Osteogenic cells differentiation on topological surfaces under ultrasound stimulation

The current trends in bone tissue engineering aim to fasten the cells osteogenic differentiation by mechanical stimulation. To date, several approaches have proved efficient for this purpose. One is related to changing the shape of the cells nuclei using topological surfaces with appropriate dimensions and stiffness. Another successful method is by low-intensity pulsed ultrasound stimulation (LIPUS) of the cells. The goal of this proof-of-concept study is to introduce and validate, for the first time, the synergistic effect of topological surfaces and LIPUS for improving the osteogenic differentiation of osteoblast-like cells. Cells were grown on topological surfaces consisting of vertical microtubes fabricated by laser direct writing. The flexibility of the topological surfaces was tuned by varying the microtubes’ height. The spatial arrangement and dimensions of the microtubes limited the cell–cell interactions and allowed us to observe individual cells. A finite element model simulation was proposed for explaining the cell–surface interaction details. We monitored the cells nuclei deformations in response to the topological surfaces in conjunction with LIPUS. The topological surfaces alone induced dramatic changes of the shape of the cells nuclei that wrapped around the microtubes. The nuclei deformation was further increased by LIPUS. This synergy between the topological surfaces and LIPUS allowed us to obtain an increase of up to 200% in the cells osteogenic differentiation, as determined by ALP activity and osteocalcin secretion measurements, in comparison with flat surfaces in static regime. A causal relationship between the nuclei deformation and the cells osteogenic differentiation was established.