Effects of substrate stiffness on dental pulp stromal cells in culture.

Dental pulp stromal cells (DPSCs) can be differentiated down lineages known to either express bone or dentin specific protein markers. Since the differentiation of cells can be heavily influenced by their environment, it may be possible to influence the osteogenic/odontogenic potential of DPSCs by modulating the mechanical properties of substrate on which they are grown. In this study, human DPSCs were grown with and without hydroxyapatite (HA) microparticles on a range of substrates including fibronectin-coated hydrogels and glass substrates, which represented an elastic moduli range of approximately 3 kPa-50 GPa, over a 21-day period. Alkaline phosphatase activity, osteopontin production, and mineralization were monitored. The presence of HA microparticles increased the relative degree of mineralized matrix produced by the cells relative to those in the same substrate and media condition without the HA microparticles. In addition, cultures with cells grown on stiffer substrates had higher ALP activity and higher degree of mineralization than those grown on softer substrates. This study shows that DPSCs are affected by the mechanical properties of their underlying growth substrate and by the presence of HA microparticles. In addition, relatively stiff substrates (>75 kPa) may be required for significant mineralization of these cultures.