Hydroxyapatite (HAp) has been widely used as an artificial bone substitute because of the its high biocompatibility and good bioaffinity, as well as osteoconductabil — ity. HAp powders have been produced using bio products like corals11, cuttlefish shells12, natural gypsum13, natural calcite14, bovine bone15, eggshell1617, etc. Chemi­cal analysis has shown that these products which are otherwise considered as bio­waste are rich sources of calcium in the form of carbonates and oxide.

Several papers reported to produce the materials for implant or prosthesis pur­poses with chemical characteristics similar to HAp18-21. Eggshell is a nonexpensive and environmental friendly material for HAp production. The eggshell is consist­ing of a three-layered structure, namely the cuticle, the spongeous layer and the lamellar layer. The cuticle layer represents the outermost surface and it consists of a number of proteins. Spongeous and lamellar layers form a matrix constituted by protein fibers bonded to calcite-calcium carbonate crystals. The eggshell repre­sents the 11% of the total weight of the egg and is composed by calcium carbonate 94%, calcium phosphate 1%, organic matter 4% and magnesium carbonate 1%22. Bone replacements are frequently required to substitute damaged tissue due to trauma, disease or surgery. Resorbable porous bioceramics, such as P-tricalcium phosphate (P-Ca3(PO4)2, P-TCP) and hydroxyapatite (Ca10(PO4)6(OH)2, Fig. 2.1) have been widely used as bone defect filling materials due to their remarkable bio­compatibility and close chemical similarity to biological apatite present in bone tissues23,26.