Morphology and adhesion strength of myoblast cells on photocurable gelatin under native and non-native micromechanical environments

We have quantitatively determined how the morphology and adhesion strength of myoblast cells can be regulated by photocurable gelatin gels, whose mechanical properties can be fine-tuned by a factor of 10³ (0.1 kPa ≤ E ≤ 140 kPa). The use of such gels allows for the investigation of mechanosensing of cells not only near the natural mechanical microenvironments (E ∼ 10 kPa) but also far below and beyond of the natural condition. Optical microscopy and statistical image analysis revealed that myoblast cells sensitively adopt their morphology in response to the substrate elasticity at E ∼ 1-20 kPa, which can be characterized by the significant changes in the contact area and order parameters of actin cytoskeletons. In contrast, the cells in contact with the gels with lower elastic moduli remained almost round, and the increase in the elasticity beyond E ∼ 20 kPa caused no distinct change in morphology. In addition to the morphological analysis, the adhesion strength was quantitatively evaluated by measuring the critical detachment pressure with an aid of intensive pressure waves induced by picosecond laser pulses. This noninvasive technique utilizing extremely short pressure waves (pulse time width ∼100 ns) enables one to determine the critical pressure for cell detachment with reliable statistics while minimizing the artifacts arising from the inelastic deformation of cells. The adhesion strength also exhibited a transition from weak adhesion to strong adhesion within the same elasticity range (E ∼ 1-20 kPa). A clear correlation between the cell morphology and adhesion strength suggests the coupling of the strain of the substrate and the mechanosensors near focal adhesion sites.