bluuebunny/crossref_metadata_2025 huggingface dataset:
Respose of Cultured Nasal Epithelial Cells to Wall Shear Stress
Authors: Even-Tzur Nurit , Zaretsky Uri , Wolf Michael , Elad David
Published: March 2014

The nasal cavity lining is rich with mucus secreting goblet cells. Nasal defense is based on the mucociliary clearance mechanism, in which the secreted mucus layer traps inhaled particles and is constantly driven towards the nasopharynx for removal of the particles from the body. The mucus layer is also important for the exchange of temperature and water vapor with the inspired air. Airway goblet cells discharge mucus in response to a wide variety of biological stimuli, including cytokines, bacterial products, proteinases, oxidants, irritant gases, and inflammatory mediators [1], as well as biophysical changes, such as osmolarity alterations [2].
Cellular Mechanics and Biology of Tumor Cell-Leukocyte Interactions in the Near Wall Region Under Shear Flow Conditions
Authors: Hoskins Meghan H. , Liang Shile , Kunz Robert F. , Dong Cheng
Published: March 2014

Malignant melanoma has a high propensity for metastatic spread, making it the most deadly form of skin cancer. Currently, no effective treatment exists to prevent melanoma metastasis or to inhibit metastatic tumors growing in distant organs [1,2].
Reduction of Intra-Aneurysmal Kinetic Energy by Intralumenal Flow Diverting Devices
Authors: Seong Jaehoon , Lieber Baruch B. , Wakhloo Ajay K.
Published: March 2014

Endovascular coiling is an acceptable treatment of intracranial aneurysms yet long term follow-ups suggest that endovascular coiling fails to achieve complete aneurysm occlusion particularly in wide-neck and giant aneurysms. Flow diverting devices can serve as an alternative to coils in endovascular bypass of human brain aneurysms for their exclusion from the cerebral circulation. They can redirect flow away from the aneurysm distally into the parent vessel thereby reestablishing physiological flow patterns. Placing of a flow diverting device across the aneurysm neck may be sufficient to occlude the aneurysm by promoting intra-aneurysmal thrombosis, however, conclusive evidence of its efficacy are still lacking. In this study [1], we investigated in vitro the efficacy of custom designed flow diverting devices and develop indices of their performance in an elastomeric model of the elastase-induced aneurysm in rabbit. The efficacy of custom designed flow divertors is investigated in terms of reducing the flow activity inside the sac. These custom made devices possess porosities that are similar to available stents, however, their pore densities are much higher. The results will help optimize the device that will be used in the animal model.
Longitudinal Measurement of In-Vivo Tendon Function Over 17 Weeks Following Repair: Technique and Preliminary Results in a Canine Rotator Cuff Model
Authors: Bey Michael J. , Brock Stephanie K. , Baker Andrew R. , Derwin Kathleen A.
Published: March 2014

Rotator cuff tears are a common injury, affecting 30–40% of the population over age 60 and representing a tremendous source of pain and disability. Rotator cuff tears are often repaired surgically, but a significant percentage (perhaps 50% or more) of large cuff tears fail after surgery and result in long-term shoulder disability. The outcome of rotator cuff repair surgery is typically assessed by measuring muscle strength, joint range of motion, pain, and other subjective indicators of function. Although these types of measurements are used extensively, they provide only an indirect assessment of tendon function. We have recently developed new experimental techniques that allow us to use a biplane x-ray system to directly assess in-vivo tendon function. The purpose of this study was to assess the feasibility of using a biplane x-ray system to quantify changes in in-vivo tendon function following tendon repair in a canine rotator cuff model. We hypothesized that tendon function will improve over the healing period (as reflected by changes in measures of repair stiffness and contracture) and approach normal tendon function by 17 weeks.
Simultaneous Measurements of Velocity and Deformation in Flows Through Compliant Orifices Used as Heart Valve Analogues
Authors: Amatya Devesh M. , Longmire Ellen K.
Published: March 2014

Both hemodynamic and structural performance are important considerations in designing replacement heart valves. In this study, silicone diaphragms of prescribed orifice and material properties are used as simplified heart valve analogues. Diaphragm deformation is quantified simultaneously with flow characteristics including pressure drop, mean flow rate and instantaneous velocity fields. The combined flow and structural data can be used to validate fluid-structure interaction codes suitable for biomedical applications, including studies of flow through heart valves.
Tissue Mechanics Lab: Pros and Cons of an Inquiry Approach for Juniors
Authors: Billiar Kristen L.
Published: March 2014

Inquiry-based instruction offers one of the most effective means of facilitating learning by compelling students to solve authentic problems through a self discovery process. In biomedical engineering (BME), there has been a recent upsurge in activity in inquiry-based (i.e., challenge-based or problem-based) instruction in the educational literature [1–4] and it appears to be especially well suited for BME laboratories where quantitative measurements of complex and variable biological systems are required [3].
MRI Evaluation of a Stented Abdominal Aorta of a Rabbit
Authors: Shin Minchul , Brott Brigitta C. , Lloyd Steven G. , Evanochko William T. , Kiss Pál , Baker Robert A. , Anayiotos Andreas S.
Published: March 2014

MRI is an attractive non-invasive angiographic modality not requiring nephrotoxic contrast agents and damaging exposure to radiation such as traditional angiography and multislice CT. It has previously been shown to provide consistently accurate non-invasive information from the stented regions of peripheral vessels even under stenotic conditions [1–3]. The aim of this study is to show that phase contrast magnetic resonance (PC-MR) can be used to provide accurate quantitative information of blood flow in smaller stented vessels such as the coronaries, using an in-vitro model and a rabbit aorta model. The ultimate goal of the project is to evaluate in-stent restenosis in stented coronary vessels, ultimately describing the degree of stenosis based on blood velocity indices such as translesional pressure gradient and peak systolic velocity ratio (PSVR).
Simulating the Independent Effects of Muscle Fiber Type Composition on Vertical Jumping Performance
Authors: Umberger Brian R. , Caldwell Graham E.
Published: March 2014

The fiber type composition of human limb muscles is believed to influence explosive movement ability. Indirect evidence is found in data from power athletes, who tend to have a greater percentage of fast twitch (FT) muscle fibers, and a lower percentage of slow twitch (ST) fibers, than endurance athletes [e.g., 1]. The apparent advantage of having a high proportion of FT fibers in explosive activities is reinforced by the existence of significant positive correlations between the percentage of FT fibers and jump height [e.g., 2].
Development of a Computational Model to Study Effects of Rotator Cuff Tear Size and Location on Muscle Moment Arms
Authors: Adams Corinne R. , Baldwin Mark A. , Laz Peter J. , Rullkoetter Paul J. , Langenderfer Joseph E.
Published: March 2014

Rotator cuff tendon tear causes alterations to cuff muscle architecture and tendons including muscle fascicle contracture and increased tendon length, fatty infiltration of the muscle fibers, muscle fiber pennation angle changes, asymmetric muscle atrophy, and altered muscle fiber type composition, e.g. [1]. These changes ultimately result in a reduction in muscle force, and frequently lead to a reduction of shoulder strength and a loss of functionality. Recently, division of the cuff tendons in a manner related to cuff tear has been shown to alter tendon excursions and cause muscle moment arms reductions in a cadaver experiment [2] and a computational study [3]. Evaluations of the effects of cuff tear size and location on cuff muscle moment arms have not been conducted. Consequently, the mechanisms by which the muscle force and moment arm changes affect joint strength are not well understood. An improved understanding of these relationships would increase potential for rehabilitation of joint strength following cuff repair. Models for evaluating rotator cuff tear are non-existent since subject-specific models have focused on healthy normal shoulders. Consequently, models have not been used to quantify the effects of clinically observed changes in muscle and tendon architecture on muscle moment arm and force generating capacity.
Leukocytes Cause Inflammatory Response to Traumatized Articular Cartilage in Acute Phase of Joint Injury
Authors: Milentijevic Dejan , Green David M. , Aslani Koosha , Torzilli Peter A. , Warren Russell F.
Published: March 2014

Painful and inflamed joints result from joint trauma involving disruption of the cartilage [1]. The pathogenesis of post-traumatic osteoarthritis is not well understood but is most likely multifactorial. Other factors, such as inflammation, may be a critical precursor for post-traumatic arthritis. Transient acute synovitis and inflammation following a traumatic event can persist for months and may be representative of a serious joint injury [2]. Joint effusion aspirates from patients in the acute phase of injury have a higher level of activated leukocytes and an increased rate of reactive oxygen species (ROS) production relative to autologous peripheral blood [3]. In an in vitro study, the presence of inflammatory leukocytes caused more chondrocyte death isolated from traumatized matrix region relative to impacted cartilage alone [4]. Our previous study showed that severe trauma may not be a good predictor for the development of post-traumatic arthritis since chondrocyte death and matrix loss was minimal up to seven days post-trauma [5].
Non-Thermal Dental Ablation Using Ultra-Short Pulsed Near Infrared Laser
Authors: Fahey Molly E. , Jaunich Megan K. , Dutta Ashim , Tata Darrell B. , Waynant Ronald W. , Mason H. Lawrence , Mitra Kunal
Published: March 2014

Ultra-short pulsed lasers are known for their ability to precisely machine materials including human hard and soft tissues while minimizing the amount of thermal energy deposited to the surroundings. Non-thermal ablation produced by ultra-short pulsed lasers in the femtosecond to picosecond range is very effective for dental applications. As shown in Figure 1, most decay occurs in the dentin, which is found between the outer surface (enamel) and the inner region containing the nerve endings (pulp) [1]. Caries removal and the preparation of cavities in dentistry are primarily performed by the use of mechanical drills. The current techniques are invasive and cause patient discomfort. Due to the vibrations of the drills it is necessary to use local anesthetic for the majority of dental procedures. A continuous water spray is used in conjunction with the drills to balance the temperature rise produced by mechanical vibrations. Drills are somewhat limited in precision causing a large amount of healthy tooth to be lost during any restoration process. Replacing a multitude of mechanical tools with one non-invasive, accurate and painless laser treatment will be a huge advancement to the current dental techniques.
Experimental Study on Non-Exit Ballistic Induced Traumatic Brain Injury
Authors: Zhang Jiangyue , Yoganandan Narayan , Pintar Frank A. , Guan Yabo , Gennarelli Thomas A.
Published: March 2014

Ballistic-induced traumatic brain injury remains the most severe type of injury with the highest rate of fatality. Yet, its injury biomechanics remains the least understood. Ballistic injury biomechanics studies have been mostly focused on the trunk and extremities using large gelatin blocks with unconstrained boundaries [1, 2]. Results from these investigations are not directly applicable to brain injuries studies because the human head is smaller and the soft brain is enclosed in a relatively rigid cranium. Thali et al. developed a “skin-skull-brain” model to reproduce gunshot wounds to the head for forensic purposes [3]. These studies focused on wound morphology to the skull rather than brain injury. Watkins et al. used human dry skulls filled with gelatin and investigated temporary cavities and pressure change [4]. However, the frame rate of the cine X-ray was too slow to describe the cavity dynamics, and pressures were only quantified at the center of skull. In addition, the ordnance gelatin used in these studies is not the most suitable simulant to model brain material because of differences in dynamic moduli [5]. Sylgard gel (Dow Corning Co., Midland, MI) demonstrates similar behavior as the brain and has been used as a brain surrogate to determine brain deformations under blunt impact loading [6, 7]. Zhang et al. used the simulant for ballistic brain injury and investigated the correlation between temporary cavity pulsation and pressure change [8, 9]. However, the skulls used in these models were not as rigid as the human cranium. The presence of a stronger cranial bone may significantly decrease the projectile velocity and change the kinematics of cavity and pressure distribution in the cranium. In addition, projectiles perforated through the models in these studies. Patients with through-and-through perforating gunshot wounds to the head have a greater fatality rate than patients with non-exit penetrating wounds [10]. Therefore, it is more clinically relevant to investigate non-exit ballistic traumatic brain injuries. Consequently, the current study is designed to investigate the brain injury biomechanics from non-exit penetrating projectile using an appropriately sized and shaped physical head model.
Contributions of Trabecular Rods of Various Orientations in Determining the Elastic Properties of Human Vertebral Trabecular Bone
Authors: Liu Xiaowei S. , Zhang X. Henry , Sajda Paul , Saha Punam K. , Wehrli Felix W. , Guo X. Edward
Published: March 2014

Osteoporosis is an age-related disease characterized by low bone mass and architectural deterioration. Other than bone volume fraction (BV/TV), microarchitecture of trabecular bone, such as trabecular type (rods or plates), connectivity, and orientation of the trabecular network is also believed to be important in governing the mechanical properties of trabecular bone. A recent study [1] showed that the microarchitecture alone affects elastic moduli of trabecular bone and, further, that trabecular plates make a far greater contribution than rods. In human vertebral trabecular bone, the roles of transverse vs. vertical rods in conferring mechanical properties of trabecular bone have been debated [2, 3]. It has been suggested that the role of transverse trabecular rod is critical in determining elastic modulus of vertebral trabecular bone. However, without explicit classifications of trabecular type, or orientation assessment at an individual trabecula level, it is not possible yet to test this hypothesis in human trabecular bone samples despite the development of three-dimensional (3D) micro computed tomography (μCT) and μCT based finite element (FE) models of human trabecular bone. With the newly developed technique of complete volumetric decomposition and individual trabecula based orientation analyses [4], now it is possible to quantitatively examine the contributions of trabecular rods of various orientations in the elastic properties of vertebral trabecular bone.
Pulsatile Pressure System for Cellular Mechanical Stimulation
Authors: Taylor Rebecca , Abilez Oscar , Cao Feng , Wu Joe , Xu Chengpei , Zarins Christopher , Pruitt Beth
Published: March 2014

Cardiovascular disease (CVD) affects more than 71 million Americans accounting annually for nearly $400 billion in US health care costs. [1] In adult tissues such as the heart, the capacity for self-regeneration is limited. Recently, stem cell therapy has emerged as a promising methodology for myocardial repair.
Development of a Two-Color Fluorescent Tracer Technique to Study Aqueous Outflow Patterns and Outflow Resistance in Human Eyes
Authors: Folz Steven J. , Gong Hiayan , Overby Darryl R.
Published: March 2014

Glaucoma is a leading cause of blindness, and elevated intraocular pressure (IOP) characteristic of glaucoma is caused by increased aqueous humor outflow resistance. Studies have localized the bulk of outflow resistance to particular regions along the outflow pathway — namely, the inner wall endothelium of Schlemm’s canal and its underlying juxtacanalicular tissue (JCT) [1] — but the hydrodynamic details of how aqueous humor flows through these tissues and how these tissues generate outflow resistance are not well understood.
Computational Investigation on the Dispersive Transport of Angiographic Contrast Injected Antegradely Into Flow in a Tube
Authors: Hao Qing , Lieber Baruch B.
Published: March 2014

When a solute such as angiographic contrast is introduced into a solvent such as blood analog fluid flowing in a straight circular tube, it spreads under the combined action of molecule diffusion and the variation of velocity over the cross-section [8]. If two molecules are being carried in the flow, for example, one in the center and one near the wall, the rate of separation caused by the difference in bulk velocity will greatly exceed that caused by molecule motion. Given enough time, any single molecule would wander randomly throughout the cross section of the pipe because of molecular diffusion, and would sample at random all the advective velocities [4]. Therefore, Taylor [8] adopted the Lagrangian approach to the problem, casting the equations in a coordinate system that moves with the average velocity of the flow and replacing the molecular diffusion coefficient with a dispersion coefficient, and the local concentration with the cross sectional mean concentration. Recasting Taylor’s equation in an inertial coordinate system one obtained the so called advection-dispersion equation.
The Dissipation of Suction Waves in Flexible Tubes
Authors: Feng J. , Khir A. W.
Published: March 2014

Wave dissipation in arteries was intensively studied previously in the frequency domain, which focused on the waves with “pushing effect”. Meanwhile, we noted that waves with “suction effect” are observed in pulmonary veins [1], and in coronary arteries [2]. In spite of this, the dissipation of “suction waves” has not been studied before.
Rapid Growth of Cerebral Aneurysms Before Rupture
Authors: Jou Liang-Der , Lee Deok Hee , Mawad Michel E.
Published: March 2014

Ruptured intracranial aneurysms often have poor clinical outcome. International Study on Unruptured Intracranial Aneurysms has demonstrated the value of treatment for unruptured intracranial aneurysms and that aneurysms larger than 7mm may benefit from treatment. Although aneurysm size appears to be the major indication for rupture, other risk factors, including anatomical location and patient history, are also important in clinical evaluation and cannot be overlooked. Aneurysms at the anterior communicating artery (ACoA) especially have higher rupture risk and rupture at smaller sizes than other aneurysms.
Sliding Contact Modulates ECM Expression in Chondroctye-Laden Agarose Gels
Authors: Huang Alice H. , Mauck Robert L.
Published: March 2014

Articular cartilage provides a low-friction bearing surface for transmitting the forces that arise with joint motion. Because cartilage possesses a limited capacity for repair, trauma or progressive joint disease leads to destruction of the joint surface [1]. Limitations in current repair strategies have increased interest in cartilage tissue engineering (TE), although to date, generating a construct with the mechanical complexity of the native tissue remains a challenge. In our previous long-term free swelling studies, and in other gel systems, the tensile properties of cell-seeded hydrogels remain far lower than those of the native tissue [2–4]. One approach for furthering tissue growth is the application of mechanical signals to engineered constructs. In developing joints, inhibition of mechanical forces results in incomplete cartilage formation [5,6]. Mechanical forces continue to play a vital role in cartilage maturation after birth; physiologic loading remodels the tissue and increases the tensile properties and spurs development of anisotropy [7,8]. In chondrocyte-seeded TE constructs, dynamic axial mechanical stimulation improves compressive properties and biochemical content [9], though the collagen content and tensile and dynamic properties remain low. As the tensile properties of cartilage emerge with load-bearing use, more complete recapitulation of the mechanical environment that arises with motion may further the maturation of engineered constructs. To test this hypothesis, we developed a sliding contact bioreactor mimicking two contacting cartilage layers and show that ECM gene expression is modulated by this loading modality depending on the duration of loading and pre-maturation of the construct.
Numerical Study of Blood Redistribution in the Circle of Willis of Patients With Carotid Artery Stenosis
Authors: Luppi Luca , Long Quan , König Carola S. , Collins Michael W.
Published: March 2014

Stroke is an acute neurological injury in which the blood supply to a part of the brain is interrupted due to either a diminution of cerebral blood flow or a sudden occlusion of a feeding artery. Blood perfusion depends not only on the status of the diseased vessels but also on the patency of collateral pathways. The primary collateral pathway is that provided by the Circle of Willis (CoW).
Stretch-Activated Calcium Signal Propagation Following Mechanical Stimulation of Focal Adhesions
Authors: Ruder Warren C. , Pratt Erica D. , Brandy Nailah Z. , LaVan David A. , LeDuc Philip R. , Antaki James F.
Published: March 2014

Cells translate environmental mechanical stimuli into biochemical reactions that govern a range of cellular processes such as proliferation, death and tissue matrix remodeling. Mechanical activation of individual focal adhesions formed between the cell and its environment directly correspond to several internal responses. Intracellular calcium concentration, [Ca2+]in, has been shown to profoundly change during force sensing. In order to understand this dynamic in cells, we compared calcium mobilization resulting from chemical stimulation and that resulting from mechanical stimulation. We have analyzed the response of fibroblasts to membrane displacements of over 5 μm resulting in eventual spikes in [Ca2+]in. Our data initially indicates that fibroblasts may process mechanical calcium events in unique manner in comparison to other cell types. This finding has implications in a range of fields including mechanobiology and magnetics based activation.
Use of Cardiac Phase-Contrast MRI to Examine Hemodynamics and Wall Deformation Within the Aortic Root for Patients With Bicuspid Aortic Valves
Authors: Barker Alex J. , Lanning Craig , Nair Devatha , Chapman Vernon , Shandas Robin
Published: March 2014

As the most common congenital heart defect, bicuspid aortic valve (BAV) occurs in 1–2 % of the population and has been associated with serious complications such as aortic valve dysfunction, infective endocarditis, aortic dilatation, aortic aneurysm, and aortic dissection [1, 2]. While the pathogenesis of this valve malformation has been postulated to be genetic, the resulting vascular environment and abnormal hemodynamics are hypothesized to contribute to the progression of the disease and its subsequently high morbidity and mortality (greater than 33% of patients with BAV develop serious complications from the disease) [1]. However, clinical details supporting the causality between altered local blood flow dynamics and development of structural abnormality at the aortic root are still lacking.
Techniques for Virtual Stenting of Intracranial Aneurysms
Authors: Appanaboyina Sunil , Mut Fernando , Löhner Rainald , Putman Christopher M. , Cebral Juan R.
Published: March 2014

Intracranial aneurysms are pathological dilations of the arteries in the brain, whose rupture is often fatal. Surgery and endovascular embolization are the two most common methods of treatment. Surgery involves opening a portion of the skull and placing metallic clips at the aneurysm neck thereby preventing blood flow into the aneurysm. In the case of embolization, a catheter is used to pack platinum coils in the aneurysm reducing the inflow and promoting thrombus formation. Due to its less invasive approach endovascular embolization is preferred over surgery. Nevertheless this approach also has some serious aftereffects. Coil compaction followed by the re-growth or the formation of the secondary aneurysm is the most common problem. The endovascular embolization approach also has a serious shortcoming that the coils alone cannot be used to block every type of aneurysm. Wide neck or fusiform aneurysms are coiled with the help of stents. Recent studies show that stent, which is a hollow cylindrical mesh, can be successfully used to limit the flow of blood into the aneurysm. However these studies have been conducted using idealized in-vitro and numerical models. Studies conducted using patient-specific models generated from medical images will provide a more realistic approach to computationally investigate the effects of stents on intra-aneurysmal flow patterns. However generation of computational grids inside the parent vessel and around these stents is a challenging task. In this paper an algorithm to map the stent to a patient-specific vascular model and an adaptive unstructured embedded gridding technique to model flow around stents are presented. Finally these techniques are demonstrated on patient-specific cases to prove their feasibility.
Multi-Lamellar and Multi-Axial Maturation of Cell-Seeded Fiber-Reinforced Tissue Engineered Constructs
Authors: Baker Brendon M. , O’Connell Grace D. , Sen Sounok , Nathan Ashwin S. , Elliott Dawn M. , Mauck Robert L.
Published: March 2014

The architecture of load-bearing fibrous tissues is optimized to enable a specific set of mechanical functions. This organization arises from a complex process of cell patterning, matrix deposition, and functional maturation [1]. In their mature state, these tissues span multiple length scales, encompassing nanoscale interactions of cells with extracellular matrix to the centimeter length scales of the anatomic tissue volume and shape. Two structures that typify dense fibrous tissues are the meniscus of the knee and the annulus fibrosus (AF) of the intervertebral disc (IVD). The mechanical function of the wedge-shaped knee meniscus is based on its stiff prevailing circumferential collagen architecture that resists tensile deformation [2,3]. Adding to its complexity, radial tie fibers and sheets are interwoven amongst these fibers, increasing stiffness in the transverse direction and binding the tissue together [4]. In the annulus fibrosus, multiple anisotropic lamellae are stacked in concentric rings with their prevailing fiber directions alternating above and below the horizontal axis in adjacent layers [5]. The high circumferential tensile properties of this laminate structure allow it to resist bulging of the nucleus pulposus with compressive loading of the spine. Given their structural properties, unique form, and demanding mechanical environments, the knee meniscus and the AF region of the IVD represent two of the most challenging tissues to consider for functional tissue engineering.
Computational Simulation of Anterior-Medial Tibial Tuberosity Transfer: Optimization With Simulated Annealing
Authors: Baldwin Mark A. , Langenderfer Joseph E. , Farr Jack , Rullkoetter Paul J.
Published: March 2014

Patellofemoral (PF) disorders remain complex and multifactorial. PF pathology, such as PF knee pain, excessive lateral pressure, and PF arthritis have been linked to excessive contact forces and pressure between the patella and femur [1]. Antero-medial transfer of the tibial tuberosity and tibial attachment of the patellar tendon is a procedure that was designed to reduce the PF contact pressure, thereby decreasing pain symptoms of early PF arthritis. The transfer procedure alters the angle between the patellar tendon and the quadriceps muscle force, and increases the patellar moment arm. These changes result in a reduction in the quadriceps force required for a given knee flexion strength, and in reduced contact pressure between the patella and femur. However, the tubercle movement also changes the flexion of the patella in the sagital plane, which alters not only regions of contact at various degrees of motion, but may also alter the contact area at these flexion ranges. PF forces, contact pressures and kinematics have been evaluated both prior to, and following, anteromedialization procedures in several cadaveric studies, e.g. [2]. Computational studies have evaluated the potential of anterior and medial tuberosity transfer to reduce PF contact pressure, including a study utilizing patient-specific models to analyze isolated anterior transfer at 15 and 20 mm, and combined antero-medial transfer at two different treatment levels for single, static flexion positions [3]. However, this study suggested that optimal tuberosity transfer required to decrease contact pressure was widely variable between patients and had less absolute decreases than earlier studies. This variability of contact pressure may translate clinically to patient comfort and thus, to maximize surgical outcome, it is likely necessary to identify a patient-specific parameter. Therefore, the purpose of the present study was to evaluate the feasibility of optimization, specifically simulated annealing, to determine the optimal amounts of anterior and medial transfer of the tibial tuberosity required to minimize peak patellofemoral contact pressure during a deep flexion cycle.
Defined Medium for the Self-Assembling Process: Enhancing Functionality of Tissue Engineered Articular Cartilage
Authors: Revell Christopher M. , Athanasiou Kyriacos A.
Published: March 2014

A self-assembling process has recently been developed that produces tissue engineered articular cartilage constructs of clinically-relevant dimensions with mechanical properties approaching one-third of native values [1]. These constructs, however, are cultured in 10% fetal bovine serum (FBS), which if eliminated, will make them more desirable as an in vitro cartilage replacement towards a translational approach. To this end, this study sought to assess the quality of self-assembled articular cartilage constructs exposed to varying amounts of FBS as well as a serum substitute that has recently been found to induce chondrogenic differentiation and increase cell proliferation [2].
Effects of Steady Spatial Wall Shear Stress Gradients on Endothelial Cell Morphology in Three-Dimensional Models
Authors: Rouleau Leonie , Farcas Monica , Tardif Jean-Claude , Mongrain Rosaire , Leask Richard
Published: March 2014

Endothelial cell (EC) dysfunction has been linked to atherosclerosis through their response to hemodynamic forces. Flow in stenotic vessels creates complex spatial gradients in wall shear stress. In vitro studies examining the effect of shear stress on endothelial cells have used unrealistic and simplified models, which cannot reproduce physiological conditions. The objective of this study was to expose endothelial cells to the complex shear shear pattern created by an asymmetric stenosis. Endothelial cells were grown and exposed for different times to physiological steady flow in straight dynamic controls and in idealized asymmetric stenosis models. Cells subjected to 1D flow aligned with flow direction and had a spindle-like shape when compared to static controls. Endothelial cell morphology was noticeable different in the regions with a spatial gradient in wall shear stress, being more randomly oriented and of cobblestone shape. This occurred despite the presence of an increased magnitude in shear stress. No other study to date has described this morphology in the presence of a positive wall shear stress gradient or gradient of significant shear magnitude. This technique provides a more realistic model to study endothelial cell response to spatial and temporal shear stress gradients that are present in vivo and is an important advancement towards a better understanding of the mechanisms involved in coronary artery disease.
A Two Dimensional Phenomenological Model for Damage of Arteries
Authors: Rachev Alexander
Published: March 2014

Loss of mechanical strength of arteries can manifest itself in many ways including rupture of a vulnerable atherosclerotic plaques, burst of saccular aneurisms, rupture of artery/graft anastomosis, and traumatic rupture of aorta by impact loading due to automobile accidents. In all cases the fracture of the tissue leads to sudden cardiovascular events that often have a lethal end. To date there are insufficient experimental data on the mechanical strength of healthy and diseased vascular tissue. Most of the results refer to the failure properties from uniaxial quasi-static tensile tests on strips and rings. It was found that the tensile strength is different in the circumferential and longitudinal direction especially when it is determined from strain controlled dynamic tests [1]. Results form load-controlled fatigue tests have shown a gradual softening of the arterial tissue, development of a residual (plastic) deformation, and existence of S-N curve [2]. However, the information from uniaxial tests is not sufficient to predict the damage of tubular segments due to coupling between circumferential and longitudinal stress via constitutive equations and deformed geometry. Moreover, the mechanisms of arterial tissue failure remain unknown.
Diametral Compression of Hollow Non-Circular Bone Sections
Authors: Womack Wesley J. , Puttlitz Christian M.
Published: March 2014

Many research endeavors involve strength testing of long bones from human or animal sources. Whole-bone four-point bending is appropriate for many applications, but recently diametral compression of short sections has been used to quantify local mechanical parameters [1, 2]. ASME standard WK88 covers strength testing of circular rings for brittle materials [3]. Testing of biologically-derived samples, however, entails a number of added complications, such as the non-circularity of bone sections, ambiguity of load orientation, thickness variation in a section, and size and shape variation between sections in a single sample. In order to quantify the effects of these confounding factors, finite element diametral compression models of a number of bone sections were compared with circular and elliptical sections.
Platelet and Shear Stress Interactions Within Asymmetric Stenotic Arteries
Authors: Shrum Jeff , Merhi Yahye , Leask Richard L.
Published: March 2014

Under normal physiological conditions platelets circulate in the plasma of blood and respond to vessel injury by changing shape, secreting granule contents and aggregating [1]. The activation of platelets in diseased or occluded arteries can form thrombosis causing a heart attack or stroke [2]. Shear stress activation has been suggested as an important contributor to increased platelet activation and adhesion seen in regions of stenosis.
Patient-Specific Finite Element Model to Simulate the Behaviour of a Scoliotic Spine
Authors: Lindberg Anne , Büchler Philippe
Published: March 2014

Adolescent idiopathic scoliosis is the most frequent deformity of the growing spine. Scoliosis predominantly affects girls during the adolescent growth spurt. Untreated deformities become social stigmas, are crippling and can compromise organ function. Therefore, uncontrollable progression of curvature and related complex deformities require operative treatment. Surgery is currently the only way to effectively decrease the angle of curvature. Unfortunately, operative methods are still based on principles introduced by Hibbs in 1911 — long, stiff bony fusion of a major portion of the thoracic and/or lumbar spine.
The Effects of Vasoactive Agents on Impedance Measures in the Pulmonary Circulation of Mice
Authors: Vanderpool Rebecca , Chesler Naomi C.
Published: March 2014

Pulmonary hypertension is a potentially fatal disease, resulting from chronic obstructive or interstitial lung disease, recurrent pulmonary emboli, antecedent heart disease, hypoxia or other unknown causes [1]. Pulmonary hypertension causes vascular remodeling with smooth muscle cell (SMC) hyperplasia and hypertrophy and accumulation of collagen and elastin [2]. This remodeling increases pulmonary vascular resistance, which can lead to increases in steady right ventricular work [3]. The effects of remodeling on pulmonary vascular impedance, which determines pulsatile right ventricular work, remain incompletely described. We have previously quantified the effects of chronic hypoxia-induced pulmonary hypertension (HPH) on pulmonary vascular impedance [4] but did not investigate the role of SMC tone either before or after HPH. The aim of this study was to investigate the effects of normal and increased SMC tone on pulsatile pulmonary hemodynamics before and after HPH-induced pulmonary vascular remodeling. We hypothesized that SMC contraction would increase input resistance but decrease the speed of wave reflections. We also hypothesized that increased arteriolar muscularization after HPH would lead to greater increases in resistance and greater decreases in wave reflections with increased SMC tone.
Modeling of Stress Fiber Organization in Cyclically Stretched Cells
Authors: Wei Zhensong , Deshpande Vikram S. , McMeeking Robert M. , Evans Anthony G.
Published: March 2014

Numerical simulations that incorporate a bio-chemo-mechanical model for the contractility of the cytoskeleton have been used to rationalize the following observations. Uniaxial cyclic stretching of cells causes stress fibers to align perpendicular to the stretch direction, with degree of alignment dependent on the stretch strain magnitude, as well as the frequency and the transverse strain. Conversely, equibiaxial cyclic stretching induces a uniform distribution of stress fiber orientations. Demonstrations that the model successfully predicts the alignments found experimentally are followed by a parameter study to investigate the influence of the straining frequency and the transverse contraction of the substrate. The primary predictions are as follows. The fiber alignment increases with increasing cycling frequency. Transverse contraction of the substrate causes the stress fibers to organize into two symmetrical orientations with respect to the primary stretch direction.
Real-Time Measurement of Multi-Component Velocity Vectors Within Abdominal Aortic Aneurysms Using Echo PIV: Comparison of In Vitro and Computational Results
Authors: Liu Lingli , Zhang Fuxing , Wang Rui , Shandas Robin
Published: March 2014

Abdominal aortic aneurysms (AAAs) are localized balloon-shaped expansions commonly found in the infrarenal segment of the abdominal aorta, between the renal arteries and the iliac bifurcation. Abdominal aortic aneurysm rupture has been estimated to occur in as much as 3%–9% of the population, and represents the 13th leading cause of death in the United States, producing more than 10,000 deaths annually [1]. Thus, determining the significant factors for aneurysm growth and rupture has become an important clinical goal. From a biomechanical standpoint, AAA rupture risk is related to certain mechanical and hemodynamic factors such as localized flow fields and velocity patterns, and flow-induced stresses within the fluid and in the aneurysm structure [2]. Disturbed flow patterns at different levels have also been found to trigger responses within medial and adventitial layers by altering intercellular communication mechanisms. Thus, localized hemodynamics proximal, within and distal to AAA formations play an important role in modulating the disease process, and non-invasive and easy-to-implement methods to characterize and quantify these complex hemodynamics would be tremendously useful.
A Novel Measure of In-Vivo Knee Joint Laxity
Authors: Küpper Jessica C. , Ronsky Janet L. , Frayne Richard , Robu Ion , Loitz-Ramage Barbara , Hart David A.
Published: March 2014

Knee joint laxity can result from soft tissue injury, such as an anterior cruciate ligament (ACL) tear, or genetic factors such as joint hypermobility syndrome (JHS). The degree of a subject’s knee laxity along a continuous spectrum depends on the mechanical properties of the structures, and increased motion that typically follows joint injury. At some threshold along the continuum, instability becomes pathologic and the risk of further joint injury increases.
Structural Mechanism for Alteration of Collagen Gel Mechanics by Glutaraldehyde Crosslinking
Authors: Chandran Preethi L. , Coughlin Dezba G. , Paik David C. , Holmes Jeffrey W.
Published: March 2014

Cross-linking of fibrous collagenous tissues occurs during late-stage wound healing and during aging. The attendant changes in micro-scale kinematics and macro-scale mechanics are not well understood. In this study we used glutaraldehyde as a model cross-linking agent, and in vitro reconstituted collagen gel as a model collagenous tissue. Collagen gels are in vitro assembled hydrated networks of collagen fibrils. Glutaraldehyde is a commonly used cross-linking agent for bioprosthetic tissues and is chemically well-characterized. Glutaraldehyde cross-linking is known to decrease the deformability of arterial valves, but the micro-scale mechanism of its action is not known. In this study, collagen gels with anisotropic fibril orientation were subjected to increasing cross-link density, and the concurrent change in biaxial mechanical properties was monitored. The extent of cross-linking is determined by biochemical analysis. Structural modeling of the biaxial mechanics of a fibrous microstructure was performed for three potential cross-link mechanisms. The trends in the simulated mechanics for increasing cross-link density were compared against that of the experimental data.
Pediatric Blood Viscoelasticity Measurements
Authors: Nair Neema , Pantalos George M. , Sharp M. Keith
Published: March 2014

Motivated by questions related to flow in pediatric cardiovascular devices, the purpose of this study was to compare pediatric and adult complex viscoelasticity η* = ηV − iηE, where ηV and ηE are viscous and elastic components, respectively, measured in oscillatory flow in a capillary tube [Thurston 1972]. For normal blood, viscosity is increased at low shear rates by red cell aggregation and reduced at high shear rates due to disaggregation, orientation and deformation of red cells. The elastic part is also normally psuedoplastic, indicative of the deformation of red cell aggregates at high shear and individual cells at low shear, respectively.
Gelatinase B (MMP-9) Modulates Joint Inflammation and Cartilage Degradation After Overload Injury
Authors: Chen C. T. Christopher , DiTullio Alexandra , Deng Xianghua
Published: March 2014

Osteoarthritis is the leading cause for disability in the U.S. Primary osteoarthritis occurs progressively with age due to a variety of factors, while secondary osteoarthritis is usually the result of a sports or accident-related joint injury. Several recent studies found that degraded matrix in synovial fluid was surged within days after initial injury along with the elevation of matrix degradative enzymes, including matrix metalloproteinases (MMPs) and aggrecanases [1]. The elevation of degraded matrix could last for up to a decade, although it is not clear whether these degradative events are related to joint inflammation, the chronic presence of which is the hallmark of rheumatoid arthritis and often leads to joint degeneration.
Toward Determining a Dynamic Impedance Boundary Condition
Authors: Clipp Rachel B. , Steele Brooke N.
Published: March 2014

Computational modeling can be used to increase the understanding of fluid dynamics and offer predictive capabilities when used in vascular surgery planning. An important consideration for studies including the pulmonary vasculature is the impact of pulmonary impedance due to respiration and vessel compliance [1]. Currently, the outlet boundary conditions for this type of model consist of a flow profile or constant pressure. These boundary conditions do not reflect the geometry of the lung, effects of respiration, or the compliance of pulmonary vessels. To improve the accuracy of computational modeling of the pulmonary circulation, a dynamic impedance boundary condition will be developed that can be used to accurately represent respiration effects and provide information regarding wave speed and reflection in compliant arteries.
Compensatory Motion During a Bilateral Lifting Task for Transradial Prosthetic Design
Authors: Carey Stephanie L. , Highsmith M. Jason , Dubey Rajiv
Published: March 2014

Current improvements in the design of a transradial prosthesis include advanced technology in control systems and electronics that improve its functions. However these improvements often require excess mass distally along the prosthesis. A transradial prosthesis without a dynamic wrist component may cause awkward compensatory motion in the shoulder and elbow. It may be important to consider bilateral tasks such as lifting a 2.27 kg (5 lb.) box during the design process of a transradial prosthesis. The main purpose of this study was to determine if restricting motion of the wrist and forearm and thus simulating a basic transradial prosthesis, would cause significant compensatory movement(s) at the shoulder and elbow of either the affected or non-affected limbs during a bilateral lifting task. The second purpose of the study was to determine if the location of added mass of 96 g (mass of an electrical wrist rotator) would affect shoulder and elbow angles of both sides during the lifting task.
Computationally Efficient, Explicit Finite Element Model for Evaluation of Patellofemoral Mechanics
Authors: Baldwin Mark A. , Rullkoetter Paul J.
Published: March 2014

Patient-specific finite element (FE) models can provide clinically relevant information about contact mechanics and kinematics that may be difficult or infeasible to obtain otherwise, and have potential to guide pre-operative planning. However, substantial uncertainty in model variables exists in patient-specific modeling, and suggests a probabilistic approach. Although efficient probabilistic methodology has been recently developed, multiple analyses are still required, and computational time for a fully deformable FE model throughout a flexion cycle has typically made this impractical. Therefore, the goal of the present study was to develop an explicit FE model of the patellofemoral joint with deformable cartilage and deformable, wrapping extensor tendons, and to compare kinematic and contact mechanics results with a model modified for computational efficiency. The efficient model incorporated rigid femoral and patellar cartilage representation with an optimized contact pressure–surface overclosure relationship, and composite-fiber tendons.