Mechanical, Electrical, and Biological Properties of Mechanochemically Processed Hydroxyapatite Ceramics

The effect of the sintering temperature on densification and the resultant mechanical, electrical, and biological properties of mechanochemically processed hydroxyapatite (HAp) samples was investigated. HAp samples were sintered at 1200, 1250, and 1300 °C for 4 h, respectively. HAp samples sintered at 1250 °C showed better mechanical properties, which was attributed to their smaller grain size compared to HAp samples at higher sintering temperatures. The nearly identical value of the dielectric constant (εr) and better cell proliferation was exhibited by HAp samples sintered at 1250 and 1300 °C, respectively. At ~210 °C, in all the samples sintered at different temperatures, a dielectric anomaly was obtained, which was attributed to the phase transition temperature of the HAp system. Dielectric properties near the phase transition temperature showed a dielectric relaxation-type of behavior, which was attributed to the re-orientational motion of OH− ions in the HAp system. Higher cell proliferation and viability were exhibited by the HAp1300 samples, whereas comparatively equivalent cell growth and higher mechanical strength were observed in the HAp1250 samples.

Dynamics of hematological parameters in rabbits for osteosubstitution by hydroxyapatite ceramics doped with germanium and in complex with blood coagulation activator

Bone tissue has powerful regenerative properties, thanks to which, with stable fixation, quite large amounts of skeletal bone damage can be successfully repaired. However, in the case of fragmentary fractures, the use of osteosynthesis methods alone does not always ensure the optimal course of reparative regeneration, as its regenerative potential is lost. Therefore, there is a need to replace post-traumatic bone defects and stimulate reparative osteogenesis. For this purpose, doped or doped with various elements (Ge, Si, Zn, Ag, Cu) composite materials. The aim of the study was to investigate the dynamics of hematological parameters in rabbits for osteosubstitution by hydroxyapatite ceramics doped with germanium and in combination with a blood clotting activator. Model defects were formed in the radial diaphysis and femur metaphysis in rabbits with a 3 mm and 4.2 mm diameter drill bit, respectively. Anesthesia included acepromazine, thiopenate, and lidocaine infiltration anesthesia. Animals of the first experimental group (n = 12) were replaced by defects with granules of hydroxyapatite ceramics doped with germanium (HTGe), the second (n = 12) – hydroxyapatite ceramics doped with germanium with blood coagulation activator (HTGe + a), the third – (n = 12). hydroxyapatite α + β with active (α + β + a), and control – granules of undoped ceramics (HT). On day 7, animals of all groups had minor post-traumatic erythrocytopenia and oligochromemia. There was also a gradual increase in the content of leukocytes in the blood with a peak on the 14th day, which in the group HTGe + a lasted until the 30th day. The increase in the number of leukocytes and their peak values occurred within the physiological norm and only approached its upper limit. In most groups there was a pronounced thrombocytosis during the first 14 days with normalization to the 30th day, but in the 2nd experimental group the number of platelets returned to normal only on the 60th day. Changes in most integral hematological indices, which reflect the relationship between blood cell populations, are characteristic of the inflammatory-resorptive phase of reparative osteogenesis. The dynamics of hematological parameters indicates the absence of a pronounced reaction of the body to the implantation of hydroxyapatite composite doped with germanium. The combination of hydroxyapatite ceramics doped with germanium with coagulation activator eliminates post-traumatic oligochromemia and erythrocytopenia and significantly increases the level of hematological integral indices, which indicates a more intensive course of inflammatory-resorptive clinical resorptive aparation phase.

Histomorphological characteristics of bone replacement in rabbits with hydroxyapatite ceramics and Platelet-Rich Fibrin

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.