A low temperature sterilization method was developed, which enables the mild sterilization of thermally instable implant materials which are functionalized with bioactive components like growth factors. The method is based on the STERRAD low temperature hydrogen peroxide gas plasma technique, which is established for medical devices like catheters. In a first approach, the method was modified and improved for collagen as a thermolabile, protein based implant material. In a next step, growth factors TGF-beta and BMP-2 were immobilized on polymer surfaces (polylactide, polycaprolactone) as a model for biofunctionalized implant materials. Low temperature sterilization was applied with variation of the main process parameters (temperature, hydrogen peroxide concentration, duration of plasma treatment). The impact of the sterilization process on the integrity of the base material as well as on the functionality of the growth factors was investigated.
Effective sterilization was achieved at a temperature of 35 °C, with partial replacement of hydrogen peroxide by peracetic acid, and with a prolonged plasma phase. As a result, the activity of growth factors was reduced by 42   66 % (TGF-beta) and 51   81 % (BMP-2), depending on the polymer substrate. However, an increased adhesion of HEK cells and osteoblasts to the polymer surface still demonstrated the ability of the growth factors to activate signaling pathways in the cells.
The improved method enables effective sterilization at low temperatures, while preserving the mechanical properties of the base material as well as the functionality of bioactive surface coatings. The technique meets the demands on a safe and gentle sterilization method as an alternative to common gamma sterilization of medical devices.