Mihail Tarassov

Publications (3) View all

• Article: Nanocrystalline diamond containing hydrogels and coatings for acceleration of osteogenesis

  L. Ivanova, C. Popov, I. Kolev, B. Shivachev, J. Karadjov, M. Tarassov, W. Kulisch, J. P. Reithmaier, M. D. Apostolova
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  ABSTRACT: In the present study, we have compared the effects of ultrananocrystalline diamond/amorphous carbon composite films (UNCD/a-C) and nanocrystalline diamond (NCD) containing hydrogels to support the osteogenesis of endothelial progenitor cells (EPCs). The course of EPCs osteogenic differentiation was followed 21 days and assayed by measuring cell-associated alkaline phosphatase activity, calcium deposition, and expression of fibronectin. We found that EPCs were capable to adhere to both surfaces in flattened and elongated morphology. The attachment and spreading on the UNCD/a-C films were faster as compared to the hydrogels containing NCDs (by day 7), and this was connected with the release and adsorption of fibronectin to the surfaces. During the process of EPCs differentiation, the release of fibronectin was favored by hydrogels + NCD (day 21). The formation of calcium nodules, characteristic of osteoblastic mineralization, was detected by Alizarin Red S staining. Differentiation-induced calcium nodules were detected in EPCs growing on both surfaces. The EPCs cultured on hydrogels containing NCD deposited more extracellular calcium in comparison with those on UNCD/a-C films on day 21. These results were consistent with the data about the alkaline phosphatase activity on the same day and verified that an active EPC transformation to osteoblast phenotype occurred on both substrates. Our results could have direct implications in the use of biomaterials in tissue engineering strategies, and this work might be useful for the improvement of the methodologies for substrate preparation (including scaffolds). Thus both surfaces studied could be used for modification of bone implants (bone-anchoring parts of joint prostheses or bone replacements) in order to improve their integration with the surrounding bone tissue, for which improved cell-substrate adhesion is also needed. (C) 2010 Elsevier B.V. All rights reserved.
  Diamond and Related Materials. 01/2011; 20(2):165-169.
• Article: Atomic arrangements in amorphous sodium titanosilicate precursor powders

  V. Kostov-Kytin, B. Mihailova, Yu. Kalvachev, M. Tarassov
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  ABSTRACT: Infrared, Raman and 29Si MAS-NMR spectroscopic methods are applied to analyse the relationship between the chemical compositions of the initial synthesis gels, the predominant type of atomic arrangement in the amorphous precursors obtained from the dried gels and the favoured crystalline titanosilicate phases formed upon hydrothermal treatment. Alkali titanosilicate gels of various molecular ratios were hydrothermally treated at 200 °C, thus leading to formation of microporous ETS-4, GTS-1 and sitinakite, layered AM-1 and AM-4, and dense natisite and paranatisite. The results show that the increase in the Na2O content enhances the formation of Si–O–Ti linkages on the account of Si–O–Si and Ti–O–Ti bridges in the ternary Na2O–TiO2–SiO2 system, prior to the hydrothermal treatment. Occurrence of precursor clusters with medium range order resembling that of the subsequently crystallised titanosilicate phases was detected in the initial amorphous substances. The ratio Na2O/TiO2 is vital for the type of incipient SiO4–TiOn clustering and thus for the formation of crystalline titanosilicate phases of desired framework topology. Frameworks with five-coordinated titanium are obtained from gels with the lowest and highest values of Na2O/TiO2 ratio (smaller than 4 and higher than 8), while six-coordinated Ti4+ is characteristic for gels prepared at intermediate values of Na2O/TiO2 ratio. Layered and microporous titanosilicates crystallise at a lower Na2O/TiO2 ratio, while dense titanosilicates crystallise preferentially at higher alkalinity.
  Microporous and Mesoporous Materials 86:223-230. · 3.29 Impact Factor
• Article: Xanthoma of the stomach--some morphometrical peculiarities and scanning electron microscopy.

  S Petrov, J Churtchev, R Mitova, L Boyanova, M Tarassov
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  ABSTRACT: "Lipid Iceland's" in gastric mucosa, a rare finding in gastroenterology, is described in this paper. The aim of our investigation was to evaluate the frequency of the so-called "gastric xanthoma" in biopsy specimens and to describe the picture elicited by scanning electron microscopy. We investigated cell characteristics histochemically, morphometrically and with scanning electron microscopy. The frequency of xanthoma in our gastrobiopsy material was 0.018% (4 of 21,650 cases) over a 6-year period. The picture of stomach xanthoma given by scanning electron microscopy is very typical of the condition and is called "rolling stones". We suggest that this diagnostic method warrants further investigation.
  Hepato-gastroenterology 46(26):1220-2. · 0.66 Impact Factor