Scalable fabrication of aligned myocardial tissues with native-like helical architecture for heart repair

The native helical alignment of myocardial fibers is essential for efficient cardiac pumping, yet replicating this architecture at scale remains a major challenge in biofabrication. Here, we present flow-led assembly for spiral hierarchical structures (FLASH), a microfluidic platform that assembles high-cell-density microfibers with a cardiomyocyte-laden collagen/Matrigel core and an endothelial cell-laden alginate sheath. FLASH integrates microfluidic spinning with dual-axis fiber collection on a rotating mandrel, enabling programmable helical alignment with high spatial fidelity. Axial confinement induces cardiomyocyte alignment and functional fiber contraction, while the enzymatic removal of the alginate sheath softens the niche and facilitates endothelial network formation. FLASH achieves > 90% cardiomyocyte alignment, tunable mechanical anisotropy, and a threefold improvement in spatial resolution/time-for-manufacturing (RTM) over conventional bioprinting techniques. Resulting helical ventricular models display coordinated chamber-scale contractions. In a rat myocardial infarction model, FLASH-derived uniaxially aligned cardiac patches improve cardiac function and reduce fibrosis.