Control of magnesium alloy corrosion by bioactive calcium phosphate coating: Implications for resorbable orthopaedic implants

Abstract

Control of the corrosion that occurs in magnesium alloys in vivo is a significant challenge for their use as resorbable orthopaedic implants. In this work, we report on the provision of bioactive calcium phosphate (CaP) coatings on magnesium alloys that can delay substrate corrosion while offering an attendant physiochemical environment with properties known to promote an osteoinductive response in vivo. RF magnetron sputtering from hydroxyapatite (HA) powder targets has been employed to create CaP coatings on AZ31 magnesium alloy substrates. Coatings of 70 and 210 nm thickness were achieved via regulation of sputtering parameters, in particular deposition time. XPS and ToF-SIMS were used to investigate the chemistry of the coating alloy interface and also to confirm composition and thickness. The Ca/P atomic ratio of the coatings was determined by EDX to be 1.54. μCT analysis showed a substrate volume loss after 14 days exposure to SBF of 5.89 ± 3.15 mm 3 for the un-coated alloy while the presence of the ~70 nm CaP coating reduced this to 3.42 ± 0.48 mm 3 and the ~210 nm coating to 0.30 ± 0.28 mm 3. The corrosion rates were calculated to be 1.74 ± 0.06 mmpy for the AZ31 control; 1.57 ± 0.09 mmpy for the ~70 nm CaP coated alloy and 1.01 ± 0.07 mmpy for the ~210 nm thick CaP coating. These data confirm that CaP coating

Direct monitoring of single-cell response to biomaterials by Raman spectroscopy

“…XPS can analyse a depth of ~5-10 nm (under the conditions employed in this study) and SEM-EDX can analyse a depth of ~0.9 µm. Both techniques confirm the presence of both Ca and P on the surface but the application of dry pressed HA targets in this study can lead to re-sputtering of the HA coating, resulting in a lower-thanexpected Ca/P ratio and possible disparities between methods [25][26][27]. In addition, said characterisation techniques provided information on coating uniformity on the Ti substrate; no Ti 2p signals were obtained by XPS (Fig.…”

Analytical Techniques for the Characterization of Bioactive Coatings for Orthopaedic Implants

“…An example of ToF-SIMS 3D depth profiling has been presented for RF magnetron-sputtered CaP coatings of different thicknesses on Mg alloy implants to confirm the successful deposition and 3D distribution of species in coatings with a thickness of 70 nm and 210 nm [ 61 ]. Moreover, depth profiling, which indicates the different intensities of phase-associated ions over time, has been shown to be useful in detecting different phase transitions, starting with the surface of plasma-deposited coatings embedded with silver nanoparticles, followed by the implant material.…”

TOFSIMS and XPS characterisation of strontium in amorphous calcium phosphate sputter deposited coatings

“…undertaken by the authors [20][21][22][31][32][33]. The coatings produced here were characterised in the as-deposited state.…”