Bioresorbable metal-free molecular magnets enable untethered organ monitoring.

Metal-free molecular magnets differ from conventional magnetic devices that predominantly rely on metallic magnets as these metal-free materials may offer biocompatibility and bioresorbability. However, existing molecular materials lack the ferromagnetic strength required for high-fidelity sensing at clinically relevant tissue depths. Here we introduce a bioresorbable metal-free molecular magnet derived from graphitic carbon nitride, combining metallic-level ferromagnetism with full bioresorbability. De-nitrogenation creates spin centres coupled through a reconstructed π-σ conjugated framework, conferring robust spontaneous magnetization that remains stable under physiological conditions. Integrated with poly(lactic-co-glycolic acid) and silk fibroin, the material forms catheter-deliverable epicardial patches for cardiac tracking and can also be dispersed in injectable hydrogels for organ-scale sensing, including the three-dimensional reconstruction of localized hepatic pathologies. Coupled with a skin-interfaced Hall array, this magnetic sensing architecture provides the continuous, untethered monitoring of multi-organ dynamics, robust against motion artifacts and tissue impedance. In porcine models, it facilitates the continuous assessment of ejection fraction over 4 weeks, followed by benign bioresorption. Benchmarked against standard-of-care echocardiography, this approach delivers clinical-grade trajectories, supporting longitudinal, infrastructure-independent physiological monitoring.