Table 2.

Commonly applied methods to modify titanium surface structures into the nanoscale in the orthopaedic field [7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24].

	Technique	Modified Layer	Objective
Mechanical	Grinding Polishing Machining Blasting	Rough or smooth surface formed by the subtraction process	Produce specific surface topographies; Clean and roughen surface; Improve adhesion in bonding
	Attrition	To fabricate nanophase surface layers on Ti of commercial purity which improve the tensile properties and surface hardness of Ti	Produce materials with nanometre size grains (1–100 nm); To produce rough morphology and higher hydrophilicity
Chemical	Acidic treatment Alkaline treatment Hydrogen peroxide treatment	<10 nm of surface oxide layer ~1 μm of sodium titanate gel ~5 nm of dense inner oxide and porous outer layer	Remove oxide scales and contamination. Improve biocompatibility, bioactivity or bone conductivity. Improve biocompatibility, bioactivity or bone conductivity
	Sol-gel	~10 μm of thin film, such as calcium phosphate, TiO2 and silica	Improve biocompatibility, bioactivity or bone conductivity
	CVD	~1 μm of TiN, TiC, TiCN, diamond and diamond-like carbon thin film	Improve wear resistance, corrosion resistance and blood compatibility
	Anodic oxidation	~10 nm–40 μm of TiO2 layer, adsorption and incorporation of electrolyte anions	Produce specific surface topographies; improve corrosion resistance; improve biocompatibility, bioactivity or bone conductivity
	Biochemical methods	Coating deposition; modification through silanized Ti, photochemistry, self-assembled monolayers, protein-resistance, etc.	Induce specific cell and tissue response by means of surface immobilized peptides, proteins, or growth factors
Physical	Thermal spray ✓ flame spray ✓ plasma spray ✓ high velocity oxy-fuel spray ✓ others	~30 to ~200 μm of coatings, such as titanium, HA, calcium silicate, Al2O3, ZrO2, TiO2	Improve wear resistance, corrosion resistance and biological properties (osteoblast adhesion)
	Physical vapour deposition ✓ Evaporation ✓ Ion plating ✓ Sputtering	~1 μm of TiN, TiC, TiCN, diamond and diamond-like carbon thin film Hydroxyapatite coating by sputtering	Improve wear resistance, corrosion resistance and blood compatibility.
	Ion implantation and deposition	~10 nm of surface modified layer and/or um of thin film	Modify surface composition; improve wear, corrosion resistance, and biocompatibility
	Glow discharge plasma treatment	~1 nm to ~100 nm of surface modified layer	Cleaning, sterilizing or oxidizing the surface; surface nitridation; removal of the native oxide layer