medical devices

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Toxicity Testing of Polymer Materials for Dialysis Equipment: Reconsidering In Vivo Testing

Per Kjellstrand, Eva Lindqvist and Carin Nilsson-Thorell

The rationale for preclinical testing of plastic materials for medical devices is the protection of patients from leachable toxic substances. A controversial and costly part of this testing is the use of animal in vivo procedures. The objective of the present study was to analyse the importance of in vivo tests in relation to the decision to approve or not to approve materials for use. A total of 1044 plastic materials were analysed by employing chemical, in vitro and in vivo tests: 5708 in vivo tests were performed. In only one out of 2650 systemic injection tests on mice did a material fail. As that material also failed in chemical tests, the systemic injection test had no influence on the decision not to approve the material. Intradermal irritation (2644 tests), implantation (398 tests) and sensitivity (11 tests) procedures on rabbits and guinea-pigs were the other in vivo tests. However, in all except three cases, the same decision on whether or not to use a material would have been reached without any of these in vivo tests. Thus, little security appears to be gained from the in vivo tests, and abandoning them would save resources, probably without any additional risk.
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An Evaluation of Sterilisation Processes

Dariusz Ĺšladowski, Iwona Grabska-Liberek, Joanna Olkowska-Truchanowicz, Kamil Lipski and Grzegorz Gut

A sterile environment is one of the basic elements of in vitro cell culture. When choosing an appropriate sterilisation method, the possibility that the physical and chemical properties of the sterilised material could be altered by the sterilisation process itself, should be considered. Avoiding any potential problems of toxicity arising as a consequence of the sterilisation process is essential, not only in in vitro cell culture procedures, but especially in the case of the sterilisation of medical devices which come into contact with human tissue (e.g. catheters, surgical tools, and containers used for transplant preparation and storage). As it is not possible to predict the potential effects of every combination of test material and sterilisation process, we have designed a simple test, which can be easily performed to ensure the absence of cytotoxicity. The test involves the culturing of a non-adherent cell line in direct contact with the test material, in micro-wells attached to the surface of the test device. By using this novel test method, three sterilisation procedures were compared for each material. The results indicated that, neither ionising irradiation nor ethylene oxide left toxic residues on the surface of polystyrene; and that, in the case of steel, neither steam sterilisation nor ethylene oxide left toxic residues on the metal. The cold plasma system, which left toxic residues on the surface of both materials, required a post-sterilisation period of 24 hours in the case of steel, and 10 days in the case of polystyrene, in order to eliminate toxic residues prior to their use.
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