Fabrication and characterization of optogenetic, multi-strip cardiac muscles.

Cardiac tissue engineering aims to recreate functional tissue constructs similar to the structure and function of the native myocardium. To date, in vitro tissue constructs lack the architectural complexity of a vascular network and the precise motor unit control of muscle fibers. Here, we present a method to construct engineered multi-strip cardiac muscle that simulates the bundle-like architecture of the native myocardium. Densely packed primary myocytes and cardiac fibroblasts were co-cultured with optogenetic, non-excitable cells. The resulting 3D syncytium triggered contraction upon localized blue light illumination to selectively activate and pace the multi-strip cardiac muscles, similar to the activity of pacemaker cells. Acting on a single load, we demonstrated graded force production through light-modulated multi-strip recruitment. These results demonstrate an in vitro platform of optogenetic, multi-strip cardiac muscles that can be used in a wide variety of applications, such as drug discovery, tissue engineering, and bio-hybrid robotic systems.