The main goal of this study is to investigate a combination of viscosity-sensitive and viscosity-insensitive fluorescent dyes to distinguish different rheological states of hydrogel based biostructural materials and carriers in biological tissues and to assess their corresponding location areas. The research is done in the example of alginate hydrogel stained with viscosity-sensitive dyes Seta-470 and Seta-560 as well as the viscosity-insensitive dye Seta-650. These dyes absorb/emit at 469/518, 565/591 and 651/670 nm, respectively. The rheological state of the alginate, the area of the fluorescence signal and the mass of the dense alginate versus the calcium gluconate concentration utilized for alginate gelation were studied in vitro. The most pronounced change in the fluorescence signal area was found at the same concentrations of calcium gluconate (below ~1%) as the change in the alginate plaque mass. The stained alginate was also implanted in situ in rat hip and myocardium and monitored using fluorescence imaging. In summary, our data indicate that the viscosity sensitive dye in combination with the viscosity-insensitive dye allow tracking the biodegradation of the alginate hydrogel and determining the rheological state of hydrogel in biological tissue, which both should have relevance for research and clinical applications. Using this method we estimated the half-life of the dense alginate hydrogel in a rat hip to be in the order of 4 d and about 6-8 d in rat myocardium. The half-life of the dense hydrogel in the myocardium was found to be long enough to prevent aneurysm rupture of the left ventricle wall, one of the more severe complications of the early post-infarction period.

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One of the new directions on which the searches used to find the methods to effectively correct the regeneration in case of different pathologies is the application of biologically active peptides and their mixtures. In the work there was investigated the biological influence of extracts of cryopreserved fragments of skin and heart of newborn piglets with the cold wound of skin and myocardial ischemia in rats respectively. For investigations the extracts were obtained from cryopreserved fragments of newborn piglets’ skin and heart. Cold wound of skin was modelled in rats by 10 mm copper applicator cooled in liquid nitrogen down to -196°C; the areas of wounds were determined by planimetric method, the white blood cells’ counts were analysed. In rats with myocardial ischemia there were studied the electrocardiograms, heart rate variability and proliferative activity of heart cells. The injection of extracts of cryopreserved fragments of skin to the animal’s abdominal cavity accelerates the healing of cold wound of skin and normalizes the response of immune system to an injury. After the injection during 2 months to the animals with myocardial ischemia with extracts of cryopreserved fragments of heart the normalization of electrophysiological indices of heart activity was observed that testified about the improved blood supply to a heart muscle. Being injected to healthy animals and those with myocardial ischemia the extracts of cryopreserved fragments of heart resulted in an increase in proliferative activity of heart cells. The studied extracts have a high biological effect and can be applied when designing the drugs for regenerative medicine.Summary statementThe extracts of cryopreserved fragments of piglets’ heart or skin were shown as stimulating reparative regeneration of heart tissues in myocardial ischemia of rats and skin in a cold wound, respectively.