Transplantation of active mitochondria condensed in liquid-liquid phase-separated hydrogels ameliorates myocardial ischemia-reperfusion injury.

Mitochondrial dysfunction is a major contributor to myocardial ischemia-reperfusion injury, and limits cardiac recovery after blood flow is restored. Although mitochondria transplantation may help restore cellular energy metabolism, its therapeutic benefit is reduced by extracellular calcium-induced mitochondrial damage. Here we show that a thermosensitive phase-separated hydrogel made of gelatin and PEG can condense, protect and deliver freshly isolated mitochondria. Compared with conventional single-phase hydrogels, this system remains injectable at physiological temperature and enables rapid mitochondria release after transplantation. Furthermore, the phase-separated structure improves mitochondrial packing and preserves activity through spatial confinement and calcium chelation by gelatin. In vitro, condensed mitochondria show improved membrane potential and ATP production. In vivo, transplanted mitochondria are efficiently internalized by cardiomyocytes, improving cardiac function and reducing tissue injury after myocardial ischemia-reperfusion. These findings identify phase-separated hydrogels as a promising platform for mitochondria transplantation.