SmartHeart: An innovative high throughput assay to generate and assess cardiac micro tissues from hiPSCs answering to the current challenges of drug discovery

Cardiac adverse events are among the top reasons for discontinuing drugs in early clinical phase studies, where drugs with cardiotoxic liabilities are responsible for one third of regulatory failures. These alarming statistics highlight the widespread occurrence and significant financial burden of ineffective drugs that proceed from preclinical animal studies. Despite advancements in cardiac bioengineering, challenges remain regarding physiological relevance, cost, and throughput. To address these challenges, an innovative 3D cardiac model, the SmartHeart (SH), was developed. This model facilitates the self-assembly and maturation of ring-shaped cardiac tissues and allows for precise in-situ measurements of various parameters (e.g. contraction stress, strain, beating metrics, membrane action potential and calcium signaling). The technology is based on standard 96-well plates coated with a structured hydrogel, which features an array of conical-shaped microwells, each surrounding a central pillar. Within less than 48 h after cell seeding, the tissues (composed of iPSC-derived ventricular cardiomyocytes (Axol) and fibroblasts) demonstrated rhythmic contractions. The contractility stress and strain as well as the beating rate of the tissues were quantified by monitoring the variation of the central pillar's area with known stiffness (12 kPa) with time. After 14 days, the tissues presented morphological signs of maturation and were exposed to several classical drugs. The presence of isoproterenol caused a positive inotropic and chronotropic response. A negative inotropic response was induced by nifedipine and the tissues became quiescent when exposed to high doses of mexiletine, which is consistent with its known pharmacological effects as a sodium channel blocker. The hydrogel's optical transparency allows compatibility with high-resolution image-based techniques. This includes the use of voltage-sensitive fluorescent dyes, such as FluoVolt that showed an intensity spike just before the tissue contraction. Likewise, cellular spatial organization and intracellular morphology, e.g. cardiomyocyte cytoskeletal fiber elongation and striation, showing signs of maturation, could be visualized using immunofluorescence. In conclusion, the SmartHeart 3D-cardiac model provides an advanced solution to the ongoing challenges in drug discovery by enabling precise, real-time monitoring of cardiac tissue function and maturation. This innovative platform offers robust and relevant readouts for high-throughput and high-content screening, significantly enhancing the assessment of drug efficacy and safety.