Effect of argon ion-implantation on mechanical and degradation properties of bulk-shaped poly(lactic acid)

Abstract

Poly(lactic acid) (PLA) has attracted much attention as a material for bioabsorbable bone fixation devices, however degradation rate of PLA is very low. Surface treatment of PLA has been investigated to increase degradation rate due to improvement in hydrophilicity. In this study, effects of ion-implantation on degradation rate and mechanical properties were investigated. Argon gas which is chemically stable was used as ion source, and argon ion was implanted in the surface of PLA. The contact angle and the surface roughness of the ion-implanted PLA were measured to evaluate hydrophilicity, and tensile tests and micro-indentation tests were conducted to evaluate mechanical properties. The difference in surface morphology after in vitro degradation test between ion-implanted and un-implanted region was observed to investigate degradation properties of ion-implanted PLA. As a result, tensile strength increased by 8.2 % compared to un-implanted specimen and Vickers hardness increased by 9.5%. The ion-implantation might affect mechanical properties in the overall specimen rather than those in the surface. The result of in vitro degradation test showed that an initial degradation rate was accelerated by ion-implantation. This result is consistent with the increasing hydrophilicity of ion-implanted PLA. Those results suggested that ion-implantation accelerates degradation of PLA without decreasing mechanical properties.