Table 6.

Summary of pretreatments and results for different biocompatible substrates.

Substrate	Pre-treatment	Surface properties
Ti and its alloys	Alkaline	Hydrated Ti oxide gel layer
	Acidic	Removes free metal, increases metal oxide layer
	H2O2	Forms titanium dioxide and titanium hydroxide
	Anodizing	Titanium dioxide nanotube layer, increases natural oxide layer
	Sandblasting	Increases roughness and surface area, activates surface.
Stainless Steel	Alkaline	Hydrous metal oxide layer
	Acidic	Removes MnS inclusions, creates Cr oxide layer, enriches Mo (noble element)
	Electron beam	Removes MnS inclusions, melted surface forms strong interfacial bond with substrate
Mg and its alloys	Alkaline	Increases surface area and roughness
	Acidic	KMgF3 cubic crystals in the protective coating
	Anodizing	Creates thick and porous oxide layer
	Micro-arc oxidation	Creates thick and porous oxide layer
CoCrMo alloy	Acidic	Creates oxide layer, including CoCr2O4, Cr2O3, Co oxides, and Mo oxides.
	ECAD	Increases adhesion strength between the HAp film and substrate as well as enhance the capability of HAp formation.