Finite Element Simulation of Opening Angle Response of Porcine Aortas Using Layer Specific GAG Distributions in One and Two Layered Solid Matrices.

Purpose: Recent studies have identified an effect of glycosaminoglycans (GAG) on residual stresses in the aorta, underscoring the need to better understand their biomechanical roles.

Methods: Aortic ring models for each of the ascending, arch and descending thoracic regions of the porcine thoracic aorta were created in FEBioStudio, using a framework that incorporates the Donnan osmotic swelling in a porous solid matrix. The distribution of fixed charge densities (FCD) through the thickness of the tissue was prescribed as calculated from experimentally quantified sulfated GAG mural distributions.

Glycosaminoglycans modulate compressive stiffness and circumferential residual stress in the porcine thoracic aorta.

The mechanical properties of the aorta are influenced by the extracellular matrix, a network mainly comprised of fibers and glycosaminoglycans (GAG). In this work, we demonstrate that GAG contribute to the opening angle (a marker of circumferential residual stresses) in intact and glycated aortic tissue. Enzymatic GAG depletion was associated with a decrease in the opening angle, by approximately 25% (p = 0.

Intramural Distributions of GAGs and Collagen vs. Opening Angle of the Intact Porcine Aortic Wall.

The heterogeneity and contribution of collagen and elastin to residual stresses have been thoroughly studied, but more recently, glycosaminoglycans (GAGs) also emerged as potential regulators. In this study, the opening angle of aortic rings (an indicator of circumferential residual stresses) and the mural distributions of sulfated GAGs (sGAG), collagen, and elastin were quantified in the ascending, aortic arch and descending thoracic regions of 5- to 6-month-old pigs. The opening angle correlated positively with the aortic ring's mean radius and thickness, with good and moderate correlations respectively.

The Contribution of Glycosaminoglycans/Proteoglycans to Aortic Mechanics in Health and Disease: A Critical Review.

While elastin and collagen have received a lot of attention as major contributors to aortic biomechanics, glycosaminoglycans (GAGs) and proteoglycans (PGs) recently emerged as additional key players whose roles must be better elucidated if one hopes to predict aortic ruptures caused by aneurysms and dissections more reliably. GAGs are highly negatively charged polysaccharide molecules that exist in the extracellular matrix (ECM) of the arterial wall. In this critical review, we summarize the current understanding of the contributions of GAGs/PGs to the biomechanics of the normal aortic wall, as well as in the case of aortic diseases such as aneurysms and dissections.

Intramural Glycosaminoglycans Distribution vs. Residual Stress in Porcine Ascending Aorta: a Computational Study.

In this computational modelling work, we explored the mechanical roles that various glycosaminoglycans (GAGs) distributions may play in the porcine ascending aortic wall, by studying both the transmural residual stress as well as the opening angle in aortic ring samples. A finite element (FE) model was first constructed and validated against published data generated from rodent aortic rings. The FE model was then used to simulate the response of porcine ascending aortic rings with different GAG distributions prescribed through the wall of the aorta.

A Computational Study on Deformed Bioprosthetic Valve Geometries: Clinically Relevant Valve Performance Metrics.

Transcatheter aortic valves (TAV) are symmetrically designed, but they are often not deployed inside cylindrical conduits with circular cross-sectional areas. Many TAV patients have heavily calcified aortic valves, which often result in deformed prosthesis geometries after deployment. We investigated the effects of deformed valve annulus configurations on a surgical bioprosthetic valve as a model for TAV.

Cam FAI and Smaller Neck Angles Increase Subchondral Bone Stresses During Squatting: A Finite Element Analysis.

Background: Individuals with a cam deformity and a decreased (varus) femoral neck-shaft angle may be predisposed to symptomatic femoroacetabular impingement (FAI). However, it is unclear what combined effects the cam deformity and neck angle have on acetabular cartilage and subchondral bone stresses during an impinging squat motion. We therefore used finite element analysis to examine the combined effects of cam morphology and femoral neck-shaft angle on acetabular cartilage and subchondral bone stresses during squatting, examining the differences in stress characteristics between symptomatic and asymptomatic individuals with cam deformities and individuals without cam deformities and no hip pain.

Material characterization of cardiovascular biomaterials using an inverse finite-element method and an explicit solver.

The ability to accurately model soft tissue behavior, such as that of heart valve tissue, is essential for developing reliable numerical simulations and determining patient-specific care options. Although several material models can predict soft tissue behavior, complications may arise when these models are implemented into finite element (FE) programs, due to the addition of an arbitrary penalty parameter for numerically enforcing material incompressibility. Herein, an inverse methodology was developed in MATLAB to use previously published stress-strain data from experimental planar equibiaxial testing of five biomaterials used in heart valve cusp replacements, in conjunction with commercial explicit FE solver LS-DYNA, to optimize the material parameters and the penalty parameter for an anisotropic hyperelastic strain energy function.

Investigation of raphe function in the bicuspid aortic valve and its influence on clinical criteria-A patient-specific finite element study.

The aortic valve is normally composed of 3 cusps. In one common lesion, 2 cusps are fused together. The conjoined area of the fused cusps is termed raphe.

UROKIN: A Software to Enhance Our Understanding of Urogenital Motion.

Transperineal ultrasound (TPUS) allows for objective quantification of mid-sagittal urogenital mechanics, yet current practice omits dynamic motion information in favor of analyzing only a rest and a peak motion frame. This work details the development of UROKIN, a semi-automated software which calculates kinematic curves of urogenital landmark motion. A proof of concept analysis, performed using UROKIN on TPUS video recorded from 20 women with and 10 women without stress urinary incontinence (SUI) performing maximum voluntary contraction of the pelvic floor muscles.

Experimental Investigation of Left Ventricular Flow Patterns After Percutaneous Edge-to-Edge Mitral Valve Repair.

Mitral valve percutaneous edge-to-edge repair (PEtER) is a viable solution in high-risk patients with severe symptomatic mitral regurgitation. However, the generated double-orifice configuration poses challenges for the evaluation of the hemodynamic performance of the mitral valve and may alter flow patterns in the left ventricle (LV) during diastole. This in vitro study aims to evaluate the hemodynamic modifications following a simulated PEtER.

Aortic Valve Cusp Coaptation Surface Area Using 3-Dimensional Transesophageal Echocardiography Correlates with Severity of Aortic Valve Insufficiency.

Objective: The aim of this study was to test both in humans and using finite element (FE) aortic valve (AV) models whether the coaptation surface area (CoapSA) correlates with aortic insufficiency (AI) severity due to dilated aortic roots to determine the validity and utility of 3-dimensional transesophageal echocardiographic-measured CoapSA.

Design: Two-pronged, clinical and computational approach.

Setting: Single university hospital.

Increased Hip Stresses Resulting From a Cam Deformity and Decreased Femoral Neck-Shaft Angle During Level Walking.

Background: It is still unclear why many individuals with a cam morphology of the hip do not experience pain. It was recently reported that a decreased femoral neck-shaft angle may also be associated with hip symptoms. However, the effects that different femoral neck-shaft angles have on hip stresses in symptomatic and asymptomatic individuals with cam morphology remain unclear.

Planar biaxial testing of heart valve cusp replacement biomaterials: Experiments, theory and material constants.

Objectives: Aortic valve (AV) repair has become an attractive option to correct aortic insufficiency. Yet, cusp reconstruction with various cusp replacement materials has been associated with greater long-term repair failures, and it is still unknown how such materials mechanically compare with native leaflets. We used planar biaxial testing to characterize six clinically relevant cusp replacement materials, along with native porcine AV leaflets, to ascertain which materials would be best suited for valve repair.

Hip Joint Stresses Due to Cam-Type Femoroacetabular Impingement: A Systematic Review of Finite Element Simulations.

Background: The cam deformity causes the anterosuperior femoral head to obstruct with the acetabulum, resulting in femoroacetabular impingement (FAI) and elevated risks of early osteoarthritis. Several finite element models have simulated adverse loading conditions due to cam FAI, to better understand the relationship between mechanical stresses and cartilage degeneration. Our purpose was to conduct a systematic review and examine the previous finite element models and simulations that examined hip joint stresses due to cam FAI.

Impact of aortic annular geometry on aortic valve insufficiency: Insights from a preclinical, ex vivo, porcine model.

Objectives: We sought to create a model of aortic insufficiency in a left heart simulator combined with 3-dimensional echocardiography and finite element modeling of the aortic valve. We examined the effects of aortic root geometry alteration on aortic insufficiency.

Methods: Porcine aortic roots were analyzed on a left heart simulator before (control, n = 8) and after intervention (n = 8).

Effect of Aortic Annulus Size and Prosthesis Oversizing on the Hemodynamics and Leaflet Bending Stress of Transcatheter Valves: An In Vitro Study.

Background: There are few data about the patient- and prosthesis-related factors influencing the hemodynamics of transcatheter heart valves (THVs). The objective of this in vitro study was to assess the effect of aortic annulus size and prosthesis oversizing on the valve hemodynamics and estimated leaflet bending stress of the Edwards SAPIEN balloon-expandable THV (Edwards Lifesciences, Irvine, CA).

Methods: The effective orifice area (EOA) of the 23-mm and 26-mm SAPIEN THVs were measured by Doppler echocardiography in a pulse duplicator under the following experimental conditions: (1) stroke volume of 20, 30, 50, 70, and 80 mL and (2) aortic annulus size of 19, 20, 21, and 22 mm for the 23-mm SAPIEN and 22, 23, and 24, and 25 mm for the 26-mm SAPIEN.

Finding the ideal biomaterial for aortic valve repair with ex vivo porcine left heart simulator and finite element modeling.

Objectives: Aortic valve (AV) repair (AVr) has become an attractive alternative to AV replacement for the correction of aortic insufficiency; however, little clinical evidence exists in determining which biomaterial at AVr would be optimal. Cusp replacement in AVr has been associated with increased long-term AVr failure. We measured the hemodynamic and biomaterial properties using an ex vivo porcine AVr model with clinically relevant biomaterials and generated a finite element model to ascertain which materials would be best suited for valve repair.

Finite element analysis to model complex mitral valve repair.

Although finite element analysis has been used to model simple mitral repair, it has not been used to model complex repair. A virtual mitral valve model was successful in simulating normal and abnormal valve function. Models were then developed to simulate an edge-to-edge repair and repair employing quadrangular resection.

An in vitro model of aortic stenosis for the assessment of transcatheter aortic valve implantation.

A significant number of elderly patients with severe symptomatic aortic stenosis are denied surgical aortic valve replacement (SAVR) because of high operative risk. Transcatheter aortic valve implantation (TAVI) has emerged as a valid alternative to SAVR in these patients. One of the main characteristics of TAVI, when compared to SAVR, is that the diseased native aortic valve remains in place.

A metric for the stiffness of calcified aortic valves using a combined computational and experimental approach.

Calcific aortic valve disease is the most common heart valve disease. It is associated with a significant increase in cardiovascular morbidity and mortality and independently increases the cardiovascular risk. It is then important to develop parameters that can estimate the stiffness of the valve.

Measuring aortic valve coaptation surface area using three-dimensional transesophageal echocardiography.

Background: As aortic valve (AV) repairs become more sophisticated, surgeons need increasingly detailed information about the structure and function of this valve. Unlike two-dimensional transesophageal echocardiography (2D-TEE), using three-dimensional (3D)-TEE makes it possible to image the entire AV. We hypothesized that measuring coaptation surface area (CoapSA) would be feasible and reproducible, and CoapSA would decrease in patients with aortic insufficiency.

Mechanical characterization of human aortas from pressurization testing and a paradigm shift for circumferential residual stress.

Material properties needed for accurate stress analysis of the human aorta are still incompletely known, especially as many reports have ignored the presence of residual stresses in the aortic wall. To contribute new material regarding these issues, we carried out measurements and pressurization testing on ascending, thoracic and abdominal aortic samples from 24 human subjects aged 38-77 years, and evaluated the opening angle describing the circumferential residual stress level present in the aorta. We determined material constants for the aorta by gender, anatomic location and age group, according to a simple phenomenological constitutive model.

Modeling leaflet correction techniques in aortic valve repair: A finite element study.

In aortic valve sparing surgery, cusp prolapse is a common cause of residual aortic insufficiency. To correct cusp pathology, native leaflets of the valve frequently require adjustment which can be performed using a variety of described correction techniques, such as central or commissural plication, or resuspension of the leaflet free margin. The practical question then arises of determining which surgical technique provides the best valve performance with the most physiologic coaptation.