Stérilisation par plasma à basse pression: Mécanismes et effets sur les polymères biomédicaux

Two articles present our work on materials alteration induced by commercial plasma-based sterilizers, in comparison with exposure to pure ethylene oxide (EO), currently the most commonly used low-temperature clinical sterilization method. In the first article, we report cumulative surface modifications generated on various polymeric devices; surface oxidation and wettability changes are observed on all samples sterilized by plasma-based techniques, oxidation tending to be more gradual with Sterrad^®. In the case of Plazlyte™, the maximum level of oxidation is already attained after the first sterilization cycle, and low molecular weight molecules (oxidized molecules created by scission on the polymer surface, or residues from the chemical agent) are released into the water bath during contact angle measurements.

To deepen our analysis and extend it to the case of possible bulk modifications, we have chosen a particular type of device, namely single-use electrophysiology polyurethane catheters used at the Montreal Heart Institute (article 2). Oxidation by plasma sterilization is restricted to the near-surface layer, while EO induces a slight but deeper-penetrating alkylation. Bulk modification is limited to the consumption of an anti-oxidant additive with Sterrad^®, and to alteration of oligomers by Sterrad^® and Plazlyte™ treatments, which lead to the more noticeable release of these products during biostability studies. These are not large changes so that mechanical properties likely remain unchanged, but the observed modifications may have potential toxic effects. We have initiated a biocompatibility study to evaluate these.

For the second part of the thesis, concerning the destruction mechanism of microorganisms by plasma, we used two microwave (MW) plasma reactors developed in the Plasma Processes Laboratory at Ecole Polytechnique, which allow one to control experimental parameters. Microbiological studies were performed using Bacillus subtilis spores, which are very resistant to sterilization processes, and to plasma in particular. Based on literature data about plasma sterilization and plasma treatment of polymers, we have put forward the hypothesis that etching (or volatilization) is the main mechanism of spore destruction (article 3). We have demonstrated, for the first time, the importance of etching in the destruction of bacterial spores.

The numerous experimental parameters which influence plasma efficiency, by determining the types and concentrations of active species reaching microorganisms, are summarized in the general discussion. (Abstract shortened by UMI.)