Low-energy electron-beam treatment as alternative for on-site sterilization of highly functionalized medical products – A feasibility study

Over the last decades, the medical device industry has grown significantly. Complex and highly functionalized medical devices and implants are being developed to improve patient treatment and to enhance their health-related quality of life. However, medical devices from this new generation often cannot be sterilized by standard methods such as autoclaving or sterilizing gases, as they are temperature sensitive, containing electronic components like sensors and microchips, or consist of polymers. Gamma irradiation for sterilization of such products is also problematic due to long processing times under highly reactive conditions resulting in material degradation or loss of functionality. Low-energy electron-beam treatment could enable irradiation sterilization of medical surfaces within seconds. This method is very fast in comparison to gamma irradiation because of its high dose rate and therefore degradation processes of polymers can be reduced or even prevented. Additionally, electron penetration depth can be precisely controlled to prevent damage of sensitive components like electronics and semiconductors. The presented study focuses on two key aspects: 1.) Can new and highly functionalized medical products in future be sterilized using low-energy electron-beam irradiation; and 2.) Is the low-energy electron-beam technology suitable to be set up on-site to speed up sterilization processing or make it available “just-in-time”. To address these questions, different test specimens were chosen with complex geometry or electronic functional parts to gather information about the limitations and chances for this new approach. The test specimens were inoculated with clinical relevant test organisms (Pseudomonas aeruginosa) as well as with approved radiation resistant organisms (Deinococcus radiodurans and Bacillus pumilus) to prove the suitability of low-energy electron-beam treatment for the above-mentioned medical products. The calculation of the D10 value for B. pumilus revealed equal efficacy when compared to standard high-energy irradiation sterilization. All of the above-mentioned germs were successfully inactivated by low-energy electron-beam treatment when test specimens were inoculated with a germ load > 10^6 CFU and treated with doses ≥ 10 kGy (for B. pumilus and P. aeruginosa) and > 300 kGy (for D. radiodurans) respectively. As an example, for specialized electronic components to be sterilized, an impedance sensor for cell culture applications was sterilized and unimpaired functionality was demonstrated even after five repeated sterilization cycles to a total dose of 50 kGy. To address the second aspect of on-site suitability of this technology, the product handling for low-energy electron-beam treatment had to be adapted to minimize the size of the electron-beam facility. Therefore, a mini electron-beam source was used and a specialized sample holder and 3D-handling regime were developed to allow reproducible surface treatment for complex product geometries. Inactivation of B. pumilus inoculated medical screws (> 10^6 CFU) was successful using the developed handling procedure. In addition, a packaging material (PET12/PE50) for medical products was investigated for its suitability for low-energy irradiation sterilization. Biocompatibility assessment revealed the material to be eligible for this application as even overdoses did not impair the biocompatibility of the material. With these results, the principal suitability of low-energy electron-beam treatment for sterilization of medical products containing electronics like sensors is demonstrated. The low-energy technology and the specialized 3D-handling regime allow the on-site setup of the technology in hospitals, medical practices or any other point of care.