Dynamic mechanical characterization of biodegradable composites of hydroxyapatite and polylactides

The thermo-mechanical analysis of some novel, totally bioactive, three-component composite systems intended for the repair and augmentation of bone has been performed. The composites are composed of hydroxyapatite (HA), particulate reinforced biodegradable polylactic acid (PDLLA), with a second reinforcing phase of semi-crystalline, unidirectional fibers of polylactic acid (PLLA) homopolymer. Dynamic mechanical analysis (DMA) applied small-strain cyclic deformations to simulate physiological loading. The effect of the two fillers on the glass transition temperature of the matrix (Tg-PDLLA) and on the viscoelastic parameters, storage modulus (EI), and tan delta were analyzed. Thermal characterization with differential scanning calorimetry (DSC) was compared to the DMA data. It was established that the addition of HA and/or PLLA fibers increased EI, both below and above Tg-PDLLA. The combination of both reinforcing agents was the most effective. The damping was reduced with the addition of HA alone and in combination with PLLA fibers. Tg-PDLLA was increased by the addition of HA, PLLA fibers, and the combination of the two reinforcing agents. The magnitude of the increase in Tg-PDLLA was similar for both types of reinforcement.