In vitro and in vivo evaluation of degradability of hydroxyapatite coatings synthesized by ion beam-assisted deposition

Degradability is among the most important properties in the biomedical field, which is crucial to bone apposition on implants, bone-implant bonding and implantation longevity. The present paper evaluated the degradability of ion beam-assisted deposition (IBAD) hydroxyapatite (HA) coatings in vitro and in vivo. In vitro testing showed that IBAD HA coatings degraded little in 37°C sterile Hank’s physiologic (pH 5.2) balanced salt solution throughout the testing time, while the plasma-sprayed HA coating tested in comparison underwent an increasing degradation: the concentration of Ca increased from the initial 1 ml to 2.75 ml at 3 days post-incubation. In vivo testing revealed that no significant degradation occurred throughout the whole implant period (12 weeks). All the results consistently suggest that the IBAD HA coating is slightly degradable. High magnification SEM observation and HRTEM investigations of the coating further pointed out that the low degradability of the IBAD HA coating derives from its dense microstructure and unique properties such as no sharp grain boundaries. The present study demonstrates that IBAD HA coatings are much more chemically stable than plasma-sprayed HA coatings. The IBAD HA coating possesses more superior adhesive properties, as would be of clinical importance in that it may favor a longer longevity of orthopedic implants.