Abstract: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 calciumcontaining 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.
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.
Abstract:The scheme of platelet/surface interaction and a kinetic model of platelet adhesion on a solid surface are suggested. The elaborated approach takes into account the platelet activation by the surface and accumulation of free activated cells in the bulk of the liquid phase. This effect has an especially important role in static experimental conditions. The suggested model explains three types of adhesion kinetic curves, obtained in experiments in vitro: sigmoid curves with or without saturation and an exponential curve with saturation. According to the model, the curve shape is determined by material surface properties, platelet functionality, and experimental conditions of the platelet/surface interaction. The data of static platelet adhesion from platelet rich plasma on glass, siliconized glass, hexadecyltrichlorosilane monolayers, and low-density polyethylene are described mathematically with the proposed model. Numerical parameters are calculated from approximation of experimental data by the model. These parameters allow quantitative characterization of platelet interaction with the material surface.
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.
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.
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