Traditional methods of sterilisation, like steam and EtO present the drawback of compatibility with some materials (high temperature, corrosion) or safety of personnel and toxicity. Existing Plasma sterilisation methods offer a large technical and economical advantage but the existing applications have serious drawbacks (use of toxic reactants, corrosion). Moreover, the precise mechanisms of plasma sterilisation are not well understood. The present project proposes to develop and validate a new plasma sterilisation method based on:
1) Use of non-toxic plasma gas mixture (water, oxygen, alcohol, etc) suppressing environmental hazard;
2) Development of plasma-compatible cellulose and plastic-based packaging;
3) Contribution to standardisation of the treatment. The new process will be applied to sterilisation of pharmaceutical packaging and medical devices.
The project Steriplas has now completed its 4th year. During this project duration, the following progress has been made:
-All the biological testing were performed by Biomatech and the method were validated following the ISO 11737 and the European Pharmacopea requirements for the bioburden, sterility and pyrogens tests.A duo plasmaline microwave source has been tested successfully at Bosch and de-pyrogenation experiments have been performed. It was demonstrated that in the plasma phase, at high power, de-pyrogenation can be achieved in less than a minute with N2/O2 mixtures. These results were heterogeneous may be because of variable destruction of the pyrogens during the transportation and/or to an increase of the glass adherence of the pyrogens after several days. With the same source, 6 Log sterilization can be obtained in 10 sec on Bac. Subtilis with N2/O2 mixtures. Efficiency of UV light depends strongly on wavelength, as demonstrated by sterilization with UV filters of different characteristics. The wavelength below 280 nm being the most efficient for microorganism destruction. Complete sterilizations were also obtained with other types of spores: Bacillus subtilis, Bacillus pumilus and Geobacillus stearothermophilus with N2/O2 mixtures for minimum tims of 300 sec. These results allowed the determination of the most resistant strain to the plasma sterilization. Geobaccilus stearothermophilus could be used as a biological indicator for the validation of this type of sterilization.
-Experiments of plasma characterization have been done at JRC. The conditions leading to major UV emission and radical production have been identified depending on pressure and gas composition. Major differences between the 2 sources available at Biomatech and JRC have been identified, allowing comparison of the 2 processes. Sterilization tests on Bac subtilis were successful at Biomatech and a complete sterilization can be obtained with 4 % O2 in N2, conditions corresponding to a major UV emission between 250 and 300 nm.
-Tests of de-pyrogenation in the near post discharge were partially successful at JRC, with a maximum efficiency at 10 min treatment, followed by a decrease of efficiency as time of treatment is increased. The results showing a large scattering, it is difficult at this time to understand the meaning of this result. Our hypothesis could be a fragmentation of pyrogens beyond a certain treatment duration, leading to an increase of the pyrogenicity of the surface. Further analysis by SEM coupled with Quartz Crystal Monitor is on-going to understand this fact. The results obtained with a lot of different gas mixtures and different parameters (power, pressure, time) on contaminated glass vials were interesting but heterogeneous according to the location within the chamber and not always reproducible in successive experiments. High temperatures have also been detected near the plasma source.
-Tests of sterilization in the near post discharge were partially successful at Biomatech. Different gas mixtures with different parameters gave various results. Because of the small size of the sterilization chamber and its configuration, high temperatures were observed inside the chamber. In these conditions, the sterilization efficacy of the plasma could not be established. In addition these conditions did not full fill the requirements for low temperature sterilization of polymers.
Funding SchemeCSC - Cost-sharing contracts