Thermally sprayed wollastonite and wollastonite-diopside compositions as new modulated bioactive coatings for metal implants

Abstract New bioactive wollastonite (W) and wollastonite-diopside (W-D) coatings have been deposited over stainless steel and titanium substrates by oxyacetylene flame spraying to optimize the bioactivity of the metallic implants and to improve the resistance to corrosion as well as the mechanical stability by chemical bonding with the bone. The objective is to analyze and compare the physicochemical characteristics and in vitro response of both wollastonite and wollastonite-diopside coatings. Surface and cross-section characterization, including phases, morphology, thickness, roughness, porosity and hardness were performed for both compositions. XRD analyses revealed that both coatings were mainly amorphous although the presence of small crystalline particles (100 nm) was detected by scanning electron microscopy inspection of the coatings cross-section. The in vitro bioactivity of the coatings was examined by observing the formation of an apatite layer on its surface after soaking the coated samples in simulated body fluid (SBF) solution at 37 °C. The W coating exhibited significantly higher dissolution rate compared with the W-D coating, whereas the latter showed the best combination of chemical and mechanical properties with a modulated interaction with the SBF associated to the presence of Mg2+. Both coatings rapidly developed a thick layer containing hydroxyapatite crystals, suggesting their potential competitive use for coating bone implants.