Raman spectroscopy determination of phases within thermal sprayed hydroxyapatite splats and subsequent in vitro dissolution examination

Abstract

Phase compositions at various locations within individual thermal sprayed hydroxyapatite (HA) splats were qualitatively determined using Raman spectroscopy analysis and, confirmed through in vitro dissolution exercise. The purpose of the present study was to verify the locations of different phases within a HA splat deposited by thermal spray techniques. The splats were prepared through dc thermal plasma and high velocity oxy-fuel (HVOF) spray processes. Raman spectroscopy studies were performed to determine the locations of various phases that exist within individual splats, and the results were verified with in vitro dissolution tests. Results showed that the Raman spectroscopy is a feasible technique for qualitative determination of the phases within a single HA splat. It was revealed that the thermal decomposition of HA into tricalcium phosphate (TCP), amorphous calcium phosphate (ACP), tetracalcium phosphate (TTCP), CaO and other phases, occurred mainly within the melted portion of the sprayed particle during the thermal spray process. The in vitro tests of the individual HA splats in simulated body fluid established a reasonable correlation between localized dissolution behavior and the phases revealed by the Raman spectroscopy plots. This study demonstrates the feasibility of employing the Raman spectroscopy technique to provide phase distribution information within a single HA splat. Henceforth, a better understanding and control of optimizing the properties of a bulk HA coating through controlling the spray process could be possible.