Morphological and X-ray diffraction studies of crystalline hydroxyapatite-reinforced polycaprolactone.

Morphological and mechanical properties of hydroxyapatite (HAP)-reinforced polycaprolactone (PCL) were studied. The objective was to examine how morphological features alter the bulk mechanical properties in our laboratory-synthesized HAP-reinforced PCL. HAP crystals were synthesized by hydrolysis of mixtures of calcium and phosphate salts in the laboratory with wet chemical methods. The properties of the commercially available hydroxyapatite (HAP(1)) are compared with that of laboratory-synthesized hydroxyapatite (HAP(2)). The HAP crystals and composition were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectrometry (FTIR). The HAP(1) and HAP(2) crystals were dispersed into polymers to examine the mechanical behavior of bioactive composites, and the interfacial interactions between the polymer and HAP crystals are addressed. The FTIR results confirmed that the two forms of HAP crystals are consistent in terms of the functional chemical groups. The wide angle X-ray diffraction study was performed to determine the crystallinity of the bioactive composites. It was observed that the crystallinty of HAP-filled PCL steadily increased as the filler concentration increased. Generally, HAP(2) has a particle size considerably smaller than HAP(1) and the composite derived had higher modulus than conventional HAP-filled polymers. This increase in modulus is attributed to better interfacial interaction. Bioresorbability tests performed on HAP particles found that the synthesized HAP had higher resorption rates. It is clear that the mechanical properties are influenced by the particle size and therefore by the processing method used.