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. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1789-1797, 2018.

The proximity of minerals found in human hard tissues may influence cell phenotype. Since cells respond to a range of environmental cues, this study sought to identify the influence of two apatite-based microparticles, hydroxyapatite (HA) and fluoroapatite (FA), upon dental and bone cells. After bone marrow stromal cells (BMSCs), 7F2 osteoblasts and dental pulp stem cells (DPSCs) were plated into media with or without HA or FA particles, the cells were analyzed for alkaline phosphatase (ALP) production, collagen I production, osteocalcin production, and mineralization for two weeks. The BMSCs and DPSCs in media without any microparticles produced more ALP compared to those with microparticles from Day 5 forward. In addition, the collagen I and osteocalcin production in cultures without microparticles was higher than in cultures containing either HA or FA particles. While some studies have shown increased osteogeonic differentiation in the presence of mineral particles, those studies used nanoparticles that were able to be internalized by the cells and were smaller than the microparticles used in this study.