N.S. Sergeeva, I.K. Sviridova, S.M. Barinov, V.S. Komlev, V.A. Kirsanova, S.A. Akhmedova, I.V. Fadeeva, T.N. Molodtsova, N.V. Petrakova, A.I. Antokhin, G.V. Pavlova, Ja.D. Shansky

The aim of the study was the comparative evaluation of wide taxonomy natural corals (NC) massive skeleton (18 species, 5 families of hermatype corals). Both physicochemical (chemical and phase composition, surface topography, solution kinetics) and biological (acute cytotoxicity, cell matrix properties, biocompatibility, osteoconductivity) characteristics of natural corals for bone tissue engineering were investigated. It was shown that only one from 18 coral species (Heliopora coerulea) was toxic for test-culture (human immortalized fibroblasts). All other NCs were not toxic and had different degree of matrix properties. Cells were actively attached to NCs corals surface and were colonized during long-term cultivation (up to 14 days). For comparative study of physicochemical properties eight NCs species from four families were selected: Acroporidae (3 spp.), Fingiidae (1 sp.), Faviidae (1 sp.) and Pocilloporidae (3 spp.). According to X-ray analysis, the main phase of studied NCs was aragonite (conformity to JCDD). It was revealed that all NCs specimens include transition metals impurities but they do not exceed admissible limit values (ASTM 1185 standard). The main element is strontium; its quantity in studied specimens did not exceed 0.81 % w/w. During NCs microstructure study a particular attention was directed to pores (their form, size and interconnections interporous partitions). The crystals morphology was also investigated . It was shown that NCs structure is different both for various families and for various NCs species of one family. The results of high-resolution scanning electronic microscopy show high dispersion crystalline formations in microstructure of studied NCs corals specimens. Biodegradation kinetics of 5 NCs species in model fluids (physiological solution and simulation body fluid (SBF)) was examined. It was shown that surface microrelief of corals changes during their degradation in SBF: the precipitation of biological apatite crystals was found and its amount was increased in dynamic of exposition of NCs specimens. These facts give evidence of high bioactivity of NCs. For evaluation of biocompatibility (model of subcutaneous NC implantation, mice) and osteoplastic potencies (model of Wistar rat tibia defect) the following NCs specimens were selected: Acroporidae (Acropora sp.2, Montipora digitata), Faviidae (Goniastrea retiformis) and Pocilloporidae (Pocillopora damicornis and P. eydouxi). It was revealed that in subcutaneous test these NCs do not induce local inflammation and rejection during all time of observation (4, 8, 12, 16, 20 weeks). These facts confirm biocompatibility of NCs. Both biodegradation rates in subcutaneous implantation area and in bone defect and osteoreparative properties of all five NCs species were similar. All NCs specimens had demonstrated their osteoconductive properties. We observe the gradual NCs biodegradation in bone defect area and their replacement by de novo forming bone tissue. The new bone ingrowth was detected not only in framework of the defect area but it was integrated with surrounding bone too, providing active vascularization of implant and osteogenic cells migration into defect zone. Therefore, the received results of physicochemical and biological study of NCs suggested that they are perspective natural biomaterial for bone defect reconstruction and as 3D matrices for different types cells in tissue engineering.