Table 3
Various techniques to deposit bio-resorbable coatings, films and layers of calcium orthophosphates on metal implants (Sun et al. 2001; Yang et al. 2005; Narayanan et al. 2010)
Technique	Thickness	Advantages	Disadvantages
Thermal spraying	30 to 200 μm	High deposition rates; low cost	Line of sight technique; high temperatures induce decomposition; rapid cooling produces amorphous coatings; high temperatures prevent from simultaneous incorporation of biological agents
Plasma spraying	30 to 200 μm	High deposition rates; improved wear and corrosion resistance and biocompatibility	Line of sight technique; high temperatures induce decomposition; rapid cooling produces amorphous coatings; high temperatures prevent from simultaneous incorporation of biological agents
Magnetron sputtering	0.5 to 3 μm	Uniform coating thickness on flat substrates; high purity and high adhesion; dense pore-free coatings; excellent coverage of steps and small features; ability to coat heat-sensitive substrates	Line of sight technique; expensive; low deposition rates; produces amorphous coatings; high temperatures prevent from simultaneous incorporation of biological agents
Pulsed laser deposition (laser ablation)	0.05 to 5 μm	Coatings with crystalline and amorphous phases; dense and porous coatings; high adhesive strength	Line of sight technique; expensive; high temperatures prevent from simultaneous incorporation of biological agents
Ion beam deposition	0.05 to 1 μm	Uniform coating thickness; high adhesive strength	Line of sight technique; expensive; produces amorphous coatings
Dynamic mixing method	0.05 to 1.3 μm	High adhesive strength	Line of sight technique; expensive; produces amorphous coatings
Dip and spin coating	2 μm to 0.5 mm	Inexpensive; coatings applied quickly; can coat complex substrates	Requires high sintering temperatures; thermal expansion mismatch
Sol–gel technique	< 1μm	Can coat complex shapes; low processing temperatures; thin coatings; inexpensive process; can incorporate biological molecules	Some processes require controlled atmosphere processing; expensive raw materials
Electrophoretic deposition	0.1 to 2.0 mm	Uniform coating thickness; rapid deposition rates; can coat complex substrates; can incorporate biological molecules	Difficult to produce crack-free coatings; requires high sintering temperatures
Electrochemical (cathodic) deposition	0.05 to 0.5 mm	Good shape conformity; room temperature process; uniform coating thickness; short processing times; can incorporate biological molecules	Sometimes stressed coatings are produced, leading to their poor adhesion with substrate; requires good control of electrolyte parameters
Biomimetic process	< 30 μm	Low processing temperatures; can form bonelike apatite; can coat complex shapes; can incorporate biological molecules	Time consuming; requires replenishment and a pH constancy of the simulating solutions (HBSS, SBF, etc.)
Hot isostatic pressing	0.2 to 2.0 μm	Produces dense coatings	Cannot coat complex substrates; high temperature required; thermal expansion mismatch; elastic property differences; expensive; removal/interaction of encapsulation material; high temperatures prevent from simultaneous incorporation of biological agents
Micro-arc oxidation	3 to 20 μm	Simple, economical and environmentally friendly coating technique, suitable for coating of complex geometries	Except of calcium orthophosphates, coatings always contain admixture phases

HBSS, Hank's balanced salt solution; SBF, simulated body fluid.

Dorozhkin Progress in Biomaterials 2012 1:1   doi:10.1186/2194-0517-1-1