Hydroxyapatite (HA) is the most favorable Calcium-Phosphate Phase for dental and orthopedic applications due to its unique characteristics such as bioactivity, chemical stability, biocompatibility,corrosion resistivity and bone-cells activation . The use of HA layers as coatings for biomedical metallic implants can stimulate the formation of bone-like calcium sulfate on the surface, thereby promoting implant fixation and improving bone ingrowth . Synthetic HA is extremely similar to the inorganic component of hard tissues,such as bone and teeth; HA is also nontoxic within any quantity, osteoconductive and preferable media for cell culture and cells growth.
Because of poor mechanical strength and low fracture toughness ofHA, HA is mostly used as coating on metallic substrates such as stainless steels (SS), titanium and its alloys . Metals exhibit high mechanical strength and shape forming ability, so metallic implants are widely used in load bearing applications. Metallic implants suffer several drawbacks such as low bioactivity and high corrosion rate, therefore metallic implants should be coated with biomaterials to overcome these problems.
There are different procedures to apply HA coatings on metallic substrates, such as Sol-Gel, Plasma Spray, electrophoretic and electrodeposition . Among different procedures to apply HA coatings, electro deposition is really preferable because different parameters such as temperature, pH, time, substrate, morphology and different Ca-P phases deposited can be controlled . Because of the composite nature of natural bone, nowadays, composite coatings are really investigated by many researchers. In order to have HA composite coatings biopolymers and bioceramics are used as composite agent .Bioceramic compounds such as zirconia and titania are used in lately researches.
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