Autosterilization of biodegradable implants by injection molding process

Sterilization of degradable implants by standard procedures may damage the parts due to the labile chemical nature of the polymers. This study examined whether the injection molding process used for the production of polymeric parts may itself sterilize the implant due to high temperature, pressure, and shear forces applied. Poly-D,L-lactic acid (PDLLA) and poly-L- lactic acid (PLLA) granules were contaminated with thermoresistant spores of Bacillus stearothermophilus (>10⁵ spores/g). Sterile and contaminated granules of both polymers were injection molded and tested for sterility. All 27 samples produced with sterile PDLLA and processed at 120 °C and all 18 samples produced with sterile PLLA at 200 °C remained sterile after injection molding and handling. However, in five out of 28 PDLLA samples and in one out of 26 PLLA samples produced with contaminated material, spores had survived the process. In conclusion, the injection molding process could not reliably sterilize parts produced with polylactic acid granules that were heavily contaminated with thermoresistant organisms. However, the number of viable spores was significantly reduced by more than 99.99%. Thus, the injection molding process might allow the autosterilization of parts produced with raw material that is not heavily contaminated.