Biomimetic Calcium Phosphate Growth over Differently Shaped Ti Substrates: Modeling the Effect of Surface Curvature

Abstract

The growth of biomimetic calcium phosphate (CaP) coatings on flat Ti coupons and rounded pins (wires) immersed in simulated body fluid (SBF) was studied. Depending on the substrate curvature and immersion time, single- or double-layer coatings were obtained, comprised of submicrometer-size hydroxyapatite (HA) and platelike crystals of octacalcium phosphate (OCP). Increasing the curvature was found to delay the growth of OCP, to increase the relative thickness of HA, and to increase the total coating thickness. A computational model of CaP deposition was developed based on the assumption that the nucleation of the kinetically favored OCP phase and its hydrolysis into the more stable HA at high initial supersaturations is superseded by OCP crystal growth due to decreasing local supersaturation on the substrate surface. The model calculations showed good agreement with the experimental results and allowed us to qualitatively predict the coating thickness and OCP/HA sublayer proportion on different diameter wires. In addition, the effect of SBF solution parameters on CaP coating growth was studied experimentally and modeled.