Biomedical coatings for orthopedic implants should facilitate osseointegration and mitigate implant-induced inflammatory reactions. Cerium oxide (CeO) ceramics possess anti-oxidative properties and can be used to decrease mediators of inflammation, which makes them attractive for biomedical applications. In our work, two kinds of CeO incorporated hydroxyapatite coatings (HA-10Ce and HA-30Ce) were prepared via plasma spraying technique and the effects of CeO addition on the responses of bone mesenchymal stem cells (BMSCs) and RAW264.7 macrophages were investigated. An increase in CeO content in the HA coatings resulted in better osteogenic behaviors of BMSCs in terms of cell proliferation, alkaline phosphatase (ALP) activity and mineralized nodule formation. RT-PCR and western blot analysis suggested that the incorporation of CeO may promote the osteogenic differentiation of BMSCs through the Smad-dependent BMP signaling pathway, which activated Runx2 expression and subsequently enhanced the expression of ALP and OCN. The expression profiles of macrophages cultured on the CeO modified coating revealed a tendency toward a M2 phenotype, because of an upregulation of M2 surface markers (CD163 and CD206), anti-inflammatory cytokines (TNF-α and IL-6) and osteoblastogenesis-related genes (BMP2 and TGF-β1) as well as a downregulation of M1 surface markers (CCR7 and CD11c), proinflammatory cytokines (IL-10 and IL-1ra) and reactive oxygen species production. The results suggested the regulation of BMSCs behaviors and macrophage-mediated responses at the coating's surface were associated with CeO incorporation. The incorporation of CeO in HA coatings can be a valuable strategy to promote osteogenic responses and reduce inflammatory reactions.
Ideal orthopedic coatings should trigger good osteogenic response and limited inflammatory response. The cerium valence states in ceria are associated with their anti-oxidative activity and anti-inflammatory property. In the study, we prepared two kinds of plasma sprayed CeO coatings with different Ce concentrations to investigate the effects of Ce valence states on the response of bone mesenchymal stem cells (BMSCs) and macrophage RAW264.7. Both the coatings (CeO-A and CeO-B) were characterized via XRD, SEM, and X-ray photoelectron spectroscopy. The CeO coatings enhanced osteogenic behaviors of BMSCs in terms of cellular proliferation, alkaline phosphatase (ALP) activity and calcium deposition activity in comparison with the Ti substrate. In particular, the CeO-B coating (higher Ce concentration) elicited greater effects than the CeO-A coating (higher Ce concentration). RT-PCR and western blot results suggested that the CeO-B coating promoted BMSCs osteogenic differentiation through the SMAD-dependent BMP signaling pathway, which activated Runx2 expression and subsequently enhanced the expression of ALP and OCN. With respect to either CeO-A coating or Ti substrate, the CeO-B coating exerted greater effects on the macrophages, increasing the anti-inflammatory cytokines (IL-10 and IL-1ra) expression and suppressing the expression of the pro-inflammatory cytokines (TNF-α and IL-6) and ROS production. Furthermore, it also upregulated the expression of osteoinductive molecules (TGF-β1 and BMP2) in the macrophages. The regulation of cerium valence states at plasma sprayed ceria coatings can be a valuable strategy to improve osteogenic properties and alleviate inflammatory response.
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