Stimulation of osteogenesis and angiogenesis by micro/nano hierarchical hydroxyapatite via macrophage immunomodulation

Biomaterial topography-based strategies are regarded as an effective way to regulate the osteoimmune environment which plays an indispensable role in the bone regeneration process. The rapid development of manufacture techniques makes it possible to investigate the cell-topography interactions by preparing various micro and nano-topographical surfaces on biomaterials. Still, it is a challenge to prepare well-defined micro/nano hierarchical structures of bioceramics due to the inherent brittleness of ceramic materials. Also, the correlation between osteoimmunomodulation initiated by micro/nano hierarchical topographies and the tissue regeneration outcomes is unclear. In this study, we prepared well-defined micro/nano hierarchical structures on hydroxyapatite (HA) bioceramics through the combination of the photolithography and hydrothermal techniques. Three different microscale circular patterns (4 μm, 12 μm and 36 μm) and nanotopographies (nanoneedle, nanosheet and nanorod) were fabricated by changing the size of the mask and the condition of the hydrothermal reaction. The macrophage responses on the nanoneedle structures with different micropatterns were investigated and the micro/nano hierarchical structures with appropriate pattern sizes could either promote or alleviate the macrophage polarization, which further affected the outcomes of the osteogenic differentiation of human bone marrow stromal cells (hBMSCs) and angiogenic activity of human umbilical vein endothelial cells (HUVECs). Our study demonstrated that osteoimmunomodulation could be manipulated via tuning the micro/nano hierarchical structures, which could lead to a new strategy for the development of bone biomaterials with favorable osteoimmunomodulatory properties.