Adhesion study of pulsed laser deposited hydroxyapatite coating on laser surface nitrided titanium

Hydroxyapatite (HA) coatings were fabricated by pulsed laser deposition (PLD) on commercially pure titanium which had been subjected to different types of pre-treatment. These include: (i) 60-grit SiC grinding, (ii) 320-grit SiC grinding, (iii) 1-µm diamond paste mirror-finishing, (iv) etching with Knoll solution, and (v) laser surface nitriding followed by selective etching. The HA coatings were pulsed laser deposited at different water-vapor pressures to determine the optimal processing conditions. The nitrided-etched specimen exhibits a three dimensional TiN dendritic network which promotes the adhesion between HA coating and titanium substrate. Among the specimens with different pre-treatments, the adhesion strength of HA is the highest for the nitrided-etched specimen, reaching about twice that for the mirror-finished specimen. Thin-film X-ray diffraction shows a high degree of crystallinity for the PLD deposited HA. According to energy-dispersive X-ray analysis, the Ca/P ratio of the deposited HA reaches an approximate value of 1.7, similar to that of the HA target. Scanning-electron microscopy reveals that the deposited HA is about 4 μm in thickness. Growth of apatite was rapidly induced on the HA coated specimens when immersed in Hanks' solution for 4 days, indicating that the PLD HA coating is highly bone bioactive. This could be partly due to the high wettability of the PLD HA surface.