The synergistic effects of multivalent ligand display and nanotopography on osteogenic differentiation of rat bone marrow stem cells

Cell–substrate interactions play a vital role in governing crucial cell functions such as adhesion, proliferation and differentiation. Surface topography and chemical properties can initiate signaling cascades modulating cell behavior. However, mimicking extracellular environment to direct cell functions through cell–surface interactions is challenging. In this report, we employed tobacco mosaic virus (TMV) as a model system to present nanotopographic features along with multivalent ligand display to study osteogenic differentiation of bone marrow stem cells (BMSCs). TMV is a rod shaped plant virus which is 300 nm in length and 18 nm in diameter. A single TMV rod comprises of 2130 identical coat proteins which assemble into the rod-like helical structure around the single strand of RNA. For the present study TMV was chemically modified with phosphate to induce calcium incorporation. Gene regulation during BMSC differentiation on TMV and TMV-phosphate (TMV-Phos) was studied over time points of 7, 14 and 21 days. We examined changes in gene expression of osteospecific genes (osteocalcin, osteopontin and runx2) which indicate that nanofeatures functionalized with phosphate groups exhibited significantly higher up regulation of osteospecific genes. Furthermore, we studied the gene regulation by coating Ti substrates with TMV and TMV-Phos. TMV-Phos coated substrates displayed higher expression of the studied genes as compared to Ti substrates. Our results imply that the differentiation capacity of BMSCs can be significantly enhanced through simple multivalent interactions with simple functional units rather than using complex biomolecules.