CPOS Seminar: "Engineering viscoelastic hydrogels for cardiomyocyte culture"
Speaker: Marissa Gionet-Gonzales, American Heart Association Postdoctoral Fellow, Departments of Bioengineering and Mechanical Engineering, UC Santa Barbara
Heart disease is the leading cause of death; however, research progress of cardiomyopathies has been limited by the lack of accurate models of human disease. Viscoelasticity in particular is important to model as it is exhibited by all tissues in the body, can influence several cell functions, and has been understudied with respect to the heart. Ultimately, we aim to measure the viscoelasticity of the heart to provide acurate measurements to incorporate into our engineered biomaterials, to better understand how human induced pluripotent stem cell derived cardiomyocytes (iPSC-CMs) are influenced by viscoelasticity. The viscoelasticity of human tissue was evaluated by stress relaxation testing on a custom-built microindenter. We characterized the stress relaxation by quantifying the τ1/2, or the time a sample takes to reach half of its maximum value. To determine how viscoelasticity was influenced by fibrosis we performed picrosirius red staining to see the collagen fiber size, alignment and compaction. We found that healthy human tissue becomes slower during Ischemic heart failure and this change correlates with fibrosis. We engineered alginate agarose interpenetrating network (IPN) hydrogels with stress relaxation properties similar to that of healthy cardiac tissue through decreasing covalent linkages and increasing agarose percentage to enhance the stress relaxation. Grooves were imprinted onto the surface of the hydrogel using a PDMS mold. Hydrogels were then coated with Matrigel, fibronectin, and Oregon Green for visualization of hydrogel surface. We evaluated how high highly viscoelastic IPNs influenced iPSC-CMs compared to less viscoelastic IPNs through confocal imaging of contracting cells. Overall, our results indicate that the heart is fast relaxing, and this property can be mimicked in an alginate agarose IPN system. These data suggest that cardiomyocytes on viscoelastic substrates exhibit both morphologically and functionally changes. Future work includes looking at other maturity markers, such as calcium handling, cytoskeletal maturity, and differential gene expression.
