The Deposition of Strontium-Substituted Hydroxyapatite Coatings

Strontium substituted hydroxyapatite (SrHA) coatings have received a lot of interestrecently as strontium (Sr) has been shown to have the dual benefit of promoting boneformation and reducing bone resorption, in vivo. In this work, SrHA coatings weredeposited onto polycrystalline titanium surfaces using radio frequency (RF) magnetronco-sputtering and compared to those deposited from HA alone. In particular, theinfluence of different levels of Sr-substitution of the sputtering targets (5% and 13% SrsubstitutedHA targets) on the properties of the deposited coatings produced at a lowdischarge power level (150 W) were investigated using FTIR, XPS, XRD, ToFSIMSand AFM techniques (both before and after annealing at 500°C). The results show thatSr could be successfully incorporated into the HA lattice to form SrHA coatings andthat they contained no other impurities. However, the coating produced from the 13%Sr-substituted target had a higher Ca+Sr/P ratio (1.95±0.14) and Sr content whencompared to the coating produced from the 5% Sr-substituted target (1.58 ± 0.20). Thedeposition rate also decreased with increasing Sr content of the sputtering targets.Furthermore, as the Sr content of the coatings increased, so did the preferred 002orientation of the coating along with increased surface roughness and heterogeneity ofthe surface features and their distribution across the surface. Therefore, this study hasshown that RF magnetron sputtering offers a means to control attendant properties ofSr-substituted HA, such as the crystallinity, stoichiometry, phase purity and surfacetopography.