Hydrogels made from the cardiac extracellular matrix (ECM) as two-dimensional (2D) or 3D cell-culture substrates have beneficial biochemical effects on the differentiation of stem cells into cardiomyocytes. The mechanical properties of the substrates that match those of the host tissues have been identified as critical biophysical cues for coaxing the tissue-specific differentiation of stem cells. The objectives of the present study are (1) to fabricate hydrogels comprising pure ventricular ECM (vECM), (2) to make the gels possess mechanical properties similar to those of the decellularized ventricular tissue, and (3) to evaluate the cellular compatibility of the hydrogels. In order to achieve these aims, (1) a simplified protocol was developed to produce vECM solution easily and rapidly, (2) N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDAC) was chosen to crosslink the hydrogels made from the vECM solution to enhance their mechanical properties and stabilize the microstructure of the gels, (3) rat embryonic fibroblasts or cardiomyocytes were cultured on these gels to determine the cellular compatibility of the gels. In particular, the nonlinearity and viscoelasticity of the gels were characterized quantitatively using a newly proposed nonlinear Kelvin model. The results showed that EDAC treatment allowed modulation of the mechanical properties of the gels to the same level as those of decellularized ventricular tissue in terms of the equilibrium elasticity and relaxation coefficient. Cell culture confirmed the cellular compatibility of the gels. Furthermore, an empirical relationship between the equilibrium elastic modulus of the gels and the vECM and EDAC concentrations was derived, which is important to tailor the mechanical properties of the gels. Finally, the influence of the mechanical properties of the gels on the behavior of cultured fibroblasts and cardiomyocytes was discussed.
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