Sol-gel derived hydroxyapatite coatings on titanium substrates

► Pure hydroxyapatite and composite coatings formed by sol-gel process on titanium. ► Interfacial strength of the coatings is determined by a lag shear strain method. ► The coatings have high interfacial strength and very low fretting wear. ► The acid-etched surfaces showed much higher interfacial shear strength.