Table 6: Summary of pretreatments and results for different biocompatible substrates.

SubstratePre-treatmentSurface properties

Ti and its alloysAlkalineHydrated Ti oxide gel layer
AcidicRemoves free metal, increases metal oxide layer
H2O2Forms titanium dioxide and titanium hydroxide
AnodizingTitanium dioxide nanotube layer, increases natural oxide layer
SandblastingIncreases roughness and surface area, activates surface.

Stainless SteelAlkalineHydrous metal oxide layer
AcidicRemoves MnS inclusions, creates Cr oxide layer, enriches Mo (noble element)
Electron beamRemoves MnS inclusions, melted surface forms strong interfacial bond with substrate

Mg and its alloysAlkalineIncreases surface area and roughness
AcidicKMgF3 cubic crystals in the protective coating
AnodizingCreates thick and porous oxide layer
Micro-arc oxidationCreates thick and porous oxide layer

CoCrMo alloyAcidicCreates oxide layer, including CoCr2O4, Cr2O3, Co oxides, and Mo oxides.
ECADIncreases adhesion strength between the HAp film and substrate as well as enhance the capability of HAp formation.