Metallic surgical instruments are normally sterilized in steam sterilizers called autoclaves at temperatures high enough to kill microorganisms (121 °C or higher), but central venous catheters and other equipment made of polymeric materials such as silicone or polyurethane cannot withstand high temperatures, so different techniques must be used to sterilize them.
The usual solution is to use microbicidal agents such as ethylene oxide or gamma radiation, but these involve expensive technology and can generate toxic residues.
An alternative sterilization procedure using an atmospheric-pressure air plasma jet has been proposed and successfully tested by Anelise Doria, a professor at Paraíba Valley University (UNIVAP) in São José dos Campos, São Paulo State, Brazil.
“We used a simple design. The device is cheap to make and operate and produces large amounts of microbicidal agents without using toxic gases or generating hazardous residues,” Doria told Agência FAPESP.
The partial ionization of atmospheric air creates a plasma consisting of molecules, ions and free electrons, with a large quantity of reactive species, such as ozone (O3), hydrogen peroxide (H2O2) and hydroxyl radical (OH-). Microorganisms are inactivated or eliminated by these reactive species.
“We studied the action of the plasma on Candida albicans biofilms grown on the surface of a polymeric material. The biofilm’s structure is known to protect microorganisms, making them far more resistant to microbicidal agents. Nevertheless, we succeeded in inactivating up to 99% of the microorganisms tested,” Doria said.
The plasma used in the study was a mixture of compressed air with small amounts of argon (Ar) and helium (He), noble gases widely used to inhibit unwanted chemical reactions. The mixture was ionized as it traveled between two electrodes subjected to a large electrical potential difference (7.5 kilovolts).
“The plasma plume was about 1 cm long. To prevent heating of the fungal biofilm by direct contact with the plume, we placed our sample 3 cm away from the ejection nozzle. Sterilization was not performed directly by the plume but by the flow of ambient air from the post-discharge region,” Doria said.
The researchers chose C. albicans because this fungus is present in 70%-90% of hospital-acquired infections with high mortality rates, but the procedure can also be used to eliminate bacteria, according to Doria.
The study was conducted in a laboratory established with funding from FAPESP via the Thematic Project “Center for excellence in plasma physics and applications”, for which the principal investigator was Ricardo Magnus Osório Galvão, a professor at the University of São Paulo’s Physics Institute (IF-USP).
The article “Inactivation of Candida albicans biofilms by atmospheric gliding arc plasma jet: effect of gas chemistry/flow and plasma pulsing” (doi: https://doi.org/10.1088/2516-1067/aae7e1) by A. C. O. C. Doria, F. R. Figueira, J. S. B. de Lima, J. A. N. Figueira, A. H. R. Castro, B. N. Sismanoglu, G. Petraconi, H. S. Maciel, S. Khouri and R. S. Pessoa can be read at https://iopscience.iop.org/article/10.1088/2516-1067/aae7e1.
Other articles by Doria on the same topic can be retrieved from https://bit.ly/32BoLYH.