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Biomedical subjects

V I Sevastianov

Publications and source records attributed to V I Sevastianov.

18 recordsLinked to original sources
PubMed2003

Production of purified polyhydroxyalkanoates (PHAs) for applications in contact with blood.

Samples of olyhydroxyalkanoates (PHAs), polyhydroxybutyrate (PHB) and copolymers poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) with 4 and 18 mol% hydroxyvalerate, synthesized by the bacteria Ralstonia eutropha B5786, were investigated. PHA films in contact with blood did not activate the hemostasis system at the level of cell response, but they did activate the coagulation system and the complement reaction. To detect biologically-active components in the PHAs, a detailed analysis of the composition of the polymers was conducted. Gas chromatography-mass spectrometry revealed long-chain fatty acids (FAs) in the tested PHAs. Their total concentration in the polymer ranged from tenths of mol% to 2-3 mol%, depending on the purification method. C16:0 constituted the largest proportion, up to 70%. Of the long-chain hydroxy acids, only beta-OH-C14:0 was detected and it did not exceed 0.06 mol%. The analysis of the hemocompatibility properties of the PHAs purified by a specialized procedure, including the quantitative and morphological estimation of platelets adherent to the surface of polymer films, the plasma recalcification time and complement activation studies, indicated that PHB and PHBV can be used in contact with blood. It has been found out that the lipopolysaccharides of bacteria producing PHAs, which contain mostly long-chain hydroxy acids, can be the factor activating the hemostasis systems. Thus, the technology of PHA purification must satisfy rather stringent specific requirements.

Biocompatible Materials↗
PubMed2001

Comparative analysis of human serum albumin adsorption and complement activation for intraocular lenses.

Intraocular liquid, in contrast to blood, has no cellular components; therefore, proteins (human serum albumin [HSA], and [alpha, beta, gamma] globulins) are the major components that determine patients' response to the intraocular lens (IOL) surface. In addition to the amount of adsorbed proteins, the possibility of its conformational changes, including conformational changes of globulins C1 and C3 that respond for the activation of the complements system by the classical and alternative pathways, cannot be excluded. The interaction between IOLs and protein components of intraocular liquid directly influences the ocular exudative reaction in the early postoperational period, the intensity of cellular and pigmental scurf on the surface of the IOLs, and the state of endothelial cells of the cornea in the distant postoperational period. Our goal was to compare the interaction of commercial IOLs made from polymethylmethacrylate, silicone, poly-2-hydroxyethyl methacrylate (p-HEMA), and copolymer p-HEMA with collagen with HSA and the complement system. The total internal reflection fluorescence (TIRF) method and hemolytic assay were used for this task, respectively. It has been demonstrated that the probability of biocompatibility of commercially produced IOLs on the stage of protein adsorption can be evaluated using the kinetic of HSA-fluorescein isothiocyanate adsorption onto the IOL surface by the TIRF METHOD: In the case of IOLs from p-HEMA, a negative correlation was shown between the degree of irreversible adsorption of HSA and the minimum relative rate constant of the surface-induced complement activation. We did not find any correlation between hydrophilicity/hydrophobicity of lenses and their adsorptional properties including complement activation. From suggested adsorptional criteria in vitro for biocompatible surfaces, the hydrogel lens from p-HEMA has a lower probability of biocompatibility in comparison with other IOLs.

Adsorption↗
PubMed1998

The role of proteins in the nucleation and formation of calcium-containing deposits on biomaterial surfaces.

In experiments in vivo using diffusion chambers, the morphology and composition of calcium-containing deposits on natural and artificial biomaterials that had no direct contact with cells were studied using scanning electron microscopy with energy dispersion X-ray microanalysis. It was revealed that the formation of a protein layer containing protein-calcium complexes is the key event in biomaterial calcification. A mechanism of formation of a calcium-containing protein matrix that creates the conditions for supersaturation of the crystal-forming medium over critical value has been proposed. The formation of nuclei of insoluble calcium phosphate starts predominantly deep in an adsorbed protein layer enriched by calcium ions.

Biocompatible Materials↗
PubMed1998

Competitive adsorption of human serum albumin and gamma-globulin from a binary protein mixture onto hexadecyltrichlorosilane coated glass.

The kinetics of competitive adsorption of proteins onto hexadecyltrichlorosilane coated glass (HTS-glass) from model solutions containing fluorescein isothiocyanate (FITC)-labeled human serum albumin (HSA-FITC) and gamma-globulin (HGG-FITC) were studied by total internal reflection fluorescence (TIRF) spectroscopy. The processes of displacement of HSA-FITC by HGG are independent of the conformational state of HSA adsorbed onto glass. On HTS-glass, displacement of protein is hindered by the presence of large numbers of CH3-terminated alkyl tails which induce conformational (reorientational) changes in HSA-FITC and HGG-FITC adsorbed from simple solutions. In contrast to HSA, adsorption of HGG onto HTS-glass from a simple solution is characterized by the absence of irreversible adsorption in the initial portion of the kinetic curve. Competition between HSA and HGG-FITC induces replacement of end-on adsorbed HGG-FITC on HTS-glass surface with subsequent desorption of the HGG-FITC into solution. Upon further increase in the HSA concentration in solution the competition of HSA for adsorption sites prevails, which leads to a decrease in the amount of adsorbed HGG-FITC and, consequently, to a decrease in the rate of its displacement.

Adsorption↗
PubMed1991

The effect of cells on biomaterial calcification: experiments with in vivo diffusion chambers.

The results of these in vivo experiments show that bovine pericardium can undergo calcification without direct contact with tissue. It is clear that the direct interaction of cells with implanted samples both promotes and accelerates the process of calcification. Moreover, dietary calcium supplements, calcium chloride and vitamin D can intensify the rate and extent of this process.

Animals↗
PubMed1991

The interaction of heparinized biomaterials with human serum, albumin, fibrinogen, antithrombin III, and platelets.

The influence of the method of heparin (HEP) immobilization on human serum albumin (HSA), fibrinogen (FG), and antithrombin III (AT-III) adsorption, platelet adhesion, and activation on the surface of polyvinylchloride, polyurethane Vitur, and a copolymer of styrene and divinylbenzene was measured. The negative correlation between the degree of irreversibility of plasma protein adsorption and the amount of adsorbed AT-III for HEP, immobilized onto the polymer surface passivated with HSA, FG, and plasma was found. The same negative correlation was observed between the amount of AT-III adsorbed on these systems and the number of adhered platelets. Schemes of the interaction of surface bound-HEP with AT-III, including the influence of an irreversibly adsorbed protein layer and adhered platelets, have been proposed. The essential role of AT-III in heparinized biomaterials/platelet interaction has been shown. A new method of combined immobilization of HEP and platelet adhesion inhibitor has been elaborated on.

Antithrombin III↗
PubMed1991

The heterogeneity of protein/surface interactions and structural alterations of adsorbed albumin and immunoglobulin G.

The theoretical model is developed for the reversible and irreversible protein adsorption in kinetic regime by assuming the continuous energetical heterogeneity for protein/surface interaction and the possibility of structural alterations of adsorbed molecules. The simplest rectangular distributions of adsorption centers in energy of activation are used to explain the logarithmic kinetics of IgG and human serum albumin (HSA) adsorption on a quartz surface. To explain the Freindlich character of HSA adsorption onto a precoated surface, the exponential distributions of adsorption centers in energy of activation are used. A competitive analysis of some of the approaches allowed for the energetical heterogeneity of protein/surface interaction is made. The possibility of lateral electrostatic repulsion to form the logarithmic kinetics of HSA adsorption is checked experimentally. The influence of the temperature on HSA adsorption onto quartz is discussed also.

Adsorption↗
PubMed1987

Fatigue and hemocompatibility of polymer materials.

Hemocompatibility and sufficient fatigue life of biomaterials are critical in the development of artificial hearts and circulatory assist devices. In this study, three segmented polyurethanes (PUs) were compared with a fourth PU (Czech PU) and the organosilicone rubber RKM to determine the interrelationships between type of synthetic polymer, degree of structural change in cyclic loading, and hemocompatibility. Uniaxial and biaxial static strain tests were conducted. Accelerated fatigue tests were used to predict the behavior of the materials in vivo. Damage from fatigue was assessed by light transmission and light scattering methods, and the number of adhering platelets and degree of morphological change in the platelets were compared between initial and fatigued materials. The relative index of platelet adhesion and the relative form factor were also obtained. The elasticity characteristics of the PUs were shown to be substantially greater than those of RKM. RKM required reinforcement. Czech PU was shown to have good mechanical characteristics (with high elasticity and low creep). The morphology of the cells after cyclic load changed insignificantly, whereas the number of adherent platelets increased in all cases.

Assisted Circulation↗
PubMed1987

Influence of endogenous albumin binding on blood-material interactions.

A method has been developed to enhance the albumin affinity of a number of medical polymers, based on alkylation of the surface with straight-chain 16- or 18-carbon alkyl groups. This method has been demonstrated to induce the rapid binding of albumin from single and binary protein solutions, from plasma, and apparently, from whole blood. The bound albumin resists fluid shear or chemically induced desorption. Fibrinogen adsorption is inhibited in vitro and in vivo. Complement protein C3 activation from plasma is inhibited. Fibrin formation and platelet aggregation is inhibited in short-term in vivo experiments. Long-term catheter implant studies suggest that the C18 alkylation is more effective than most, if not all, currently available treatments for the retention of a clean, biocompatible, blood-contacting surface. No data have been obtained to date that conflict with the hypothesis that a renewable albumin layer, so formed, blocks the adsorption or conformational alteration of plasma proteins that otherwise might initiate or participate in various host defenses.

Animals↗
PubMed1983

In vitro assessment of the hemocompatible properties of polymers.

Based on the available data in the literature and personal results, a system of in vitro tests, consisting of two levels of selection, was proposed for assessment of hemocompatible properties of polymers. The first level consists of rapid methods for preliminary assessment (clotting time, hemolytic activity of the sample, and number of adhesive platelets). The second level involves methods for final selection and consists of measurement of the kinetics of the initial stages of adsorption of albumin, the degree of activation of the complement system, the intensity of radical oxidation of the lipid fraction of the blood, and the degree of platelet spreading. Comparative experimental assessment of these methods was conducted with a number of polymers and revealed the confidence limits for the application of each test and suggested quantitative criteria for selection.

Biocompatible Materials↗
PubMedDate not supplied

Carbon coated polyethylene: effect of surface energetics and topography on human platelet adhesion.

The influence of surface energy and structural properties of carbon coated polyethylene (PE) on the human platelet adhesion was studied. Three types of amorphous carbon coating were obtained by plasma pulse discharge, with the number of pulses grading as 10, 50, 100. Human serum albumin adsorption experiments have been carried out with all samples in vitro. Platelet adhesion analysis by SEM included determination of total quantity of adherent platelets, and respective quantities of platelets at different stages of activation (single, spread, aggregates). Surface topographies ranged from bare PE and such (10 pulses), to globular 0.5 microm in size (50 pulses), and complex fibrillar 3-4 microm structures (100 pulses). Surface free energy varies from 31.7 +/- 0.6 to 40.4 +/- 0.6 mN/m for uncoated PE and 10 pulse coatings, respectively, as determined by contact angle techniques. All studied coatings demonstrate weaker platelet activation properties in comparison with untreated PE. Among all studied coatings, the 50 pulse coated surface seems to be the least suitable for contact with platelets, mainly due to its structural rather than to its energy properties. These data are related to a sharp decrease in the adsorbed protein level for the samples with 50 pulse coatings. The applied analysis of platelet activation enables more accurate characterization of platelet-biomaterial interaction.

Adsorption↗
PubMedDate not supplied

Biomaterial calcification without direct material-cell interaction.

This report summarizes 1) features of the local redistribution of calcium ions and formation of complexes with calcium (Ca) in the presence of polymer samples; 2) the adsorption of Ca ions and Ca containing complexes onto biomaterial surfaces; 3) the character and composition of Ca containing deposits; and 4) the role of cellular and humoral factors in calcification. All experiments were done with three types of medical grade polymer material (from USSR): silicone rubber (SR), polyurethane "Vitur" (PU), and polyethylene (PE). Biochemical, radioisotopic, SEM, and EDAX methods were used in in vitro and in vivo experiments. The diffusion chamber model was used in animal experiments. SR was shown to induce greater changes in complex formation processes and to adsorb more Ca containing complexes than PE or PU. In addition to the degree of SR calcification seen after 21 days, implantation accentuated these findings. The possibility of calcification of polymer materials without direct contact of material and cells was observed. Combining the in vitro and in vivo experimental data, the authors propose a hypothetical scheme of biomaterial calcification.

Adsorption↗
PubMedDate not supplied

Influence of mold properties on surface structure of a polyurethane-siloxane block co-polymer. Implications for blood compatibility.

The authors studied the surface structure of organosiloxane-polyether urethane co-polymer films cast against low and high surface free energy materials (glass/ceramic and metal). A novel surface interaction parameter, the gold nucleus density distribution (GND), determined by partial gold decoration transmission electron microscopy, was used to indirectly assess the dispersive contribution to interfacial surface free energy. A water wetting assay was used to characterize the hydrophobic/hydrophilic balance of the polymer film surfaces. Two biological interaction parameters, one involving the kinetics of albumin and fibrinogen adsorption from plasma and the other a platelet adhesion index (RIPA), were used to estimate blood compatibility. Results indicate that mold properties influence the surface structure of this block co-polymer, sequestering polysiloxane groups at mold, and possibly air interfacial regions of the film. However, as shown by ESCA and FTIR analysis, specific chemical groups did not correlate with the blood compatibility indices. The GND correlate with initial albumin and fibrinogen adsorption rates. Initial protein adsorption was less well predicted by surface water wettability. Neither surface structure nor surface interaction data predicted later (60-120 min) protein sorption or platelet adhesion. Subsequent events may be influenced by protein turnover and cell-surface interactions, and are less influenced by polymer surface properties.

Adsorption↗
PubMedDate not supplied

Analysis of albumin deposits on hydroxylated siloxane films. Implications for surface treatment of medical devices.

The authors have developed methods to enhance albumin binding to modified silicone rubber (SR) films. An intermediate bifunctional coupling agent, polyvinylmethyl siloxane-comethyl-1-ethanol siloxane (PVMS-CO-MES), is prepared from a cyclic tetramer, vinyl-methyl siloxane, by an oxymercuration-demercuration reaction, and cross-linked to silicone rubber under mild peroxide catalytic conditions. Free mercury on the surface was obtained under many reaction conditions and is shown to materially enhance 125I-labeled albumin binding. The mechanism most likely occurs via disulfide bond breakage, protein denaturation, and aggregation. The possible role of iodine-mercury bonds, an artefactual source, is ruled out with the aid of total internal reflectance-fluorescence measurements of the albumin adsorption rate constant. Although in situ albumin aggregation via disulfide bond breakage is a potentially attractive method for biocompatible protein gel formation, the toxicity of mercury makes the current method unfit for clinical practice.

Adsorption↗
PubMedDate not supplied

An N-substituted polyurea coating with high affinity for heparin.

A new N-substituted polyurea with tertiary amino groups in the polycarbamidic chain (NPUTA) has been synthesized. The polymer is soluble in C1-C4 alcohols, has high adhesion to polar molds, and has high H2O uptake (130-150%). The material can be coated on many biomaterials (polyurethanes, charcoal hemosorbents, cellulosic hemodialysis membranes), and high amounts of heparin can be adsorbed onto treated surfaces. NPUTA cast from 0.5-3.5% ethanol solutions can absorb large amounts of heparin from anti-coagulant solution (40-60 micrograms/cm2) and heparinized plasma. Heparin release into phosphate buffered saline (PBS) solution or plasma is minimal. The influence of NPUTA solution concentration and pre-absorbed heparin on the protein adsorption, platelet adhesion, surface induced hemolysis, and complement activation of these films has been investigated. Radiolabeled protein assays, radiolabeled platelet assays, and other methods were used. It was shown that modified surfaces for the listed materials, with heparinization, demonstrate improved in vitro blood compatibility without any changes in functional properties. For example, treatment with NPUTA/heparin does not reduce sorption of middle molecules by activated charcoal hemosorbent, while markedly and significantly decreasing platelet adhesion and complement activation. NPUTA/heparin modified, glutaraldehyde treated bovine pericardium exhibited significantly reduced calcification in a rat subcutaneous implant model. Other ex vivo circulation experiments also confirm the blood compatibility of different NPUTA treated surfaces.

Adsorption↗