Identification of viscoelastic properties of Dacron aortic grafts subjected to physiological pulsatile flow

Amabili, Marco; Balasubramanian, Prabakaran; Franchini, Giulio; Giovanniello, Francesco; Tubaldi, Eleonora

doi:10.1016/j.jmbbm.2020.103804

Cited by 22 publications

(5 citation statements)

References 33 publications

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“…Unfortunately, this strategy can not be used for the valve leaflets since the model is the real prosthesis (λ = λ m and E = E m ) that, however, is subjected to different hydrodynamic loads. Similar problems occur if the prosthesis is the aortic wall itself as it is usually a Dacron (polyethylene terephthalate; PET) vascular graft with a complex fabric structure (figure 18a) aimed at reproducing the orthotropic mechanical properties of the natural tissue (Amabili et al 2020). It must be noted, however, that the Dacron fibre is quite rigid and, for the physiological pressure differences, the stretching is very limited; considering the negligible inertia of the graft with respect to that of the fluid therein, the flow motion turns out to be well reproduced by the experiment even if the internal loads of the structure are not representative of the real problem.…”

Section: Heart Modelsmentioning

confidence: 99%

Electro-fluid-mechanics of the heart

Verzicco

2022

J. Fluid Mech.

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This article presents an overview of the dynamics of the human heart and the main goal is the discussion of its fluid mechanic features. We will see, however, that the flow in the heart can not be fully described without considering its electrophysiology and elastomechanics as well as the interaction with the systemic and pulmonary circulations with which it is strongly connected. Biologically, the human heart is similar to that of all warm-blooded mammals and it satisfies the same allometric laws. Since the Paleolithic Age, however, humans have improved their living conditions, have modified the environment to satisfy their needs and, more recently, have developed advanced medical knowledge which has allowed triple the number of heartbeats with respect to other mammals. In the last century, effective diagnostic tools, reliable surgical procedures and prosthetic devices have been developed and refined leading to substantial progress in cardiology and heart surgery with routine clinical practice which nowadays cures many disorders, once lethal. Pulse duplicators have been built to reproduce the pulsatile flow and ‘blood analogues’, have been realized. Heart phantoms, can attain deformations similar to the real heart although the active contraction and the tissue anisotropy still can not be replicated. Numerical models have also become a viable alternative for cardiovascular research: they do not suffer from limitations of material properties and device technologies, thus making possible the realization of truly digital twins. Unfortunately, a high-fidelity model for the whole heart consists of a system of coupled, nonlinear partial differential equations with a number of degrees of freedom of the order of a billion and computational costs become the bottleneck. An additional challenge comes from the inherent human variability and the uncertainty of the heart parameters whose statistical assessment requires a campaign of simulations rather than a single deterministic calculation; reduced and surrogate models can be employed to alleviate the huge computational burden and all possibilities are currently being pursued. In the era of big data and artificial intelligence, cardiovascular research is also advancing by exploiting the latest technologies: equation-based augmented reality, virtual surgery and computational prediction of disease progression are just a few examples among many that will become standard practice in the forthcoming years.

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Section: Heart Modelsmentioning

confidence: 99%

Electro-fluid-mechanics of the heart

Verzicco

2022

J. Fluid Mech.

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“…This enables active adjustments to pressure waveforms and variations in compliance. In another MCL setup with Windkessel chambers, they tested descending aortas 21 and Dacron aortic grafts 38 , 39 in separate studies to examine diameter‐based compliance in different HRs with precise pressure waveforms.…”

Section: Discussionmentioning

confidence: 99%

An active approach of pressure waveform matching for stress‐based testing of arteries

et al. 2021

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Background Arterial compliance assists the cardiovascular system with three key roles: (i) storing up to 50% of the stroke volume; (ii) ensuring blood flow during diastole; (iii) dampening pressure oscillations through arterial distension. In mock circulation loops (MCLs), arterial compliance was simulated either with membrane, spring, or Windkessel chambers. Although they have been shown to be suitable for cardiac device testing, their passive behavior can limit stress‐based testing of arteries. Here we present an active compliance chamber with a feedback control of variable compliance as part of an MCL designed for biomechanical evaluation of arteries under physiological waveforms. Materials and Methods The chamber encloses a piston that changes the volume via a cascaded controller when there is a difference between the real‐time pressure and the physiological reference pressure with the aim to equilibrate both pressures. Results The experimental results showed repeatable physiological waveforms of aortic pressure in health (80–120 mm Hg), systemic hypertension (90–153 mm Hg), and heart failure reduced ejection fraction (78–108 mm Hg). Statistical validation (n = 20) of the function of the chamber is presented against compared raw data. Conclusion We demonstrate that the active compliance chamber can track the actual pressure of the MCL and balance it in real time (every millisecond) with the reference values in order to shape the given pressure waveform. The active compliance chamber is an advanced tool for MCL applications for biomechanical examination of stented arteries and for preclinical evaluation of vascular implants.

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“…These properties are known to be time-dependent and were not measured due to the lack of a suggested method by the ISO 7198 standard. However, a review of the literature indicated that stress relaxation and viscoelastic recovery are meaningful, as demonstrated by Amabili et al [58], who underscored the significance of cyclic axisymmetric diameter alterations acquired under physiological pulsatile conditions. Studies have shown that Dacron grafts are noticeably stiffer around their circumference than the aortic vessels they replace, resulting in a significant mechanical mismatch between the grafts and the native tissue.…”

Section: Tensile Properties Of Films and Tubesmentioning

confidence: 99%

A Comparison of Three-Layer and Single-Layer Small Vascular Grafts Manufactured via the Roto-Evaporation Method

Zumbardo-Bacelis,

Peponi,

Vargas-Coronado

et al. 2024

Polymers

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This study used the roto-evaporation technique to engineer a 6 mm three-layer polyurethane vascular graft (TVG) that mimics the architecture of human coronary artery native vessels. Two segmented polyurethanes were synthesized using lysine (SPUUK) and ascorbic acid (SPUAA), and the resulting materials were used to create the intima and adventitia layers, respectively. In contrast, the media layer of the TVG was composed of a commercially available polyurethane, Pearlbond 703 EXP. For comparison purposes, single-layer vascular grafts (SVGs) from individual polyurethanes and a polyurethane blend (MVG) were made and tested similarly and evaluated according to the ISO 7198 standard. The TVG exhibited the highest circumferential tensile strength and longitudinal forces compared to single-layer vascular grafts of lower thicknesses made from the same polyurethanes. The TVG also showed higher suture and burst strength values than native vessels. The TVG withstood up to 2087 ± 139 mmHg and exhibited a compliance of 0.15 ± 0.1%/100 mmHg, while SPUUK SVGs showed a compliance of 5.21 ± 1.29%/100 mmHg, akin to coronary arteries but superior to the saphenous vein. An indirect cytocompatibility test using the MDA-MB-231 cell line showed 90 to 100% viability for all polyurethanes, surpassing the minimum 70% threshold needed for biomaterials deemed cytocompatibility. Despite the non-cytotoxic nature of the polyurethane extracts when grown directly on the surface, they displayed poor fibroblast adhesion, except for SPUUK. All vascular grafts showed hemolysis values under the permissible limit of 5% and longer coagulation times.

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Identification of viscoelastic properties of Dacron aortic grafts subjected to physiological pulsatile flow

Cited by 22 publications

References 33 publications

Electro-fluid-mechanics of the heart

Electro-fluid-mechanics of the heart

An active approach of pressure waveform matching for stress‐based testing of arteries

A Comparison of Three-Layer and Single-Layer Small Vascular Grafts Manufactured via the Roto-Evaporation Method

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