Driving pluripotent stem cell expansion to advance 3D cardiac tissue engineering

Abstract

Recent advancements in stem cell biology and biofabrication have greatly expanded the potential for creating complex, representative tissues for the study of nearly any system of the body and associated diseases. To better understand and treat cardiac diseases, which lead to over 600,000 deaths annually in the United States alone, our lab has developed a stem cell-derived, 3D-bioprinted chambered cardiac model, termed the human chambered muscle pump (hChaMP). In this model, human induced pluripotent stem cells (hiPSCs) are bioprinted in a cardiac bioink, expanded for two weeks, and then differentiated to the functional cells of the heart, cardiomyocytes. The resulting tissue is capable of generating macroscale contraction, allowing for measurement of clinically-relevant functional metrics. While the hChaMP is thus an exciting tool for improving cardiac modeling, limitations remain, including suboptimal thickness of viable tissue and insufficient reproducibility of hiPSC expansion and cardiac function. In this work, we develop a perfusion bioreactor that enables increased stem cell expansion in the hChaMP, with high distribution of cells across the tissue wall. We discuss initial attempts to differentiate the hiPSCs in the bioreactor and methods to improve the culture of cardiomyocytes under perfusion, with the goal of increasing viable tissue thickness and providing biomimetic load for improved cardiomyocyte maturation. We also uncover how stem cell expansion differs in the same scaffold from different vendors, as well as methods to enhance growth for improved consistency among bioprinted constructs. With improved and consistent hiPSC expansion, we aim to obtain a thick layer of cardiomyocytes, leading to reliable, physiologic function in the hChaMP. Future applications for hChaMP culture in the bioreactor, in addition to the potential for deriving pacemaker cardiomyocytes, are also outlined. The work described here will enable improved study of cardiac diseases, particularly cardiomyopathies, with the goal of informing therapies and reducing the global disease burden.