surgical tools and medical devices do not transfer any infectious pathogens to the patients, it is important to use sterilization and disinfectants practices for sterilization and disinfection of instruments respectively. Based on the usage of each item, health care policies should mention cleaning, sterilize or disinfection processes for the items as it is not important to sterilize all the items related to patient-care.
Many countries have conducted studies in which the guidelines for sterilization and disinfection are not followed properly which have led to many occurrences of infections.
This article will discuss a pragmatic approach to the use and selection of practices of sterilization and disinfection based on the well-designed studies’ results which assess the efficacy through laboratory research and effectiveness through clinical investigations of the said procedures.
A RATIONAL APPROACH TO DISINFECTION AND STERILIZATION
A rational approach to the sterilization and disinfection of patient-care tools and items was established by Spaulding almost 35 years ago. During the planning process for sterilization and disinfection, this approach has been widely used by the professionals and other infection-control personnel as it presents a logical and clear procedure which has been refined over time. According to this approach, if the tools and instruments of patient-care are categorized in three groups, the nature of disinfection could be understood more – non critical, semi critical and critical – which is based on the level of infection risk associated with the usage of items. Documents called ‘Guideline for Disinfection and Sterilization in Healthcare Facilities’ and ‘Guidelines for Environmental Infection Control in Health Care Facilities’ use this terminology as given by the Centers for Disease Control and Prevention (CDC).
Critical items
If item is polluted with microorganism such as bacterial spores it leads to some critical objects and has got high risk of getting infected. It is important to sterilize the objects which penetrate into sterlie tissue or the vascular system and is decisive to sterilize them with care. If it is not handled properly it can cause transmission of disease because of the microbial contamination. Surgical instruments, implants, cardiac and urinary catheters, and ultrasound prod which are used in cavities of sterile bodies and are included in this category. Steam sterilization should be used by these items to sterilize or to purchase as sterile. There are various methods for sterilization when the item becomes heat sensitive. Ethylene oxide (ETO) or hydrogen peroxide gas plasma or liquid chemical sterilants can be used as a method to prevent items. Various germicides are categorized as chemical sterilants and are shown in tables 1 and 2. Formulations may vary and may include 2.4% glutaraldehyde with the formulation base, 1.12% of glutaraldehyde with 1.93% phenol/phenate, 7.5% of stabilized hydrogen peroxide, 7.35% of hydrogen peroxide with 0.23% peracetic acid, 0.2% of peracetic acid, and 1.0% of hydrogen peroxide with 0.08% peracetic acid. The range for this exposure time is between 3-12h and has an exception of peracetic acid of 0.2% with 12 minutes time of sporicidal and at 50 to 56 centigrades. A reliable method for sterilization is the using of liquid chemical sterilants but there needs to be treatment of cleaning precedes which helps in removing organic and inorganic material but for this they need to follow guidelines properly regarding concentration and the contact time along with temperature and pH. Sterilizing the devices with sterliants of liquid chemical leads to few other constraints as that of having difficulty in wrapping of devices. While processing is done the devices cannot be wrapped in the sterilant of liquid chemical. Therefore, it is not possible to sterilize after the processing and in the period of storage. Moreover, it is required to rinse the devices with water after they have been exposed to the liquid chemical sterilant. While keeping such constraints in mind regarding the liquid chemical sterilant especially in nonautomated reprocessor the use of such sterilant should be controlled for reprocess of the critical devices which are primarily heat sensitive and contrary with various other methods of sterilization. Semicritical items. The items which appear to be in contact with the membrances of mucous and non intact skin are called semicritical items. In this category equipments used for anesthesia, respiratory-therapy, endoscopes, anorectal manometry catheters, laryngoscope blades, diaphragm-fitting rings, and esophageal manometry probes are incorporated. There should be no microorganisms like fungi, mycobacteria, viruses, and bacteria in such medical devices. However there may be small little bacterial spores present.
Bacterial spores help in resisting to the infections of whole mucous membrances and gastrointestinal tract. However, they are vulnerable to some other organisms like mycobacteria, viruses and other bacteria’s. A high level of disinfection is needed for semicritical items by the use of chemical disinfectants. The US Food and Drug Administration (FDA) have cleared some of the peroxide like glutaraldehyde, chlorine
,ortho-phthalaldehyde (OPA), peracetic acid with hydrogen peroxide and hydrogen peroxide. Moreover, according to tables 1 and 2 there are high level of disinfectants especially when guidelines are followed regarding the effective germicidal procedures. The time duration for exposure of high level of disinfectants may vary ranging from 10 minutes to 45 minutes at a temperature of 20 to 25 centigrade. With the use of ineffective disinfectants an eruption of infection keeps on occurring and also includes alcohol, iodophor and overdiluted glutaraldehyde for the use of high level of disinfection. Chemical compatibility needs to be measured for the items which are disinfected when specific item is used for taking care of the patient. An example shows that cosmetic and functional changes have been seen by the use of compatibility testing which was conducted by the Olympus America with 7.5% of hydrogen peroxide. These changes were seen in the tested endoscopes and likewise it is not supported by the Olympus America to use products which contain hydrogen peroxide especially with peracetic acid. The reason for this is the damages occurred due to the cosmetic and functional changes.
Any semi critical products that came in contact with mucous membranes present in the respiratory and gastrointestinal organs need to be thoroughly washed up with clean, sterile water, or water direct from the tap, which is to be followed by a rinsing from alcohol. The possibility of contamination occurring or a air drying mark being left behind is reduced with the help of the alcohol rinse as it cures and sterilizes the wet area where there can be a possible formation of bacteria. Following this rinsing process, the items should be kept away in a dry place where they can be prevented from being contaminated or damaged in any way. There is no restriction to use only sterilized water or filtered water for the semi critical equipment that are used with the mucous membrane in the rectal probes and anoscopes or in the vaginal probes. These items can be washed with plain tap water. (e.g., anoscopes or rectal probes ) or vagina (e.g., vaginal probes)
Noncritical items.
The equipment that comes in contact with the part that has intact skin is known as non critical items. This equipment is not used in areas of the mucous membrane. Intact skin acts as a successful barricade against the microorganisms, thus it is not critical to ensure the sterility of these equipments. Bedpans, blood-pressure cuffs, crutches, bedrails, linens, bedside tables, patient furniture and the floor are some examples of items that can be classified as non critical. The advantage gained with the non critical items is the fact that they can be decontaminated at their own location after they have been used rather than having to carry them to a central area where they can be sterilized again. This is not the case with critical and semi critical items. There is no evidence of infections and diseases being transmitted to the patients through the use of non critical products when they are used with the mucous membranes or with the nonintact skin areas.
These items (e.g., bedside tables or bed rails) may however be a part of transmitting secondary germs or diseases via contamination through the hands of the hospital staff and workers or by coming in contact with the equipment that will later come in contact with the patients. The following table outlines some of the disinfectants that can be used with this non critical equipment so as to reduce the transmission risk. The time span of the disinfectants is approximately a minute or more.
CURRENT ISSUES IN DISINFECTION ND STERILIZATION
Reprocessing of endoscopes.
Endoscopes are used by the physicians to detect and then treat various diseases. Though endoscopes are effective medical tools and a beneficial tool in the modern science and their use has rarely been linked to any occurrence of an infection, the care-related eruption of infection has frequently been associated to contaminated endoscopes as compared to any other medical tool. In order to avoid the health-related infections, all the heat-sensitive endoscopes such as bronchoscopes, gastrointestinal endoscopes and nasopharyngoscopes should be cleaned and at least should be disinfected at high levels after each use. Although a small number of bacterial spores may be present when there are a good number of spores present, disinfecting at high level destroys all microorganisms.
Recommendations for disinfecting and cleaning the endoscopes are published therefore should be followed closely. Audit results have shown that the guidelines are not being followed on reprocessing by the personnel, thus sadly there is a continuous eruption of infections. Individuals who are responsible for reprocessing should be required to undergo initial as well as annual competency testing in order to be sure that the personnel who should reprocess are properly taught.
After performing leak testing, there are 5 steps that should be followed to disinfect endoscope or to sterilize it with a sterilant liquid chemical or disinfecting at high levels. The first step involves cleaning. Internal as well as external surfaces should be cleaned mechanically which should also include brushing internal channels and with an enzymatic cleaner, flushing each internal channel with water. The second step is disinfecting. Submerge the disinfectant endoscope in a high level disinfectant or a chemical sterilant. Next, suffuse the disinfectant, in such a way that all the air pockets are eliminated and contact with the germicide is assured with the internal channels, to all reachable channels i.e. biopsy/suction channel as well as the water/air channel and then finally disclose the endoscope for septic products as per the recommended time. The third step is rinsing. The endoscope should be rinsed well with sterile water, tap water or filtered water. The fourth step is drying. Before storing and after disinfecting, the inner channels and insertion tube should be rinsed with alcohol and dried with forced air. The final step is storage. The endoscope should be stored in such a way that recontamination is avoided and drying is promoted (hanging vertically is an option).
Sadly, inadequate compliance exists with respect to reprocessing endoscopes. Sometimes the claims regarding the usage of the sterilants and disinfectants of the scientific literature and recommendations differ as that on the manufacturer’s label. An instance of the difference in claims is the time required to achieve a high level disinfection with 2% glutaraldehyde. The efficacy of their germicide formulations in the most awful case conditions and the presence of organic soil is tested by the manufacturers under the FDA requirements. The organic loading represents the soil in which the device is disclosed during genuine use and in the absence of cleaning, it will on the device.
These rigorous tests are developed to ensure a margin of safety for the test bacteria elimination by ensuring that the conditions for germicide contact are complete, if the most complex disinfectant areas are immunized to break in, in the absence of cleaning.
Before the chemical disinfection can be done at 20 C for 20 min, that is, 4-6 log10cfu is to be reduced, it is necessary that the reduction of the levels of M. tuberculosis should be done by minimum 8 log10cfu with cleaning, that is, 4 log10cfu is to be reduced. According to the above information, it is suggested by approximately 14 organizations, which are operating globally, in their authorized endoscope-reprocessing instructions that in order to attain high level of disinfection, a contact should be made at 20 C for 20 min with 2% glutaralehyde, or 20 min exterior of the United States, but simultaneously it contradicts with the manufacturer’s suggestions, provided by them on the tag.
It is crucial to accentuate that cleaning, which is an important phase in the process of disinfection, is not included in the FDA tests. In order to remove all the vegetative bacteria effectively, contact is to be made for 20 min with 2% glutaralehyde in the cleaning phase.
Inactivation of Creutzfeldt-Jakob disease (CJD) agent.
It was found that in the United States one person in a million is effected by CJD, which is a degenerative disease in humans, found every year in the same ratio [35]. A proteinaceous infectious agent or prion could be the reason of this disease. There is a relation between CJD and other human transmissible spongiform encephalopathies (TSEs), including, kuru (also known as eradicated), Gertsmann-Straussler-Sheinker syndrome (one person in 40 million, single year), and fatal insomnia syndrome (one person in 40 million, single year). The physical decontamination and conventional chemical methods were shown an odd confrontation, demonstrated by the agents of TSEs and CJD. There are two reasons behind, one is that the sterilization procedures and the conventional disinfection, which do not inactive the CJD agents, and the other one is the outcome of CJD, which is consistently disastrous. Since many years the disinfection and sterilization processes of the CJD prion remained contentious and unadventurous.
The prevalent recommendations incorporate inactivation data as well as utilize infectivity of human tissue, efficacy of eradicating proteins by cleaning, and epidemiological studies regarding prion transmission. Scientific data explicates that; unique prion reprocessing should be applied to the crucial devices (for instance, surgical equipment) as well as semi-crucial devices which are infected by high-risk tissues (for instance, spinal cord, eye tissues, or brain) pertaining to patients with high-risk (for instance, CJD and other identified prion diseases).
In an instance where high-risk patients, crucial or semi-crucial medical paraphernalia, and high-risk tissues are incorporated then it is appropriate to pursue following methodologies: cleaning the equipment and sterilizing it by means of combining sodium hydroxide with autoclaving (for instance, submerge it in NaOH for one hour, after that remove it and thoroughly rinse it with water, finally for autoclaving shift it to a particular open pan for one hour [on 121 centigrade in gravity displacement sterilizer or on 134 centigrade in porous prevacuum sterilizer)]; after that autoclaving on 134 centigrade in prevacuum sterilizer for eighteen minutes; or autoclaving on 132 centigrade in gravity displacement sterilizer. In the sterilizer, the temperature in any point of time must not increase from 134 centigrade due to the fact that as temperature augments the efficiency of autoclaving diminishes (for instance, to 136 centigrade or 138 centigrade). The medical paraphernalia which has been infected by prion and is complicated to sanitize then it should be disposed. In reprocessing, flash sterilization (for instance, at 132 centigrade steam sterilizing an uncovered paraphernalia for three minutes) must not be implemented. In order to lessen environmental contamination, surfaces which are not crucial environmentally must be wrapped by means of plastic papers; hence, when infected by high-risk tissue, then the paper must be adequately disposed. Those surfaces which are not crucial environmentally (for instance, laboratory surface) and are infected by high-risk tissue must be sanitized and after that the area must be decontaminated through a dilution of 1:10 hypochlorite solution.
Antibiotic-resistant bacteria, bioterrorism agent, and emerging pathogen.
Infection-control experts along with general populace are becoming concerned regarding the emerging pathogens. Significant pathogens entail Escherichia coli O157:H7, hepatitis C virus, multidrug-resistant M. tuberculosi, nontuberculosis mycobacteria (or instance, Mycobacterium chelonae), Cryptosporidium parvum, HIV, rotavirus, Helicobacter pylori, and human papillomavirus. Furthermore, latest studies and papers have contemplated on the biological terrorism’s prospective nature. CDC has segregated numerous agents in “high priority” class due to the act that they are swiftly transmitted from one person to another; they can spur higher rates of mortality, and their identification amidst a populace can effortlessly instigate social disruptions and public fright. The prominent of such agents are, Yersinia pestis (plague), Francisella tularensis (tularemia), arenaviruses (Junin [Argentine hemorrhagic fever] and Lassa [Lassa fever]), Bacillus anthracis (anthrax), variola major (smallpox), filoviruses (Ebola and Marburg [hemorrhagic fever]), and other associated viruses.
Dictated by uncommon omissions (for instance, human papillomavirus), inclination of the above stated pathogens to sterilants and chemical disinfectants have been contemplated; furthermore, every single pathogen (surrogate microbes, like vaccinia pertaining to variola, Bacillus atrophaeus [previously Bacillus subtilis] pertaining to B. anthracis, and feline calicivirus pertaining to Norwalk virus) have been deduced as inclined to the prevalent accessible sterilants and disinfectants.
The customary disinfection and sterilization methodologies pertaining to patient-care paraphernalia (mentioned in this paper) are apposite for disinfection or sterilization of equipment or a device which is infected by blood or any body fluid of a patient who has been identified to be infected by emerging pathogens, bioterrorism agents, or bloodborne pathogens, with the omission of prions (refer to preceding section). In the methodologies of disinfecting, sterilizing or cleaning, there is no necessity of alterations. Additionally, no relevant information exists which can express that the antibiotic-resistant bacteria (for instance, Enterococcus faecium a vancomycin-resistant, M. tuberculosis a multidrug-resistant, and Staphylococcus aureus a methicillin-resistant) are less responsive to the liquid chemical germicide analogous to the antibioticsensitive bacteria on prevalently utilized germicides contact concentration and condition.
Advances in disinfection and sterilization methods.
In the health care sector, new and advance methods have been introduced. For the past number of years these methods of sterilization and disinfection have been used. A type of chemical sterilant named as OPA have been receiving the clearance of FDA at the end of the year 1999. This chemical contains benzenedicarboxaldehyde which is almost 0.55% 1.2. The microbicidal activity has found to be very efficient. Moreover, OPA has been showing a great mycobactericidal performance, it lead to 5 log10in and 5 min being reduced. The result seems to be improved when compared to glutaradehyde. The table 2 below illustrates the benefits and disadvantages of OPA along with its characteristics.
In a recent case, FDA had been able to clear a disinfectant that contained a high level of liquid. This disinfectatnt was superoxidized water that contained chlorine of around 650-675 ppm as estimated. This also contained a fresh sterilization system that uses ozone. Due to data being limited, for assessment of activities of antimicrobial or compatibility of material, these processes have not yet been introduced or have come into practice in USA.
The items of patient care are sterilized in several ways. Some of the methods are, using of steam sterilization, system of acid-immersion, ETO and gas plasma of hydrogen peroxide. The table below illustrates both the benefits and disadvantages of the system
In the year 1987 a new and advance technology of sterilization was patented. It introduced its marketing in USA. The marketing began in 1993 and this technology has plasma as its base, that gas plasma’s included solid, liquid, gas plasma and gas. All the four states of matter. The place from where this gas plasma’s are being generated is a type of deep vacuum which has enclosed chambers. The charged particles are produced through the excitation of gas molecules, this is followed by using of radio frequency or instead microwave energy could be used. Several bacterial spores which are a kind of micro organisms can be inactivated with the help of this process. Different studies have been carried out in against to vegetative bacteria, one of them which include mycobacteria. Others are viruses, yeasts bacterial spores and fungi. To measure how effective the sterilization processes have been various elements would be considered such as lumen diameter and length, salts that are inorganic and other organic materials
CONCLUSION
When properly used, sterilization and disinfection can guarantee the harmless use of noninvasive and invasive medical instruments. The technique of sterilization and disinfection is based on the medical instrument’s planned use: it must be done before use for critical items (which comes in contact with sterile tissue); high-degree disinfection is must for semi-critical items (which comes in contact with non-intact skin or mucous membranes); and low-level sterilization is required for non-critical items (which comes in contact with intact skin). High-level sterilization and disinfection should always be preceded with cleaning and guidelines pertaining to sterilization and disinfection should be adhered to strictly.
ENGINEERING ADHESIVES FOR REPETITIVE STERILIZATION
Introduction
Various sterilization techniques have been employed to disinfect medical instruments during the last four decades. The nature of materials used for manufacturing of these devices during the 60s and 70s required that very careful development of sterilization methods. These materials included glass, metal and rubber in general. Subsequently, newer materials were introduced for manufacturing of these devices as they became better performing and intricate. The older materials have been replaced with new materials which include thermoplastics and thermoset. Moreover, the methods used for assembling the medical devices have been modified also.
The previous medical devices were manufactured by using those methods which were beneficial to the substrates being used. These methods included molding, mechanical fastening or machining. These materials and joining methods used in manufacture of earlier medical devices were easily able to endure various sterilization methods which even included some rigorous techniques.
Progress in contagious diseases along with high performance sterilization devices required a change in the fabrication and assembling techniques of these devices. Specifically, the use of plastics in these devices showed the way to new assembly methods and new issues for resistance to sterilization. Adhesives became the automatic choice for many manufacturers of sterilization devices for a variety of reasons which include:
Capability to bond a range of substrates
Capability to seal and bond
Capability to fill up large gaps
easily automated
Medical devices’ classification comprises of different classifications such as sterile disposables, non-sterile reusable and the modern era’s classification as sterile reusable and resposables. Typical objects such as syringes, oxygenators and catheters are considered as sterile disposables and they were made in such a way that they could only be used for one time. Moreover, sterile disposables are gone through sterilization cycle once or twice before their actual use. Whereas, non-sterile reusables require minimal sterilization requirements and they neither come in to direct blood contact nor with the bodily fluids.
In today’s modern era, normally surgeries do not required incision in patient’s body and insertion of medical instruments. This methodology has given birth to the medical devices known as sterile reusables and responsables as they also help in cost reduction through their re-use. Endoscopes and laproscopes are mainly considered as sterile reusables, whereas, sterile resposables are devices which were initially designed for one time use, but now, they are considered for re-use also, and for both the afore-mentioned devices, repeated sterilization is required. Sterilization method, duration of exposure and the sterilization cycle requirement is based on the type of device being sterilized. Moreover, autoclaving, hydrogen peroxide and chemical immersion are the most likely methods that would be used for the sterilization because of their quick turn-around, advantageous and low toxicity.
Sterilization Methods
The method of eliminating all the traces of living organism from medical instruments, making it sure that they are suitable for human use through heat, chemicals and radiations is referred to as sterilization. Most commonly used sterilization methods are briefly defined in Table I. It is most likely that the methods defined below would be used for the sterilization of reusable/resposable medical devices under typical exposure to temperature.
The biggest challenge which the manufacturers have to tackle is created because of the amalgamation of moisture, pressure and temperature as approximately 80% of the medical devices involve a sterilization method known as Autoclaving. Substrates and joining procedures which are versatile and user friendly must be adopted by the manufacturers, to grasp in most meticulous environments. Under meticulous environments, materials that have advance resistance like autoclaving have been started to get developed by the suppliers of plastic. Like polysulfone and polycarbonate that have specialty grades can be obtained commercially.
Adhesives
Approximately thirty years have been passed since the market started utilizing adhesives. However there are numerous adhesives are offered from the industries but biocompatibility compliance is not possessed by all.
In order to assemble the medical devices urethane and epoxy adhesives, dual UV moisture curable silicone, light curing acrylic, light curing cyanoacrylate and cyanoacrylate are utilized commonly. Normally, in comparison with other methods for assembling medical devices many benefits have been offered by adhesives which include abilities that when it is incarcerated between two substrates it generate a hermetic seal, transversely a bondline stress is allocated in an even way, it has ability to generate bond between the materials that are not similar and large gaps can be filled.
Cyanoacrylate adhesives are the molecules which are polar and linear and they have to pass through an anionic polymerization reaction. Significantly over every surface, moisture or base which is weak in nature is present which prompt the reaction so that the linear chains can be formed. As a stabilizer, weak acids are introduced so that the products do not lose their liquid form. Cyanoacrylate formulations that have disparities in their resistance in temperature, strength properties, cure times and viscosities are also present in numerous varieties.
When Cyanoacrylates are cured they make thermoplastic resins. Numerous limitations in performance were pointed out with formulation alterations, by Eastman Kodak in 1950, when cyanoacrylate resins was introduced for the commercial use initially. Peel strengths and impact which is low, solvent resistance that is lower to moderate has been typically applied by Cyanoacrylates that are based upon the standard unfilled ethyl monomer and the maximum limit of temperature while operation reaches 160 to 180°F. To deal with the initial restraints, specialty formulations are now present that includes for peel strengths and enhanced impact, rubber toughened cyanoacrylates are available, for the cure under environment which has low acidity/humidity and rapid fixture, surface insensitive formulations are present, for minimized frosting, products with low bloom/odor are available and products whose temperature remain up to 250°F while continuous operations are also present.
The pace in the cure is not the only outcome of the considerable development in the accelerator and primer formulations but it has also fastened the capability to bond the plastics which are “hard to bond”, this has been attain beside the technology of ethyl cyanoacrylate. Over the “dead” substrates, reactive species have been deposited by solvent-based systems called primers. Bond strength rises up extensively due to these reactive species for the materials like acetal homopolymer, fluoropolymer, polypropylene and polyethylene as they do not bond easily.
The results through sterilization methods which contain many disparities have been obtained from the examination of cyanoacrylate adhesives. Normally, Cyanoacrylate adhesives are exposed to endure and hydrogen peroxide is involved with (50) cycles of liquid sterilization. Adding to it, resistance in a temperate ratio has been exhibited to autoclave exposure by cyanoacrylate adhesives where some ethyl grades which possesses 100% expertise of their original power goes to be exhibited to (50) autoclave cycles. In order to maintain the strength of bond, cyanoacrylate adhesives are considered as critical aspect, which are followed by the substrates’ assortment while the revelation of autoclave as moderate to high level strength has been offered by them including the steam environment, pressure, rigorous temperature is endured by substrates.
A thermoset resin is formed as a result of its exposure in the light which got suitable intensity and wavelength while through a free radical reaction of light curing acrylics. The viscosities in which light curing acrylic adhesives for example cyanoacrylates are obtainable starts from a lower range (~50cP) to thixotropic gels. Moreover, the resins which are in final cured from vary from soft flexible resins to hard resins which look like glass as they are light curing adhesives.
For the treatment of any adhesive the light reaching fully to the bond line is the most important dispensation key for acrylic adhesives that are the remedial of light otherwise the adhesive which comes under the shadow will not be cure properly. Approximately all the acrylic systems cure the adhesives with the maximum deepness of” 0.5”. The instruments need in the process of the product is another important point to take into consideration when selecting a light cure adhesive.
For the occurrence of result in polymerization light curing adhesives need precise radiant energy that is light energy. As this process is very dangerous therefore, the adhesive with the apposite light source are being coordinated by the end user. Acrylic systems that are typically low in intensity have the standard price of $1000 on the other hand the systems with high intensity can run into the tens of thousands of dollar so the manufacturers of adhesives are suggested to use appropriate system.
Vital benefits of quick fixture are accessible by the light curing acrylic technology for example as little as 5 seconds for select joints, subsequent exposure and this will help in decreasing the work in process (WIP). The broad range of substrates can be cured by the newly designed light curing acrylic formulations and it also clear bond line in a yield when applied in slender sections. The light curing acrylics are improved than that of cyanoacrylate adhesives because of the final resins are thermo set plastics, thermal, chemical and environmental resistance.
Extensively unstable performances followed by the autoclave revelation are also offered by the light curing acrylic adhesives, they also diverge in the preservation of bond strength following formulation based on the exposure, , substrates chosen and preliminary strengths attained. According to the testing 50% or less of initial strengths following fifty autoclave cycles are maintained by the light curing acrylic adhesive.
The benefits of both cyanoacrylate technology and light curing acrylic technology were merged in 1998 in United States and a new technology was commenced. Light curing cyanoacrylates are ethyl based products which have photo initiators in its formulation photo initiators were added. The outcome we get from this product is quick fixture and it also cures the shadowed areas. In general physical performance characteristics are comparable to those attain with a traditional cyanoacrylate because the light curing cyanoacrylates are ethyl monomer based. There are some more advantages given by the new technology for instance, as the exposure of uncured cyanoacrylate can be immediately cured by ultraviolet and/or visible light the blooming/frosting will be decreased. The maximum of 0.010 inches can be increased the deepness of cure over the traditional cyanoacrylate and and compatibility with primers for “hard-to-bond” plastics. Light curing cyanoacrylates would be predictable to execute correspondingly to standard ethyl cyanoacrylates following sterilization exposure including autoclave.
The plastic polymers are formed when the silicone adhesives are cured and it is similar to polyurethane adhesives, however no unbending segments are possessed by silicon so it demonstrate lower cohesive strength and the strength of the polymer itself. There are many types of silicon available including one part moisture care, one part heat cure, and one part dual moisture and light cure formulations. Eventhogh there is the existence of two part silicon in industries, the system be unsuccessful in the biocompatibility screening due to catalyst used in such materials. The moisture curing silicon has limited use in the medical device market because of its primary characteristics. The manufacturers also look for the substitutes for the quic fixture and cure in order to evolve by-product like acetic acid with in 24 hours. The utilization of double curing systems which act in response at first to light and then moisture cure provide cure-on-demand fixture strength followed by full cure up to 72 hours later.
Because of the inferior potential cohesiveness of the polymer, the measurement of the sterilization resistance of silicone adhesives is usually done on the bulk polymer. A minor impact on the percent elongation of the adhesives, however, an around 60% reduction in tensile strength was noted during the examination of dual light cure/moisture silicone cements subsequent exposure to fifty (50) autoclave cycles was performed.
Epoxy adhesives cure to give out thermoset plastics, similar to the prior discussed light curing acrylic adhesives. A catalyst, for example, an amine or mercaptan initiates ring opening of an epoxide group by means of which the polymerization reaction takes place. The availability of room temperature and heat curing one and two part systems is positive. Epoxies present better chemical environmental and thermal resistance because of their capability to crosslink. Epoxies are made utilizable for deep section potting of medical apparatus and needle manufacturing due their capability to unite a broad range of substrates along with their greater gap filling abilities.
The utilization of epoxies on temperature responsive components must be intimately observed due to the fact that they cure via an exothermic reaction (releasing heat in curing). The epoxy has inflexible character when cured, which characteristically end up in low peel strengths, thus making it a second prospective disadvantage of their utilization.
In the availability of one and two part formulations, Polyurethane adhesives are similar to epoxies. The polyol and isocyanate, which are the two major formulation components, react to structure hard and soft sections in the resultant polymer, thus forming a urethane linkage. The exclusively flexible, however strongly cured material is contributed by segments like these. Polyurethane adhesives form thermoset resins once they are cured, therefore displaying fine chemical and environmental resistance, alike various formerly stated chemistries. On the whole, the thermal stability of cured polyurethanes is comparatively lesser than that of cured epoxies, which is, however, significant to notice.
Even though the polyurethane adhesives are substrate flexible, at times they require a surface primer to improve the reactivity of the material that is to be glued. For effective preparation of the surface for the glue, most primers need long on part times. Another downside of using polyurethane adhesives is their innate vulnerability to moisture. Too much dampness on a fraction or in any of the components causes a reaction, which leads to the production of carbon dioxide, follow-on in bubbles in the final product. The superb chemical and thermal properties of epoxy and urethane are one reason why they are often chosen for application. Due to this resistance adhesives are appropriate contenders for the latest medical devices; sterile reusables and reposables. Since there is prospective of continual autoclaving exposure, it is imperative that the producers of reuasable and resposable devices use the adhesives which can tolerate high temperatures and high steam pressure conditions.
Autoclave Resistant Epoxy & Polyurethane Adhesives
The adhesives that were generally used for the production of disposable and reusable medical tools, mainly cyanoacrylates and light curing acrylics, showed low to modest resistance to autoclaving. Lately a research was carried out to find the adhesives that can be used be used for repetitive autoclave sequences whilst having the fringe of ease of use, substrate adaptability and excellent performance. Five adhesives were chosen to be assessed as prospectives to be used for processes that require continuous autoclave exposure; three of the products were epoxy-based and two were polyurethane-based. In the study five substrates evaluated included polycarbonate (PC), stainless steel (S/S), glass, polyvinyl chloride (PVC) and polyetherimide (PEI). Each of them, except for PC, was used for assemblies, divulged to ten and twenty-five repeated autoclave rotations. The sterilization exposure control incorporated six minutes of prevac sterilization at 132°C allowing a three minute period to dry in between the cycles.
The results showed that the epoxy adhesives with low and medium consistency gave great results after ten and twenty five autoclave cycles; there strength remained close to the original. The polyurethane adhesives with medium and low viscosity showed strengths pretty close to the initial. Most of the assemblies pertaining to stainless steel showed adhesive failure.
The three epoxy adhesives executed very well after the twenty five autoclave cycles, upholding their strengths close to the initial. However, after the autoclave exposure, the medium and low viscosity polyutherane adhesives showed a vast decrease in potency. Most of the assemblies that included the epoxy adhesives demonstrated downfall of the substrate; on the other hand, the urethane assemblies presented both, adhesive and cohesive failure.
The five adhesives were also tested on PC lapshear samples. Because of the different qualities of plastic used, the testing with PC was restricted to up to ten autoclave cycles. The epoxy and urethane adhesives with low density showed strengths that were very close to that at the start, while the strengths of the substrates increased in most of the cases. Other adhesives showed a large loss of strength after sterilization ans adhesive failure.
Testing the five adhesives on PVC lap shear showed that overall the assemblies withheld 100-350% of their strengths subsequent to the autoclave exposure. Moreover, all of the autoclaved variety displayed a vast increase in length of the substrate, during the test. This might be one of the causes of the slight melting of the plastic, given that some qualities of PVC have melting temperatures as low as 132°C.
Additionally, the chosen adhesives were also examined on PIE lap shear specimens. At the end it was only the low viscosity samples that retained strengths close to the initial, majority of the epoxy assemblies demonstrated failure successive to autoclave exposure. The urethanes with medium viscosity retained strengths close to and more than the original. Assemblies with urethane showed a blend of adhesive and cohesive and failure.
Summary
It was concluded that adhesive resistance to continual autoclave cycles depends upon adhesive formulation and the substrate being used. Overall, it was deducted that majority of the epoxy and urethane adhesives tested can resist up to twenty five continuous autoclave cycles on a number of different substrates, counting glass, metal and plastic. However, the patent low viscosity epoxy, along with the off-white moderate viscosity urethane adhesives showed strengths of the substrates ranging from70% of the original, to in excess after twenty five autoclave cycles. As adhesive performance is dependent on the substrate, it is best execution is completely assessed to guarantee that the blend of adhesive and substrate are harmonizing with the constant autoclave environments, especially the autoclave.
Careful screening of substrates (like PVC, Glass, and PC) should be conducted in order to ascertain their capability to withstand the conditions in which they will be put under operations for frequent autoclave sterilization. Even before the usage of substrate in resposable or reusable device, close interaction should be maintained with the substrate supplier regarding the evaluation of weakening or/and deformation of substrate.
During 1996, almost 46,500,000 processes of surgery and large number of invasive medical processes took place in the United States. For instance, almost every year 5 million gastrointestinal endoscopies are practiced in United States. Every process such as this uses medical instrument or surgical tool which has contact with the mucous membranes or sterile tissue of the patient. One of the major risks associated with such processes is infection which can begin because of induction of pathogenic microbes. For instance, if the instrument is not properly sterilized or disinfected, it can lead to contaminated instruments through transmission from patient-to-patient such as contaminated bronchoscopes or Mycobacterium tuberculosis.
For ensuring that the surgical tools and medical devices do not transfer any infectious pathogens to the patients, it is important to use sterilization and disinfectants practices for sterilization and disinfection of instruments respectively. Based on the usage of each item, health care policies should mention cleaning, sterilize or disinfection processes for the items as it is not important to sterilize all the items related to patient-care.
Many countries have conducted studies in which the guidelines for sterilization and disinfection are not followed properly which have led to many occurrences of infections.
This article will discuss a pragmatic approach to the use and selection of practices of sterilization and disinfection based on the well-designed studies’ results which assess the efficacy through laboratory research and effectiveness through clinical investigations of the said procedures.
A RATIONAL APPROACH TO DISINFECTION AND STERILIZATION
A rational approach to the sterilization and disinfection of patient-care tools and items was established by Spaulding almost 35 years ago. During the planning process for sterilization and disinfection, this approach has been widely used by the professionals and other infection-control personnel as it presents a logical and clear procedure which has been refined over time. According to this approach, if the tools and instruments of patient-care are categorized in three groups, the nature of disinfection could be understood more – non critical, semi critical and critical – which is based on the level of infection risk associated with the usage of items. Documents called ‘Guideline for Disinfection and Sterilization in Healthcare Facilities’ and ‘Guidelines for Environmental Infection Control in Health Care Facilities’ use this terminology as given by the Centers for Disease Control and Prevention (CDC).
Critical items
If item is polluted with microorganism such as bacterial spores it leads to some critical objects and has got high risk of getting infected. It is important to sterilize the objects which penetrate into sterlie tissue or the vascular system and is decisive to sterilize them with care. If it is not handled properly it can cause transmission of disease because of the microbial contamination. Surgical instruments, implants, cardiac and urinary catheters, and ultrasound prod which are used in cavities of sterile bodies and are included in this category. Steam sterilization should be used by these items to sterilize or to purchase as sterile. There are various methods for sterilization when the item becomes heat sensitive. Ethylene oxide (ETO) or hydrogen peroxide gas plasma or liquid chemical sterilants can be used as a method to prevent items. Various germicides are categorized as chemical sterilants and are shown in tables 1 and 2. Formulations may vary and may include 2.4% glutaraldehyde with the formulation base, 1.12% of glutaraldehyde with 1.93% phenol/phenate, 7.5% of stabilized hydrogen peroxide, 7.35% of hydrogen peroxide with 0.23% peracetic acid, 0.2% of peracetic acid, and 1.0% of hydrogen peroxide with 0.08% peracetic acid. The range for this exposure time is between 3-12h and has an exception of peracetic acid of 0.2% with 12 minutes time of sporicidal and at 50 to 56 centigrades. A reliable method for sterilization is the using of liquid chemical sterilants but there needs to be treatment of cleaning precedes which helps in removing organic and inorganic material but for this they need to follow guidelines properly regarding concentration and the contact time along with temperature and pH. Sterilizing the devices with sterliants of liquid chemical leads to few other constraints as that of having difficulty in wrapping of devices. While processing is done the devices cannot be wrapped in the sterilant of liquid chemical. Therefore, it is not possible to sterilize after the processing and in the period of storage. Moreover, it is required to rinse the devices with water after they have been exposed to the liquid chemical sterilant. While keeping such constraints in mind regarding the liquid chemical sterilant especially in nonautomated reprocessor the use of such sterilant should be controlled for reprocess of the critical devices which are primarily heat sensitive and contrary with various other methods of sterilization. Semicritical items. The items which appear to be in contact with the membrances of mucous and non intact skin are called semicritical items. In this category equipments used for anesthesia, respiratory-therapy, endoscopes, anorectal manometry catheters, laryngoscope blades, diaphragm-fitting rings, and esophageal manometry probes are incorporated. There should be no microorganisms like fungi, mycobacteria, viruses, and bacteria in such medical devices. However there may be small little bacterial spores present.
Bacterial spores help in resisting to the infections of whole mucous membrances and gastrointestinal tract. However, they are vulnerable to some other organisms like mycobacteria, viruses and other bacteria’s. A high level of disinfection is needed for semicritical items by the use of chemical disinfectants. The US Food and Drug Administration (FDA) have cleared some of the peroxide like glutaraldehyde, chlorine
,ortho-phthalaldehyde (OPA), peracetic acid with hydrogen peroxide and hydrogen peroxide. Moreover, according to tables 1 and 2 there are high level of disinfectants especially when guidelines are followed regarding the effective germicidal procedures. The time duration for exposure of high level of disinfectants may vary ranging from 10 minutes to 45 minutes at a temperature of 20 to 25 centigrade. With the use of ineffective disinfectants an eruption of infection keeps on occurring and also includes alcohol, iodophor and overdiluted glutaraldehyde for the use of high level of disinfection. Chemical compatibility needs to be measured for the items which are disinfected when specific item is used for taking care of the patient. An example shows that cosmetic and functional changes have been seen by the use of compatibility testing which was conducted by the Olympus America with 7.5% of hydrogen peroxide. These changes were seen in the tested endoscopes and likewise it is not supported by the Olympus America to use products which contain hydrogen peroxide especially with peracetic acid. The reason for this is the damages occurred due to the cosmetic and functional changes.
Any semi critical products that came in contact with mucous membranes present in the respiratory and gastrointestinal organs need to be thoroughly washed up with clean, sterile water, or water direct from the tap, which is to be followed by a rinsing from alcohol. The possibility of contamination occurring or a air drying mark being left behind is reduced with the help of the alcohol rinse as it cures and sterilizes the wet area where there can be a possible formation of bacteria. Following this rinsing process, the items should be kept away in a dry place where they can be prevented from being contaminated or damaged in any way. There is no restriction to use only sterilized water or filtered water for the semi critical equipment that are used with the mucous membrane in the rectal probes and anoscopes or in the vaginal probes. These items can be washed with plain tap water. (e.g., anoscopes or rectal probes ) or vagina (e.g., vaginal probes)
Noncritical items.
The equipment that comes in contact with the part that has intact skin is known as non critical items. This equipment is not used in areas of the mucous membrane. Intact skin acts as a successful barricade against the microorganisms, thus it is not critical to ensure the sterility of these equipments. Bedpans, blood-pressure cuffs, crutches, bedrails, linens, bedside tables, patient furniture and the floor are some examples of items that can be classified as non critical. The advantage gained with the non critical items is the fact that they can be decontaminated at their own location after they have been used rather than having to carry them to a central area where they can be sterilized again. This is not the case with critical and semi critical items. There is no evidence of infections and diseases being transmitted to the patients through the use of non critical products when they are used with the mucous membranes or with the nonintact skin areas.
These items (e.g., bedside tables or bed rails) may however be a part of transmitting secondary germs or diseases via contamination through the hands of the hospital staff and workers or by coming in contact with the equipment that will later come in contact with the patients. The following table outlines some of the disinfectants that can be used with this non critical equipment so as to reduce the transmission risk. The time span of the disinfectants is approximately a minute or more.
CURRENT ISSUES IN DISINFECTION ND STERILIZATION
Reprocessing of endoscopes.
Endoscopes are used by the physicians to detect and then treat various diseases. Though endoscopes are effective medical tools and a beneficial tool in the modern science and their use has rarely been linked to any occurrence of an infection, the care-related eruption of infection has frequently been associated to contaminated endoscopes as compared to any other medical tool. In order to avoid the health-related infections, all the heat-sensitive endoscopes such as bronchoscopes, gastrointestinal endoscopes and nasopharyngoscopes should be cleaned and at least should be disinfected at high levels after each use. Although a small number of bacterial spores may be present when there are a good number of spores present, disinfecting at high level destroys all microorganisms.
Recommendations for disinfecting and cleaning the endoscopes are published therefore should be followed closely. Audit results have shown that the guidelines are not being followed on reprocessing by the personnel, thus sadly there is a continuous eruption of infections. Individuals who are responsible for reprocessing should be required to undergo initial as well as annual competency testing in order to be sure that the personnel who should reprocess are properly taught.
After performing leak testing, there are 5 steps that should be followed to disinfect endoscope or to sterilize it with a sterilant liquid chemical or disinfecting at high levels. The first step involves cleaning. Internal as well as external surfaces should be cleaned mechanically which should also include brushing internal channels and with an enzymatic cleaner, flushing each internal channel with water. The second step is disinfecting. Submerge the disinfectant endoscope in a high level disinfectant or a chemical sterilant. Next, suffuse the disinfectant, in such a way that all the air pockets are eliminated and contact with the germicide is assured with the internal channels, to all reachable channels i.e. biopsy/suction channel as well as the water/air channel and then finally disclose the endoscope for septic products as per the recommended time. The third step is rinsing. The endoscope should be rinsed well with sterile water, tap water or filtered water. The fourth step is drying. Before storing and after disinfecting, the inner channels and insertion tube should be rinsed with alcohol and dried with forced air. The final step is storage. The endoscope should be stored in such a way that recontamination is avoided and drying is promoted (hanging vertically is an option).
Sadly, inadequate compliance exists with respect to reprocessing endoscopes. Sometimes the claims regarding the usage of the sterilants and disinfectants of the scientific literature and recommendations differ as that on the manufacturer’s label. An instance of the difference in claims is the time required to achieve a high level disinfection with 2% glutaraldehyde. The efficacy of their germicide formulations in the most awful case conditions and the presence of organic soil is tested by the manufacturers under the FDA requirements. The organic loading represents the soil in which the device is disclosed during genuine use and in the absence of cleaning, it will on the device.
These rigorous tests are developed to ensure a margin of safety for the test bacteria elimination by ensuring that the conditions for germicide contact are complete, if the most complex disinfectant areas are immunized to break in, in the absence of cleaning.
Before the chemical disinfection can be done at 20 C for 20 min, that is, 4-6 log10cfu is to be reduced, it is necessary that the reduction of the levels of M. tuberculosis should be done by minimum 8 log10cfu with cleaning, that is, 4 log10cfu is to be reduced. According to the above information, it is suggested by approximately 14 organizations, which are operating globally, in their authorized endoscope-reprocessing instructions that in order to attain high level of disinfection, a contact should be made at 20 C for 20 min with 2% glutaralehyde, or 20 min exterior of the United States, but simultaneously it contradicts with the manufacturer’s suggestions, provided by them on the tag.
It is crucial to accentuate that cleaning, which is an important phase in the process of disinfection, is not included in the FDA tests. In order to remove all the vegetative bacteria effectively, contact is to be made for 20 min with 2% glutaralehyde in the cleaning phase.
Inactivation of Creutzfeldt-Jakob disease (CJD) agent.
It was found that in the United States one person in a million is effected by CJD, which is a degenerative disease in humans, found every year in the same ratio [35]. A proteinaceous infectious agent or prion could be the reason of this disease. There is a relation between CJD and other human transmissible spongiform encephalopathies (TSEs), including, kuru (also known as eradicated), Gertsmann-Straussler-Sheinker syndrome (one person in 40 million, single year), and fatal insomnia syndrome (one person in 40 million, single year). The physical decontamination and conventional chemical methods were shown an odd confrontation, demonstrated by the agents of TSEs and CJD. There are two reasons behind, one is that the sterilization procedures and the conventional disinfection, which do not inactive the CJD agents, and the other one is the outcome of CJD, which is consistently disastrous. Since many years the disinfection and sterilization processes of the CJD prion remained contentious and unadventurous.
The prevalent recommendations incorporate inactivation data as well as utilize infectivity of human tissue, efficacy of eradicating proteins by cleaning, and epidemiological studies regarding prion transmission. Scientific data explicates that; unique prion reprocessing should be applied to the crucial devices (for instance, surgical equipment) as well as semi-crucial devices which are infected by high-risk tissues (for instance, spinal cord, eye tissues, or brain) pertaining to patients with high-risk (for instance, CJD and other identified prion diseases).
In an instance where high-risk patients, crucial or semi-crucial medical paraphernalia, and high-risk tissues are incorporated then it is appropriate to pursue following methodologies: cleaning the equipment and sterilizing it by means of combining sodium hydroxide with autoclaving (for instance, submerge it in NaOH for one hour, after that remove it and thoroughly rinse it with water, finally for autoclaving shift it to a particular open pan for one hour [on 121 centigrade in gravity displacement sterilizer or on 134 centigrade in porous prevacuum sterilizer)]; after that autoclaving on 134 centigrade in prevacuum sterilizer for eighteen minutes; or autoclaving on 132 centigrade in gravity displacement sterilizer. In the sterilizer, the temperature in any point of time must not increase from 134 centigrade due to the fact that as temperature augments the efficiency of autoclaving diminishes (for instance, to 136 centigrade or 138 centigrade). The medical paraphernalia which has been infected by prion and is complicated to sanitize then it should be disposed. In reprocessing, flash sterilization (for instance, at 132 centigrade steam sterilizing an uncovered paraphernalia for three minutes) must not be implemented. In order to lessen environmental contamination, surfaces which are not crucial environmentally must be wrapped by means of plastic papers; hence, when infected by high-risk tissue, then the paper must be adequately disposed. Those surfaces which are not crucial environmentally (for instance, laboratory surface) and are infected by high-risk tissue must be sanitized and after that the area must be decontaminated through a dilution of 1:10 hypochlorite solution.
Antibiotic-resistant bacteria, bioterrorism agent, and emerging pathogen.
Infection-control experts along with general populace are becoming concerned regarding the emerging pathogens. Significant pathogens entail Escherichia coli O157:H7, hepatitis C virus, multidrug-resistant M. tuberculosi, nontuberculosis mycobacteria (or instance, Mycobacterium chelonae), Cryptosporidium parvum, HIV, rotavirus, Helicobacter pylori, and human papillomavirus. Furthermore, latest studies and papers have contemplated on the biological terrorism’s prospective nature. CDC has segregated numerous agents in “high priority” class due to the act that they are swiftly transmitted from one person to another; they can spur higher rates of mortality, and their identification amidst a populace can effortlessly instigate social disruptions and public fright. The prominent of such agents are, Yersinia pestis (plague), Francisella tularensis (tularemia), arenaviruses (Junin [Argentine hemorrhagic fever] and Lassa [Lassa fever]), Bacillus anthracis (anthrax), variola major (smallpox), filoviruses (Ebola and Marburg [hemorrhagic fever]), and other associated viruses.
Dictated by uncommon omissions (for instance, human papillomavirus), inclination of the above stated pathogens to sterilants and chemical disinfectants have been contemplated; furthermore, every single pathogen (surrogate microbes, like vaccinia pertaining to variola, Bacillus atrophaeus [previously Bacillus subtilis] pertaining to B. anthracis, and feline calicivirus pertaining to Norwalk virus) have been deduced as inclined to the prevalent accessible sterilants and disinfectants.
The customary disinfection and sterilization methodologies pertaining to patient-care paraphernalia (mentioned in this paper) are apposite for disinfection or sterilization of equipment or a device which is infected by blood or any body fluid of a patient who has been identified to be infected by emerging pathogens, bioterrorism agents, or bloodborne pathogens, with the omission of prions (refer to preceding section). In the methodologies of disinfecting, sterilizing or cleaning, there is no necessity of alterations. Additionally, no relevant information exists which can express that the antibiotic-resistant bacteria (for instance, Enterococcus faecium a vancomycin-resistant, M. tuberculosis a multidrug-resistant, and Staphylococcus aureus a methicillin-resistant) are less responsive to the liquid chemical germicide analogous to the antibioticsensitive bacteria on prevalently utilized germicides contact concentration and condition.
Advances in disinfection and sterilization methods.
In the health care sector, new and advance methods have been introduced. For the past number of years these methods of sterilization and disinfection have been used. A type of chemical sterilant named as OPA have been receiving the clearance of FDA at the end of the year 1999. This chemical contains benzenedicarboxaldehyde which is almost 0.55% 1.2. The microbicidal activity has found to be very efficient. Moreover, OPA has been showing a great mycobactericidal performance, it lead to 5 log10in and 5 min being reduced. The result seems to be improved when compared to glutaradehyde. The table 2 below illustrates the benefits and disadvantages of OPA along with its characteristics.
In a recent case, FDA had been able to clear a disinfectant that contained a high level of liquid. This disinfectatnt was superoxidized water that contained chlorine of around 650-675 ppm as estimated. This also contained a fresh sterilization system that uses ozone. Due to data being limited, for assessment of activities of antimicrobial or compatibility of material, these processes have not yet been introduced or have come into practice in USA.
The items of patient care are sterilized in several ways. Some of the methods are, using of steam sterilization, system of acid-immersion, ETO and gas plasma of hydrogen peroxide. The table below illustrates both the benefits and disadvantages of the system
In the year 1987 a new and advance technology of sterilization was patented. It introduced its marketing in USA. The marketing began in 1993 and this technology has plasma as its base, that gas plasma’s included solid, liquid, gas plasma and gas. All the four states of matter. The place from where this gas plasma’s are being generated is a type of deep vacuum which has enclosed chambers. The charged particles are produced through the excitation of gas molecules, this is followed by using of radio frequency or instead microwave energy could be used. Several bacterial spores which are a kind of micro organisms can be inactivated with the help of this process. Different studies have been carried out in against to vegetative bacteria, one of them which include mycobacteria. Others are viruses, yeasts bacterial spores and fungi. To measure how effective the sterilization processes have been various elements would be considered such as lumen diameter and length, salts that are inorganic and other organic materials
CONCLUSION
When properly used, sterilization and disinfection can guarantee the harmless use of noninvasive and invasive medical instruments. The technique of sterilization and disinfection is based on the medical instrument’s planned use: it must be done before use for critical items (which comes in contact with sterile tissue); high-degree disinfection is must for semi-critical items (which comes in contact with non-intact skin or mucous membranes); and low-level sterilization is required for non-critical items (which comes in contact with intact skin). High-level sterilization and disinfection should always be preceded with cleaning and guidelines pertaining to sterilization and disinfection should be adhered to strictly.
ENGINEERING ADHESIVES FOR REPETITIVE STERILIZATION
Introduction
Various sterilization techniques have been employed to disinfect medical instruments during the last four decades. The nature of materials used for manufacturing of these devices during the 60s and 70s required that very careful development of sterilization methods. These materials included glass, metal and rubber in general. Subsequently, newer materials were introduced for manufacturing of these devices as they became better performing and intricate. The older materials have been replaced with new materials which include thermoplastics and thermoset. Moreover, the methods used for assembling the medical devices have been modified also.
The previous medical devices were manufactured by using those methods which were beneficial to the substrates being used. These methods included molding, mechanical fastening or machining. These materials and joining methods used in manufacture of earlier medical devices were easily able to endure various sterilization methods which even included some rigorous techniques.
Progress in contagious diseases along with high performance sterilization devices required a change in the fabrication and assembling techniques of these devices. Specifically, the use of plastics in these devices showed the way to new assembly methods and new issues for resistance to sterilization. Adhesives became the automatic choice for many manufacturers of sterilization devices for a variety of reasons which include:
Capability to bond a range of substrates
Capability to seal and bond
Capability to fill up large gaps
easily automated
Medical devices’ classification comprises of different classifications such as sterile disposables, non-sterile reusable and the modern era’s classification as sterile reusable and resposables. Typical objects such as syringes, oxygenators and catheters are considered as sterile disposables and they were made in such a way that they could only be used for one time. Moreover, sterile disposables are gone through sterilization cycle once or twice before their actual use. Whereas, non-sterile reusables require minimal sterilization requirements and they neither come in to direct blood contact nor with the bodily fluids.
In today’s modern era, normally surgeries do not required incision in patient’s body and insertion of medical instruments. This methodology has given birth to the medical devices known as sterile reusables and responsables as they also help in cost reduction through their re-use. Endoscopes and laproscopes are mainly considered as sterile reusables, whereas, sterile resposables are devices which were initially designed for one time use, but now, they are considered for re-use also, and for both the afore-mentioned devices, repeated sterilization is required. Sterilization method, duration of exposure and the sterilization cycle requirement is based on the type of device being sterilized. Moreover, autoclaving, hydrogen peroxide and chemical immersion are the most likely methods that would be used for the sterilization because of their quick turn-around, advantageous and low toxicity.
Sterilization Methods
The method of eliminating all the traces of living organism from medical instruments, making it sure that they are suitable for human use through heat, chemicals and radiations is referred to as sterilization. Most commonly used sterilization methods are briefly defined in Table I. It is most likely that the methods defined below would be used for the sterilization of reusable/resposable medical devices under typical exposure to temperature.
The biggest challenge which the manufacturers have to tackle is created because of the amalgamation of moisture, pressure and temperature as approximately 80% of the medical devices involve a sterilization method known as Autoclaving. Substrates and joining procedures which are versatile and user friendly must be adopted by the manufacturers, to grasp in most meticulous environments. Under meticulous environments, materials that have advance resistance like autoclaving have been started to get developed by the suppliers of plastic. Like polysulfone and polycarbonate that have specialty grades can be obtained commercially.
Adhesives
Approximately thirty years have been passed since the market started utilizing adhesives. However there are numerous adhesives are offered from the industries but biocompatibility compliance is not possessed by all.
In order to assemble the medical devices urethane and epoxy adhesives, dual UV moisture curable silicone, light curing acrylic, light curing cyanoacrylate and cyanoacrylate are utilized commonly. Normally, in comparison with other methods for assembling medical devices many benefits have been offered by adhesives which include abilities that when it is incarcerated between two substrates it generate a hermetic seal, transversely a bondline stress is allocated in an even way, it has ability to generate bond between the materials that are not similar and large gaps can be filled.
Cyanoacrylate adhesives are the molecules which are polar and linear and they have to pass through an anionic polymerization reaction. Significantly over every surface, moisture or base which is weak in nature is present which prompt the reaction so that the linear chains can be formed. As a stabilizer, weak acids are introduced so that the products do not lose their liquid form. Cyanoacrylate formulations that have disparities in their resistance in temperature, strength properties, cure times and viscosities are also present in numerous varieties.
When Cyanoacrylates are cured they make thermoplastic resins. Numerous limitations in performance were pointed out with formulation alterations, by Eastman Kodak in 1950, when cyanoacrylate resins was introduced for the commercial use initially. Peel strengths and impact which is low, solvent resistance that is lower to moderate has been typically applied by Cyanoacrylates that are based upon the standard unfilled ethyl monomer and the maximum limit of temperature while operation reaches 160 to 180°F. To deal with the initial restraints, specialty formulations are now present that includes for peel strengths and enhanced impact, rubber toughened cyanoacrylates are available, for the cure under environment which has low acidity/humidity and rapid fixture, surface insensitive formulations are present, for minimized frosting, products with low bloom/odor are available and products whose temperature remain up to 250°F while continuous operations are also present.
The pace in the cure is not the only outcome of the considerable development in the accelerator and primer formulations but it has also fastened the capability to bond the plastics which are “hard to bond”, this has been attain beside the technology of ethyl cyanoacrylate. Over the “dead” substrates, reactive species have been deposited by solvent-based systems called primers. Bond strength rises up extensively due to these reactive species for the materials like acetal homopolymer, fluoropolymer, polypropylene and polyethylene as they do not bond easily.
The results through sterilization methods which contain many disparities have been obtained from the examination of cyanoacrylate adhesives. Normally, Cyanoacrylate adhesives are exposed to endure and hydrogen peroxide is involved with (50) cycles of liquid sterilization. Adding to it, resistance in a temperate ratio has been exhibited to autoclave exposure by cyanoacrylate adhesives where some ethyl grades which possesses 100% expertise of their original power goes to be exhibited to (50) autoclave cycles. In order to maintain the strength of bond, cyanoacrylate adhesives are considered as critical aspect, which are followed by the substrates’ assortment while the revelation of autoclave as moderate to high level strength has been offered by them including the steam environment, pressure, rigorous temperature is endured by substrates.
A thermoset resin is formed as a result of its exposure in the light which got suitable intensity and wavelength while through a free radical reaction of light curing acrylics. The viscosities in which light curing acrylic adhesives for example cyanoacrylates are obtainable starts from a lower range (~50cP) to thixotropic gels. Moreover, the resins which are in final cured from vary from soft flexible resins to hard resins which look like glass as they are light curing adhesives.
For the treatment of any adhesive the light reaching fully to the bond line is the most important dispensation key for acrylic adhesives that are the remedial of light otherwise the adhesive which comes under the shadow will not be cure properly. Approximately all the acrylic systems cure the adhesives with the maximum deepness of” 0.5”. The instruments need in the process of the product is another important point to take into consideration when selecting a light cure adhesive.
For the occurrence of result in polymerization light curing adhesives need precise radiant energy that is light energy. As this process is very dangerous therefore, the adhesive with the apposite light source are being coordinated by the end user. Acrylic systems that are typically low in intensity have the standard price of $1000 on the other hand the systems with high intensity can run into the tens of thousands of dollar so the manufacturers of adhesives are suggested to use appropriate system.
Vital benefits of quick fixture are accessible by the light curing acrylic technology for example as little as 5 seconds for select joints, subsequent exposure and this will help in decreasing the work in process (WIP). The broad range of substrates can be cured by the newly designed light curing acrylic formulations and it also clear bond line in a yield when applied in slender sections. The light curing acrylics are improved than that of cyanoacrylate adhesives because of the final resins are thermo set plastics, thermal, chemical and environmental resistance.
Extensively unstable performances followed by the autoclave revelation are also offered by the light curing acrylic adhesives, they also diverge in the preservation of bond strength following formulation based on the exposure, , substrates chosen and preliminary strengths attained. According to the testing 50% or less of initial strengths following fifty autoclave cycles are maintained by the light curing acrylic adhesive.
The benefits of both cyanoacrylate technology and light curing acrylic technology were merged in 1998 in United States and a new technology was commenced. Light curing cyanoacrylates are ethyl based products which have photo initiators in its formulation photo initiators were added. The outcome we get from this product is quick fixture and it also cures the shadowed areas. In general physical performance characteristics are comparable to those attain with a traditional cyanoacrylate because the light curing cyanoacrylates are ethyl monomer based. There are some more advantages given by the new technology for instance, as the exposure of uncured cyanoacrylate can be immediately cured by ultraviolet and/or visible light the blooming/frosting will be decreased. The maximum of 0.010 inches can be increased the deepness of cure over the traditional cyanoacrylate and and compatibility with primers for “hard-to-bond” plastics. Light curing cyanoacrylates would be predictable to execute correspondingly to standard ethyl cyanoacrylates following sterilization exposure including autoclave.
The plastic polymers are formed when the silicone adhesives are cured and it is similar to polyurethane adhesives, however no unbending segments are possessed by silicon so it demonstrate lower cohesive strength and the strength of the polymer itself. There are many types of silicon available including one part moisture care, one part heat cure, and one part dual moisture and light cure formulations. Eventhogh there is the existence of two part silicon in industries, the system be unsuccessful in the biocompatibility screening due to catalyst used in such materials. The moisture curing silicon has limited use in the medical device market because of its primary characteristics. The manufacturers also look for the substitutes for the quic fixture and cure in order to evolve by-product like acetic acid with in 24 hours. The utilization of double curing systems which act in response at first to light and then moisture cure provide cure-on-demand fixture strength followed by full cure up to 72 hours later.
Because of the inferior potential cohesiveness of the polymer, the measurement of the sterilization resistance of silicone adhesives is usually done on the bulk polymer. A minor impact on the percent elongation of the adhesives, however, an around 60% reduction in tensile strength was noted during the examination of dual light cure/moisture silicone cements subsequent exposure to fifty (50) autoclave cycles was performed.
Epoxy adhesives cure to give out thermoset plastics, similar to the prior discussed light curing acrylic adhesives. A catalyst, for example, an amine or mercaptan initiates ring opening of an epoxide group by means of which the polymerization reaction takes place. The availability of room temperature and heat curing one and two part systems is positive. Epoxies present better chemical environmental and thermal resistance because of their capability to crosslink. Epoxies are made utilizable for deep section potting of medical apparatus and needle manufacturing due their capability to unite a broad range of substrates along with their greater gap filling abilities.
The utilization of epoxies on temperature responsive components must be intimately observed due to the fact that they cure via an exothermic reaction (releasing heat in curing). The epoxy has inflexible character when cured, which characteristically end up in low peel strengths, thus making it a second prospective disadvantage of their utilization.
In the availability of one and two part formulations, Polyurethane adhesives are similar to epoxies. The polyol and isocyanate, which are the two major formulation components, react to structure hard and soft sections in the resultant polymer, thus forming a urethane linkage. The exclusively flexible, however strongly cured material is contributed by segments like these. Polyurethane adhesives form thermoset resins once they are cured, therefore displaying fine chemical and environmental resistance, alike various formerly stated chemistries. On the whole, the thermal stability of cured polyurethanes is comparatively lesser than that of cured epoxies, which is, however, significant to notice.
Even though the polyurethane adhesives are substrate flexible, at times they require a surface primer to improve the reactivity of the material that is to be glued. For effective preparation of the surface for the glue, most primers need long on part times. Another downside of using polyurethane adhesives is their innate vulnerability to moisture. Too much dampness on a fraction or in any of the components causes a reaction, which leads to the production of carbon dioxide, follow-on in bubbles in the final product. The superb chemical and thermal properties of epoxy and urethane are one reason why they are often chosen for application. Due to this resistance adhesives are appropriate contenders for the latest medical devices; sterile reusables and reposables. Since there is prospective of continual autoclaving exposure, it is imperative that the producers of reuasable and resposable devices use the adhesives which can tolerate high temperatures and high steam pressure conditions.
Autoclave Resistant Epoxy & Polyurethane Adhesives
The adhesives that were generally used for the production of disposable and reusable medical tools, mainly cyanoacrylates and light curing acrylics, showed low to modest resistance to autoclaving. Lately a research was carried out to find the adhesives that can be used be used for repetitive autoclave sequences whilst having the fringe of ease of use, substrate adaptability and excellent performance. Five adhesives were chosen to be assessed as prospectives to be used for processes that require continuous autoclave exposure; three of the products were epoxy-based and two were polyurethane-based. In the study five substrates evaluated included polycarbonate (PC), stainless steel (S/S), glass, polyvinyl chloride (PVC) and polyetherimide (PEI). Each of them, except for PC, was used for assemblies, divulged to ten and twenty-five repeated autoclave rotations. The sterilization exposure control incorporated six minutes of prevac sterilization at 132°C allowing a three minute period to dry in between the cycles.
The results showed that the epoxy adhesives with low and medium consistency gave great results after ten and twenty five autoclave cycles; there strength remained close to the original. The polyurethane adhesives with medium and low viscosity showed strengths pretty close to the initial. Most of the assemblies pertaining to stainless steel showed adhesive failure.
The three epoxy adhesives executed very well after the twenty five autoclave cycles, upholding their strengths close to the initial. However, after the autoclave exposure, the medium and low viscosity polyutherane adhesives showed a vast decrease in potency. Most of the assemblies that included the epoxy adhesives demonstrated downfall of the substrate; on the other hand, the urethane assemblies presented both, adhesive and cohesive failure.
The five adhesives were also tested on PC lapshear samples. Because of the different qualities of plastic used, the testing with PC was restricted to up to ten autoclave cycles. The epoxy and urethane adhesives with low density showed strengths that were very close to that at the start, while the strengths of the substrates increased in most of the cases. Other adhesives showed a large loss of strength after sterilization ans adhesive failure.
Testing the five adhesives on PVC lap shear showed that overall the assemblies withheld 100-350% of their strengths subsequent to the autoclave exposure. Moreover, all of the autoclaved variety displayed a vast increase in length of the substrate, during the test. This might be one of the causes of the slight melting of the plastic, given that some qualities of PVC have melting temperatures as low as 132°C.
Additionally, the chosen adhesives were also examined on PIE lap shear specimens. At the end it was only the low viscosity samples that retained strengths close to the initial, majority of the epoxy assemblies demonstrated failure successive to autoclave exposure. The urethanes with medium viscosity retained strengths close to and more than the original. Assemblies with urethane showed a blend of adhesive and cohesive and failure.
Summary
It was concluded that adhesive resistance to continual autoclave cycles depends upon adhesive formulation and the substrate being used. Overall, it was deducted that majority of the epoxy and urethane adhesives tested can resist up to twenty five continuous autoclave cycles on a number of different substrates, counting glass, metal and plastic. However, the patent low viscosity epoxy, along with the off-white moderate viscosity urethane adhesives showed strengths of the substrates ranging from70% of the original, to in excess after twenty five autoclave cycles. As adhesive performance is dependent on the substrate, it is best execution is completely assessed to guarantee that the blend of adhesive and substrate are harmonizing with the constant autoclave environments, especially the autoclave.
Careful screening of substrates (like PVC, Glass, and PC) should be conducted in order to ascertain their capability to withstand the conditions in which they will be put under operations for frequent autoclave sterilization. Even before the usage of substrate in resposable or reusable device, close interaction should be maintained with the substrate supplier regarding the evaluation of weakening or/and deformation of substrate.
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