Pierre Levif

Packaging materials for plasma sterilization with the flowing afterglow of an N2–O2 discharge: damage assessment and inactivation efficiency of enclosed bacterial spores

In conventional sterilization methods (steam, ozone, gaseous chemicals), after their proper cleaning, medical devices are wrapped/enclosed in adequate packaging materials, then closed/sealed before initiating the sterilization process: these packaging materials thus need to be porous. Gaseous plasma sterilization being still under development, evaluation and comparison of packaging materials have not yet been reported in the literature. To this end, we have subjected various porous packagings used with conventional sterilization systems to the N2–O2 flowing afterglow and also a non-porous one to evaluate and compare their characteristics towards the inactivation of B. atrophaeus endospores deposited on a Petri dish and enclosed in such packagings. Because the sterilization process with the N2–O2 discharge afterglow is conducted under reduced-pressure conditions, non-porous pouches can be sealed only after returning to atmospheric pressure. All the tests were therefore conducted with one end of the packaging freely opened, post-sealing being required. The features of these packaging materials, namely mass loss, resistance, toxicity to human cells as well as some characteristics specific to the plasma method used such as ultraviolet transparency, were examined before and after exposure to the flowing afterglow. All of our results show that the non-porous packaging considered is much more suitable than the conventionally used porous ones as far as ensuring an efficient and low-damage sterilization process with an N2–O2 plasma-afterglow is concerned.

Sterilization/disinfection using reduced-pressure plasmas: some differences between direct exposure of bacterial spores to a discharge and their exposure to a flowing afterglow

The use of plasma for sterilization or disinfection offers a promising alternative to conventional steam or chemical approaches. Plasma can operate at temperatures less damaging to some heat-sensitive medical devices and, in contrast to chemicals, can be non-toxic and non-polluting for the operator and the environment, respectively. Direct exposure to the gaseous discharge (comprising an electric field and ions/electrons) or exposure to its afterglow (no E-field) can both be envisaged a priori, since these two methods can achieve sterility. However, important issues must be considered besides the sterility goal. Direct exposure to the discharge, although yielding a faster inactivation of microorganisms, is shown to be potentially more aggressive to materials and sometimes subjected to the shadowing effect that precludes the sterilization of complex-form items. These two drawbacks can be successfully minimized with an adequate flowing-afterglow exposure. Most importantly, the current paper shows that direct exposure to the discharge can lead to the dislodgment and release of viable microorganisms from their substratum. Such a phenomenon could be responsible for the recontamination of sterilized devices as well as possible contamination of the ambient surroundings, additionally yielding an erroneous over-appreciation of the inactivation efficiency. The operation of the N2–O2 flowing afterglow system being developed in our group is such that there are no ions and electrons left in the process chamber (late-afterglow regime) in full contrast with their presence in the discharge. The dislodgment and release of spores could be attributed, based on the literature, to their electrostatic charging by electrons, leading to an (outward) electrostatic stress that exceeds the adhesion of the spores on their substrate.

The flowing afterglow of the N 2 -O 2 discharge as a means of decontaminating/sterilising through UV irradiation: Summary of the research achieved and recent results

Summary form only given. The plasma systems for disinfection/sterilization that we have been working on are mainly based on UV irradiation while most plasma “sterilisers” are calling on ions and radicals. In the latter case, inactivation generally proceeds from erosion of the microorganisms while, in the former case, the UV photons create enough lesions to the DNA genetic material to prevent its repair. Inactivation of microorganisms through UV photons in the afterglow is, however, much slower than in the discharge itself. The UV photons stem from NO excited molecules, which are generated following the interaction of N and O atoms, in the flowing afterglow, which are coming from the dissociation of N 2 and O 2 in the (microwave) discharge. Since the N and O atoms can diffuse into crevices before joining into NO molecules, there is no limited accessibility of the UV photons as with a UV lamp. The NO γ molecular system shows band heads that cover almost continuously the 180–350 nm range.

Control of biocidal properties conferred to polymers by dry ozone exposure for achieving inactivation of B.atropaheus spores

Summary form only given. Surfaces of materials can be modified to ensure specific interaction features with microorganisms. Polymeric surfaces subjected to dry gaseous ozone acquire the ability to inactivate microorganisms, including those as resistant as bacterial spores [1]. However, the inactivation efficacy level depends strongly on the type of polymer considered: for instance, polymers such as silicone, polyurethane and polystyrene provide high inactivation rates, while polypropylene and polymethylmetacrylate are particularly inefficient; polyethylene and Teflon show no biocidal activity at all [2]. The originality and advantages of this ozone treatment of polymer surfaces rest on its simplicity (achieved at ambient temperature and pressure, a one step process) and its efficacy.