Regulation of an osteon-like concentric microgrooved surface on osteogenesis and osteoclastogenesis

Topographical cues provided by micropatterns on material surfaces have been demonstrated to control multiple cell functions. However, the majority of currently studied micropatterns fail to recapitulate the key characteristics of an osteon, which is the structural unit of natural cortical bone. Thus, in the present study, a micropatterned polycaprolactone (PCL) surface comprising a series of concentric circular microgrooves was fabricated by combining photolithography with the melt-casting method to mimic the concentric structure of an osteon in a two-dimensional setting. By culturing mouse mesenchymal stem cells (mMSCs) and osteoclast progenitor cells (RAW264.7 cells) on the osteon-like concentric microgrooved surface, the effects of this micropatterned surface on the osteogenesis of mMSCs and the osteoclastogenesis of RAW264.7 cells were systematically investigated. Osteoclastogenic differentiation was significantly inhibited in RAW264.7 cells on the fabricated osteon-like concentric microgrooved surface compared to that on the parallel linear microgrooved and flat surfaces, as indicated by the downregulated expression of key osteoclast-specific function genes (TRAP, CATK and MMP9), the lower activity of TRAP and less formation of TRAP-positive multinucleated giant osteoclasts. Further investigation indicated that RANK-Nf-kappa B signaling may have been involved in mediating the inhibited osteoclastogenesis of RAW264.7 cells by the osteon-like concentric microgrooved surface. In addition, the osteon-like concentric microgrooved surface greatly modulated the osteoclastogenic-related paracrine secretion of mMSCs (RANKL, M-CSF and OPG), despite its small effect on the osteogenesis of mMSCs. This secretory profile was found to be able to effectively inhibit osteoclastogenesis in RAW264.7 cells, confirming the enhanced osteoclastogenesis inhibitory functions of mMSCs on the osteon-like concentric microgrooved surface. Our findings demonstrate the importance of the microgroove orientation and arrangement in affecting cellular behaviors and highlight the potential benefits of incorporating osteon-like concentric microgrooved patterns on the surface of scaffolds for bone repair.