The deposition of strontium-substituted hydroxyapatite coatings

Abstract

Strontium substituted hydroxyapatite (SrHA) coatings have received a lot of interest recently as strontium (Sr) has been shown to have the dual benefit of promoting bone formation and reducing bone resorption, in vivo. In this work, SrHA coatings were deposited onto polycrystalline titanium surfaces using radio frequency (RF) magnetron co-sputtering and compared to those deposited from HA alone. In particular, the influence of different levels of Sr-substitution of the sputtering targets (5 and 13% Sr-substituted HA targets) on the properties of the deposited coatings produced at a low discharge power level (150 W) were investigated using FTIR, XPS, XRD, ToFSIMS and AFM techniques (both before and after annealing at 500 °C). The results show that Sr could be successfully incorporated into the HA lattice to form SrHA coatings and that 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 when compared to the coating produced from the 5% Sr-substituted target (1.58±0.20). The deposition rate also decreased with increasing Sr content of the sputtering targets. Furthermore, as the Sr content of the coatings increased, so did the preferred 002 orientation of the coating along with increased surface roughness and heterogeneity of the surface features. Therefore, this study has shown that RF magnetron sputtering offers a means to control attendant properties of Sr-substituted HA, such as the crystallinity, stoichiometry, phase purity and surface topography.

Osteoblastic differentiation of periodontal ligament stem cells on non‐stoichiometric calcium phosphate and titanium surfaces

“…It should also be noted that the CaP coatings were thermally annealed to 500°C, as coatings sputter deposited under the conditions employed here are typically amorphous in nature, and inherently physiologically unstable . The chemistry of the sputtered CaP detected here reflects the low sputtering power employed (150 W), as such coatings have been shown to contain only HA‐like properties with no other additional CaP phases or byproducts presence . This means that this coating is consistent with the requirements of various international standards (ASTM 1185–03(2014), ASTM 1609–(08)2014, and ISO 13779 (Parts 2 and 3)).…”

“…A very weak O‐H libration band is observed around 632 cm −1 as a weak shoulder, with a further peak associated with O‐H groups observed at 3570 cm −1 . This peak may be associated with O‐H stretching groups within the film . The absence of strong ‐OH functional groups, commonly observed at approximately 632 cm −1 and 3568 cm −1 , indicate that a degree of dehydroxylation has occurred within the CaP crystal structure deposited from the HA target under the conditions employed here.…”

“…This peak may be associated with O-H stretching groups within the film. 16 The absence of strong -OH functional groups, commonly observed at approximately 632 cm 21 and 3568 cm 21 , indicate that a degree of dehydroxylation has occurred within the CaP crystal structure deposited from the HA target under the conditions employed here. Peaks indicative of CO 22 3 species were also observed in the FTIR spectrum for Ca-P coating between 1550 and 1400 cm 21 .…”

“…O‐P‐O bending vibrations are also present between 620 and 560 cm −1 . Hydrogen phosphate bands ( ) can also be observed at 1122 and 582 cm −1 . A very weak O‐H libration band is observed around 632 cm −1 as a weak shoulder, with a further peak associated with O‐H groups observed at 3570 cm −1 .…”

“…Hydrogen phosphate bands (HPO 22 4 ) can also be observed at 1122 and 582 cm 21 . 16 A very weak O-H libration band is observed around 632 cm 21 as a weak shoulder, with a further peak associated with O-H groups observed at 3570 cm 21 . This peak may be associated with O-H stretching groups within the film.…”