Integrated response of stem cells to mechanobiological properties of biomaterials

Mesenchymal stem cells (MSCs) are a promising cell source for the regeneration of connective tissues, including those of the craniofacial region. Effective regeneration of functional tissues requires the design of “instructive” biomaterials that predictably and optimally direct MSC function. Both biomaterial stiffness and adhesion characteristics have been shown to independently impact stem cell function. However, the combined effects of matrix stiffness and adhesion ligands on the integrated response of MSCs have not been defined. Objective: To determine the integrated effects of different combinations of matrix stiffness and adhesion proteins on the proliferation of MSCs. Methods: Polyacrylamide hydrogels of various stiffness (3, 25, 68, or 200 kPa) were coated with 7 ug/mL type I collagen or fibronectin. Mouse C3H10T1/2 MSCs were seeded on the matrix protein-coated gels at a density of 2400 cells/cm² and cultured for up to four days. Cell numbers were quantified at seeding and at day four by measuring total DNA. Results: MSC proliferation on the collagen-coated gels was the greatest on the stiffest (200 kPa) gels (35±3.0(SE)-fold cell expansion). Proliferation on the 200 kPa collagen-coated gels was more than twice of that on the more compliant collagen-coated substrates (P<0.0001). In contrast, on the fibronectin-coated gels the greatest proliferation occurred on the 68 kPa substrates (15±4.7-fold expansion), which was two-fold greater than that on 3 kPa substrates. Proliferation on the 25, 68, and 200 kPa substrates was not significantly different. Conclusions: MSC function, in this case proliferation, is regulated by both substrate stiffness and matrix adhesion ligands; these effects are not independent, but interact to determine the integrated MSC response. Thus, the combined effects of biomaterial design parameters must be considered to predictably guide stem cell survival and differentiation.

Supported by the CIHR and NSERC of Canada.