**9. Porous hydroxyapatite ceramic and its biomedical applications**

Hydroxyapatite (HA) porous ceramics are substitute materials for bone and teeth in repairing and regeneration applications due to their chemical and biological similarity to human hard tissue [20]. In the design of these porous ceramic for bone repairing or regeneration, it is important to control their pore structures. Pore ceramic structure can be designed using the size and morphology of the Hydroxyapatite particles that are utilized to build these porous ceramics. Porous hydroxyapatite ceramic exhibits strong joining to the bone, the pores provide a strong mechanical interlock leading to a firmer fixation of the structure. Porous hydroxyapatite is more resorbable and osteoconductive than HA dense counterpart [21]. The surface area of porous Hydroxyapatite form is greatly increased which allows more bone cells to be carried in comparison with dense hydroxyapatite. The most common techniques used to make porosity in a biomaterial are gas foaming, salt leaching, freeze-drying, phase separation and sintering depending on the material used to make the scaffold. The minimum pore size required to regenerate mineralized bone is generally considered to be around 100 μm.
