Cardiac Microtissue Platform with Dynamically Tunable Afterload Control to Show Contractile Reserve and Pathologic Hypertrophy

Abstract

Introduction Increased afterload induces structural and functional changes in the myocardium that ultimately lead to heart failure. Our lab uses engineered cardiac microtissues, composed of a well with two cantilevers that serve as tethering points for the tissue to model myocardium. We have created a platform with dynamically tunable in vitro afterload (cantilever stiffness) to study hypertrophy. We hypothesized that an instantaneous increase in stiffness will reveal contractile reserve, resulting in increased force, work, contraction velocity, and relaxation velocity. We also hypothesized that prolonged increases in stiffness will induce pathologic hypertrophy, showing decreases in these parameters. Methods and Results We used iron-doped polydimethylsiloxane to create cantilevers that stiffen in a magnetic field. After seeding a mixture of fibroblasts, cardiomyocytes, and collagen matrix, cardiac microtissues were matured over 48 hours, after which baseline testing was performed. Cardiac microtissues were then exposed to low or high stiffness conditions ( 0.6 N/m) for 48 hours and tested at 24 and 48 hours with and without a magnetic field. At baseline, an instantaneous 12.0% increase in stiffness (95% CI 9.4 - 14.6) caused a 13.0% increase in force development (95% CI 6.8 - 19.1) and a 14.8% increase in work (95% CI 1.7 - 28.0). At 24 hours, tissues exposed to high stiffness had significantly decreased work (92.2 vs. 50.6 μN*μm, p = 0.02), contraction velocity (-86.9 vs. -50.9 μm/s, p = 0.0002), and relaxation velocity (49.6 vs. 31.0 μm/s, p = 0.0003), with no significant change in force (31.1 vs. 26.7 μN, p = 0.26). Tissues exposed to high stiffness at 48 hours had significantly decreased work (81.2 vs. 44.4 μN*μm, p = 0.03), contraction velocity (-86.6 vs. -52.9 μm/s, p Conclusions Our data indicates that instantaneous exposure to increased afterload reveals contractile reserve, while sustained increased afterload induces pathologic changes in cardiac microtissues. The addition of dynamically tunable afterload to a cardiac microtissue model provides a variety of new opportunities to study load-dependent myocardial adaptations for translational research applications.