Development of high strength hydroxyapatite by solid-state-sintering process

Hydroxyapatite (HAp) is a potential material for various biomedical applications. In the present study, an attempt has been made to synthesize this material using simpler and cheaper method of solid-state-reaction process. Samples were prepared by mixing the ingredients and then sintering the cold compacted pellets at various temperatures from 500 to 1250 °C. X-ray diffraction, thermo-gravitometric and differential thermal analysis and Fourier transform infrared (FTIR) spectroscopy techniques were used for structural characterization of the samples. It was found that Monetite phase of hydroxyapatite forms in the unsintered powder. Upon heating up to 1250 °C, samples undergo several structural transformations with final structure being α-tri calcium phosphate (TCP) after sintering at 1250 °C. Presence of various chemical groups in the samples was analyzed using Fourier transform infrared spectrometry and the results are in accordance with the literature. Mechanical tests showed that increasing compaction pressure during cold pressing improves mechanical strength of sintered product by reducing overall porosity. Compressive, tensile and bending strength, bulk modulus (in compression), and microhardness values were found to improve after resintering the pellets at 1250 °C, which were previously sintered at the same temperature. It was also found that the mechanical properties of synthesized HAp were better as compared to the natural products. In vitro biological studies in a simulated body fluid showed around 15–20% change in the surface roughness of the samples albeit with negligible weight gain in dry state.