Magnetic torque-mediated early asymmetric mechanical stimulation directs structural and functional maturation in human cardiac organoids

The human heart establishes functional left-right asymmetry through region-specific mechanical cues; however, current methodologies provide limited capacity for spatially localized force stimulation within 3D tissues. To address this limitation, we developed a magnetic torque stimulation (MTS) platform that enables remote, non-contact mechanical loading of human induced pluripotent stem cell (hiPSC)-derived cardiac organoids functionalized with magnetic microbeads covalently conjugated to the membrane-binding lectin, allowing stable anchorage to cell-surface glycoconjugates. We then applied this system to asymmetric fusion organoids composed of bead-conjugated (Bead⁺) and bead-free (Bead⁻) regions to recapitulate spatially localized mechanical cues that mimic endogenous region-specific signaling. A 96-h rotating magnetic field (organoid day 3-7) generated controlled torque forces in individual organoids, resulting in robust activation of mechanotransduction pathways, including transcriptional upregulation of ITGB1, FN1, ZYX, VCL, ACTN2, and TEAD1, along with increased fibronectin and vinculin protein accumulation. In fusion organoids, the same mechanical stimulation elicited domain-specific activation, with mechanotransduction markers selectively elevated in the Bead⁺ region immediately after stimulation (Day 7), confirming spatially restricted force transmission within a 3D tissue environment. Following an additional culture period without further stimulation (until Day 15), MTS-treated fusion organoids exhibited enhanced maturation, characterized by increased expression of cardiomyocyte structural and ion-channel genes, enhanced fibronectin deposition, reinforced focal adhesion assembly, upregulated Piezo1 expression, and improved sarcomere organization. Collectively, these results demonstrate that an early asymmetric mechanostimulation can contribute to the emergence of maturation-related phenotypes in cardiac organoids. This work suggests that magnetic torque-based actuation can serve as a useful platform for studying biomechanical contributions in cardiac organoid models.