Nonlinear Dynamics of Human Aortas for Material Characterization

Abstract

Evaluating the nonlinear dynamics of human descending thoracic aortas is essential for building the next generation of vascular prostheses. This study characterizes the nonlinear dynamics, viscoelastic material properties, and fluid-structure interaction of 11 ex-vivo human descending thoracic aortas the full range of physiological heart rates. The aortic segments are harvested from heart-beating donors screened for transplants. A mock circulatory loop is developed to reproduce physiological pulsatile pressure and flow. The results show cyclic axisymmetric diameter changes, which are satisfactorily compared to in-vivo measurements at a resting pulse rate of 60 bpm, with an additional bending vibration. An increase of the dynamic stiffness (i.e., storage modulus) with age is also observed. This increase is accompanied by a strong reduction with age of the cyclic diameter change during the heart pulsation at 60 bpm and by a significant reduction of the loss factor (i.e., damping). Large dissipation is observed at higher pulse rates due to the combined effects of fluid-structure interaction and viscoelasticity of the aortic wall. This study presents data necessary for developing innovative grafts that better mimic the dynamics of the aorta.

Role of smooth muscle activation in the static and dynamic mechanical characterization of human aortas

“…The aorta is subjected to cyclic pulsatile pressure at a frequency in the range of 1 to about 3 Hz (i.e., 60 to 180 beats per minute). The pulsatile pressure is not harmonic ( 3 ), but it can be expanded in a Fourier series with harmonic components. In this study, the strips were loaded by a harmonic cyclic strain with an amplitude of 7% of their length.…”

“…Prosthetic tubes made of polyester (Dacron) or polytetrafluoroethylene are often used for the surgical repair of large arteries in aneurysms or acute dissection. Unfortunately, these grafts are so stiff to diameter expansion ( 3 ) that they can cause cardiovascular and perfusion problems because they fail to reduce the highly pulsatile nature of the blood flow exiting the heart. This is the reason for an increasing interest in the development of a new generation of grafts ( 4 ) in innovative biomaterials or in tissue engineering that mimic the dynamic behavior of the aorta, which is achieved through the correct adjustment of mechanical properties and the introduction of a layered design.…”

“…The passive dynamic material properties (also referred to as viscoelastic) of the human aortas, on the other hand, are much less studied, even if they are of great importance since the aorta is dynamically loaded by pulsating pressure under physiological conditions. The experiments were performed on a mock circulatory loop under physiological pulsatile pressure and flow ( 3 , 16 ) and on strips of thoracic descending aortas ( 8 , 17 ). Viscoelastic models have been developed ( 18 , 19 ), but they can only partially describe the experimental results.…”

Tuning nonlinear damping in graphene nanoresonators by parametric–direct internal resonance

“…In the last decade, nonlinear dissipation has attracted much attention with applications that span nanomechanics 1 , materials science 2 , biomechanics 3 , thermodynamics 4 , spintronics, 5 and quantum information 6 . It has been shown that the nonlinear dissipation process follows the empirical force model where τ nl1 is the nonlinear damping coefficient, x is the displacement, and velocity.…”

Resonances in pulsatile channel flow with an elastic wall

“…[9,[14][15][16][17]) are comparatively scarce despite the pulsatile nature of blood flows. A notable exception is Amabili et al's recent study [18] in which part of an excised human aorta was mounted between two rigid pipes and subjected to physiological pulsatile pressure and flow rates.…”