Clark Meyer - Academia.edu (original) (raw)

Papers by Clark Meyer

Published article titled, mechanobiological model of arterial growth and remodeling.

Scientific Reports, 2021

Numerical simulations of coupled hemodynamics and leukocyte transport and adhesion inside coronar... more Numerical simulations of coupled hemodynamics and leukocyte transport and adhesion inside coronary arteries have been performed. Realistic artery geometries have been obtained for a set of four patients from intravascular ultrasound and angiography images. The numerical model computes unsteady three-dimensional blood hemodynamics and leukocyte concentration in the blood. Wall-shear stress dependent leukocyte adhesion is also computed through agent-based modeling rules, fully coupled to the hemodynamics and leukocyte transport. Numerical results have a good correlation with clinical data. Regions where high adhesion is predicted by the simulations coincide to a good approximation with artery segments presenting plaque increase, as documented by clinical data from baseline and six-month follow-up exam of the same artery. In addition, it is observed that the artery geometry and, in particular, the tortuosity of the centerline are a primary factor in determining the spatial distribution...

INTRODUCTION Atherosclerosis is the leading cause of death in developed countries. Minimally inva... more INTRODUCTION Atherosclerosis is the leading cause of death in developed countries. Minimally invasive procedures utilizing catheter-based delivery systems are promising therapies, but those employing endovascular prosthetics such as stents, can initiate a cascade of events resulting in neointimal hyperplasia and restenosis. The presence of a relatively rigid and oversized (at least 10% larger than the healthy lumen size during systole) stent induces significant stress concentrations in the vessel wall. It is hypothesized that these stress concentrations play a significant role in the activation of processes culminating in restenosis. With the impetus to reduce morbidity and mortality produced by stent implantation, the finite element method was used to quantify how the stress environment in the artery is altered upon stent implantation. The specific aim of this work was to identify important stent design parameters and examine their influence on the stress distribution in the artery...

Tissue Engineering Part C: Methods, 2019

Over the past two decades, the increase in prevalence of cardiovascular diseases and the limited ... more Over the past two decades, the increase in prevalence of cardiovascular diseases and the limited availability of autologous blood vessels and saphenous vein grafts have motivated the development of tissue-engineered vascular grafts (TEVGs). However, compliance mismatch and poor mechanical properties of the TEVGs remain as two major issues that need to be addressed. Researchers have investigated the role of various culture conditions and mechanical conditioning in deposition and orientation of collagen fibers, which are the key structural components in the vascular wall; however, the intrinsic complexity of mechanobiological interactions demands implementing new engineering approaches that allow researchers to investigate various scenarios more efficiently. In this study, we utilized a coupled agent-based finite element analysis (AB-FEA) modeling approach to study the effect of various loading modes (uniaxial, biaxial, and equibiaxial), boundary conditions, stretch magnitudes, and growth factor concentrations on growth and remodeling of smooth muscle cellpopulated TEVGs, with specific focus on collagen deposition and orientation. Our simulations (12 weeks of culture) showed that biaxial cyclic loading (and not uniaxial or equibiaxial) leads to alignment of collagen fibers in the physiological directions. Moreover, axial boundary conditions of the TEVG act as determinants of fiber orientations. Decreasing the serum concentration, from 10% to 5% or 1%, significantly decreased the growth and remodeling speed, but only affected the fiber orientation in the 1% serum case. In conclusion, in silico tissue engineering has the potential to evolve the future of tissue engineering, as it will allow researchers to conceptualize various interactions and investigate numerous scenarios with great speed. In this study, we were able to predict the orientation of collagen fibers in TEVGs using a coupled AB-FEA model in less than 8 h.

Journal of conservative dentistry : JCD

The purpose of this study was to compare the stress distributions in the teeth treated through mi... more The purpose of this study was to compare the stress distributions in the teeth treated through minimally invasive access (MIA) designs to those of the teeth treated through traditional straight-line access and their relationship to the final restoration using three-dimensional finite element analysis (FEA). Four FEA models of an extracted mandibular first molar were constructed. An intact model served as the control, whereas the other three were prepared with either an MIA or traditional straight-line access. Simulated composite access fillings with or without a simulated gold crown were applied to the models, followed by application of an occlusal load of 100 N. Von Mises stresses in the teeth were then calculated and analyzed. Stress values within the dentin for baseline, MIA with composite filling, MIA with composite filling and crown, and traditional access with composite filling and crown were 10.14 MPa, 6.98 MPa, 11.79 MPa, and 16.81 MPa, respectively. Higher stress values ind...

The Cleft palate-craniofacial journal : official publication of the American Cleft Palate-Craniofacial Association, 2018

Sculpted physical models and castings of the anatomy of cleft lip and palate are used for parent,... more Sculpted physical models and castings of the anatomy of cleft lip and palate are used for parent, patient, and trainee education of cleft lip and palate conditions. In this study, we designed a suite of digital 3-dimensional (3D) models of cleft lip and palate anatomy with additive manufacturing techniques for patient education. CT scans of subjects with isolated cleft palate, unilateral and bilateral cleft lip and palate, and a control were obtained. Soft tissue and bony structures were segmented and reconstructed into digital 3D models. The oral soft tissues overlying the cleft palate were manually molded with silicone putty and scanned using CT to create digital 3D models. These were then combined with the original model to integrate with segmentable soft tissues. Bone and soft tissues were 3D printed in different materials to mimic the rigidity/softness of the relevant anatomy. These models were presented to the parents/patients at our craniofacial clinic. Visual analog scale (V...

Biomechanics and Modeling in Mechanobiology, 2017

A coupled agent-based model (ABM) and finite element analysis (FEA) computational framework is de... more A coupled agent-based model (ABM) and finite element analysis (FEA) computational framework is developed to study the interplay of bio-chemo-mechanical factors in blood vessels and their role in maintaining homeostasis. The agent-based model implements the power of REPAST Simphony libraries and adapts its environment for biological simulations. Coupling a continuum-level model (FEA) to a cellular-level model (ABM) has enabled this computational framework to capture the response of blood vessels to increased or decreased levels of growth factors, proteases and other signaling molecules (on the micro scale) as well as altered blood pressure. Performance of the model is assessed by simulating porcine left anterior descending artery under normotensive conditions and transient increases in blood pressure and by analyzing sensitivity of the model to variations in the rule parameters of the ABM. These simulations proved that the model is stable under normotensive conditions and can recover from transient increases in blood pressure. Sensitivity studies revealed that the model is most sensitive to variations in the concentration of growth factors that affect cellular proliferation and regulate extracellular matrix composition (mainly collagen).

Clinical and Experimental Dental Research, 2016

Recent literature indicates that the long-term success of dental implants is, in part, attributed... more Recent literature indicates that the long-term success of dental implants is, in part, attributed to how dental crowns are attached to their associated implants. The commonly utilized method for crown attachmentcementation, has been criticized because of recent links between residual cement and peri-implant disease. Residual cement extrusion from crown-abutment margins post-crown seating is a growing concern. This study aimed at (1) identifying key abutment features, which would improve dental cement flow characteristics, and (2) understanding how these features would impact the mechanical stability of the abutment under functional loads. Computational fluid dynamic modeling was used to evaluate cement flow in novel abutment geometries. These models were then evaluated using 3D-printed surrogate models. Finite element analysis also provided an understanding of how the mechanical stability of these abutments was altered after key features were incorporated into the geometry. The findings demonstrated that the key features involved in improved venting of the abutment during crown seating were (1) addition of vents, (2) diameter of the vents, (3) location of the vents, (4) addition of a plastic screw insert, and (5) thickness of the abutment wall. This study culminated in a novel design for a vented abutment consisting of 8 vents located radially around the abutment neck-margin plus a plastic insert to guide the cement during seating and provide retrievability to the abutment system.Venting of the dental abutment has been shown to decrease the risk of undetected residual dental cement post-cement-retained crown seating. This article will utilize a finite element analysis approach toward optimizing dental abutment designs for improved dental cement venting. Features investigated include (1) addition of vents, (2) diameter of vents, (3) location of vents, (4) addition of plastic screw insert, and (5) thickness of abutment wall.

ASME 2009 Summer Bioengineering Conference, Parts A and B, 2009

Abdominal aortic aneurysm (AAA) rupture occurs when wall stress exceeds wall strength. Endografts... more Abdominal aortic aneurysm (AAA) rupture occurs when wall stress exceeds wall strength. Endografts aim to prevent rupture by reducing wall stress. However, after implantation, AAA may shrink, grow, or stabilize in diameter, even in the absence of apparent flow into the sac or pressurization. This may result in graft failure through loss of seal, kinking, or component separation. Insight from models of treated AAA could provide insight into treatment methods/limitations and for device design. The nature of the stress reduction in AAA by endograft treatment was modeled using FEM in two patients followed at three time points each (pre-treatment, early follow-up, and late follow-up) — one with a “stable” aneurysm and one with a “shrinking” aneurysm.Copyright © 2009 by ASME

Medical engineering & physics, 2014

This work proposes an in vitro tensile testing protocol that is able to characterize abdominal ao... more This work proposes an in vitro tensile testing protocol that is able to characterize abdominal aortic (AA) analogues under physiologically inspired mechanical loadings. Kinematic parameters are defined in agreement with in vivo measurements of aortic dynamics. A specific focus is given to the choice of the applied loading rates, deriving from the knowledge of aortic Peterson modulus and blood pressure variations from diastolic to systolic instants. The influence of physiological elongation rates has been tested on both porcine AAs and a thermoplastic polyurethane (TPU) material used to elaborate AA analogues. The diastolic and systolic elongation rates estimates vary between orders of magnitude O(10(-2)) and O(10(-1))s(-1). Negligible differences are obtained when comparing stress-elongation responses between both physiological elongation rates. In contrast, a noticeable stiffening of the TPU mechanical response is observed compared to that obtained under the common low traction rat...

Frontiers in physiology, 2012

Effects of hypertension on arteries and arterioles often manifest first as a thickened wall, with... more Effects of hypertension on arteries and arterioles often manifest first as a thickened wall, with associated changes in passive material properties (e.g., stiffness) or function (e.g., cellular phenotype, synthesis and removal rates, and vasomotor responsiveness). Less is known, however, regarding the relative evolution of such changes in vessels from different vascular beds. We used an aortic coarctation model of hypertension in the mini-pig to elucidate spatiotemporal changes in geometry and wall composition (including layer-specific thicknesses as well as presence of collagen, elastin, smooth muscle, endothelial, macrophage, and hematopoietic cells) in three different arterial beds, specifically aortic, cerebral, and coronary, and vasodilator function in two different arteriolar beds, the cerebral and coronary. Marked geometric and structural changes occurred in the thoracic aorta and left anterior descending coronary artery within 2 weeks of the establishment of hypertension and...

ASME 2007 Summer Bioengineering Conference, 2007

ABSTRACT The implantation of a balloon expandable stent induces chronic stent-induced stresses on... more ABSTRACT The implantation of a balloon expandable stent induces chronic stent-induced stresses on the artery wall. These highly non-physiologic stresses can provoke inflammation and smooth muscle cell proliferation. Ultimately, this cascade of events leads to restenosis, or the development of a new blockage in the stented artery. Since the initial human implantation of balloon expandable stents, technological advances in stent design, material properties, and deliverability have expanded the application and success rate of the procedure. More recently, anti-restenotic strategies such as drug-eluting stents have aimed to counteract the restenosis process. While clinical trials have demonstrated the success of drug eluting stents in coronary arteries [1], risk of late thrombosis [2] and failure to prevent restenosis in peripheral arteries [3] has limited this technology. A further investigation into the artery wall stresses induced by stent implantation, and the pursuit of strategies to minimize them could reduce the restenosis rates for both bare metal and drug-eluting stents.

Wiley Encyclopedia of Biomedical Engineering, 2006

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Mechanics of Biological Tissue, 2006

Medical Engineering & Physics, 2013

An in vitro dynamics set-up of the flow in a compliant abdominal aortic aneurysm (AAA) model with... more An in vitro dynamics set-up of the flow in a compliant abdominal aortic aneurysm (AAA) model with an anterior posterior asymmetry, aorto-iliac bifurcation, and physiological inlet flow rate and outlet pressure waveforms was developed. The aims were first to show that the structural mechanical behavior of the used material to mimic the AAA wall was similar to this of patients with AAA and then to study the influence of the aorto-iliac bifurcation presence and to study the influence of the imbalanced flow rate in the iliac branches on the AAA flow field. 3D visualizations, never performed in the literature, have clearly put into evidence the development of a vortex ring generated at the AAA proximal neck during the decelerating phase of flow rate, which detaches and progresses downstream during the cardiac cycle, impinges on the anterior wall in the distal AAA region, breaks up, and separates into two vortices of which one rolls on upstream along the anterior wall. 2D particle image velocimetry measurements, swirling strength and enstrophy calculations allowed quantification of the vorticity, vortex trajectory and energy for the different geometrical and hydrodynamical conditions. The main results show that the instant and the intensity of the vortex ring impingement depend on the presence of the aorto-iliac bifurcation, with higher intensity, by about 90%, for an AAA without bifurcation. The imbalance of the flow rates into the iliac branches induces different propagation velocities of the vortex ring and lowers the intensity of the vortex impact by about 60%. The potential influence of the AAA dynamics is discussed in terms of AAA remodeling and rupture.

Journal of Vascular Surgery, 2013

Journal of Biomechanics, 2006

Coronary bypass grafting is widely applied in cardiac surgery aiming at rehabilitating pathologic... more Coronary bypass grafting is widely applied in cardiac surgery aiming at rehabilitating pathological arteries. This has led to the development of composite arterial coronary grafts (CACGs) in the shape of Y, T and H or sequential graft. It has been proven that the best method for good surgical results is to anastomose the left internal thoracic artery (LITA) to left anterior descending (LAD). Thus, it is of paramount importance for the flow in the LAD to remain undisturbed and uniformly distributed [1]. In this study, two idealized geometric configurations of CACGs, with shapes of T and H-grafts, are considered [2]. The flow is assumed to be unsteady and laminar and the fluid incompressible and Newtonian. 0he pulsatile nature of blood is also investigated by comparing a pure sinusoidal with a physiological flow. The host artery is characterized by a constriction of 25%, 50% and 75%. The 3-D Navier-Stokes equations for unsteady flow coupled with the continuity equation are solved numerically using a CFD model based on finite volumes and the SIMPLEST algorithm [3]. The results focus on the wall shear-stress (WSS) distribution and the secondary flow in both host and graft arteries. At peak systole, the velocity profile shows wide regions of recirculation and stagnation flow. Secondary vortices and oscillating WSS are strongly associated with vessel constriction and flow rates imposed at the inlet of the CACG. The time-varying physiological flow rate through the CACGs produces a more disturbed flow field than a pure sinusoidal flow, especially at peak cardiac systole.