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Cell transplantation via direct intramyocardial injection is a promising therapy for patients with myocardial infarction; however, retention of the transplanted cells at the injection sites remains a central issue following injection of dissociated cells. Using a thermoresponsive hydrogel system with a multiwell structure, we successfully developed an efficient technique to generate spherically symmetric bodies of mesenchymal stromal cells (MSCs) inherent with endogenous extracellular matrices (ECMs) for direct intramyocardial injection. After injection through a needle and upon transferring to another growth surface, the time required to attach, migrate, and proliferate was significantly shorter for the MSC bodies than the dissociated MSCs. Employing a syngeneic rat model with experimental myocardial infarction, an intramyocardial injection was conducted with a needle directly into the peri-infarct areas. There were four treatment groups (n 5 10): sham, phosphate-buffered saline, dissociated MSCs, and MSC bodies. The results obtained in the echocardiography and catheterization measurements demonstrated that the MSC body group had a superior heart function to the dissociated MSC group. Histologically, it was found that MSC bodies could provide an adequate physical size to entrap into the interstices of muscular tissues and offer a favorable ECM environment to retain the transplanted cells intramuscularly. Additionally, transplantation of MSC bodies stimulated a significant increase in vascular density, thus improving the cardiac function. These results indicated that the spherically symmetric bodies of MSCs developed in the study may serve as a cell-delivery vehicle and improve the efficacy of therapeutic cell transplantation.

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