bluuebunny/crossref_metadata_2025 huggingface dataset:
Biomechanical Implications of the Bicuspid Aortic Valve: A Finite Element Study From In Vivo Data
Authors: Conti Carlo A. , Votta Emiliano , Della Corte Alessandro , Del Viscovo Luca , Bancone Ciro , Cotrufo Maurizio , Redaelli Alberto
Published: July 2013

The bicuspid aortic valve (BAV) is the second most common congenital cardiac malformation, with an estimated prevalence of 0.9% to 2% in the general population [1]. BAV is widely recognized as a frequent cause of aortic stenosis and/or aortic regurgitation and as a risk factor for the early development of aortic aneurysms [2].
The Effect of Mesh Refinement on the Predictions of Finite Element Models of Spine
Authors: Ayturk Ugur M. , Puttlitz Christian M.
Published: July 2013

Mesh refinement is among the verification steps crucial for developing finite element models [1]. However, it is often omitted during the development of spine models in spite of its necessity due to the geometric complexity and heterogeneity of human spine. Few studies have demonstrated convergence of certain parameter predictions [2], but no extensive study has been done on the convergence behavior of individual components and tissues in spine. In order to investigate this, we generated finite element models of the L4/L5 functional spinal unit (FSU) with varying mesh resolutions, and tested the effect of refinement under complete nonlinear loading ranges.
Accounting for Differences Between Echo Particle Image Velocimetry (EPIV) and Pulse Wave Doppler (PWD) Velocity Measurements
Authors: Walker Andrew M. , Johnston Clifton R. , Dobson Gary M.
Published: July 2013

Currently, an echo particle image velocimetry (ePIV) system for the investigation of in vivo blood flow and shear stress is under development at the University of Calgary. To date, encouraging preliminary results have been obtained when comparing ePIV derived velocities to analytical solutions. However, large discrepancies were noted between our steady state ePIV derived velocities and velocities measured using pulse wave Doppler (PWD). Ultrasound beam thickness, off axis centerline measurements and PWD angle of interrogation likely account for the differences observed.
Non-Thermal Atmospheric Pressure Dielectric Barrier Discharge Plasma Enhances Endothelial Cell Proliferation via Fibroblast Growth Factor-2 Release
Authors: Kalghatgi Sameer , Fridman Alexander , Friedman Gary , Clyne Alisa Morss
Published: July 2013

Cold atmospheric pressure plasma is currently being investigated for a wide range of clinical applications, including skin sterilization, blood coagulation [1, 2], malignant cell apoptosis [1], and wound healing [1]. However, the effect of non-thermal plasma on the vasculature is unclear. Blood vessels are affected during plasma treatment of all tissues, and vessels themselves may be an important potential target for clinical plasma therapy.
Tissue Effects of Q-Switched, High Power, Visible Laser Irradiation: In Vitro Experiments and Simulation
Authors: Elkhalil Hossam , Akkin Taner , Barocas Victor H. , Bischof John C.
Published: July 2013

Benign prostatic hyperplasia (BPH) is one of the most common disorders and the most common cause of lower urinary tract symptoms (LUTS) in elderly men [1]. Transurethral resection of the prostate (TURP) is considered the gold standard treatment; however, laser prostatectomy has several advantages with regard to reduced catheterization and morbidity particularly in high-risk patients [2]. Of the many lasers that can be used in the laser prostatectomy, the GreenLight potassium-titanyl-phosphate (KTP) laser is one of the most commonly used [3]. The optimum outcome of this laser procedure is ablation with minimal or no coagulation. Our objective was to experimentally and theoretically characterize the KTP laser-tissue interactions in order to understand the laser and tissue parameters that lead to an optimal outcome.
Subject-Specific Evaluation of Patellofemoral Joint Function During Stair Ascent
Authors: Akbarshahi Massoud , Fernandez Justin W. , Schache Anthony , Pandy Marcus G.
Published: July 2013

Recent interest in better understanding the biomechanical behavior of the patellofemoral joint is driven, in part, by the frequency with which patellofemoral osteoarthritis is reported to occur in the general population. Abnormal joint-contact stress is believed to be one of the possible causes of cartilage degeneration and anterior knee pain [1]. A number of literature studies suggest that stair ascent is one of the most demanding daily activities in relation to patellofemoral joint loading [2]. Accurate measurement of in vivo kinematics is essential for a thorough understanding of patellofemoral function during weight-bearing activity [3]. In this study, an innovative experimental setup involving two synchronized single-plane X-ray fluoroscopy units, 3D motion capture, portable force plates, computed muscle forces and MRI-derived bone geometries were integrated to evaluate patellofemoral joint function in four healthy subjects during stair walking. Our specific aim was to quantify medial and lateral patellofemoral joint loading, joint pressure distribution, and cartilage pressure maps on a subject-specific basis.
Parallel Adaptive Computation of Blood Flow in a 3D “Whole” Body Model
Authors: Zhou Min , Figueroa C. Alberto , Kim Hyun Jin , Taylor Charles A. , Sahni Onkar , Jansen Kenneth E.
Published: July 2013

Due to the systemic nature of the response of the human body to vascular trauma, accurate simulation may require the consideration of larger portions of the vasculature than have previously been modeled. A patient-specific 3D model, composed of 78 arteries extending from the neck to the toes, was constructed to meaningfully represent many of the major arteries in the systemic circulation. Recently developed boundary conditions are applied at the 78 outlets to realistically represent the remaining vasculature not resolved by the 3D domain. The pulsatile blood flow simulation is started on an initial boundary layer mesh with a few million elements which is then adapted to a higher resolution by applying solution-based adaptivity. The effects of the mesh resolution on flow features are studied. Pressure, velocity and wall shear stress results will be presented.
Using MR Imaging and X-Ray Fluoroscopy to Quantify the Effects of Soft-Tissue Artifact on Measurement of Knee-Joint Kinematics
Authors: Akbarshahi Massoud , Fernandez Justin W. , Schache Anthony , Baker Richard , Pandy Marcus G.
Published: July 2013

The ability to accurately measure joint kinematics in vivo is of critical importance to researchers in the field of biomechanics [1]. Applications range from the quantitative evaluation of different surgical techniques, treatment methods and/or implant designs, to the development of computer-based models capable of simulating normal and pathological musculoskeletal conditions [1,2]. Currently, non-invasive marker-based three dimensional (3D) motion analysis is the most commonly used method for quantitative assessment of normal and pathological locomotion. The accuracy of this technique is influenced by movement of the soft tissues relative to the underlying bones, which causes inaccuracies in the determination of segmental anatomical coordinate systems and tracking of segmental motion. The purpose of this study was to quantify the errors in the measurement of knee-joint kinematics due solely to soft-tissue artifact (STA) in healthy subjects. To facilitate valid inter-subject comparisons of the kinematic data, relevant anatomical coordinate systems were defined using 3D bone models generated from magnetic resonance imaging (MRI).
Muscle and Contact Contributions to Inverse Dynamic Knee Loads During Gait
Authors: Fregly Benjamin J. , Lin Yi-Chung , Walter Jonathan P. , Pandy Marcus G. , Banks Scott A. , D’Lima Darryl D.
Published: July 2013

Musculoskeletal computer models capable of predicting muscle and joint contact forces accurately during human movement could facilitate the design of improved joint replacements and new clinical treatments for articular cartilage defects or movement-related disorders [1]. A primary challenge to developing such predictions is the non-uniqueness of the calculated muscle forces, often referred to as the “muscle redundancy problem” [2]. Since more muscles act on the skeleton than the number of degrees of freedom in the skeleton, an infinite number of possible muscle force solutions exist.
Controlled Cellular Growth by Superhydrophobic Microstructured Surfaces of Implantable Biodegradable Polymer Substrate
Authors: Garg Nitin , Tran Richard , Yang Jian , Moon Hyejin
Published: July 2013

Biodegradable polymers with elastomeric properties have recently received attention for their potential use in the engineering of soft tissues such as blood vessel, heart valves, cartilage, tendon, and bladder, which exhibit elastic properties [1, 2]. In this paper, microfabrication technology has been applied successfully to biodegradable polymer films to encourage cell growth in designated area. This work is presented with the final goal of fabricating implantable polymer scaffolds to produce blood capillaries in controlled manner spatially by using the concept of superhydrophobic surfaces.
Impact of Secondary Chordal Cutting on Mitral Valve Closure and Chordal Force Distribution in an Ischemic Dilated Ventricle: Engineering Insight and Clinical Implications
Authors: Padala Muralidhar , Gyoneva Lazarina I. , Yoganathan Ajit P.
Published: July 2013

The Mitral Valve (MV) is the left atrioventricular valve that controls blood flow between the left atrium and the left ventricle (Fig 1A-B). It has four main components: (i) the mitral annulus – a fibromuscular ring at the base of the left atrium and the ventricle; (ii) two collagenous planar leaflets – anterior and posterior; (iii) web of chordae tendineae – classified into primary (inserting at the free edge of the leaflet), secondary (inserting into the base of the leaflet), tertiary (inserting into the annulus); and (iv) two papillary muscles that are part of the left ventricle. Normal function of the mitral valve involves a delicate force balance between different components of the valve.
A Biomechanical Comparison of Knot-Minimizing Rotator Cuff Tendon Repair Systems
Authors: McDonald Erik , Chu Thomas , Buckley Jenni M. , Kandemir Utku , Ma C. Benjamin
Published: July 2013

Arthroscopic rotator cuff repair has become a popular alternative to more invasive open repair techniques due to quicker recovery times and lower morbidity rates [1,3,4]. In order for the tendon to heal it must be held tightly to its insertion site with surgical sutures to restore the tendon’s original footprint [1]. Recently several companies have begun to offer products decreasing the number of knots a surgeon is required to tie during a repair. Most incorporate the use of four bone anchors, one pair (medial) that are integrated with the sutures and the other (lateral) that capture the free end of the sutures. Two particular systems, specifically PushLock (Arthrex) and Versalok (DePuy Mitek) are typically used in similar configurations, but have yet to be fully analyzed in biomechanical studies. The purpose of this study was to characterize the mechanical integrity of each repair system. We used a human cadaveric model and compared gap formation, stiffness, and ultimate strength between the PushLock and Versalok systems.
Effect of Stent Design Parameters on Coronary Artery Flow
Authors: Karri Satyaprakash , Peter Stephen , Vlachos Pavlos P.
Published: July 2013

The most widely accepted modality for treating diseased arteries is the implantation of endovascular stents. Stents are metallic wireframe devices used to reopen clogged arteries. Despite their widespread use, problems persist post-implantation of these devices beginning with sub-acute thrombus formation followed by inflammation, proliferation and remodeling [1]. The specific stent design and its design parameters profoundly impact the hemodynamic environment of the stent [2], in turn affecting thrombus accumulation between struts and thus restenosis [3]. Prior research examining the hemodynamic effects of stents has been performed in simplified geometries [4] however the effects of stent design parameters such as strut thickness and crown radius of curvature or analysis in realistic geometries is generally lacking. A more thorough understanding of the effect of a stent’s geometric parameters on the arterial flow will provide insight into their long-term performance and will lead to better design.
Biomechanical Modeling of Atherosclerotic Lesions in ApoE Deficient Mice
Authors: Vengrenyuk Yuliya , Kaplan Theodore J. , Cardoso Luis , Randolph Gwendalyn J. , Weinbaum Sheldon
Published: July 2013

Cardiovascular disease remains the principal killer in the western world despite major advances in treatment of its patients [1]. It is generally accepted that sudden rupture of vulnerable plaque followed by thrombus formation underlies most cases of myocardial infarction and is responsible for more than a half of 500,000 coronary heart disease deaths every year. Although histopathological analysis of postmortem specimens have provided important data on histological features of ruptured human plaques, there is an urgent need for good representative animal models of plaque rupture. Over the last decade and a half, genetically engineered mice have been widely used to study the pathogenesis and potential treatment of atherosclerotic lesions, as well as genetic, hormonal and environmental influences on development of atherosclerosis. Though many of the features of plaque development and progression that occur in human plaques are similarly observed in murine plaques, these mouse models have long been regarded as poor models to study plaque rupture because the aortic sinus lesions seldom show any signs of fibrous cap disruption. Several recent studies reported potentially unstable atherosclerotic lesions in older apoE-deficient mice in another anatomic site, the proximal part of the brachiocephalic artery (BCA) [2, 3]. The unusual stability of aortic lesions compared to the BCA lesions in ApoE knockout mice is an unexplained paradox in developing a mouse model of plaque rupture. In this paper, we use histology based finite element analysis to evaluate peak circumferential stresses in aortic and BCA lesions from high fat fed ApoE KO mice.
Tribological Characterization of Biomimetic Low-Friction Gels
Authors: Michalenko Michelle M. , Ovaert Timothy C.
Published: July 2013

Cartilage injury and disease are significant health issues that affect people of all ages. With an increase in active lifestyles, extended life expectances, and diseases such as osteoarthritis, millions of people worldwide are being treated with some form of joint replacements [1], and that number is expected to increase. Although current joint replacements have been successful thus far, typically patients experience long term failure due to wear between the two major contacting surfaces; for example, a cobalt chrome femoral head and a polyethylene tibial plate [2]. While tissue engineered constructs with natural cellular materials are a subject of intense research, their load carrying ability and mechanical function are still far from what is necessary for long-life contacting surfaces. A vastly improved contact surface is desirable, utilizing materials that better mimic the structure and excellent tribological properties of natural cartilage. Such a material could also potentially be designed for use against natural cartilage, when defects are more localized.
Changes of Biomechanics-Based Indices for Patient-Specific Abdominal Aortic Aneurysms Over Time
Authors: Vorp David A. , Shah Samarth , Makaroun Michel S.
Published: July 2013

Abdominal aortic aneurysm (AAA) rupture is the 13th leading cause of death in the US. Clinicians attempt to avoid rupture by performing elective repair. Since AAAs are often times asymptomatic, impending AAA rupture can be without warning. Additionally, patients with AAA are often elderly or have co-morbid conditions. Therefore, the treatment of AAA patients presents a dilemma for the surgeon: surgery should only be recommended when the risk of rupture of the AAA outweighs the risks associated with the interventional procedure.
NCAP Star Rating and Safety of Rear Seat Occupant
Authors: Esfahani Elham Sahraei , Soudbakhsh Damoon , Digges Kennerly
Published: July 2013

New Car Assessment Program (NCAP) gives star ratings to the vehicles based on their crashworthiness. The program uses results of crash tests performed with 50% male HYBRID III dummies in the driver and right front passenger seats and gives separate star ratings for the driver and right front passenger positions. These star ratings are available from the safer car website [1], and are perceived as an indicator of general safety of the vehicles for people trying to purchase a vehicle. A one-star rating would show the lowest, and five-star would be the highest safety ranking. As the NCAP star ratings of the vehicles have improved over years, front occupant protection has improved as well; however, recent studies have shown that rear occupants are less protected in newer model years of vehicles [2]. Safety of rear occupants is not evaluated with the NCAP program. In this paper an attempt is made to verify whether the NCAP scores can show the level of protection provided to the rear occupants or not.
Flow Patterns in a Flow-Stretch-Flexure Bioreactor System: Implications for the Conditioning of Engineered Heart Valve Tissue
Authors: Ramaswamy Sharan , Schmidt David E. , Boronyak Steven M. , Sacks Michael S.
Published: July 2013

In heart valve tissue engineering, there is general agreement that appropriate mechanical conditioning may provide the necessary stimuli to promote proper tissue formation [1–3]. For example, in combined flow-flexure-stretch (FSF) studies conducted in our laboratory [4], we demonstrated that flow or flexure bio-mechanical conditioning alone only produced marginally enhanced mass and quality of the engineered tissue. However, combined fluid and flexural stresses resulted in substantially larger de-novo synthesized tissue mass accumulations rates. Interestingly, surface fluid induced stresses acting on the forming tissue/scaffold were the sole difference in the mechanical environment under combined stimulation regimes. However, combined flow and flexural modes of biomechanical conditioning produce highly complex local flow patterns. Understanding these patterns can help identify specific fluid-induced shear characteristics that can potentially be responsible for improving tissue formation in tissue engineered heart valves (TEHVs). In the present study, we developed a computational fluid dynamic (CFD) model to simulate the motion of rectangular scaffold strips housed in the bioreactor. In order to maximize the benefits of flow-based conditioning at physiological scales that emulates the native valve environment, we also present our efforts in designing a new FSF bioreactor system.
Assessing the Appropriate Number of Days Needed to Approximate Physical Activity Level in the Active Elderly
Authors: Rylander Jonathan H. , Boyer Katherine A. , Andriacchi Thomas P. , Beaupre Gary S.
Published: July 2013

Activity monitoring is an important consideration for a number of conditions associated with health maintenance in an aging population. For example, reduced bone mineral density (BMD) in the aging population puts this group at a higher risk of fall related fractures [1]. Bone density and bone health is in part dependent upon mechanical stimuli caused by everyday physical activity and loading [2]. The number of steps taken per day and walking velocity [3] are important parameters to consider when studying bone density as well as other health related conditions. However, there is a need for effective and efficient methods/protocols to ensure that representative daily activity data can be collected.
Effect of Simvastatin on the Apoptosis and Permeability of Endothelial Cell Monolayers
Authors: Piraino Francesco , Cancel Limary M. , Redaelli Alberto , Tarbell John M.
Published: July 2013

Atherosclerosis is a chronic inflammatory response in the walls of arteries promoted by plasma proteins that carry cholesterol and triglycerides. The initiating event in atherosclerosis is the transport of low density lipoprotein (LDL) into the subendothelial space.
A Preliminary Study on the Mechanics of Ankle-Foot Orthoses: From 3D Laser Scan to Smooth Finite Element Model
Authors: Praet Tomas , De Beule Matthieu , Van Cauter Sofie , Verhegghe Benedict
Published: July 2013

Ankle-foot orthoses or AFO’s are external mechanical devices that support the foot and ankle to assist and improve the gait of patients with muscular and/or neurological problems in the lower leg region. To improve the functionality of these orthoses quite some experimental research projects have been carried out and published in the past. However, only a handful of projects included basic finite element analyses (FEA) [1–3], mainly because of the diversity and complex geometry of the AFO’s. This preliminary study should give raise to a series of detailed finite element analyses based on 3D laser scans of ankle-foot orthoses.
Necrotic Core in Advanced Atherosclerotic Plaques in Human Coronaries Is Exposed to Elavated Shear Stress
Authors: Gijsen Frank , Schuurbiers Johan , Groen Harald , Gonzales Nieves , Serruys Patrick , Wentzel Jolanda
Published: July 2013

In early atherosclerosis, plaques localize in low shear stress regions. During plaque development, the lumen of the artery remains patent due to vascular remodeling and unfavorable low shear stress conditions can persist. Consequently, a continuous influx of lipids can be anticipated in these regions, possibly leading to the development vulnerable plaques. If the plaque exceeds a certain size, vascular remodeling will not be able to maintain the lumen dimensions and the plaque will cause lumen narrowing. This is generally accompanied by shear stress increase in certain regions of the plaque. Evidence is accumulating that increased levels of shear stress influences plaque composition in such a way that it might induce plaque destabilization and ulcer formation.
Clinical Education for Engineers: ESTEEM Project
Authors: Matsuki N. , Takeda M. , Yamano M. , Imai Y. , Ishikawa T. , Yamaguchi T.
Published: July 2013

Current engineering applications in the medical arena are extremely progressive. On this occasion, the most frequently encountered and difficult problem must be an insufficient communication between engineers and medical practitioners. The reason is mainly due to the difference of their own cultures. Medical practitioners tend to think about everything based on their experiences episodically. They take it granted that medicine cannot be usually expressed in a strict manner. Another common obstacle is the safety of patients. On the other hand, engineers are usually trained to think about everything based on physical law expressed mathematically. In addition, engineers and medical practitioners cannot always understand one another’s jargon. It is therefore very hard though even not impossible to understand each other without special effort.
Morphometric Characterization and Finite Element Modeling of the Physiological Tricuspid Valve
Authors: Stevanella Marco , Votta Emiliano , Lemma Massimo , Antona Carlo , Redaelli Alberto
Published: July 2013

The tricuspid valve (TV) is the right atrio-ventricular valve. The most common TV disease is secondary or functional tricuspid regurgitation (FTR), an important complication of left-sided valvular heart lesions, which frequently persists after mitral and aortic valve operations. FTR is associated with high mortality and morbidity and requires surgical intervention, the preferential solution being TV repair through techniques such as annuloplasty performed during left heart surgery. However, significant residual regurgitation persists or recurs in 10% to 20% after annuloplasty, thus highlighting the incomplete understanding of the underlying mechanisms and the need for deeper insight into TV pathophysiology. At this purpose finite element models (FEMs) could be adopted, as suggested by their effective application to the biomechanical analysis of left heart valves. However, while for those several data are available regarding morphology and tissue mechanical properties, such information is missing for the TV, making it difficult to implement a FEM of the TV.
Changes in Extracellular Glutamate Release on Repetitive Transient Occlusion in Global Ischemia Model
Authors: Lee Gija , Choi Seokkeun , Kang Sungwook , Choi Samjin , Park Jeonghoon , Park Dong Hyun , Park Youngho , Kim Kyungsook , Oh Bermseok , Park Hunkuk
Published: July 2013

During the operation, surgeons in neurosurgical area usually performed the multiple temporary occlusions of parental artery which may induce the neuronal damage. It is generally thought that neuronal damage by cerebral ischemia is associated with extracellular concentrations of the excitatory amino acids. In this experiment, we measured the dynamics of extracellular glutamate release in 11 vessel occlusion (VO) model during repeated within short interval. Changes in cerebral blood flow were monitored by laser-Doppler flowmetry simultaneously with cortical glutamate level measured by amperometric biosensor. During ischemia, the peak level of glutamate release was gradually decreased as 112.38±26.21 μM in first period, 82.63±18.50 μM in second period, and 48.58±11.89 μM in third period. The time interval between the ischemia induction and the beginning of glutamate release was increased as 106.7 ± 10.89 (sec) at first attack, 139.11 ± 3.87 (sec) in second attack, 169.00 ± 14.56 (sec) in third ischemic period. From the results of real-time monitoring about glutamate release in 11-VO model during repetitive ischemic episode, it was demonstrated that repetitive ischemia induced less glutamate release from neuronal cell than single ischemia due to endogeneous protective mechanism which delayed glutamate release time in later ischemic injury.
Phase Contrast MRI Derived Boundary Conditions for Patient Specific AAA Fluid Flow Modeling
Authors: Chandra Santanu , Raut Samarth S. , Malve Mauro , Scotti Christine M. , Finol Ender A.
Published: July 2013

Abdominal Aortic Aneurysm (AAA) is a common disease among Caucasian males above the age of 60 and its rupture is the 10th leading cause of death in the U.S. [1] An AAA is commonly defined as a 50% local increase in diameter of the normal infrarenal aorta, and is located below the renal arteries and the iliac bifurcation. At present the measured maximum diameter or the rate of increase of the diameter over time are used as clinical parameters to judge the suitability of surgical intervention to prevent rupture. As a clinical diagnosis rule, aneurysms with diameter less than 4 cm are kept under periodic surveillance and between 5 cm and 6 cm, or expansion rates greater than 1 cm / year, are recommended for surgical or endovascular intervention. Unfortunately, retrospective studies reveal that about 33% of ruptured aneurysms had a maximum diameter less than 5 cm at the time of the rupture [2]. This demonstrates that the correlation between a critical diameter and rupture risk assessment of AAAs has its limitations and thus opens the opportunity for further research on other critical parameters that may be suitable for future diagnosis and rupture prediction. Our ongoing computational efforts [3] focus on this issue as we propose the use of patient specific fluid-structure interaction (FSI) models to investigate the potential of individual flow-induced wall stress as a key biomechanical parameter that can be used for rupture risk evaluation. In this work we report on the setup of the computational protocol for patient specific analysis and assess the effect of modeling parameters on the derivation of individual inflow and outflow boundary conditions for AAA fluid flow simulation and validation.
Biomechanical Analysis of Stent Placement in a Coronary Bifurcation Considering the Anisotropic Response of the Wall
Authors: Mortier Peter , Verhegghe Benedict , De Beule Matthieu , Verdonck Pascal , Holzapfel Gerhard A.
Published: July 2013

The role of finite element simulations during the design and evaluation of medical devices is gaining importance. Such simulations provide insights into the mechanical behaviour of medical devices and help to identify the critical design parameters. One important category are vascular implants such as stents, stent grafts, aortic valve stents among others. A realistic vascular geometry and an adequate constitutive model are basic requirements in order to accurately assess the behaviour of such vascular implants during and after implantation by numerical analysis. Many recently described vascular models, for example in the field of stenting, contain rather severe simplifications both on the geometrical and the constitutive level, although the feasibility of using accurate models has been demonstrated recently by, for example, Kiousis et al. [1]. This observation may be explained by the fact that specific anisotropic material models suitable to describe the large deformations of vascular tissue are not available in standard material libraries of some of the widely used finite element solvers. For example, the ABAQUS’ material library only contains two forms of anisotropic hyperelastic materials.
Development of a Pulsatile Simulator for In-Vitro Analysis of the Mitral Valve Under Controlled Morphometric Conditions
Authors: Pavesi Andrea , Vismara Riccardo , Votta Emiliano , Fiore Gianfranco B.
Published: July 2013

Mitral valve (MV) pathologies of high prevalence, such as ischemic and functional mitral regurgitation, are secondary to the alteration of left ventricle geometry. The latter can lead to abnormal hemodynamics and induce annular dilation and papillary muscles (PMs) dislocation, thus modifying the physiologic balance of forces within the MV [1].
Elastic Network Normal Mode Analysis for Microtubule Mechanics
Authors: Deriu Marco A. , Soncini Monica , Orsi Mario , Patel Mishal , Essex Jonathan W. , Montevecchi Franco M. , Redaelli Alberto
Published: July 2013

The cellular microtubules MTs are hollow cylinder-shaped biopolymers with inner and outer diameter of about 17 and 25 nm and length ranging from 1 to 10 μm. They are constituted by αβ-tubulins arranged in protofilaments with a head-to-tail motif [1]. The protofilaments bind together laterally along the MT’s long axis with a slight shift generating a spiral with a pitch of 2, 3 or 4 monomers’ length (Fig.1a). The building-block of the MT, the αβ-tubulin, is a hetero-dimer made of two globular monomers, α- and β-tubulin, each of them consisting of about 450 residues with high degree of sequence similarity from the primary to the tertiary structure level [1].
Experimental Validation of the Influence of Stent Strut Compression on Artery Wall Drug Mass Transport
Authors: O’Connell Barry M. , McGloughlin Tim M. , Walsh Michael T.
Published: July 2013

Atherosclerosis is a degenerative disease that affects coronary, carotid and other peripheral arteries in the body. Arterial occlusions ensuing from aggressive atherosclerotic plaque progression can often culminate in an ischemic attack, such as an apoplectic attack or a myocardial infarction [1–3]. Several interventional procedures are available to the clinician but in recent years drug eluting stents (DES) have become the preferred choice and by the beginning of 2006 more than 8 out of 10 coronary stents were DES [4] at a cost of between $4 and $5 billion annually [5].
Effect of Blood Viscosity on Thrombosis Potential Near a Step Wall Transition
Authors: Corbett Scott C. , Ajdari Amin , Coskun Ahmet U. , N.-Hashemi Hamid
Published: July 2013

Thrombosis and hemolysis are two problems encountered when processing blood in artificial organs. Physical factors of blood flow alone can influence the interaction of proteins and cells with the vessel wall, induce platelet aggregation and influence coagulation factors responsible for the formation of thrombus, even in the absence of chemical factors in the blood. These physical factors are related to the magnitude of the shear rate/stress, the duration of the applied force and the local geometry. Specifically, high blood shear rates (or stress) lead to damage (hemolysis, platelet activation), while low shear rates lead to stagnation and thrombosis [1].
Micro-Mechanics of Post-Mortem Retrieved Cement-Bone Interfaces: Influence of Interface Morphology
Authors: Mann Kenneth A. , Miler Mark A. , Verdonschot Nico , Eberhardt Alan W.
Published: July 2013

PMMA bones cements are used routinely to fix implants to bone. The interface between cement and bone is relied on for fixation and it is well recognized that there is a biologic response to the presence of PMMA. Bleeding of the bone bed during the arthroplasty procedure, thermal necrosis from the polymerization process, and bone remodeling has been described as factors affecting the integrity of the cement-bone interface. While substantial efforts have been made to understand the mechanical characteristics of the cement-bone interface from lab-prepared specimens there is actually very little understanding of the mechanics of cement-bone interfaces that have been in service.
Investigating the Effect of Intraluminal Thrombus in Abdominal Aortic Aneurysm by Computational and Experimental Methods
Authors: Ene Florentina , Gachon Carine , Delassus Patrick , Morris Liam
Published: July 2013

Abdominal aortic aneurysm (AAA) represents an abnormal dilatation and weakening of the abdominal aorta with high risk of rupture. Most aneurysms of the infrarenal aorta possess an asymmetrical fusiform morphology.
Chitosan-Collagen Based Channeled Scaffold for Cardiac Tissue Engineering
Authors: Zhang Ting , Wan Leo Q. , Marsano Anna , Maidhof Robert , Yan Yongnian , Pan Jiluan , Vunjak-Novakovic Gordana
Published: July 2013

Tremendous efforts have been made for engineering cardiac tissue for myocardial infarction therapy [1]. Various materials and forming methods have been explored, but due to the specific physiological properties of cardiac muscle tissue, challenges still exist [2]. One of those is to create biomimetic extracellular materials to support cell function and electromechanical coupling. The scaffold material should be biocompatible, biochemically stable, mechanically strong, and highly extensible, just like native heart tissue [2]. Another challenge is to create vascular networks for oxygen and nutrient supply, much as the capillaries do in natural heart tissue [3]. In this study, chitosan and collagen were chosen to fabricate cardiac constructs with channels as small as 200 μm in diameter. Several factors such as chitosan and crosslinker concentrations and coating proteins were optimized for mechanical strength and cell seeding efficiency. Engineered tissues of significant size (12 mm in diameter × 2 mm thick) were generated in vitro using this method.
CT Visualization and Histopathological Assessment of Cryoablation in Pulmonary Veins
Authors: Shenoi Mithun M. , Zhang Xiaoqing , Venkatasubramanian Ramji T. , Grassl Erin D. , George Lenny , Schmechel Stephen , Coad James E. , Bischof John C.
Published: July 2013

Over 2 million adults in the United States are affected by atrial fibrillation (AF), a common cardiac arrhythmia that is associated with decreased survival, increased cardiovascular morbidities, and a decrease in quality of life. Atrial fibrillation can be initiated by ectopic beats originating in the myocardial sleeves surrounding the pulmonary veins [1]. Pulmonary vein (PV) isolation via radiofrequency ablation is the current gold standard for treating patients with drug-refractory AF [2]. However, cryoablation is emerging as a new minimally-invasive technique to achieve PV isolation. Cryoablation is fast gaining acceptance due to its minimal tissue disruption, decreased thrombogenicity, and reduced complications (RF can lead to low rate of pulmonary vein stenosis) [2]. One important question in regard to this technology is whether the PV lesion is transmural and circumferential and to what extent adjacent tissues are involved in the freezing process. As ice formation lends itself to image contrast in the body, we hypothesized that intraprocedural CT visualization of the iceball formation would allow us to predict the extent of the cryolesion and/or provide us with a measure of the adjacent tissue damage.
Geometry of Abdominal Aortic Aneurysms and the Intraluminal Thrombus From 3D Image Reconstruction Using Active Contours
Authors: Ashton John H. , Ayyalasomayajula Avinash , Vande Geest Jonathan P.
Published: July 2013

Abdominal aortic aneurysm (AAA) is a significant disease in the United States, and an intraluminal thrombus (ILT) develops in the majority of AAAs. Rupture prediction of AAA has been performed on patient specific models based on reconstruction of computed tomography (CT) images. The ILT alters stress distribution in the AAA wall [1], and ILT growth and thickness are correlated to rupture risk [2, 3]. Drug treatment of AAA is under investigation by several groups [4]. It is also known that the wall covered by the ILT is weaker than other areas [1]. If local drug delivery through the lumen is to be achieved, the barriers for transport through the ILT must be investigated. Patient specific geometries of the ILT would be necessary for such analysis.
Block-Fixation Finite Element Lumbar Spine Model to Examine Load-Sharing, Bone-Screw Interaction, and Stress in Carbon Fiber Reinforced PEEK Construct
Authors: Guan Yabo , Bruner Harlan , Yoganandan Narayan , Pintar Frank A. , Maiman Dennis J.
Published: July 2013

Carbon-fiber-reinforced (CFR) polyetheretherketone (PEEK) combines the high strength of metals with the extensive biocompatibility and imaging compatibility of polymers. CFR PEEK composite is similar to the stiffness of cortical bone (approximately 15–20 GPa) and shows comparable performance to metallic materials such as titanium alloy, cobalt chrome alloy, and stainless steel in terms of strength. CFR-PEEK becomes an attractive alternative to the metallic materials traditionally used in spinal implants (e.g. pedicle screw rod fixation). Finite element (FE) models have been developed to study the biomechanical behaviors of spinal structures with pedicle screw rod fixation ([1–5]). However, it is limited to implement these models to study the bone screw interaction, and local bone strain at the bone screw interface due to the intrinsic low mesh density of the intact model. The aim of this study is to develop a refined block fixation FE model to investigate the load sharing, bone screw interaction, and strain/stress in CFR PEEK construct.
Generation of Realistic Physical Models of Cerebral Aneurysms for In Vitro Flow Visualisation
Authors: Fahy Paul , McGloughlin Tim , Delassus Patrick , Morris Liam
Published: July 2013

An aneurysm is a localised persistent dilation of the blood vessel wall. Aneurysm formation is hypothesised to be a consequence of haemodynamically generated forces working on the arterial wall leading to degeneration of the media layer (1). This focal degeneration typically occurs at curved arterial segments and at bifurcation points around the circle of Willis. Intracranial aneurysms are traditionally classified by aetiology and morphology. The majority are idiopathic and saccular. It is estimated that 1.5–6% of the general population have or will develop an intracranial aneurysm, predominantly occurring in women, most of them being asymptomatic (1). If left undetected these aneurysms may rupture with a 30 day mortality rate of 45% (1). There are two treatment options surgical clipping or endovascular coiling. Both of these techniques exclude the aneurysm from the normal circulation. Endovascular coiling is preferred due to its minimally invasive nature. Numerous studies have been done so far based on idealized glass models and using FVM, FEA methods, but very little testing has been carried out on devices using realistic silicone models. This is mainly because of the complexity of the cerebral vasculature. Silicone replicas of both realistic and idealised models were manufactured based on CT scans and anatomical dimensions obtained from literature, respectively (2).
Remodeling in Cell-Seeded Fibrin Gels: Changes in Composition, Organization, and Planar Biaxial Mechanical Behavior
Authors: Sander Edward A. , Johnson Sandra L. , Barocas Victor H. , Tranquillo Robert T.
Published: July 2013

Engineered tissues are necessary to replace diseased and damaged tissues incapable of healing on their own. One method employed to produce them involves cell entrapment in a fibrin gel constrained by specially designed molds [1]. As the cells compact and remodel the gel, the combination of mold constraints and cell tractions produces fiber alignment similar to native tissues [2]. One potentially important factor in the remodeling outcome is the local mechanical environment that develops during the compaction and remodeling process. It is well established that the global stress environment leads to changes in remodeling in an isotropic sample [3], but we do not know the effect of local variations in stress field in a heterogeneous sample. To begin to assess the local mechanical environment’s role, we examined the remodeling process in cross-shaped Teflon molds (cruciforms). In this experiment, two mold geometries with differing channel widths were examined: a 1:1 aspect ratio in which the both axes possessed 8 mm wide channels, and a 1:0.5 aspect ratio in which one axis had 8 mm wide channels and the other 4 mm wide channels (fig. 1).
Identifying the Distribution of Heterogeneous Anisotropic Elastic Properties in Cerebral Aneurysms
Authors: Zhao Xuefeng , Raghavan Madhavan L. , Lu Jia
Published: July 2013

Cerebral aneurysms are focal dilatations of the intracranial arterial wall, whose rupture risk is likely related to pressure induced wall stress. Fundamental to stress and strain prediction in aneurysms is the constitutive behavior of wall tissue. However, delineating the constitutive equation of aneurismal tissue, in particular, experimental determination of the material parameters, presents some significant challenges due to the nonlinear, anisotropic and heterogeneous nature of the aneurysmal tissue.
Effects of Growth Factors and Stress Conditioning on the Induction of Heat Shock Proteins and Osteogenesis
Authors: Chung Eunna , Rylander Marissa Nichole
Published: July 2013

Tissue engineering is an emerging field that focuses on development of methods for repairing and regenerating damaged or diseased tissue. Successful development of engineered tissues is often limited by insufficient cellular proliferation and insufficient formation of extracellular matrix. To induce effective bone regeneration, many research groups have investigated the cellular response and capability for tissue regeneration associated with bioreactor conditions and addition of growth factors [1]. Bioreactors in tissue engineering have been developed to expose cells to a similar stress environment as found within the body or induce elevated stress levels for potential induction of specific cellular responses associated with tissue regeneration. Native bone encounters a diverse array of dynamic stresses such as shear, tensile, and compression daily. Stress conditioning protocols in the form of thermal or tensile stress have been shown to induce up-regulation of molecular chaperones called heat shock proteins (HSPs) and bone-related proteins like MMP13 (matrix metallopeptidase 13) [2] and OPG (osteoprotegerin) [3, 4]. HSPs have important roles in enhancing cell proliferation and collagen synthesis. Osteogenic growth factors such as TGF-β1 (transforming growth factor beta 1) and BMP-2 (bone morphogenetic protein 2) are related to bone remodeling and osteogenesis as well as HSP induction [5]. Therefore, identification of effective preconditioning using growth factors and stress protocols that enhance HSP expression could substantially advance development of bone regeneration. The purpose of this research was to identify preconditioning protocols using osteogenic growth factors and tensile stress applied through a bioreactor system to enhance expression of HSPs and bone-related proteins while minimizing cellular injury for ultimate use for bone regeneration.
On the Use of Quaternions to Characterize the Dynamics of a Vertebral Motion Segment
Authors: Faruk Senan Nur Adila , O’Reilly Oliver M.
Published: July 2013

The characterization of the kinematics and kinetics of anatomical joints is a central problem in biomechanics. Traditionally, the kinematics of the joint has been characterized using the helical axis of motion (HAM) and Euler angles. The estimation of these quantities from optical measurements of landmarks placed on the anatomical parts constituting the joint is difficult and often fraught with error.
Motion-Derived Joint Coordinate Systems Reduce Inter-Subject Variability of Elbow Flexion Kinematics
Authors: Ferreira Louis M. , King Graham J. , Johnson James A.
Published: July 2013

Anatomic coordinate systems are widely used in biomechanics research and have found some applications in orthopaedic surgical procedures such as joint arthroplasty. With respect to the elbow, coordinate systems for the humerus and ulna are often derived from surface scans or digitizations of specific anatomical features.
Characterizing the Compressive Resistance and Recovery of Shape Memory Polymer Cylinders
Authors: Harper John L. , Herlihy Rachelann N. , Vande Geest Jonathan P.
Published: July 2013

Each year, approximately 200,000 people in the United States are diagnosed with abdominal aortic aneurysms (AAAs). Despite improved preventative screening programs, AAAs are still listed as the cause of death for an estimated 15,000 Americans each year [1–2]. Despite the relatively low mortality rate for open surgical repair of AAA, the minimally-invasive nature of endovascular repair has made this treatment extremely popular. Our research team seeks to develop the next generation of endovascular stent-grafts which resist the two main modes of graft failure — endoleak and graft migration [3–5]. We believe that such a stent-graft can be made from novel smart polymer formulations. Towards this end, shape memory polymer (SMP) cylindrical tubes were fabricated and tested for their recovery force.
CFD Comparison of Steady and Unsteady Flow Through a Human Nasal Passage
Authors: Savilonis Brian , Smith Kalen
Published: July 2013

Understanding of the transnasal pressure and flow behavior during normal breathing conditions has been a subject of much discussion and research. In particular we are interested in testing the hypothesis of quasi-steady flow as well as the role of turbulence on nasal flow dynamics.
Determination of Anisotropic Solute Diffusivity in Human Lumbar Annulus Fibrosus by a Video-FRAP Method
Authors: Travascio Francesco , Jackson Alicia R. , Gu Wei Yong
Published: July 2013

The intervertebral disc (IVD) is the largest avascular structure in the human body, consisting of the nucleus pulposus (NP) surrounded by the annulus fibrosus (AF), see Figure 1. Cellular nutrition occurs mainly by diffusion from the vascular network surrounding the disc [1]. Poor nutritional supply is believed to be one of the causes for disc degeneration [2–4]. Thus, it is important to investigate solute transport in IVD for understanding the etiology of IVD degeneration.