Modulation of stem cell response using biodegradable polyester films with different stiffness

Matrix stiffness is a crucial regulator of cell fate in both in vitro and in vivo setting. Although studies with non-degradable polymers have contributed to our understanding of the influence of rigidity on cell response, very little work has been conducted with biodegradable polymers that constitute the building blocks of implantable devices. Herein, we investigated human bone marrow stem cell response as a function of rigidity (7 kPa, 10 kPa, 12 kPa, 22 kPa, 15 MPa elastic modulus values) that induced by five different aliphatic polyesters (tissue culture plastic with ~ 3 GPa rigidity was used as control). Cell morphology analysis revealed that stiff substrates stimulated a large cell area with defined stress fibres, whilst soft substrates prompted a small cell area without evident stress fibres. Immunocytochemistry analysis made apparent that YAP was accumulated at the nuclei when the cells were seeded on stiff substrates and at the cytoskeleton on soft substrates. Substrate stiffness did not affect (p > 0.05) the expression of positive (> 97% CD73, CD90, CD105, CD44), but increased (p < 0.05) the expression of negative (< 44% CD45, < 14% CD31, < 28% CD146) mesenchymal stem cell markers after 21 days of culture. With respect to trilineage differentiation, the 15 MPa substrate induced the highest (p < 0.05) calcium deposition and SPP1 mRNA expression in osteogenic media, the 22 kPa substrate induced the highest (p < 0.05) COMP and ACAN mRNA expression in chondrogenic media and the 10 kPa substrate induced the highest (p < 0.05) FABP4 and CEBPA mRNA expression in adipogenic media, all after 21 days in culture. Although some issues associated with degradation were encountered, our data clearly illustrate that biodegradable polymers also contribute to cell phenotype and function in a rigidity dependant manner.