Physical, chemical, and mechanical characterization of the bovine pericardium to improve the Epygon mitral bio-prosthesis

Heart valve disease, which occurs when the heart valves do not work the way they should, represents a diffused cause of death (according to the American Heart Association, about 5 million Americans are diagnosed with heart valve disease each year). There are several types of heart valve disease and the treatment depends on the type of disease and how severe it is, as well as on the overall health status of the patient, the age and weight. In most of the cases, valve replacement with prosthetic devices is required. The new generations of prosthetic heart valves are fabricated using biological tissues for valve leaflets, in particular pericardial tissue. Surprisingly, notwithstanding the large number of valves in the world every year, a standard protocol for the mechanical characterization of the pericardial tissue adopted for valve leaflets fabrication is still lacking. In this context, the aim of this thesis work is to identify a protocol guiding the pericardial tissue for valve leaflets production selection process. The final goal is contributing to improve the performance and manufacturability of the prosthetic device. In detail, an experimental protocol was identified for a through-scales mechanical characterization of pericardial tissue samples, including the macroscopic mechanical response of the tissue as well as its mechanical behavior at the microscale. Technically, uniaxial tensile tests were performed to quantify the tensile strength of the tissue. As the uniaxial tests for ultimate strength characterization are destructive by nature and cannot be adopted for selecting tissue samples to be used for manufacturing bio-prostheses, the use of nanoindentation was explored to unveil the micromechanical properties of the tissue providing measurements of elastic modulus and indentation stress, similarly to the macroscopic tensile test. The identification of the link between the mechanical properties measured at different scales will make possible the introduction of nanoindentation as non-destructive test to obtain information about the mechanical behavior of the pericardial tissue without damaging it, minimizing the manufacturing waste and making the tissue selection process more standardizable. A complete characterization of pericardial tissue was carried out in this thesis work, including the evaluation of tissue thickness uniformity. Moreover, shrinkage temperature tests were performed to verify the level of collagen cross-linking in the tissue samples. This experimental work was made possible within the collaboration between the company Epygon, manufacturer of a transcatheter mitral bio-prostheses, and the research laboratories of the Politecnico di Torino.