Regulation of macrophage polarization through surface topography design to facilitate implant-to-bone osteointegration

Abstract

Proper immune responses are critical for successful biomaterial implantation. Here, four scales of honeycomb-like TiO₂ structures were custom made on titanium (Ti) substrates to investigate cellular behaviors of RAW 264.7 macrophages and their immunomodulation on osteogenesis. We found that the reduced scale of honeycomb-like TiO₂ structures could significantly activate the anti-inflammatory macrophage phenotype (M2), in which the 90-nanometer sample induced the highest expression level of CD206, <i>interleukin-4</i>, and <i>interleukin-10</i> and released the highest amount of <i>bone morphogenetic protein-2</i> among other scales. Afterward, the resulting immune microenvironment favorably triggered osteogenic differentiation of murine mesenchymal stem cells in vitro and subsequent implant-to-bone osteointegration in vivo. Furthermore, transcriptomic analysis revealed that the minimal scale of TiO₂ honeycomb-like structure (90 nanometers) facilitated macrophage filopodia formation and up-regulated the Rho family of guanosine triphosphatases (<i>RhoA, Rac1, and CDC42</i>), which reinforced the polarization of macrophages through the activation of the RhoA/Rho-associated protein kinase signaling pathway.