A novel hydroxyapatite –Hardystonite nanocomposite ceramic

Natural Hydroxyapatite (NHA)-Hardystonite (HT) nanocomposite ceramic with different percentage of HT was prepared through mechanical milling and subsequent annealing process. Although HA is biocompatible and has been used for bone regeneration, its mechanical properties are inadequate, making it unable to be used as a load bearing implant. This study shows that the addition of HT to NHA not only increases the mechanical properties of HA, but also improves its bioactivity behavior. According to the results obtained, the nanocomposite samples with 10wt. %HT have the maximum value of the density, which is attributed to the formation of Hardystonite silicate phases between the matrix particles and subsequently the formation of glass bonds. It was found that the NHA-15wt. %HT nanocomposite samples have the lower cold crushing strength in comparison with other ones investigated in this study (i.e. NHA-5 wt. %HT and NHA-10 wt. %HT). The event originates from the overlapping of glass bonds and their subsequent failure. The ability and rate of apatite formation on the sample surface was evaluated by Simulated Body Fluid (SBF) test, a method that is well recognized to characterize the in vitro bioactivity of ceramic materials. The test based results showed that the samples with the higher amount of HT have more Si than the samples with the lower amount of HT. This may lead to the conclusion that the increase of the percentage of HT results in the increase of the Si-OH nucleation sites and therefore the ease of formation of the apatite layers as well as the increase of the nanocomposite ceramic bioactivity.