One-dimensional experimental mechanical characterisation of porcine aortic root wall.

The human aortic valve, in cases of disease, can be substituted with a stentless biological prosthesis that is made of both porcine aortic root and leaflets. In particular, the aortic root plays a very important part in the opening mechanics of the valve. Therefore, to understand the behaviour of the prosthesis, a knowledge of the mechanical characteristics of each element constituting the system is useful. For a structural and mechanical characterisation of the porcine aortic root wall tissue, specific measuring devices are made. A uni-axial tensile apparatus, operating in a temperature-controlled saline bath, is equipped with special pneumatic clamps. A test rig for the measurement of the specimen cross-sectional area is developed. To determine the porcine aortic root wall mechanical properties, 189 tensile tests are carried out. Specimens of both natural and chemically fixed tissue are used to consider the conditions of both natural valves and prostheses. Tensile tests are carried out on both axial and circumferential specimens taken from 12 areas of one-sixth of the entire aortic root, with the aim of identifying the anisotropic and non-homogeneous behaviour of the tissue. The behavior changes considerably depending on the direction in which the specimen is strained, the chemical treatment and the zone from which it has been taken. The paper presents the stress-strain characteristics of fresh and fixed tissue in all zones of the aortic wall, both in circumferential and axial directions.