- HAp derived from converted coral has been used as a bone graft substitute in orthopaedic surgery for nearly twenty years. After grafting it is desirable for bone ingrowth to occur as quickly as possible as the strength of the region which has been implanted is dependent on a good mechanical bond forming between the implant and the surrounding regions in the body. The rate at which ingrowth occurs is dependent on many factors, including the pore size and interconnectivity of the implanted structure. It is therefore necessary to develop a precise knowledge of the factors, which influence the microstructure and the pore size in the converted HAp structure. A specific Australian coral were used for analysis. A modified and improved hydrothermal conversion process was used to convert the corals from calcium carbonate to HAp. The effects of heat treatment and hydrothermal conversion on the pore size and the surface morphology of HAp structure have been studied using scanning electron microscopy. Samples after hydrothermal conversions were further dip-coated via an alkoxide sol-gel method were also examined to determine the morphology. The sol-gel/coralline hydroxyapatite interface and the mechanical properties have also been studied.