Engineering Shape-Controlled Microtissues on Compliant Hydrogels with Tunable Rigidity and Extracellular Matrix Ligands

Abstract

In vitro models that recapitulate key aspects of native tissue architecture and the physical microenvironment are emerging systems for modeling development and disease. For example, the myocardium consists of layers of aligned and coupled cardiac myocytes that are interspersed with supporting cells and embedded in a compliant extracellular matrix (ECM). These cell–cell and cell–matrix interactions are known to be important regulators of tissue physiology and pathophysiology. In this protocol, we describe a method for mimicking the alignment, cell–cell interactions, and rigidity of the myocardium by engineering an array of square, aligned cardiac microtissues on polyacrylamide hydrogels. This entails three key methods: (1) fabricating elastomer stamps with a microtissue pattern; (2) preparing polyacrylamide hydrogel culture substrates with tunable elastic moduli; and (3) transferring ECM proteins onto the surface of the hydrogels using microcontact printing. These hydrogels can then be seeded with cardiac myocytes or mixtures of cardiac myocytes and fibroblasts to adjust cell–cell interactions. Overall, this approach is advantageous because shape-controlled microtissues encompass both cell–cell and cell–matrix adhesions in a form factor that is relatively reproducible and scalable. Furthermore, polyacrylamide hydrogels are compatible with the traction force microscopy assay for quantifying contractility, a critical function of the myocardium. Although cardiac microtissues are the example presented in this protocol, the techniques are relatively versatile and could have many applications in modeling other tissue systems.