The development of regenerative medicine is to improve existing and to search for new tools for morphological and functional tissue repair, among which plasma or fi brin enriched with platelets (PRP and PRF) can be signifi cant. Autogenic platelet masses stimulate collagen synthesis, induce vascular growth, reduce pain, provide hemostasis, accelerate regeneration, reduce the risk of postoperative infectious and infl ammatory complications, and also have powerful osteoinductive properties. Due to the ability to produce the majority of growth factors, platelets can aff ect all stages of the infl ammatory-regenerative process, and therefore their biological products are of great importance in solving the problems of regenerative medicine. The technologies for obtaining PRP and PRF are based on centrifugation of blood, as a result of which its active components are concentrated in certain areas of the centrifuge. Blood sampling with or without an anticoagulant, as well as modifi cation of centrifugation protocols, allows to obtain various forms of platelet masses, such as a liquid, gel or clots. They are classifi ed, depending on the cellular content and architecture of fi brin, into several categories, namely: pure plasma enriched in platelets (P-PRP), plasma enriched in leukocytes and platelets (L-PRP); injectable fi brin enriched with platelets (i-PRF) and pure fi brin enriched with platelets (P-PRF), as well as fi brin enriched with white blood cells and platelets (L-PRF). The main diff erence in the manufacture of PRP compared to PRF is the use of anticoagulants and activators, as well as the possibility of using two-stage centrifugation. Platelet mass is used as an independent component mainly to stimulate the restoration of muscle tissue, to heal chronic wounds, to treat articular pathologies, and in combination with other materials, in particular to replace bone defects. The mechanisms of infl uence of each of the categories of platelet mass on tissue regeneration remains poorly understood. It is necessary to standardize the protocols for their preparation, taking into account the infl uence of additional substances, such as platelet activators or blood clotting and anticoagulants, as well as optimization of the methods for using each of the platelet mass forms. Key words: platelets, PRP, PRF, centrifuges, centrifugal force.

The results of the dynamics of the morphological parameters of the blood of a rabbit with model defects of the opening of the spongy and compact bone tissue at diff erent periods of reparative osteogenesis are presented. Formed 4 groups of rabbits. Bone lesions in the fi rst experimental group were fi lled with injectable platelet-rich fi brin, in the second - platelet-rich fi brin, in the third - a combination of platelet-rich fi brin, and hydroxyapatite with β-tricalcium phosphate.In the control group, the defects remained healed under a blood clot. All animals were in the same conditions of feeding and keeping, had unlimited access to water. During the study, rabbits were clinically observed. Blood was taken for morphological examination before surgery and on the 3rd, 7th, 14th, 21st, 42nd day. Animals were taken from the experiment on the 14th, 21st and 42nd days, an X-ray examination was carried out, bone tissue samples were taken. It was established that trauma of bone tissue leads to a number of reactions of the body aimed at restoring the damaged area. Against the background of the general picture of the obtained morphological results, the level of platelets signifi cantly changes compared to the physiological norm, while the number of red blood cells and white blood cells does not go beyond it. There is a slight increase in hemoglobin levels, especially in the experimental groups on the twenty-fi rst and forty-second day. Signifi cant changes in the number of red blood cells, white blood cells, platelets and hemoglobin concentration in the experimental groups were noted compared with the control group at diff erent periods of reparative osteogenesis.The use of various types of platelet concentrates aff ects the overall reaction of the body. On radiographs of the radial bones (compact bone tissue) on the twenty-fi rst day in the second and third experimental groups, where fi brin enriched with platelets and its combination with hydroxyapatite materials with β-tricalcium phosphate were used to replace bone defects, the infl ammatory reaction was manifested to a lesser extent. There was no signifi cant formation of bone callus compared with the fi rst, in which model defects were fi lled with injectable platelet-rich fi brin and the control group. Each of the types of platelet concentrates and their combination with hydroxyapatite ceramics have a diff erent eff ect on the restoration of bone defects and is accompanied by the appearance of a number of reactions, both local and general. According to the degree of intensity of this process, they can be placed in the following sequence: i-PRF ˂ PRF ˂ PRF+GT. Macromorphologically and radiologically signifi cant diff erences were not detected for diff erent types of bone tissue due to the use of each of the substances that concentrates platelets. The combination of hydroxyapatite granules with β-tricalcium phosphate and platelet-rich fi brin proved to be the best option for repairing the damaged area. Its use provides a signifi cantly smaller manifestation of the local infl ammatory reaction and causes the formation of optimal bone marrow. Key words: PRF, i-PRF, granules, centrifuges, growth factors, bone marrow.

Osteo-replacement materials are considered to be the most promising direction in solving the problem of restoring the regenerative potential of bone tissue, especially fragmentary fractures. However, the mechanism of their influence on the histomorphology of bone regenerates and the pathochemical phase of reparative osteogenesis require further and comprehensive justification. The aim of the study was to establish the dynamics of hematological parameters and acute phase response to osteosubstitution by hydroxyapatite ceramics with β-tricalcium phosphate and platelet-enriched autofibrin in fragmentary bone fractures in dogs. Control and research groups of animals were formed, each of which included dogs with fractures of both shoulder and forearm bones, which came in 2019- 2021 to the clinic of small pets of the Faculty of Veterinary Medicine of Bila Tserkva NAU. After general and local anesthesia, extracortical osteosynthesis and replacement of bone defects were performed: in the first experimental group (n = 10) autofibrin enriched with platelets (PRF), and in the second (n = 10) - its combination with hydroxyapatite ceramics (PRF + HA/β -TCP-700); in the control group (n = 10) the defects were left to heal under the blood clot. Blood samples for hematological and biochemical studies were taken after injury no later than 24 hours and on the 3rd, 7th, 14th, 21st and 42nd day after osteosynthesis. In peripheral blood, the number of erythrocytes, platelets and leukocytes was determined by conventional methods, and hemoglobin - hemoglobin cyanide. The content of nitric oxide (NO) in the blood serum was determined by the method of Green in the modification of Golikov, haptoglobin - by reaction with rivanol kits PJSC "Reagent" (Ukraine) and α2-macroglobulin - by KM Veremeenko. Statistical processing of the results was performed using the program Statistica 10 (StatSoft Inc, USA, 2011). It was found that bone trauma in dogs is accompanied by a decrease in peripheral blood of erythrocytes by 1.3 times (p <0.001) and an increase of 1.1 times (p <0.05) the number of leukocytes with a tendency to increase hemoglobin and platelets, compared with indicators of clinically healthy animals. After osteosynthesis in all groups leukocytosis developed. During osteosubstitution, the intensity and duration of the leukocyte reaction decreased significantly. In the first experimental group, the peak of NO concentration occurred on the 21st day, and in the case of combined osteosubstitution, the phase of its changes was noted, which had two peaks: on the 7th in 1.5 and on the 21st in 1.8 (p <0.001) is several times higher than in the control group. The concentration of haptoglobin after bone injury in dogs increased 1.1 times (p <0.001) compared with clinically healthy animals and reached its peak in all groups on the 3rd day (p <0.001). No changes in α2-macroglobulin concentration were observed in the groups during the entire study period. Combined osteosubstitution by calcium-phosphate ceramics with platelet-enriched fibrin induces early osteogenic processes at a lower intensity of the acute phase reaction at the phase peaks of nitric oxide - an inducer of angiogenesis, which indicates the viability of animals. Key words: nitric oxide, acute phase proteins, reparative potential, platelets.

The results of a histomorphological study of bone regenerates in rabbits after osteosubstitution with platelet-rich fibrin and its combination with hydroxyapatite granules with β-tricalcium phosphate in spongy and compact bone tissue at different periods of reparative osteogenesis are presented. Three groups of rabbits were formed. In the control group, the defects were left to heal under the blood clot. Bone lesions in the first experimental group were filled with platelet-rich fibrin, in the second – with a combination of platelet-rich fibrin and hydroxyapatite with β-tricalcium phosphate. All animals were kept in the same conditions of feeding and housing, had unlimited access to water. During the study, the rabbits were monitored clinically. The animals were taken out of the experiment on the 14th, 21st and 42nd days, samples of bone tissue were taken, they were fixed, decalcified, dehydrated in alcohols of increasing concentration and embedded in paraffin. In the presented study, it is most likely that the newly formed bone tissue is formed precisely due to osteoinduction in the experimental groups. When using granules of hydroxyapatite and β-tricalcium phosphate with platelet-rich fibrin, bone regenerate is between the composite granules and is not associated with contact with the maternal bone. Its cells appear in different places of the defect. In the spongy bone tissue on the 21st day, regeneration proceeded more fully and faster in the second experimental group, as evidenced by the significant density of cells of the osteoblastic row, the thickness of the bone trabeculae and their volume, filling the site of the defect. On the 42nd day, in the second experimental group, when using a combination of autobiomaterial and hydroxyapatite granules with β-tricalcium phosphate, the regenerate contained a significantly larger number of osteogenic cells in the thickness of the trabeculae, which indicated a more intensive course of reparative osteogenesis in comparison with the first experimental and control groups. In the compact bone on day 21, regeneration was more complete and faster in the second experimental group. On the 42nd day, according to the degree of maturity of the bone regenerate, calcium-phosphate ceramics in combination with platelet-rich fibrin optimizes reparative osteogenesis most clearly. According to the degree of intensity of the osteoregeneration process, the groups can be placed in the following sequence: control ˂PRF˂PRF+HA/β-TCP–700. According to histomorphological characteristics, the combination of hydroxyapatite with β-tricalcium phosphate and platelet-rich fibrin gives greater osteoinduction to the composite material, which is confirmed by the high cell density, namely of osteoblasts and osteocytes. The use of PRF in combination with other materials may become promising for the correction of reparative osteogenesis in conditions of limited or reduced regenerative potential of bone tissue.

Due to the similarity of its composition to bone tissue, bioactive ceramics based on hydroxyapatite are considered the most promising for osteosubstitution of fragmentary fractures, and topical application of pharmacological agents and autologous agents bioactive substances, in particular, platelet-rich fibrin (PRF). The work aims to clinically and radiologically, and pathochemically substantiate osteosubstitution by hydroxyapatite ceramics with β-tricalcium phosphate and platelet-enriched fibrin for fragmentary bone fractures in dogs. A control and two experimental groups of animals were formed, including patients (n = 10) with humerus and forearm fractures. After general and local anesthesia and extracortical osteosynthesis, the first experimental group was injected with platelet-rich autofibrin between bone fragments. The second group was osteosubstituted with a combination of PRF and hydroxyapatite ceramics; in the control group, the defects remained without replacement. For biochemical studies, blood samples were taken after injury no later than 24 hours and on the 3rd, seventh, 14th, 21st, and 42nd day after osteosynthesis. In the postoperative period, clinical and radiological studies were performed. The activity of bone isoenzyme alkaline phosphatase (BAP), tartrate-resistant acid phosphatase (TrAP), the level of total calcium (Ca), inorganic phosphorus (P), and total protein were determined in blood serum. It was found that complete recovery of limb function in the experimental groups was 1.2–1.4 times faster (P < 0.001) compared with the control group and radiologically confirmed earlier consolidation of fractures. In both experimental groups, the maximum activity of BAP was observed on the 14th day, in the absence of a significant difference between these groups, while in control – it peaked on the 21st day. In the case of bone injury, the level of TrAP decreased by 1.2 times (P < 0.05) and then gradually increased, which was significant in the control group on the 42nd day, in the first experimental group on the 21st, and the second on the 14th day. On the third day after osteosynthesis, the concentration of P was still lower in the control (P < 0.05) and the first experimental (P < 0.01) group compared with clinically healthy animals. The concentration of Ca on the third day was reduced in all groups by 1.2 times (P < 0.001) and then gradually returned to normal. The use of PRF with calcium-phosphate ceramics for osteosubstitution helps to optimize regeneration processes in the area of bone injury by activating osteoblastic cells and reducing the intensity of the osteoresorption reaction with an earlier reaction of bone regeneration remodeling.