Laser deposition of thin hydroxyapatite films on titanium implants

The coating of biomedical devices with bioceramic films is an important aspect in the study of orthopedic prostheses and dental implants. The coating has the aim of improving the device biocompatibility, the prostheses anchorage to the bone, the resistance to corrosion and wear and the life time of the device. The most widely used bioceramic is hydroxyapatite (HA), Ca 10 (PO 1) 6 (OH) 2-, which shows high biocompatibility and osseointegration. The deposition of HA films by traditional methods, such as plasma spraying, physical vapor deposition and sintering processes, has limitations because the temperatures involved are too high, exceeding, 900 °C, at which HA decomposes into tricalcium phosphate, calcium oxide and unbound water. Moreover, deposition methods based on ion sputtering and electrophoresis produce nonstoichiometric and amorphous films of HA. This article presents an alternative deposition method using a pulsed ruby laser to remove HA molecules from an HA target (dental enamel) and to deposit them on a nearby substrate heated to a temperature of 400 °C. The results obtained indicate that laser pulses can be used to deposit thin films of HA on medical prostheses and implants. Nevertheless, the films obtained have a porosity which is still too low compared with that obtainable with the traditional plasma spraying method. Work is in progress to improve the laser deposition method to obtain large grains and highly porous HA films.