Engineering a Novel Device to Implement Afterload on Human Stem Cell-Derived Cardiac Tissues

Abstract

Cardiac tissue engineering is a promising approach towards regenerating healthy myocardium and restoring the function of infarcted hearts. Using human embryonic stem cell (hESC) derived cardiomyocytes seeded in a collagen or fibrin scaffold, we have previously been able to generate engineered heart tissues (EHTs) that spontaneously contract, but with an amplitude that is far inferior to that of the native myocardium. In order to improve tissue maturation, our goal is to exercise and strengthen EHTs by applying the same mechanical load that the left ventricle faces during contractions—cardiac afterload. My investigation focuses on designing, building, and optimizing a device to apply cardiac afterload on hESC-EHTs. The afterload system involves anchoring tissues between two flexible posts made from polydimethylsiloxane: a rigid post that positions the tissue, and a flexible post containing a neodymium cube magnet that can be manipulated by an external bar magnet. The device is capable of providing a tunable resistance to tissue contractions that models the levels of afterload occurring in the developing heart at particular time points. We tested the load and rate dependency of afterload conditioning on constructs and found that tissues treated with afterload displayed 12.5-fold higher active stresses compared to unloaded controls, and were comparable with tissues undergoing isometric contractions (i.e. infinite afterload). The afterload device has provided us with an insight into the role of mechanical stimuli in promoting the maturation of hESC-EHTs. Our findings suggest that both static loads at 2 and 4 kPa, and steady increases in resistive loads from 0 to 8 kPa do not promote tissue contractility compared with isometric controls. Future work includes testing different static and dynamic loading regimes to identify the optimum level of afterload to promote construct maturation. In summary, we were able to engineer a novel system that applies physiological levels of afterload onto hESC-EHTs. With this new system, we performed the first studies to investigate the role of afterload conditioning in promoting the maturation of hESC-EHTs.