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Human pluripotent stem cells can recapitulate significant features of mammalian organ developmentin vitro, including key aspects of heart development. We hypothesized that the organoids thus created can be made substantially more relevant by mimicking aspects ofin uterogestation, leading to higher physiological and anatomical resemblance to theirin vivocounterparts. Here, we report steps towards generating developmentally inspired maturation methodologies to differentiate early human heart organoids into patterned heart-tube-like structures in a reproducible and high-throughput fashion by complete self-organization. The maturation strategy consists of the controlled and stepwise exposure to metabolic (glucose, fatty acids) and hormonal signals (T3, IGF-1) as present during early heart development. These conditions elicit important transcriptomic, cellular, morphological, metabolomic, and functional changes over a 10-day period consistent with continuously increasing heart complexity, maturation, and patterning. Our data reveals the emergence of atrial and ventricular cardiomyocyte populations, valvular cells, epicardial cells, proepicardial-derived cells, endothelial cells, stromal cells, conductance cells, and cardiac progenitors, all of them cell types present in the primitive heart tube. Anatomically, the organoids elongate and develop well-differentiated atrial and ventricular chambers with compacted myocardial muscle walls and a proepicardial organ. For the first time in a completely self-organizing heart organoid, we show anterior-posterior patterning due to an endogenous retinoic acid gradient originating at the atrial pole, where proepicardial and atrial populations reside, mimicking the developmental process present within the primitive heart tube. Collectively, these findings highlight the ability of self-organization and developmental maturation strategies to recapitulate human heart development. Our patterned human heart tube model constitutes a powerfulin vitrotool for dissecting the role of different cell types and genes in human heart development, as well as disease modeling congenital heart defects, and represents a step forward in creating fully synthetic human hearts.

Materials which selectively transport molecules offer powerful opportunities for concentrating and separating chemical agents. Here, utilizing static and dynamic chemical gradients, transport of molecules within swollen crosslinked polymers is demonstrated. Using an ≈200 μm static hydroxyl to hexyl gradient, the neutral ambipolar nerve agent surrogate diethyl (cyanomethyl)phosphonate (DECP) is directionally transported and concentrated 60-fold within 4 hours. To accelerate transport kinetics, a dynamic gradient (a "travelling wave") is utilized. Here, the non-polar dye pyrene was transported. The dynamic gradient is generated by an ion exchange process triggered by the localized introduction of an aqueous NaCl solution, which converts the gel from hydrophobic to hydrophilic. As the hydrophilic region expands, associated water enters the gel, and pyrene is pushed ahead of the expansion front. The dynamic gradient provides about 10-fold faster transport kinetics than the static gradient.

Congenital heart defects (CHD) constitute the most common birth defect in humans, affecting approximately 1% of all live births. Our ability to understand how these disorders originate is hindered by our limited ability to model the complexity of the human heart in vitro. There is a pressing need to develop more faithful organ-like platforms recapitulating complex in vivo phenotypes to study human development and disease in vitro. Here we report a novel method to generate human heart organoids by self-assembly using pluripotent stem cells. Our method is fully defined, highly efficient, scalable, shows high reproducibility and is compatible with screening and high-throughput approaches. Human heart organoids (hHOs) are generated using a two-step canonical Wnt signaling modulation strategy using a combination of chemical inhibitors and growth factors in completely defined culture conditions. hHOs faithfully recapitulate human cardiac development and are similar to age-matched fetal cardiac tissues at the transcriptomic, structural and cellular level. hHOs develop sophisticated internal chambers with well-organized multi-lineage cell-type regional identities reminiscent of the heart fields and the atrial and ventricular chambers, as well as the epicardium, endocardium, and coronary vasculature, and exhibit functional activity. We also show that hHOs can recreate complex metabolic disorders associated with CHD by establishing the first in vitro human model of diabetes during pregnancy (DDP) to study embryonic CHD. morphological and metabolically effects of increased glucose and insulin, showing the capability of modeling the effects of diabetes during pregnancy (DDP). Our heart organoid model constitutes a powerful novel tool for translational studies in human cardiac development and disease.