Nanopit-induced osteoprogenitor cell differentiation: The effect of nanopit depth.

We aimed to assess osteogenesis in osteoprogenitor cells by nanopits and to assess optimal feature depth. Topographies of depth 80, 220 and 333 nm were embossed onto polycaprolactone discs. Bone marrow-derived mesenchymal stromal cells were seeded onto polycaprolactone discs, suspended in media and incubated. Samples were fixed after 3 and 28 days. Cells were stained for the adhesion molecule vinculin and the osteogenic transcription factor RUNX2 after 3 days. Adhesion was lowest on planar controls and it was the shallowest, and 80-nm-deep pits supported optimal adhesion formation. Deep pits (80 and 220 nm) induced most RUNX2 accumulation. After 28 days, osteocalcin and osteopontin expression were used as markers of osteoblastic differentiation. Deep pits (220 nm) produced cells with the highest concentrations of osteopontin and osteocalcin. All topographies induced higher expression levels than controls. We demonstrated stimulation of osteogenesis in a heterogeneous population of mesenchymal stromal cells. All nanopit depths gave promising results with an optimum depth of 220 nm after 28 days. Nanoscale modification of implant surfaces could optimise fracture union or osteointegration.