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Hydroxyapatite (HA) has drawn great attention to biomedical applications due to their bone mineral similarity, strong bioactivity, biocompatibility and osteoconductive. Despite the fact that HA has many advantages, several properties are still lacking, emphasising the crucial need for ion doping/substitution. Many attempts have been made to incorporate ions into HA structure to increase their physical, chemical, and biological properties. With such a diverse range of methods available for the synthesis of doped HA, this article discussed the importance of doping for HA and summarizes four common techniques used to prepare doped hydroxyapatites which include precipitation, hydrothermal, sol-gel and mechanochemical method.

Carbon nanotubes (CNTs) have a great potential to be used as filler to enhance the mechanical properties of polymer composites due to excellent properties. However, CNTs have limitation of difficult to disperse in polymer matrix. The hybridization of CNTs and inorganic fillers can improve the dispersion and combine their properties in polymer composites. In the present work, the properties of the epoxy composites filled with carbon nanotube-calcium carbonate (CNTs-CaCO3) hybrid, at various filler loading (i.e., 1-5 wt.%) were studied. The CNTs-CaCO3 hybrid fillers were prepared by physically mixing (PHY) method and chemical vapor deposition (CVD) method. The tensile properties and hardness of both composites were investigated at different weight percentages of filler loading. The CNTs-CaCO3 CVD hybrid composites showed higher tensile strength and hardness than the CNTs-CaCO3 PHY hybrid composites. This increase was associated with the homogenous dispersion of CNT–CaCO3 particle filler. The morphological studies of fracture surfaces after tensile test by means of SEM showed homogenous dispersion of CNTs-calcium carbonate CVD hybrid in epoxy matrix. The result shows that the CNTs-calcium carbonate CVD hybrid composites are capable in increasing tensile strength by up to 116.4%, giving a tensile modulus of 40.3%, and hardness value of 39.2% as compared to a pure epoxy.

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