Fabrication and mechanical properties of PLA/HA composites: A study of in vitro degradation

The adverse effects of stress shielding from the use of high-modulus metallic alloy bio-implant materials has led to increased research into developing polymer-ceramic composite materials that match the elastic modulus of human bone. Of particular interest are poly-l-lactic acid- hydroxyapatite (PLA/HA)-based composites which are fully resorbable in vivo. However, their bioresorbability has a deleterious effect on the mechanical properties of the implant. The purpose of this study is to investigate, from a micromechanistic perspective, the in vitro degradation behavior of such composites manufactured using a simple hot-pressing route for two different hydroxyapatite particles: a fine-grained (average particle size ∼5 microm) commercial powder or coarser whiskers (∼25-30 microm long, ∼5 microm in diameter). We observed that composites with ceramic contents ranging between 70 and 85 wt.% have mechanical properties that match reasonably those of human cortical bone. However, the properties deteriorate with immersion in Hanks' Balanced Salt Solution due to the degradation of the polymer phase. The degradation is more pronounced in samples with larger ceramic content due to the dissolution of the smaller amount of polymer between the ceramic particles.