A study on extracellular and cellular composition to advance towards the rational design of contractile human myocardium.

The recapitulation of the physiological cellular composition, 3D structure and mechanics of the human myocardium is key to improving the biofabrication of cardiac tissues. To advance the development of engineered heart patches, with significant potential for human cardiac repair, we assessed the impact of their cellular and extracellular constituents on tissue organization and function, by using advanced biofabrication and next-generation sequencing technologies. Combining melt electrowriting (MEW) fibrillary scaffolds with human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes (hiPSC-CMs) and cardiac fibroblasts (-CFs), we generated human engineered cardiac tissues (MEW-hECTs) by casting in two different biomaterial compositions (fibrin and gelatin-methacryloyl (GelMA)), and varying proportions of the cardiac constituent cells. Under the conditions tested, fibrin-hECTs displayed improved tissue formation, coordinated contraction, structural organization, and electrophysiological behavior compared with GelMA-hECTs. Transcriptomics analysis indicated that fibrin-hECTs exhibited an increase in maturation-associated gene expression signatures compared with GelMA-hECTs, whereas a longer remodeling process of the synthetic environment was required in GelMA. Surprisingly, within the investigated MEW-based composite system, the inclusion of CFs had no positive impact on tissue organization and impaired the electrophysiological properties of myocardial constructs, increasing susceptibility to arrhythmias in computational simulations calibrated with experimental electrophysiological data. This information will help devise advanced myocardial tissues by enabling a comprehensive assessment of the main components, ultimately reflecting the unique native cardiac 3D organization.