Tissue and microstructural deformations in aortic tissue under stretch and after deformation recovery

Elucidating how cardiovascular biomechanics is regulated during health and disease is critical for developing diagnostic and therapeutic methods. The extracellular matrix of cardiovascular tissue is composed of multiple fibrillar networks embedded in an amorphous ground substance and has been found to reveal time-dependent mechanical behavior. Given the multiscale nature of tissue biomechanics, an accurate description of cardiovascular biomechanics can be obtained only when microstructural morphology is characterized and put together in correlation with tissue-scale mechanics. In this study, we sought to determine how the microstructural configuration in aortic tissue changes with tissue-scale loading protocols. At the tissue level, rather intuitively, the width and thickness decrease when specimens undergo elongation and it is found that there is a higher inverse correlation between the elongation of circumferential specimens and the shrinkage along the thickness than along the width. After deformation recovery, the specimens show levels of permanent deformation in both thickness and width as neither recovers the initial values for the unstretched specimen, with higher permanent deformation measured for thickness. At the microstructural level, the networks in the wall inner layer show straighter fibrillar structure under stretch, which partly returns to the crimping structure after deformation recovery. This study indicates a microstructural basis for observations of regional permanent tissue stretch in artery tissues, and furnishes early data for developing multiscale models of cardiovascular viscoelastic/viscoplastic modeling.