Engineering viscoelastic alginate hydrogels for hiPSC cardiomyocyte culture.

Heart disease is the leading cause of death worldwide, however research progress of heritable cardiomyopathies has been limited by the lack of cost effective and accurate human models. Human induced pluripotent stem cells (hiPSCs) are a renewable cell source that can be differentiated into human cardiomyocytes (CMs), presenting a reliable tool for in vitro cellular models. The physiological environmental cues that CMs are exposed to are extraordinarily complex and in vitro systems typically fail to mimic key aspects such as viscoelasticity and adhesion ligand type. Viscoelasticity in particular is important to model as it is exhibited by virtually all tissues in the body and can influence several cell functions including spreading, differentiation and proliferation. However, the majority of experiments with CMs to date have used covalently crosslinked hydrogels that do not exhibit any stress relaxing properties. Here, we engineered biomaterials to recapitulate these viscoelastic heart tissue characteristics. Since the stress relaxation properties of heart tissue have not been directly measured, we first mechanically characterized left ventricular porcine tissue. The elastic modulus was around 7 kPa, within range of reported values. However, the tissue exhibited much faster stress relaxation values than we anticipated; relaxing to half its max value in less than 10 s while skeletal muscle tissue is reported to relax closer to 100 s. We synthesized an alginate hydrogel with conjugated PEG chains to mimic these fast-relaxing properties while maintaining similar elastic modulus values. We then seeded CMs on the hydrogels, imaged and analyzed the structure and function via confocal microscopy to assess cell adherence and morphology. These studies have validated our engineered hydrogel system as a hiPSC-CM culture platform and model system to investigate how viscoelasticity influences iPSC-CM function in wild-type and disease cell lines.