Sterilisation of polymers

Some Additional Notes on the Toxic Chemicals Evolving from Degradation, Combustion and Sterilisation of Polymers... 

The interaction of blood with PVC-P based on a phthalate and trimellitate plasticiser has shown that there is a higher reactivity for the trimellitate, which correlated with the plasticiser distribution at the polymer surface (316). Another important aspect is for the medical packaging to be suitable for sterilisation of the contents. Details are available of improving the gamma irradiation stability of PVC-P in order to retain colour (447). In addition to unacceptable colour formation, excessive shifts in pH and extractables can occur in inappropriately stabilised PVC-P (301). An additive system, based on materials approved for medical use, has been developed to give low extractables and low blush with good colour and processability (239). The effects of different plasticisers... 

The solubility of sterilising gases in polymers is important in determining the retention of residues which may, as in the case of ethylene oxide residues, be toxic. The quality control problems of polymers and plastics are considerable. Both the chemical and physical nature of the material has to be taken into account, as well as purity. 

A 100 mg sample of each coating was cut into small pieces, sterilised by UV light, and then dispersed in 9 ml of sterile saline water (0.85 wt%). 1 ml of bacterial (Escherichia coli or Staphylococcus aureus) culture (10 CFU/ml) was subsequently added to this solution and finally the concentration of polymer in the suspension was diluted to reach 10 mg/ml. The flasks were shaken at 90 rpm for 24 h and the temperature was maintained at 37 °C blanks without the coating were also run. The surviving bacteria before and after shaking were counted using the plate count method. 

The blood bag case study illustrates the use of polymeric film as a flexible container. It considers the permeability of polymers, plus processes for fabricating plastics film. Plasticised PVC has dominated the market for years, but there could be a changeover to flexible polyolefin films. The case study on replacement joints for implanting in the body illustrates wear and the effects of wear debris. Research continues on improving the wear resistance of the ultra high molecular weight polyethylene (UHMWPE) and mitigating the effects of sterilisation on the implant properties. 

The cytotoxicity assay is usually performed by determining the viability of suitable cell lines in the presence of polymers. For this test, 3-5 mm discs of polymer film are cut and sterilised under standard conditions (at 121 C and 6.8 kg (15 lb) pressure for 15 min). The cell growth in the presence of the polymer films is measured under a controlled atmosphere (CO2 incubator, 37"C) using an appropriate culture medium, supplemented by 10% fetal bovine serum and penicillin-streptomycin antibiotic solution. Confluent monolayers are propagated by trypsinisation (0.25% trypsin and 0.02% EDTA, ethylene diamine tetraacetic acid) and re-plated at 2 x 10 cells/mL in a sterile polystyrene cell culture plate, then incubated for 24,48 and 72 h. The morphology of the cells is analysed by light naicroscopy (Leica) after... 

Sterilisation by high-energy beams, e.g. y rays or fast electrons beams, is very efficient, as these beams are usually not stopped by materials. However, some covalent bonds of the polymeric network can be broken easily by such a high energy. Depending on the type of polymer and the dose and dose rate of the radiation, permanent chain scission or cross-linking can result from this process, modifying the polymeric structure and properties of the material. 

Evaluating the mechanical and surface properties, toxicity and biocompatibility of polymers and devices before and after sterilisation is relevant in order to select for a given polymer or device a sterilisation process that is efficient against bacteria but is as benign as possible for the polymer, the... 

Other applications of polymers are chemical, solvent, chemical and oil resistant parts, sterilisation, medical components, washing machine and dishwasher components, marine protection, aerospace, missiles, aircraft jet engines, helicopter, helicopter blades, gamma radiation resistant parts, sporting gear, glazing, battery cases and solar panels. 

The mechanical, electrical and thermal properties of polymers are discussed as are other diverse applications such as solvent and detergent resistance, frictional and hardness properties, food packaging applications and gas barrier properties. In addition a very important application is discussed of the resistance of plastics to gamma and other forms of radiation namely their use in nuclear industry, medical applications and food sterilisation. 

Dry heat sterilisation (160-190 °C) No toxic residues Melting and softening of polymers, not usable for PLA-PGA... 

The best method of sterilisation for polymers sensitive to heat and moisture, such as PLA and PGA, is chemical sterilisation by gases such as ethylene oxide (EO). However, this leaves residues in harmful quantities on the surface and within the polymers. Hence, the polymeric implants must then be subjected to degassing or aeration so that residual EO concentrations are reduced to acceptable levels. ... 

Sterilisation by means of ionising radiation of pharmaceutical preparations is not allowed in a number of countries. Many active substances and raw materials are decomposed by the doses required for sterilisation. Some polymers become brittle and glass may become discoloured. For these reasons there is only limited application for this sterilisation method for pharmaceutical preparations. Radiation sterilisation is however widely used in the medical device industry. 

DMA can also be used to investigate the effect of sterilisation on the structural and thermal properties of polymers and composites intended for biomedical use. Due to the sensitivity of some polymers to heat and solvent attack, one option to sterilise would be to y -irradiate. In a study investigating the properties of composite materials consisting of bioceramic fillers. 

It has a low heat distortion temperature (85°C) and, hence, articles made of it cannot be sterilised with steam, yellowing and cracking of the polymer on outdoor exposure is another main drawback. 

Since MIPs are highly stable and can be sterilised, they are valuable for use in biotransformation processes (Ramstrom and Mosbach, 1999). The application of MIP in catalytic reaction has been demonstrated with reference to the enzymic condensation of Z-L-aspartic acid with L-phenylalanine methyl ester to give Z-aspartame (Ye et al., 1999). In this study, when the product-imprinted polymer was present, a considerable increase (40%) in product yield was found. 

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