Table 4.

Summary of surface techniques for depositing Ca & P coatings on metal implants and their characteristics.

Methods	Characteristics
Dip and immersion coating	High temperature for post-sintering HA layer can degrade the strength of the metal and impair the interfacial adhesion and cause the decomposition of HA
Electrophoresis deposition	Low bond strength and non-uniform thickness of the coating
Hot isostatic pressing	Difficult to seal borders on implants with complex shapes, high temperature during the process may denature HA
Solution deposition	A low temperature deposition method resulting in a pure, highly crystalline, firmly adherent coating
Sputtering deposition	A line-of-sight technique with low deposition rate and high cost, but the coatings are dense and with uniform thickness on flat substrates
Thermal spraying	A line-of-sight technique with high deposition rates and low cost; high temperature may cause decomposition of HA; high cooling rate may result in the formation of nanostructure, coatings usually have micro-rough surface
Sol-gel	Not a line-of-sight technique suitable for coating substrates with complex shapes; processing temperature is low; raw materials are expansive and sometimes including organic toxic solvent.
Biomimetic coating	Low processing temperature technique capable of coating complex-shaped substrates; time-consuming
Laser deposition	Be capable to restore complex stoichiometries and to produce crystalline and highly adherent coatings, but process temperature may cause the oxidation of metal or alloy substrates.