Fabrication and characterization of a thick, viable bi-layered stem cell-derived surrogate for future myocardial tissue regeneration.

Cardiac tissue surrogates show promise for restoring mechanical and electrical function in infarcted left ventricular (LV) myocardium. For these cardiac surrogates to be useful in vivo, they are required to support synchronous and forceful contraction over the infarcted region. These design requirements necessitate a thickness sufficient to produce a useful contractile force, an area large enough to cover an infarcted region, and prevascularization to overcome diffusion limitations. Attempts to meet these requirements have been hampered by diffusion limits of oxygen and nutrients (100-200 μm) leading to necrotic regions.This study demonstrates a novel layer-by-layer (LbL) fabrication method used to produce tissue surrogates that meet these requirements and mimic normal myocardium in form and function. Thick (1.5-2 mm) LbL cardiac tissues created from human induced pluripotent stem cell-derived cardiomyocytes and endothelial cells were assessed, in vitro, over a four week period for viability (< 5.6 ± 1.4 % nectrotic cells), cell morphology, viscoelastic properties and functionality. Viscoelastic properties of the cardiac surrogates were determined via stress relaxation response modeling and compared to native murine LV tissue. Viscoelastic characterization showed that the generalized Maxwell model of order 4 described the samples well (0.7 < R2 < 0.98). Functional performance assessment showed enhanced t-tubule network development, gap junction communication as well as conduction velocity (16.9 ± 2.3 cm s-1). These results demonstrate that LbL fabrication can be utilized successfully in creating complex, functional cardiac surrogates for therapeutic applications.