Morphological changes in fibrous tissue of rat myocardium after administration of dispersed allogeneic biomaterial.

To improve the structure of the heart muscle after myocardial infarction, methods of regenerative medicine are used. One of the promising areas is the intra-myocardial administration of acellular allogeneic biomaterial (AB). The AB stimulates the regeneration of organs and tissues. But, the effect of AB on the myocardium after its fibrous ischemic degeneration has not been assessed. The aim of the study was to assess the morphological structure of the heart after cryodestruction in the late period and the use of AB. Chronic myocardial infarction was modeled in 80 male rats. To simulate chronic myocardial infarction and fibrosis formation, contact cryodestruction was performed. After 45 days, during repeated thoracotomy in the main group, AB suspension was injected into the area of the cryogenic myocardial scar. Six injections of 0.50 mg of dry substance were administered. In the control group, physiological solution was injected. After AB administration, following 7, 14, 30, and 45 days, the animals were withdrawn from the experiment, and the hearts were excised for histological and immunohistochemical studies. The AB underwent gradual phagocytosis by macrophages and gradually replaced by loose fibrous connective tissue with the presence of cardiac troponin I⁺ labeled muscle cells, which over time underwent hypertrophy. Cardiomyocytes were grouped in the AB implantation zone as separate clusters. The heart mass did not change in both experimental groups. The use of AB in the area of the formed cryogenic myocardial scar promoted the transformation of dense fibrous connective tissue into loose tissue and its replacement with cardiac muscle tissue.