The causes of heart valve bioprosthetic calcification are still not clear. In this paper, we compared the calcification in the porcine aorta (Ao) and the bovine jugular vein (Ve) walls, as well as the bovine pericardium (Pe). Biomaterials were crosslinked with glutaraldehyde (GA) and diepoxide (DE), after which they were implanted subcutaneously in young rats for 10, 20, and 30 days. Collagen, elastin, and fibrillin were visualized in non-implanted samples. Atomic absorption spectroscopy, histological methods, scanning electron microscopy, and Fourier-transform infrared spectroscopy were used to study the dynamics of calcification. By the 30th day, calcium accumulated most intensively in the collagen fibers of the GA-Pe. In elastin-rich materials, calcium deposits were associated with elastin fibers and localized differences in the walls of Ao and Ve. The DE-Pe did not calcify at all for 30 days. Alkaline phosphatase does not affect calcification since it was not found in the implant tissue. Fibrillin surrounds elastin fibers in the Ao and Ve, but its involvement in calcification is questionable. In the subcutaneous space of young rats, which are used to model the implants’ calcification, the content of phosphorus was five times higher than in aging animals. We hypothesize that the centers of calcium phosphate nucleation are the positively charged nitrogen of the pyridinium rings, which is the main one in fresh elastin and appears in collagen as a result of GA preservation. Nucleation can be significantly accelerated at high concentrations of phosphorus in biological fluids. The hypothesis needs further experimental confirmation.

Titanium oxide (TiO₂) and oxynitride (N-TiO₂) coatings can increase nitinol stents’ cytocompatibility with endothelial cells. Methods of TiO₂ and N-TiO₂ sputtering and cytocompatibility assessments vary significantly among different research groups, making it difficult to compare results. The aim of this work was to develop an integral cytocompatibility index (ICI) and a decision tree algorithm (DTA) using the “EA.hy926 cell/TiO₂ or N-TiO₂ coating” model and to determine the optimal cytocompatible coating. Magnetron sputtering was performed in a reaction gas medium with various N₂:O₂ ratios and bias voltages. The samples’ morphology was studied by scanning electron microscopy (SEM) and Raman spectroscopy. The cytocompatibility of the coatings was evaluated in terms of their cytotoxicity, adhesion, viability, and NO production. The ICI and DTA were developed to assess the cytocompatibility of the samples. Both algorithms demonstrated the best cytocompatibility for the sample sputtered at U_bias = 0 V and a gas ratio of N₂:O₂ = 2:1, in which the rutile phase dominated. The DTA provided more detailed information about the cytocompatibility, which depended on the sputtering mode, surface morphology, and crystalline phase. The proposed mathematical models relate the cytocompatibility and the studied physical characteristics.

Calcification is the major factor limiting the clinical use of bioprostheses. It may be prevented by the immobilization of bisphosphonic compounds (BPs) on the biomaterial. In this study, we assessed the accumulation and structure of calcium phosphate deposits in collagen-rich bovine pericardium (Pe) and elastin-rich porcine aortic wall (Ao) and bovine jugular vein wall (Ve) cross-linked with glutaraldehyde (GA) or diepoxy compound (DE). These tissues were then modified with pamidronic (PAM) acid or 2-(2′-carboxyethylamino)ethylidene-1,1-bisphosphonic (CEABA) acid. Tissue transformations were studied using Fourier-transform infrared spectroscopy. After subcutaneous implantation of the biomaterials in 220 rats, calcification dynamics were examined using atomic absorption spectrophotometry, light microscopy after von Kossa staining, and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy The calcium content in all GA-cross-linked tissues and DE-cross-linked Ao increased to 100–160 mg/g on day 60 after implantation. BPs prevented the accumulation of phosphates on the surface of all materials and most effectively inhibited calcification in GA-cross-linked Ao and DE-cross-linked Pe. PAM containing -OH in the R1 group was more effective than CEABA containing -H in R1. The calcification-inhibitory effect of BPs may be realized through their ability to block nucleation and prevent the growth of hydroxyapatite crystals.

Background. Heart valve bioprostheses made from glutaraldehyde-treated bovine and porcine pericardia are widely used in open and transcatheter valve surgeries. However, the glutaraldehyde cross-linkage leads to bioprosthetic calcification in many patients. Epoxides are advantageous alternatives to glutaraldehyde, since they engender the biomaterial with better calcification resistance. The cross-linking features of an epoxy compound depend on its chemical structure and have not been fully studied so far.Aim. The study is aimed at comparing the effectiveness and molecular mechanisms of biomaterial treatment using diepoxide vs pentaepoxide compounds.Methods. We studied the stability of diepoxide and pentaepoxide in water and aqueous buffered solutions, as well as the amino acid composition, type of epoxide links with collagen matrix (infrared spectroscopy) and mechanical properties of bovine and porcine pericardia treated with 5% diepoxide, a mixture of 2% diepoxide and 1% pentaepoxide, and with alternating 5% diepoxide and 2% pentaepoxide treatments.Results. Diepoxide and pentaepoxide are both stable in aqueous buffer solutions (pH 7.4). Diepoxide provides high linkage density in bovine and porcine pericardia due to reactions with the amino groups of the OHLys, Lys, His, and Arg residues, and the hydroxyl groups of OHPro, Ser, and Tyr, while pentaepoxide reacts only with Met. Pentaepoxide enhances the strength and elasticity of the xenopericardium. Specimens consecutively treated with diepoxide and pentaepoxide were significantly thinner and featured the highest maximal tensile stress, maximal strain and elastic modulus in comparison with tissues treated with 5% diepoxide and diepoxide-pentaepoxide mixture.Conclusion. The alternating diepoxide-pentaepoxide combination for biomaterial cross-linking is a promising trend for bioprosthetic pericardium treatment. Received 26 September 2018. Revised 19 October 2018. Accepted 22 October 2018. Funding: The study was carried out with the support of a grant of the Russian Science Foundation No. 16-15-10315. Conflict of interest: Authors declare no conflict of interest. Author contributionsConception and study design: I.Yu. Zhuravleva, E.V. Karpova, L.A. OparinaData collection and analysis: I.Yu. Zhuravleva, E.V. Karpova, L.A. Oparina, N. Cabos, A.L. Ksenofontov, B.A. TrofimovStatistical data analysis: A.S. ZhuravlevaDrafting the article: I.Yu. Zhuravleva, E.V. Karpova, L.A. Oparina, A.S. ZhuravlevaCritical revision of the article: I.Yu. Zhuravleva, E.V. Karpova, L.A. Oparina, N.R. Nichay, A.V. Bogachev-Prokophiev, A.M. KaraskovFinal approval of the version to be published: I.Yu. Zhuravleva, E.V. Karpova, L.A. Oparina, N. Cabos, A.L. Ksenofontov, A.S. Zhuravleva, N.R. Nichay, A.V. Bogachev-Prokophiev, B.A. Trofimov, A.M. Karaskov ORCID IDI.Yu. Zhuravleva, https://orcid.org/0000-0002-1935-4170E.V. Karpova, https://orcid.org/0000-0001-8803-4237L.A. Oparina, https://orcid.org/0000-0003-1286-2866N. Cabos, https://orcid.org/0000-0002-8178-7946A.L. Ksenofontov, https://orcid.org/0000-0003-1585-7907A.S. Zhuravleva, https://orcid.org/0000-0001-8427-1366N.R. Nichay, https://orcid.org/0000-0002-1763-9535A.V. Bogachev-Prokophiev, https://orcid.org/0000-0003-4625-4631B.A. Trofimov, http://orcid.org/0000-0002-0430-3215A.M. Karaskov, https://orcid.org/0000-0001-8900-8524