Tri-layered constitutive modelling unveils functional differences between the pig ascending and lower thoracic aorta

• Published in: Journal of the mechanical behavior of biomedical materials 2023-05, Vol.141, p.105752-105752, Article 105752
• Main Authors: Giudici, A., Spronck, B., Wilkinson, I.B., Khir, A.W.
• Format: Article
• Language: English
• Subjects: Adventitia - physiology; Animals; Aorta, Thoracic - physiology; Ascending aorta; Biomechanical Phenomena; Constitutive modelling; Layer-specific arterial mechanics; Stress, Mechanical; Swine; Thoracic aorta; Tri-layered arterial wall modelling
• ISSN: 1751-6161; 1878-0180
• DOI: 10.1016/j.jmbbm.2023.105752

The arterial wall's tri-layered macroscopic and layer-specific microscopic structure determine its mechanical properties, which vary at different arterial locations. Combining layer-specific mechanical data and tri-layered modelling, this study aimed to characterise functional differences between the pig ascending (AA) and lower thoracic aorta (LTA). AA and LTA segments were obtained for n=9 pigs. For each location, circumferentially and axially oriented intact wall and isolated layer strips were tested uniaxially and the layer-specific mechanical response modelled using a hyperelastic strain energy function. Then, layer-specific constitutive relations and intact wall mechanical data were combined to develop a tri-layered model of an AA and LTA cylindrical vessel, accounting for the layer-specific residual stresses. AA and LTA behaviours were then characterised for in vivo pressure ranges while stretched axially to in vivo length. The media dominated the AA response, bearing>2/3 of the circumferential load both at physiological (100 mmHg) and hypertensive pressures (160 mmHg). The LTA media bore most of the circumferential load at physiological pressure only (57±7% at 100 mmHg), while adventitia and media load bearings were comparable at 160 mmHg. Furthermore, increased axial elongation affected the media/adventitia load-bearing only at the LTA. The pig AA and LTA presented strong functional differences, likely reflecting their different roles in the circulation. The media-dominated compliant and anisotropic AA stores large amounts of elastic energy in response to both circumferential and axial deformations, which maximises diastolic recoiling function. This function is reduced at the LTA, where the adventitia shields the artery against supra-physiological circumferential and axial loads. [Display omitted] •Uniaxial testing was used to study the layer-specific biomechanics of the ascending (AA) and lower thoracic aorta (LTA).•Tri-layered modelling was used to investigate functional differences between AA and LTA.•The AA layer-specific load bearing is insensitive to changes in circumferential and axial loads.•Increasing circumferential and axial loads shifts the LTA load bearing from the compliant media to the stiff adventitia.•AA but not LTA largely increases the storage of elastic energy in response to both increased circumferential and axial loads.