We present a novel design of elastic micropillars for tissue self-assembly in engineered heart tissue (EHT) platforms. The innovative tapered profile confines reproducibly the tissue position along the main micropillar axis, increasing the accuracy of tissue contraction force measurement. Polydimethylsiloxane-based pillars were designed and fabricated by wafer-level molding in an hourglass shape, with symmetric tapering producing a restriction for tissue movement in the middle of the pillars’ length. Confinement efficacy of the new geometry was validated by comparing the tissue performance in straight versus tapered (75° or 80° tapering angle) micropillars. While in all three cases compact tissues formed successfully, for both tapered designs the functionality assays evidenced yield increase from 15% to 100%, higher spatial tissue confinement, and correspondingly higher accuracy and smaller dispersion in measurements of tissue contraction force.@en

Human heart tissues grown as three-dimensional spheroids and consisting of different cardiac cell types derived from pluripotent stem cells (hiPSCs) recapitulate aspects of human physiology better than standard two-dimensional models in vitro. They typically consist of less than 5000 cells and are used to measure contraction kinetics although not contraction force. By contrast, engineered heart tissues (EHTs) formed around two flexible pillars, can measure contraction force but conventional EHTs often require between 0.5 and 2 million cells. This makes large-scale screening of many EHTs costly. Our goals here were (i) to create a physiologically relevant model that required fewer cells than standard EHTs making them less expensive, and (ii) to ensure that this miniaturized model retained correct functionality. We demonstrated that fully functional EHTs could be generated from physiologically relevant combinations of hiPSC-derived cardiomyocytes (70%), cardiac fibroblasts (15%) and cardiac endothelial cells (15%), using as few as 1.6 × 104 cells. Our results showed that these EHTs were viable and functional up to 14 days after formation. The EHTs could be electrically paced in the frequency range between 0.6 and 3 Hz, with the optimum between 0.6 and 2 Hz. This was consistent across three downscaled EHT sizes tested. These findings suggest that miniaturized EHTs could represent a cost-effective microphysiological system for disease modelling and examining drug responses particularly in secondary screens for drug discovery.@en