Dissolution control and cellular responses of calcium phosphate coatings on zirconia porous scaffold

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Abstract
Different types of calcium phosphates [hydroxyapatite (HA), fluorapatite (FA), tricalcium phosphate (TCP), and their composites (HA + FA, HA + TCP)] were coated on a zirconia (ZrO2) porous scaffold using a powder slurry method. The ZrO2 porous scaffold was intended for a load-bearing implant, and the apatite layers were coated to improve osteoconductivity. The insertion of an FA intermediate layer between the coating layer and ZrO2 scaffold effectively suppressed the reaction between the calcium phosphate and ZrO2 and maintained the coating layer at the initial powder composition. The obtained coating layer, of a thickness of ∼30 μm, was relatively microporous and firmly adherent to the ZrO2 scaffold. Dissolution tests in physiological solution showed typical differences depending on the coating layers, with the dissolution rate increasing in the order TCP > HA + TCP > HA > HA + FA > FA. This result suggests the functional coating of the calcium phosphates in view of tailoring the solubility. Osteoblast-like cells, MG63 and HOS, responded similarly in terms of cell growth, morphology, and proliferation rate regardless of the coating types, indicating favorable and comparable cell viability. However, the alkaline phosphatase (ALP) activity of the cells on the pure HA and HA composite coatings (HA + FA and HA + TCP) expressed at higher levels compared to those on pure FA and pure TCP coatings for both MG63 and HOS cells, suggesting a selective cell activity depending on the coating types. All the calcium phosphate-coated-ZrO2 scaffolds showed higher ALP levels compared to pure ZrO2 scaffold. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res 68A: 522–530, 2004