How to effectively decontaminate heat-sensitive materials, and why the usual methods are not sufficient? Conventional autoclaves are most commonly used for sterilization and operate at temperatures above 100°C and pressures greater than 2 bar. For example, various medical instruments and tools, such as scalpels, dental instruments, etc., are commonly sterilized and decontaminated using autoclaves.
Heat-sensitive materials (e.g., biological) cannot be decontaminated or sterilized using high-temperature processes. Higher temperatures would destroy such material. Heat-sensitive materials are advanced catheters, variously shaped 3D and polymer materials, or standard medical supplies such as disposable gloves. In the healthcare and chemical industries, it is also essential to consider the environmentally friendly and safe disposal of the used materials.
This issue has been addressed by scientists from the research group Plasma Nanotechnologies and Bioapplications at the Department of Plasma Physics and Technology and CEPLANT within the framework of the TAČR ZÉTA-4 project TJ04000329 entitled "Optimization of the generation of plasma-activated media with high ozone and hydrogen peroxide content for decontamination of heat-sensitive materials." The lead investigator at MU was Dr. Zlata Kelar Tučeková. The project partner was Roplass s.r.o., a spin-off company of Masaryk University and scientists from the Department of Microbiology of MU Faculty of Medicine.
At the beginning of the project was the previous collaboration within the project TG02010067 of Dr. Richard Krumpolec with scientists from the Faculty of Medicine of Masaryk University on plasma activation of water vapor. The TAČR ZÉTA-4 project followed the results of previous research. The project aimed to determine the conditions for effective decontamination of heat-sensitive materials using atmospheric pressure plasma technology.
A unique surface dielectric barrier discharge (SDBD) generates a plasma that activates the working gas to form active decontamination particles in a gaseous medium. The tested gas mixture contained ozone (O3) and hydrogen peroxide (H2O2). The scientists determined the inactivation of various pathogens through microbiological tests.
The DPPT research team investigated the plasma properties and studied the composition and concentration of gaseous products depending on the set conditions and plasma parameters. In doing so, they optimized the used plasma source. "The TAČR ZETA project focused on the application potential. We do not yet understand much about the plasma chemistry of the tested process. However, this is part of the long-term research at the DPPT," comments Dr. Kelar Tučeková.
The company Roplass ensures the production of plasma sources characterized by stable conditions in the long-term operation, which can generate sufficient concertation of active particles. The company, with Dr. Jakub Kelar in the role of principal investigator of the project, is responsible for producing the prototype of the decontamination chamber, its commercialization, and sales. Under the Roplass company, two Biophysics students, Eliška Kostrůnková and Lenka Smílková, participated in this project. Their bachelor theses dealt with the decontamination of pathogens with plasma-activated media.
Because the research took place during the COVID-19 pandemic, scientists had to deal with limited testing capacity. The Department of Microbiology was responsible for the COVID testing and evaluation of PCR and ATG tests. "Our team managed to squeeze in limited microbiology laboratory capacity and work on weekends. Despite all the complications, we continued to work according to the original plan, even though it was very challenging due to operational and COVID restrictions. Thanks to the commitment of all involved, there were no delays to the project plan," adds Dr. Kelar Tučeková.
The research team at the Department of Microbiology of the Faculty of Medicine, under the leadership of Prof. Filip Růžička, focused on testing and measurement of pathogen inactivation. Planktonic bacteria were used for the cold decontamination process, and resistant bacterial biofilms were used for testing of hot process. Lukáš Vacek from the project research team developed his own method for evaluating bacterial inactivation in biofilms (already tested in the project TG02010067). This approach quantifies bacterial units within biofilm clusters compared to standard microbiological evaluation methods.
Decontamination chamber as a result of the project
The most significant result is the decontamination chamber itself. The whole device is scalable depending on the desired application. First, the researchers worked with a laboratory version of the chamber with a volume of 6L and then with a volume of 12L. Compared to other chemical or thermal decontaminators, the input power of the device is very low, less than 100 W. The decontamination cycle using the prototype can take up to 30 minutes, and two different decontamination processes can be executed in the chamber: hot and cold.
The researchers refer to a hot process as a process in the presence of plasma-activated water vapor with a higher temperature (around 100°C). A multi-hollow barrier discharge generates plasma, and the resulting activated gaseous products are fed directly into the chamber. The hot process is suitable for the decontamination of solid materials.
The cold process is for decontamination at lower temperatures (up to 40°C). So-called plasma-activated gasses with water vapor admixture mediate the decontamination. Ozone and hydrogen peroxide are formed in these gases, achieving better decontamination effects than the process at lower humidity. "With the cold process, we achieved inactivation of up to 6 orders of the tested bacteria after only 5 minutes of the decontamination cycle!" Adds Dr. Kelar Tučeková.
The project resulted in verified technology and, especially, a decontamination chamber prototype. The scientists have presented their results at conferences and are preparing a scientific publication. The Roplass company also presented the chamber at the 16th ThGOT, 13th Biomaterials Colloquium 2022 in Zeulenroda, Germany, and at the Business Research Forum 2023 in Brno, Czechia.
The proposed decontamination chamber meets all the requirements for the safe decontamination of various heat-sensitive materials for their subsequent safe disposal or reuse. Other possible applications of achieved results promote hand-held cleaners for local decontamination or contact cleaning of differently shaped surfaces. The chamber is undergoing a three-year implementation process, where it will be introduced to the general public and scientists and hopefully find market application soon, both for research and commercial use.