Experimental and constitutive modeling approaches for a study of biomechanical properties of human coronary arteries.

The study concerns the determination of mechanical properties of human coronary arterial walls with both experimental and constitutive modeling approaches. The research material was harvested from 18 patients (range 50-84 years). On the basis of hospital records and visual observation, each tissue sample was classified according to the stage (0, I, II, III) of atherosclerosis development (SAD). Then, strip samples considered as a membrane with the shape of rectangular parallelepiped were preconditioned and subjected to uniaxial tensile tests in longitudinal (n=27) and circumferential (n=4) direction. With experimental data obtained, the stress-strain characteristics were prepared. Furthermore, tensile strengths and related strains, stiffness coefficients and tangent modules of elasticity were computed. For a constitutive model of passive mechanical behavior of coronary arteries, values of material parameters were computed. The studies led to the following conclusions. Most importantly, the atherosclerotic changes affect all the mechanical properties of arterial walls. A progress of arteriosclerosis contributes to an increase of vascular stiffness. The highest values of the stiffness coefficients are obtained for the tissues in the advanced stage of the disease. We were also able to observe that gradual calcification, progression of atherosclerosis and degradation of collagen in the tissue caused a decrease of tensile strengths and related strains. Finally, a comparison made for the tissues with the advanced SAD showed that the tensile strengths and strains were much higher in the case of the samples with the circumferential orientation rather than those with the longitudinal one.

Mechanical, biological, and microstructural properties of biodegradable models of polymeric stents made of PLLA and alginate fibers.

Due to lack of effective methods for preventing the complications associated with stent implantation, the search for new solutions is conducted, including those based on the use of biodegradable polymers. Such materials could allow us to develop a temporary implant that would ensure flow in the vessel until its regeneration, while minimising the negative effects connected with long-term implant-tissue interaction. In this study, models in the form of biodegradable stents of different materials and geometry were prepared. Due to the fact that one of the basic requirements imposed on vascular stents is the ability to resist radial loads caused by the surrounding tissue, the maximum radial forces causing destruction of prepared models were investigated. The results were compared with the values obtained for commercially used metallic implants. Models were also incubated in Eagle's medium enriched with albumin in order to assess potential adhesion capacity of proteins on their surface. Scanning electron microscope enabled monitoring of microstructural changes during incubation. The results obtained were used to evaluate the ability to obtain a functional, biodegradable vascular stent.