Chemical and microstructural characterization of natural hydroxyapatite derived from pig bones

Hydroxyapatite (HAp) is the most popular bioceramic material and reknown for its excellent biocompatibility. It can be used for orthopedic replacements, bone reconstruction and also as dental implants. It stimulates osteoconduction being gradually replaced by the host bone after implantation. Three applications of HAp are of high importance: a) a porous or granulated material used in bone surgery, b) an additive to organic polymers improving their biofunctionality and c) plasma-sprayed or prepared by laser ablation coatings of metallic surfaces of bone implants. All these applications require a heat treatment of the material at elevated temperature. Natural HAp derived from animal bones has the advantage of inheriting a "true" chemical composition and structure of the raw material. Therefore, it seems to be an alternative solution for products based on the synthetic HAp. In this work pig bones were used as a source of the HAp material. Presented study was focused on chemical and microstructural characterization of natural HAp after heat treatment. HAp material was investigated by use of scanning electron microscopes with variable gas pressure. Ca/P ratio was determined by means of energy dispersive spectrometry. Reduced Ca/P ratio was recorded for HAp after heat treatment; however, in all cases it was higher than that of synthetic HAp. Biological tests revealed that the CAL-72 (human osteosarcoma) cells grow differently on the specimens of natural HAp depending on heat treatment conditions applied during sintering of HAp.