Low-temperature low-damage sterilization based on UV radiation through plasma immersion

Abstract

This paper introduces a new type of high-frequency (HF) sustained discharge where the HF field applicator is a planar transmission line that allows us to fill with plasma a long chamber of rectangular cross-section (typically 1 m × 15 cm × 5 cm). Peculiar interesting features of this plasma source are a low gas temperature (typically below 40 °C in the 1 Torr range in argon), broadband impedance matching with no need for retuning, stability and reproducibility of the discharge (non-resonant behaviour). This type of plasma source could be useful for web processing; nonetheless, it is applied here to plasma sterilization, taking advantage of its low gas temperature to inactivate microorganisms on polymer-made medical devices to avoid damaging them. The predominant biocide species are the UV photons emitted by the discharge whereas most plasma sterilization techniques call for reactive species such as O atoms and OH molecules, which induce significant erosion damage on polymers. Polystyrene microspheres are actually observed to be erosion-free under the current plasma sterilization conditions (scanning electron micrographs have been examined). Moreover, inactivation is quite fast: 106 B. atrophaeus spores deposited on a Petri dish are inactivated in less than 1 min. Correlation of the UV radiation with the spore inactivation rate is examined by (i) considering the emitted light intensity integrated over the 112–180 nm vacuum UV (VUV) range with a photomultiplier; (ii) looking with an optical spectrometer at the emission spectrum over the 200–400 nm UV range; (iii) using absorption spectroscopy to determine the role of the VUV argon resonant lines (105 and 107 nm) on spore inactivation. It is found that the test-reference spores are mainly inactivated by VUV photons (112–180 nm) that are primarily emitted by impurities present in the argon plasma.

Designing plasmas for chronic wound disinfection

“…This 'loading effect' has been described previously for the plasma sterilization of solid surfaces [14,15]. The observed correlation between the initial bacterial density and the efficacy of surface sterilization was nonlinear and differed for plasma and UV radiation.…”

“…A major portion of the bactericidal effect of plasma-generated UV is attributed to the mutagenic properties of short-wavelength UV [31,32]. Short-wavelength UV radiation is dangerous for mammalian cells as well [8,33].…”

“…In addition, the results of this experiment show that the relative bactericidal contribution of the plasma-generated UV and 'non-UV' plasma components also depends on the initial bacterial density in the liquid medium. There are several factors that explain the observed correlation including (i) the geometry of bacterial distribution in the irradiated liquids (shadowing by bacteria [15] and shadowing by the medium) and (ii) buffering (antioxidative) activity of the bacterial suspension. The geometry of bacterial distribution has the major effect on the sterilizing efficacy of UV radiation.…”

Sterilization/disinfection of medical devices using plasma: the flowing afterglow of the reduced-pressure N2-O2discharge as the inactivating medium

“…Furthermore, in actual life, these microorganisms can be embedded in a bio-burden (bio-products), as in Figure 1b (which originates, for example, from coagulated blood), thereby reducing or even preventing their contact with the biocidal agents. Some bio-products, including proteins 3 and various organic molecules, can furthermore have an infectious or pyrogenic action: this is the case, respectively, of the Creutzfeldt-Jakob pathogenic prion proteins and of some pyrogenic molecules, the latter stemming mostly from the membranes of Gram-negative and Gram-positive bacteria. 4 The bottom line is that: (i) bio-products, in principle, should not be found on MDs once the latter have gone through an appropriate cleaning procedure (e.g., agitation, brushing, washing and sonicating, followed by visual inspection) prior to their submission to the sterilization process; (ii) nonetheless, low-level infectious loads can (a) (b) Fig.…”

“…1. Scanning electron microscopy (SEM) images of: (a) "clean" isolated as well as stacked spores [3]; (b) spores embedded in a bio-product [4].…”