Skip to main content

STERILIZATION OF VARIETY OF MATERIALS, BIOMEDICAL AND FOOD PRODUCTION EQUIPMENT USING LOW THERMAL ATMOSPHERIC PRESSURE PLASMA JET COMBINED WITH ADVANCED OXIDATION PROCESSES

Final Report Summary - PLASMA STERILIZATION (STERILIZATION OF VARIETY OF MATERIALS, BIOMEDICAL AND FOOD PRODUCTION EQUIPMENT USING LOW THERMAL ATMOSPHERIC PRESSURE PLASMA JET COMBINED WITH ADVANCED OXIDATION PROCESSES)

Presently many medical wards, biotechnological facilities and food production factories struggle with persistent microbial infections caused by biofilms deposited on various inert and living surfaces e.g.:
-walls of equipment (water supplies, catheters, tubing, masks, dental units, ventilation units)
- linen, fabrics and wound dressing
-living tissues (diabetic ulcers, pressure ulcers, venous leg ulcers, recalcitrant chronic wounds)
- medical prosthetics, implants, stents
-food containers (bottles, boxes, foils)
-food itself

There are many precautions and treatments implemented to avoid the risk of clinical infections, still thousands of cases appear every year affecting not only patients’ and consumers’ well-being, but also organizations’ budgets. There is an urgent need for development of the time- and cost-effective sterilization tool, which could be safely and flexibly applied to various surfaces and materials.
For medical sterilization several techniques have been implemented so far:
- the most popular thermal sterilization: dry and moist heat. Temperature in the autoclave is about 121°C, which cannot be applied to the heat-sensitive materials.
- membrane filters for liquid heat-sensitive components (problem with filter recycling)
- commercially used ethylene oxide sterilizers (EtO), method with many questions concerning the carcinogenic properties of the EtO residues adsorbed on the materials after processing [5] and worries about the safety of operators when opening the sterilizer before the end of the very long vent time. Because of high toxicity one cycle of EtO operating ranges from 12 to 48 h (sterilization itself- about 60 min).
- liquid formaldehyde and glutaraldehyde, not applicable to the tissues, not environmental-friendly
- costly gamma irradiation process, with many questions about the location of the operation site and damaging of the disinfected materials’ surface [1]. Method is sometimes used for sterilizing selected kinds of foods.

The idea of plasma sterilization was already proposed in sixties [2] as a good, low toxicity method for patients and operating staff. In spite of fact that the number of research papers and devices related to this topic is constantly increasing, most of the solutions were not fully implemented, mostly because of the lack of system optimization, lack of comparability between the proposed reactors and methods, lack of matching between plasma properties and sterilized material, and because of the incomplete sterilization in the case of multi-microorganisms biofilms. Therefore, industrial plasma-based decontamination is still a great challenge. However, plasma can inactivate most of pathogens: gram negative and positive bacteria, microbial spores, molds and fungi, viruses and maybe even prions. In perspective, device might help in preventing and fighting pandemic outbreaks.
Presently, low-pressure plasma sterilizers as are commercially offered in the market [3]. Low-pressure plasma besides the costly vacuum system shares some of the disadvantages of traditional sterilizers- it requires closed reactor and cannot be applied to the living tissues.
Many research groups concentrate on the efforts of designing plasma sterilizing device working in the ambient conditions [4-12] using variety of methods such as barrier discharge, pulsed corona reactors or plasma jets. To maintain the uniform discharge under atmospheric pressure mainly quite expensive gases as helium and argon are used in high concentrations. Plasma disinfection time given in the literature varies from several minutes to even hours. Treatment can be considered as a surface one.
The main objective of the proposal is development of low temperature atmospheric pressure plasma sterilizer, which should have operation cycle length at least the same as traditional devices, should be applicable toward broad range of materials and surfaces without damaging them irreversibly and should be operator- and environmental- friendly.

Experimental set-up, which is presently realized under PIRG05-GA-2009-249257 Maria-Curie Reintegration Grant consists of the following sub-systems:
- gas and liquid dosing sub-system,
- electrical discharge generating sub-system
- control and data acquisition sub-system
- chemical and biological analyzing sub-system

Atmospheric-pressure plasma jet (APPJ) is compact, portable, low-temperature gas discharge plasma device for cold sterilization of various heat-sensitive surfaces and materials.
The main part of the device is RF-powered changeable rod electrode. Two electrode materials: acid-proof stainless steel and tungsten are tested. Electrode diameters are 4, 5, and 6 mm. It is possible to control the length of electrodes. We use 3 types of shapes: flat surface, screw-type and turtle-type surface electrodes. From the discharge homogeneity point of view, the most beneficial are flat and turtle shape tungsten electrodes. The electrode is powered by a regulated RF supply (AG 1021 RF generator, T&C Power Conversion) via impedance matching network elaborated in our laboratory. It is possible to power plasma reactor with frequencies from 10 kHz to 20 MHz.
LabVIEW based TGAs measurement and control sub-system was developed for the purpose of this project. TGAs enables whole monitoring and measurement process through subsequent setting of electrical and gas-flow parameters, conditioning and amplification of electrical signals. TGAs also automatically collects the data from oscilloscope.
In dependence on the gas flow, we are able to produce discharge plasma sizing from 10 to 20 mm and 5-15 mm in diameter and length, respectively. It is possible to achieve temperatures below 40oC compromising applied power, frequency and gas flow-rate [11, 12].

Ozone concentration was measured in dependence on the gas type, gas flow rate, power and the type of electrode. The maximum achieved ozone concentration ranged 0,82 g/m3. Comparison of ozone concentration depending on the fraction of the argon and helium as a carrier gas added to oxygen, at 5 mm diameter, flat-surface electrode condition.
Possibilities of not-heat resistant materials modification without changing of rigid properties of polymers were tested and enhancement of treated surface hydrophilic properties was achieved.

Features of the developed APPJ are as follows:
- ability to work at the atmospheric pressure in several gas flow, frequency and current- voltage regimes,
- application of various feed gases

Additionally, exchangeable sub-units for the device: gas, vapor, liquid spray and foam distribution unit are also developed and being tested to establish if some synergetic effect takes place. Experiments with surface treatment and treatment of biological samples have been started.
Positive results of proposed experiments may lead to the decreasing number of clinical infections (through their prevention and elimination), to the assured security and well being of the patients. Further, the applicability of device will be tested for sterilization of food packages and for preservation of solid foods. Therefore, preventive application of plasma sterilizer might bring to tangible money savings.

References:
[1] G. Henn, C. Birkinshaw, M. Buggy, E. Jones , J. Mat. Sci.(Mater. Med.) 7, 1996, 591–595.
[2] W. Menashi, Treatment of surfaces, US Patent 3 383 163, 1968.
[3] www.sterrad.com
[4] M. Laroussi, F. Leipold, Int. J. Mass Spectrom. 233, 2004, 81–86.
[5] M. Moisan, J. Barbeau, J. Pelletier, N. Philip, B. Saoudi, 13th CIP, 2001, 12–18.
[6] H. Ohkawa, T. Akitsu, M. Tsuji, H. Kimura, M. Kogoma, K. Fukushima, Surface and Coatings Tech., 200(20-21), 2006, 5829-5835.
[7] T. Montie, K. Kelly-Wintenberg, J.Roth IEEE Trans Plasma Sci., 28(1), 2000, 41 – 50.
[8] M. Vleugels, G. Shama, X. Deng, E. Greenacre, T. Brocklehurst, M. Kong, IEEE Trans Plasma Sci., 33, 2005, 824–828.
[9] www.cerionx.com
[10] H. Liu, J. Chen, L. Yang, Y. Zhou, Appl.Surface Sci., 254(6), 2008, 815-1821.
[11] Pawłat J., ELMECO-7– AoS-10, Nałęczów. Poland, 2011, 123-124
[12] Pawłat J., Giżewski T., Stryczewska H. D., 17th International Conference on Advanced Oxidation Technologies for Treatment of Water and Soil, San Diego, California, USA, 2011, p. 54

Figures were uploaded as additional file.