Fig. 1: Contact stiffness defines the relationship between local ECM deformation and the force imposed by the cell adhesion.

A Schematic diagram of a CS-based frame of reference for interpreting the effects of various ECM mechanics on cell behaviors. CS defines the relationship between local ECM deformation and the force imposed by the cell, integrating mechanical variables such as ECM modulus, ECM thickness, and cell spreading area into one variable. B Schematic diagram of the fabrication of ECM composed with a gradient thickness gel. C Fluorescence images of F-actin and nuclei in hMSCs cultured on gradient thickness gels with moduli of 0.5 kPa, 40 kPa, and 100 kPa were obtained. F-actin and nuclei were stained with phalloidin (green) and DAPI (blue), respectively. Scale bar: 75 μm. D Statistical analysis of the cell spreading area of hMSCs cultured on gradient-thickness gels with moduli of 0.5, 10, 40, and 100 kPa as a function of gel thickness. E Statistical analysis of cell spreading area of hMSCs cultured on gradient-thickness gels versus gel modulus. F Statistical analysis of contact stiffness in hMSCs cultured on gradient-thickness gels with moduli of 0.5, 10, 40, and 100 kPa across distinct thickness regions. G Grey patterns show the relative size of micropatterned fibronectin islands on which cells were grown. H Fluorescence images of F-actin and nuclei in hMSCs grown on micropatterned fibronectin islands. F-actin and nuclei were stained with phalloidin (green) and DAPI (blue), respectively. Scale bar: 30 μm. I The statistical analysis of contact stiffness in hMSCs grown on a micropatterned fibronectin islands as shown in (H). All error bars are S.E.M. (324 μm²: n = 11 cells; 529 μm²: n = 12 cells; 2025 μm²: n = 8 cells. *** P < 0.001; ns, not significant).