Manufacturing and characterization of poly(lactic acid) composites with hydroxyapatite

Hydroxyapatite (HA), a naturally occurring calcium orthophosphate, possesses the most similar chemical composition to human bone. In this research work, composite materials were prepared using poly(lactic acid) (PLA) as a polymer matrix and HA as an osteoconductive filler for potential use in medical applications. Composites with varying HA content comprised in the 10-30 wt% range were obtained by extrusion-compounding followed by injection molding. The effect of the HA loading on overall properties was assessed by mechanical characterization using tensile, flexural, impact, and hardness standard tests. Main thermal transitions of PLA-HA composites were obtained by differential scanning calorimetry (DSC) and degradation/decomposition at high temperatures was followed by thermogravimetric analysis. Dynamical behavior was assessed by dynamic mechanical thermal analysis and the dimensional stability was studied by thermomechanical analysis (TMA). As per the results, PLA-HA composites with 20-30 wt% HA offer the best-balanced properties with a remarkable increase in the Young's modulus. The glass transition temperature remained almost constant with slight changes of less than 1 degrees C as measured by both DSC and TMA. TMA also revealed a remarkable decrease in the coefficient of linear thermal expansion. The overall results confirm the usefulness of these materials from a mechanical point of view for biomedical applications as they are characterized by high stiffness, tensile strength, and dimensional stability.