Crossbow Bioreactors for Studying the Effects of Time-Varying Mechanical Preload and Afterload on Engineered Cardiac Tissues.

Mechanical loading plays a critical role in heart development and function, with cardiac preload (tissue stretch during chamber filling) and afterload (resistance against which the heart works to eject blood) potentially playing distinct roles in postnatal cardiomyocyte maturation. To dissect the effects of various types of mechanical loading on postnatal cardiomyocytes, we developed a novel "crossbow" bioreactor system capable of independently and dynamically modulating preload and afterload under auxotonic conditions in 3D engineered cardiac tissues. The system employs tunable, curved polydimethylsiloxane (PDMS) cantilever arms that increase resistance to cardiac contractions as they are deflected and a ratcheted center beam to allow for control of preload via change in cardiac tissue length. Culture of cardiobundles made from neonatal rat cardiomyocytes embedded in a fibrin-based hydrogel on the crossbow system reveals physiological, rather than pathological, responses to loading. Progressively increased afterload over two weeks of culture enhances cardiomyocyte contractile force, while progressively increased preload promotes cardiomyocyte elongation and cycling. The crossbow system holds potential for refining our understanding of mechanosensing in cardiac developmental and pathological remodeling, making it a promising tool for in vitro studies of cardiac biology, disease modeling, and pharmaceutical testing.