Effect of sterilization on the physicochemical properties of molded poly(L-lactic acid)

In this study, the process of manufacturing and sterilizing an orthopedic implant constructed from poly(L-lactic acid) (PLLA) was closely simulated. The hydrogen peroxide gas plasma (HPGP) sterilization process was comparatively investigated against ethylene oxide (EtO). Characterization of the physical, thermal, mechanical, morphological, and chemical properties was monitored. The results indicate that the HPGP sterilization process did not have a significant influence on M(n) or M(w) initially or through 12 weeks of in vitro conditioning when compared with EtO. Only indications of physical aging were evident in the analysis of the thermal and mechanical properties by differential scanning calorimeter and tensile testing for each sterilization processes. Using wide angle X-ray diffraction to determine morphology characteristics, it was determined that no changes were observed between the as molded, HPGP, and EtO specimens initially or through the 12 week in vitro conditioning period. Contact angle measurements revealed a significant reduction in the surface energy following treatment by the HPGP process, suggesting the formation of polar groups. However, surface chemistry analysis by ATR-FTIR indicated no significant chemical modification from either sterilization method. PLLA showed intermediate levels of residual hydrogen peroxide absorption following processing by HPGP.