Collagen tissue treated with chitosan solution in H2O/CO2 mixtures: Influence of clathrates hydrates on the structure and mechanical properties.

A mixture of water/carbon dioxide is a "green" perspective solvent from the viewpoint of biomedical applications. Clathrate hydrates are formed this solvent under certain conditions and a very interesting question is the impact of clathrates hydrates on the structure and properties of bovine pericardium, which is used in biomedicine, in particular as a main part of biological heart valve prostheses. The aim of the present work is to investigate the influence of clathrates on the structure and mechanical properties of the collagen tissue treated with chitosan in H2O/CO2 mixtures under pressure 3.0-3.5MPa and temperatures 2-4°C. It was first found that the clathrate hydrates in this media due to the strong fluctuations "bomb" collagen tissue of bovine pericardium, which is manifested in the appearance of numerous small gaps (pores) with mean size of 225±25nm and large pores with size of 1-3μ on the surface and within collagen matrices. High porosity leads to averaging characteristics of the organization structure in tissues with different orientation of the collagen fibers. As a result, the mechanical properties of the collagen tissue with a different orientation of the collagen fibrils become similar, which is quite different from their original properties. The structural changes caused by the influence of the environment clathrate hydrates led to a significant decrease of the tensile strength (30-47% in total, p<0.05) and initial elastic moduli (74-83%, p<0.05). However, the final elastic moduli and the maximum tensile virtually unchanged compared to the control. Nevertheless, it was found that the direct deposition of chitosan from the H2O/CO2 mixtures with clathrate improve the mechanical-strength properties of the porous matrices. We believe that these improved mechanical properties are achieved due to particularly deep and uniform impregnation of the collagen matrix with chitosan from its pressurized solutions in H2O/CO2 mixtures.