Osteoimmunomodulatory Effects of Zirconia-Modified Titanium: Promoting Macrophage Activation and Osteoblast...

Immune cells are the first to interact with implant surfaces, yet their contribution to osseointegration is often underestimated. Understanding how titanium-based and zirconia-enriched surface properties regulate macrophage polarization is essential for designing regenerative biomaterials. This study evaluates how these physicochemical characteristics modulate macrophage behavior and how macrophage-derived signals affect osteoblast mineralization, a key determinant of successful clinical outcomes.

Human monocytes were differentiated into pro-inflammatory (M1) or anti-inflammatory (M2) macrophages on hydrophobic and hydrophilic titanium (P, SLA/modSLA) or zirconia-enriched titanium (R/modR) surfaces. Macrophage polarization was assessed by Real Time-PCR, fluorescent immunoassays, and Luminex analysis of pro-/anti-inflammatory cytokines and bone-related markers. Conditioned media from M1/M2 macrophages cultured on each surface were used to culture human osteoblast-like cells, and their differentiation and mineralization were evaluated by gene expression analysis and Alizarin Red staining.

The obtained results indicate that surface chemical composition, rather than hydrophilicity, is the main driver of early macrophage phenotype modulation. Zirconia incorporation induced effects comparable to titanium on macrophage activation while increasing transcription of pro- and anti-inflammatory genes. Moreover, zirconia enhanced M1 activation and the release of angiogenic and osteogenic mediators, including VEGF and OPN. Although seemingly contradictory, these effects contribute to an immune microenvironment favorable to bone formation by promoting a balanced macrophage response. Consistently, zirconia-enriched surfaces enhanced osteoblastic differentiation and mineralization, regardless of hydrophilic differences compared with conventional titanium surfaces.

Our findings indicate that zirconia-supplemented titanium alloys may provide a useful model to elucidate the concept of osseointegration as an osteoimmune process rather than a conventional bone healing response. The data emphasize the critical role of early M1 macrophage activity controlling the release of specific cytokines, supporting the hypothesis that the use of titanium/zirconia alloys may provide an osteoiummunomodulatory advantage that may contrast peri-implant bone loss.