Cold sintering process of hydroxyapatite derived from natural bone and co-precipitation method: a comparative study

This study uses a novel sintering technique at very low temperatures (below 300°C) named the Cold Sintering Process to produce highly dense Hydroxyapatite (HA) samples. Nano hydroxyapatite was prepared using two different methods: Synthesis by chemical precipitation method (HA 1 ) and natural source from Boven bone (HA 2 ). The samples are characterized using scanning electron microscope (SEM), X-ray energy dispersive spectrometry (EDS), X-ray diffractogram (XRD), transition electron microscope (TEM), Fourier transform infrared spectrometry (FTIR) and Nuclear magnetic resonance spectroscopy (NMR). Also, physical and mechanical properties measurements were detected, including density and hardness. The results indicated that cold sintering could result in Hydroxyapatite with high densification, high purity, and high stability without thermal decomposition compared with traditional sintering. The relative density and hardness for HA 1 are 99% and 502HV, respectively. The relative density and hardness for HA 2 are 69% and 350HV, respectively. It can be observed that the HA 1 sample has higher densification than HA 2 due to the presence of organic matter in natural Hydroxyapatite HA 2 . This organic material will be removed during the cold sintering process, leaving pores that lead to low densification of HA 2 samples. It can be concluded that the synthesis hydroxyapatite (HA 1 ) can be easily sintered by a cold sintering process compared with natural one(HA 2 ).