Macroporous bioceramics: a remarkable material for bone regeneration.

This review summarises the major developments of macroporous bioceramics used mainly for repairing bone defects. Porous bioceramics have been receiving attention ever since their larger surface area was reported to be beneficial for the formation of more rigid bonds with host tissues. The study of porous bioceramics is important to overcome the less favourable bonds formed between dense bioceramics and host tissues, especially in healing bone defects. Macroporous bioceramics, which have been studied extensively, include hydroxyapatite, tricalcium phosphate, alumina, and zirconia. The pore size and interconnections both have significant effects on the growth rate of bone tissues. The optimum pore size of hydroxyapatite scaffolds for bone growth was found to be 300 µm. The existence of interconnections between pores is critical during the initial stage of tissue ingrowth on porous hydroxyapatite scaffolds. Furthermore, pore formation on β-tricalcium phosphate scaffolds also allowed the impregnation of growth factors and cells to improve bone tissues growth significantly. The formation of vascularised tissues was observed on macroporous alumina but did not take place in the case of dense alumina due to its bioinert nature. A macroporous alumina coating on scaffolds was able to improve the overall mechanical properties, and it enabled the impregnation of bioactive materials that could increase the bone growth rate. Despite the bioinertness of zirconia, porous zirconia was useful in designing scaffolds with superior mechanical properties after being coated with bioactive materials. The pores in zirconia were believed to improve the bone growth on the coated system. In summary, although the formation of pores in bioceramics may adversely affect mechanical properties, the advantages provided by the pores are crucial in repairing bone defects.