Biomaterial Property Effects on Platelets and Macrophages: An in Vitro Study

The purpose of this study was to evaluate the effects of surface properties of bone implants coated with hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP) on platelets and macrophages upon implant installation and compare them to grit-blasted Ti and Thermanox used as a control. Surface properties were characterized using scanning electron microscopy, profilometry, crystallography, Fourier transform infrared spectroscopy, and coating stability. For platelets, platelet adherence and morphology were assessed. For macrophages, morphology, proliferation, and polarization were evaluated. Surface characterization showed similar roughness of similar to 2.5 mu m for grit-blasted Ti discs, both with and without coating. Coating stability assessment showed substantial dissolution of HA and beta-TCP coatings. Platelet adherence was significantly higher for grit-blasted Ti, Ti-HA, and Ti-beta-TCP coatings compared to that of cell culture control Thermanox. Macrophage cultures revealed a decreased proliferation on both HA and beta-TCP coated discs compared to both Thermanox and grit-blasted Ti. In contrast, secretion of pro-inflammatory cytokine TNF-alpha and anti-inflammatory cytokine TGF-beta were marginal for grit-blasted Ti and Thermanox, while a coating-dependent increased secretion of pro- and anti-inflammatory cytokines was observed for HA and beta-TCP coatings. The results demonstrated a significantly upregulated pro-inflammatory and anti-inflammatory cytokine secretion and marker gene expression of macrophages on HA and beta-TCP coatings. Furthermore, HA induced an earlier M1 macrophage polarization but more M2 phenotype potency than beta-TCP. In conclusion, our data showed that material surface affects the behaviors of first cell types attached to implants. Due to the demonstrated crucial roles of platelets and macrophages in bone healing and implant integration, this information will greatly aid the design of metallic implants for a higher rate of success in patients.