Irradiation sterilisation

Lu S, Orr JF, Buchanan FJ. The influence of inert packaging on the shelf ageing of gamma-irradiation sterilised ultra-high molecular weight polyethylene. Biomaterials 2003 January 24(l) 139-45. 

Following the favourable response of this committee, steps were taken to amend the existing UK legislation which permitted only the radiation sterilisation of foods for people whose immune response was compromised. New regulations came into force in early 1991 which permitted the irradiation of seven groups of foods under strictly controlled conditions (Anon., 1990a) (Table 1). 

The methods of preparation of glassware are indicated in Chapter 8, and if sterilisation is monitored as described the glassware should not be a source of contamination. Likewise plasticware is obtained from the manufacturer in a sterile condition. Usually sterilisation of plastic is achieved using ethylene oxide or irradiation procedures and vessels are supplied wrapped in cellophane. 

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... 

Plasticised PVC was surface modified by nucleophilic substitution of the chlorine atoms of PVC by sulphide ions in aqueous media in the presence of a phase-transfer catalyst. The modified PVC was sterilised by steam autoclaving and gamma irradiation and subjected to plasticiser extraction. Surfaces were evaluated by contact angle measurements, SEM, cell culture studies, haemolysis assay and whole-blood clotting time measurements. Mechanical properties were examined. 31 refs. 

In a current developing standards document being considered for the international sterilisation community, under a section on Dosimeters , it is specified that each batch of dosimeters to be used must be properly calibrated. This entails either (1) irradiation of a user s dosimeter in a standards or accredited reference (secondary) laboratory, and subsequent appropriate evaluation by the user, (2) irradiation in a suitably designed irradiation geometry in the user s laboratory along with dosimeters issued by a standards or reference laboratory, or (3) use of a radiation field where the calibration is traceable to a standards laboratory, according to an acceptable accreditation procedure. 

Seille, J.M. Delattre, L. Meurice, L. Jaminet, F. Etude de I effet d une sterilisation a I oxide d ethylene sur les teneurs residuelles en chlorhydrine du glycol et en ethyleneglycol dans des articles medico-chirurgicaux a base de PVC, prea-lablement irradies au cobalt 60. J. Pharm. Belg. 1985,40 (4), 213-221. 

Similar reactions are involved with the organotin stablilisers in PVC wrapping film when food is sterilised by y-irradiation.57... 

The ampoules were filled with the CRM solution and left in contact with the solution for at least 24 h. After the conditioning each ampoule was emptied, filled with the solution and immediately heat-sealed. The samples were sterilised by gamma-irradiation with a °Co source, dose 25 kGy. After irradiation the ampoules were stored at ambient temperature in the dark. Some differences were observed in the contents before and after irradiation, particularly in the CRM 408 for hydronium, ammonium and nitrate. It was suspected that nitrate could have been formed from ammonium upon irradiation. Nitrite was also detected immediately after irradiation but was probably rapidly oxidised. 

The optimal stabilisation procedure (by gamma-irradiation) investigated on the test material in the interlaboratory study [17] was used on the candidate CRM. The optimal gamma-ray irradiation dose was found to be 8 kGy upon which the sterilisation of the sediment was achieved without affecting the methylmercury content [17,19). 

Packaging for sterile products must be effectively contained and sealed to prevent microbial contamination, and must be robust enough to withstand any sterilisation process required. The sterilisation process can affect the leaching of components from the container into the product or affect the physical properties of the container. For example, autoclaving can soften plastic containers, and gamma irradiation can cause certain polymers to cross link. 

Semi-solid products have been traditionally packed in collapsible tin tubes. Metal tubes are a potential source of metal particles in ophthalmic products, and so the tubes have to be cleaned carefully prior to sterilisation. Also, the final product must meet limits for the number of metal particles found. Plastic tubes are not suitable because of their non-collapsible nature, which causes air to enter the tube after withdrawal of each dose. However, collapsible tubes made from laminates of plastic, aluminium foil and paper are a good alternative to tin tubes. Laminated tubes fitted with polypropylene caps can be sterilised by autoclaving, whereas tubes fitted with polyethylene caps are sterilised by gamma irradiation. The tubes are usually filled aseptically, sealed with an adhesive and then crimped. 

Process development studies showed that terminal sterilisation of the gel was not possible. Heat sterilisation and gamma irradiation methods both caused unacceptable physical degradation of the gel and also caused chlorbutol hydrolysis. Aseptic filtration was not possible because the drug was suspended in the gel vehicle and viscosity would also have been a problem. The process described below was therefore developed with consideration of the sterilisation of the product components and the maintenance of asepsis throughout manufacture. 

Any plastic constituent in addition to the function it serves must have heat stability, UV light stability, weather resistance, low solubility in terms of extraction, compatibility with other constituents and good dispensability. Where plastics have to be sterilised by irradiation, certain constituents may be degraded, or even continue to degrade after irradiation. Certain antioxidants are degraded by gamma irradiation. 

The accelerated electrons method is similar to gamma irradiation but milder in its effects on plastics. For this reason its usage is slowly increasing, with a number of plants now in use. Accelerated electrons or beta rays have lower penetration powers (compared with gamma irradiation) and sterilisation is normally achieved in seconds rather than hours. Effective checks are essential to establish whether any physical or chemical changes have any significance. 

Gamma irradiation of 25 kGy or above and accelerated electrons tend to cause similar changes to the product/pack. These processes are normally used as part of an aseptic process to sterilise the pack components before use, since many products tend to degrade if terminally sterilised. Some contact lens solutions and normal saline products can be satisfactorily gamma irradiated in a suitable plastic or metal pack (aerosols). 

Resistance to sterilisation process (dry heat, moist heat, irradiation, UV, etc.). 

Thicker grades can be thermoformed (medical and pharmaceutical applications) and subsequently sterilised by steam autoclaving, gamma irradiation, etc. Non-oriented PET has a high melting point, around 250°C. 

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