Abstract
Mechanical testing and constitutive modelling of isolated arterial layers yields insight into the individual layers’ mechanical properties, but per se fails to recapitulate the in vivo loading state, neglecting layer-specific residual stresses. The aim of this study was to develop a testing/modelling framework that integrates layer-specific uniaxial testing data into a three-layered model of the arterial wall, thereby enabling study of layer-specific mechanics under realistic (patho)physiological conditions. Circumferentially and axially oriented strips of pig thoracic aortas (n = 10) were tested uniaxially. Individual arterial layers were then isolated from the wall, tested, and their mechanical behaviour modelled using a hyperelastic strain energy function. Subsequently, the three layers were computationally assembled into a single flat-walled sample, deformed into a cylindrical vessel, and subjected to physiological tension-inflation. At the in vivo axial stretch of 1.10 ± 0.03, average circumferential wall stress was 75 ± 9 kPa at 100 mmHg, which almost doubled to 138 ± 15 kPa at 160 mmHg. A ~ 200% stiffening of the adventitia over the 60 mmHg pressure increase shifted layer-specific load-bearing from the media (65 ± 10% → 61 ± 14%) to the adventitia (28 ± 9% → 32 ± 14%). Our approach provides valuable insight into the (patho)physiological mechanical roles of individual arterial layers at different loading states, and can be implemented conveniently using simple, inexpensive and widely available uniaxial testing equipment.
Highlights
The mechanical properties of the arterial wall are highly influenced by the structural arrangements of its constituents
Elastin and collagen are commonly considered the major determinants of the passive mechanical response of arteries, as smooth muscle cells have a relatively low passive stiffness
We proposed a new modelling framework to simulate the response of the arterial wall to inflation and axial extension using the mechanical information gathered from simple uniaxial testing of the three anatomical layers
Summary
The mechanical properties of the arterial wall are highly influenced by the structural arrangements of its constituents. Elastin and collagen are commonly considered the major determinants of the passive mechanical response of arteries, as smooth muscle cells have a relatively low passive stiffness.. As reported in several studies, the relative amount, as well as the spatial organisation, of elastin and collagen fibres varies considerably across the arterial wall, conferring different mechanical properties and function to the intimal, medial, and adventitial layers. The intima directly interfaces with the blood flow and has a marginal contribution the overall wall mechanics of young healthy arteries.. The media, characterised by ‘concentric’ elastin lamellae that confer the compliant function to elastic arteries, determines the wall behaviour at physiological pressures.. The adventitia is the outermost, highly collagenous layer that protects arteries from rupture at supraphysiological pressures. The intima directly interfaces with the blood flow and has a marginal contribution the overall wall mechanics of young healthy arteries. The media, characterised by ‘concentric’ elastin lamellae that confer the compliant function to elastic arteries, determines the wall behaviour at physiological pressures. The adventitia is the outermost, highly collagenous layer that protects arteries from rupture at supraphysiological pressures.
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