The immunomodulatory effects of Zn-incorporated micro/nanostructured coating in inducing osteogenesis

Micro/nanostructured TiO₂/ZnO coating has been shown to possess multiple functions, including antibacterial activity and bioactivity. Osteoblast-like SaOS-2 cells were employed for evaluating the in vitro osteogenic capacity of this coating and positive results were obtained. However, traditional principles of osseointegration focus only on the osteogenic differentiation alone. The effects of immunomodulation on the osteogenic activity have been largely ignored. In this study, the inflammatory responses of macrophages on the micro/nanostructured TiO₂/ZnO coating were investigated. The extract media of macrophage cell line RAW264.7 cultured on the TiO₂/ZnO coating were collected as indirect co-culture conditioned media. The osteogenic activity of SaOS-2 cells in the conditioned media was investigated. Adhesion, ALP activity and extracellular mineralization of cells grown in the conditioned media extracted from the micro/nanostructured TiO₂/ZnO coating were found to be enhanced, compared to those grown in the conditioned media extracted from the macroporous TiO₂ coating. The immune microenvironment produced by the micro/nanostructured TiO₂/ZnO coating showed excellent capacity to promote osteogenesis, indicating that this coating could be a promising candidate for implant surface modification in orthopaedic and dental applications. Furthermore, this work could help us understand the interplay between the host immune system and the osteoimmunomodulatory properties of the biomaterials, and optimize the design for coating biomaterials.