Engineering Cellular Alignment in Contractile Cardiac Tissues Using Coherent Light Biofabrication

Biofabricating three-dimensional cardiac tissues that mimic the native myocardial tissue is a pivotal challenge in tissue engineering. In this study, we fabricate three-dimensional cardiac tissues with controlled cellular alignment and directed contractility. We use coherent light biofabrication with optically tuned bioinks of high cell density (15-60 million cells/mL) to fabricate hydrogel microstructures for cardiac cell alignment. Cardiac tissues with microstructures expressed higher levels of protein alpha 1 (GJA1) (1.6x) and exhibited higher uniaxial contractility (3.8x) relative to unstructured tissues. Tissues that were bioprinted at high cell density (30-60 million cells/mL) contracted synchronously (27 µm uniaxially). However, cell-induced light scattering hinders microstructure formation and cellular alignment at increased light propagation depth (> 400 um). Furthermore, cell-induced light attenuation caused anisotropic tissue remodeling and contractility. We mitigated these limitations by projecting light bidirectionally. This approach minimized the light propagation depth and allowed us to rapidly bioprint larger tissues with microstructures (ø 0.6 mm x 2 mm). Our approach provides a new strategy for engineering cellular alignment in cardiac tissues used for drug screening, regenerative medicine, and biohybrid robots.