Development of Low-temperature Sterilization Technique Using Microwave Plasma and Its Medical Application

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In this research, we aimed at developing a novel low-temperature sterilization technique using large-volume microwave plasma and finally applying the results to the medical field. In the fiscal year 2004, we have carried out the experiments to clarify the mechanism of plasma sterilization and to study the possibility of improving the characteristics of rapid sterilization at low temperature. In the fiscal years 2005 and 2006, we have performed the experimental verification of low-temperature internal sterilization for the wrapped medical instruments using the volume-wave plasma in order to confirm the sterilization of specific medical equipments such as catheter. In the following, we listed the main results of the present research.(1) Clarification of the sterilization mechanism of oxygen plasma: It was experimentally confirmed that the etching effect due to the oxygen radicals was the main sterilizing factor in the oxygen plasma. While no strong UV emission was observed in the oxygen … More plasma, it was shown that the UV emissions were main factor in the nitrogen plasma, since there were several strong UV emissions in the range of 290〜400 nm.(2) Reduction of thermal effect by means of on-off control of microwave plasma: It is required to avoid thermal effect in the case of plastic medical instruments, because of non-heat resist materials. By introducing the time-modulated operation of microwave plasma, we succeeded to reduce the temperature of the samples less than 70 ℃.(3) Experiment of volume-wave plasma production: To sterilize inside the wrapped articles, we have carried out the sterilization experiment using the volume-wave plasma. We confirmed that the plasma was produced inside the plastic bottle. By using the pulsed-microwave plasma, we confirmed the sterilization of biological indicators (Bacillus Atrophaous) wrapped by glassine paper within 20 min.(4) Effect of OH radicals: We have investigated the effect of water vapor addition on the sterilization performance using the microwave plasma with air-simulated nitrogen-oxygen gas mixture. From the results, it was deduced that the water vapor played an important role on the improvement of sterilization speed. The collapse of spore cells might be attributed to the OH radicals generated in the plasma.(5) Summary of results: We reported 16 journal papers, 2 books, 38 proceeding of international conferences, and 132 presentations in the domestic meetings. We also applied 7 domestic and foreign patents relating with the present plasma sterilization, and we have taken one patent on the plasma sterilization method. Less