Nonlinear active stress – Principal strain relation during pulsation of human iPS cell derived cardiomyocyte sheet

Recently, a technique for differentiating human iPS cells into cardiomyocytes has been established and therefore, human iPS cell derived cardiomyocytes (hiPS-CM) can be utilized for the biomechanical study of myocardial tissues. In the present study, a sheet structure of hiPS-CM was fabricated using cell sheet technology and the pulsation behavior was measured using a high speed imaging system. The minimum principal strain was then evaluated using the digital correlation method and the active stress was calculated on the basis of the theoretical model proposed by Guccione et al. It was found that the active stress-strain behavior clearly exhibited a nonlinear viscoelastic response characterized by a hysteresis loop. This nonlinear response was also found to be effectively predicted by the constitutive equation derived from the viscoelastic Maxwell model. A microscopic mechanism involved in the hysteresis loop was also proposed on the basis of the sarcomere structure and mechanical behavior.