A MECHANICAL INVESTIGATION OF FLUORAPATITE, MAGNESIUMWHITLOCKITE, AND HYDROXYLAPATITE PLASMA-SPRAYED COATINGS IN GOATS

Ceramic coatings of fluorapatite (FA), magnesiumwhitlockite (MW), and hydroxylapatite (HA), and noncoated Ti-6Al-4V alloy (Ti) implants were evaluated before and after implantation in an animal study. Cylindrical plugs were coated by plasma-spraying with FA, MW, and HA. X-ray-diffraction patterns showed for FA and HA a crystalline and for MW an amorphous-crystalline coating structure. The plugs were implanted into the right femora and left humeri of 16 adult goats. Follow-up periods were 12 and 25 weeks. The in vivo results were evaluated using push-out tests and scanning electron microscopy. There were significant differences in push-out strengths between femur and humerus. The FA and HA implants showed significantly higher push-out strengths than the MW and Ti alloy implants, especially for the 12 week follow-up period. Furthermore, at 12 weeks, MW showed significantly lower push-out strengths than Ti alloy. SEM-investigation of the interfaces revealed that FA did not degrade while both MW and HA showed extensive degradation at 12 and 25 weeks. In addition, the interface after push-out testing showed for the MW, HA, and Ti alloy implants to be fractured at the implant-tissue interface and for the FA to be fractured at the coating-titanium interface.