Tong et al. (2019) recellularized decellularized rat hearts with a mixture of mesenchymal stem cells (MSCs), primary neonatal cardiomyocytes, and primary endothelial cells (after characterizing MSC-derived cardiomyocyte and endothelial lineages in vitro); the constructs showed only partial electrical activity on electrocardiography (R waves without P waves), no native-heart comparison, no single-cell electrophysiology, and no measurement of mechanical performance or blood flow. The problem, which the source states remains a challenge for the field, is to determine how to generate a bioartificial heart functionally capable of physiological conduction: which cell populations (in particular conduction-system or pacemaker-type cells) and which differentiation and maturation conditions are required to restore organized atrial and atrioventricular-coordinated electrical activity, whether stem-cell-derived cardiac cells can mature to native-like electrophysiology in the scaffold, and whether such a construct can generate normal mechanical performance and blood flow. A 2025 systematic review confirms that no recellularized whole-heart construct has achieved this: all reported bioartificial hearts display only marginal electrical activity and negligible or unmeasured hemodynamic performance.

Background

Patients with end-stage heart failure ultimately require a donor heart, and donor supply falls far short of demand, which motivates engineering a transplantable bioartificial heart. The dominant strategy is decellularization–recellularization: a donor heart is perfused with detergent (typically sodium dodecyl sulfate, SDS) to wash out all cells while leaving the extracellular matrix — the fibrous network of collagen and other proteins that preserves chamber geometry, valves, and a perfusable vascular tree — and the resulting scaffold is then seeded with cardiac cells and matured in a perfusion bioreactor. The native heart's electrical function is organized by a specialized conduction system: the sinoatrial node (a cluster of pacemaker cells in the right atrium) initiates each heartbeat, the excitation spreads over the atria, slows through the atrioventricular node, and then rapidly activates the ventricles through the His–Purkinje fiber network. On an electrocardiogram (ECG), atrial depolarization appears as the P wave and ventricular depolarization as the QRS complex; a normal ECG with P waves, QRS complexes, and physiological intervals and rates therefore certifies coordinated conduction from atria to ventricles. MSCs are bone-marrow-derived stromal stem cells that can be differentiated toward cardiomyocyte and endothelial lineages; cardiomyocytes can also be derived from induced pluripotent stem cells (iPSC-CMs, heart muscle cells generated by reprogramming adult cells to pluripotency and re-differentiating them). The lineage of results defines the gap. Ott et al. (2008) established the platform: perfusion-decellularized rat hearts reseeded with cardiac and endothelial cells contracted by day 4 and, under electrical stimulation and physiological load, generated pump function equivalent to about 2% of an adult heart — far from physiological, and without demonstrated organized whole-organ conduction. Yasui et al. (2014) optically mapped recellularized rat hearts (optical mapping records a fluorescent voltage or calcium signal across the tissue with a high-speed camera, tracing the electrical activation wave) and found well-organized excitation propagation in places but marked arrhythmogenic propensity, random cell alignment, and strongly reduced connexin 43 (the gap-junction protein that couples cardiomyocytes electrically). Lu et al. (2013) repopulated decellularized mouse hearts with human iPSC-derived cardiovascular progenitor cells; the constructs contracted spontaneously, generated force, and responded to drugs, but no physiological ECG or pump function was reported. Tao et al. (2015), the report Tong et al. cite for the missing-conducting-cells interpretation, seeded neonatal rat cardiac cells into decellularized hearts and concluded that bioartificial hearts replicate only a partial subset of natural heart properties. Guyette et al. (2016) scaled the approach to human scaffolds partially recellularized with human iPSC-CMs and obtained force-generating tissue with electrical conductivity and left-ventricular pressure development — real but partial function. Weymann et al. (2014) decellularized human-sized porcine hearts, an early step toward clinical scale. Taylor et al. (2018) proposed bypassing in vitro limits by heterotopically transplanting decellularized hearts (transplanting them at a non-anatomical site in a living recipient) to harness the recipient's own repopulation capacity plus load and electrical input; this in vivo route also remains preclinical. Within this lineage, Tong et al. (2019) asked whether MSC-based mixed-cell seeding — attractive because MSCs are easily obtained and less immunogenic than pluripotent-cell derivatives — could move the field forward, and found the electrophysiological ceiling sharply: after 10 days of perfusion culture the constructs displayed only R waves with no P waves, indicating ventricular electrical activity but absent atrial conduction, which the authors attributed to missing conducting cells. Their study further lacked native-heart ECG controls, single-cell (patch-clamp, microelectrode recording of the ion currents of an individual cell) characterization of the MSC-derived cardiomyocytes, and any mechanical or flow measurement, so the degree of functional restoration could not be quantified.

Problem Statement

Determine how to generate a bioartificial heart — a whole decellularized cardiac scaffold recellularized with appropriate cardiac cell populations and matured in vitro (or via supported in vivo maturation) — that is functionally capable of physiological conduction and performance, as asked by Tong et al. (2019). Specifically: (1) identify which cell populations (e.g., conduction-system, pacemaker, atrial, ventricular, and endothelial cells, and their ratios) must be seeded, and under which differentiation and maturation conditions, to restore organized atrial conduction that is absent in current constructs (which show ventricular R waves but no P waves on ECG); (2) establish whether stem-cell-derived cardiomyocytes and endothelial cells in the scaffold can mature to native-like electrophysiology at the single-cell level (assayed by patch-clamp or an equivalent single-cell technique); and (3) determine whether the resulting engineered whole-heart tissue can generate normal mechanical performance and blood flow. The completion boundary, following the source's own criteria, is a recellularized whole-heart construct whose ECG shows atrial depolarization (P waves) and atrioventricular-coordinated ventricular excitation with waveforms, intervals, and rates quantitatively comparable to native rat hearts measured side by side, together with single-cell electrophysiological characterization of the seeded cells and measured contractile/pump performance and blood flow, with the responsible cell populations and culture conditions identified. Because that endpoint is defined by wet-lab measurements, the deliverable is the construction specification itself — the cell populations and ratios, the differentiation and maturation protocol, and, for each property named above, the measurement to be used and the success criterion to be met against native rat controls; an evidence-grounded protocol that meets these requirements discharges the task.

References

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