Assessment of the uniaxial experimental parameters utilised for the mechanical testing of bovine pericardium

Bovine pericardium (BP) is an extensively used biomaterial utilised in a wide range of biomedical devices such as bioprosthetic heart valves. However, the mechanical testing techniques that assess soft biomaterial tissue like BP are varied with no common method utilised across the literature, producing variations and contradictions in reported values. Uniaxial testing is a common technique used to measure traditional mechanical characteristics of ultimate tensile strength (UTS), modulus and the percentage strain at failure. The aim of this study was to take two standard uniaxial test parameters, strain rate and the number of preconditioning cycles and to elucidate recommendations for the standardisation of a uniaxial method, while also measuring not so common parameters of low modulus and hysteresis. Samples post uniaxial testing were treated and analysed with scanning electron microscopy (SEM) and an imaging software (ImageJ) to measure the effect of the parameters on the crimping structure and orientation of the collagen fibres. The study recommends an extension rate of 10 mm min and 5 preconditioning load-unload cycles as a starting point for the standardisation of a uniaxial testing method. The image analysis of the collagen structure carried out provides a quantitative assessment of the BP post mechanical testing and allows for a better understanding of the behaviour of BP under stress.