Recently
Recently, regenerated bone graft has been considered as a promising new bone grafting technology in tissue engineering approach. Such regenerated bone graft is generally constructed by using porous scaffold with cells 1. This scaffold is a porous structure that acts as a substrate, upon the surface of which cells adhere and grow. The scaffold provides structural and mechanical support as well as the surface for cell growth. An important role of the scaffold is to provide a temporary home for the growth and culture of cells in a bioreactor environment. Its presence allows cells to generate the biological structural components of the extracellular matrix (ECM) in culture conditions 2. The porous scaffold can be fabricated using both bioactive ceramics and polymers. Bioactive ceramics have chemical composition resembling that of natural bone, allow osteogenesis and can provide a bony contact or bonds with host bone 3, 4. Bioceramics, hydroxyapatite (HAp) and ?-tricalcium phosphate (?-TCP) for an instant, have been introduced to bone tissue engineering for their unique properties of bioactivity, biocompatibility and osteoconductivity 5, 6. HAp has been introduced in bone tissue engineering as a scaffold material mainly due to its unique properties such as excellent bioactivity, biocompatibility, osteoconductivity and non-toxicity 6-9. However, low strength and brittleness of HAp have limited its wide applications in hard tissue implant 10. The main reason of this low mechanical property of HAp is decomposition of HAp into some calcium phosphate phases such as tricalcium phosphate (TCP) and even tetra-calcium phosphate (TTCP) 11. Calcium phosphate phases are brittle and have weaker strength. Therefore, overcoming this limitation of HAp is of great importance in the area of tissue engineering application. Different techniques have been tried to improve the strength and fracture toughness of HAp, such as making composites and using different pressing/sintering methods like underwater shock compaction, hot press sintering, microwave, and spark plasma sintering process 12-16.
