Long-term survival and growth of pulsatile myocardial tissue grafts engineered by the layering of cardiomyocyte sheets

Recently researchers have attempted to bioengineer three-dimensional (3-D) myocardial tissues using cultured cells in order to repair damaged hearts. In contrast to the conventional approach of seeding cells onto 3-D biodegradable scaffolds, we have explored a novel technology called cell sheet engineering, which layers cell sheets to construct functional tissue grafts. In this study, in vivo survival, function, and morphology of myocardial tissue grafts were examined. Neonatal rat cardiomyocytes were noninvasively harvested as contiguous cell sheets from temperature-responsive culture dishes simply by reducing the culture temperature. Cardiomyocyte sheets were then layered and transplanted into the subcutaneous tissues of athymic rats. The microvasculature of the grafts was rapidly organized within a few days with macroscopic graft beatings observed 3 days after transplantation and preserved up to one year. Size, conduction velocity, and contractile force of transplanted grafts increased in proportion to the host growth. Histological studies showed characteristic structures of heart tissue, including elongated cardiomyocytes, well-differentiated sarcomeres, and gap junctions within the grafts. In conclusion, long-term survival and growth of pulsatile myocardial tissue grafts fabricated by layering cell sheets were confirmed, demonstrating that myocardial tissue regeneration based on cell sheet engineering may prove useful for permanent myocardial tissue repair.