bluuebunny/crossref_metadata_2025 huggingface dataset:
CFD Simulation of the Sidewall Fired Tubular Reforming Furnace
Authors: Nielsen Per , Christiansen Lars J.
Published: July 2013

This paper describes simulations of Haldor Topsoe designed reforming furnaces. These furnaces are fired by a matrix of burners on the two sidewalls. The burners provide the heat needed for the reactions taking place inside vertical catalyst-filled tubes. The main objective is to get a better understanding of the flow and temperature field on the flue gas side, thus making it possible to enhance the design of high efficiency reformers. The simulations on the furnace side include models for combustion and thermal radiation. A separate CFD simulation is performed on the process side. An appropriate method has been introduced for the coupling of the furnace model with the process model thus eliminating the need for using an assumed temperature profile as boundary condition on the outer tube walls. The computational model has been verified by performing simulations on a pilot reformer. The numerical results agree well with the experimental data.
A Diameter Matched Comparison of Wall Stress and Rupture Potential Index for Abdominal Aortic Aneurysm
Authors: Gee M. W. , Maier A. , Reeps C. , Eckstein H.-H. , Wall W. A.
Published: July 2013

Increased blood pressure and arterial wall degradation lead to formation of abdominal aortic aneurysms (AAA). As elective AAA surgery is not without potential risk it is common practice to balance risk of rupture against risk of intervention. Usually a max. AAA diameter is the clinically accepted parameter where diameter > 55mm indicates intervention. However, it has been shown that computational wall stress analyses is a better indicator for rupture risk, e.g. by Fillinger et al 2003. In the presented study we use highly advanced FEA and statistical wall strength models to investigate whether current computational biomechanics analyses yields significant results when applied to groups of AAA with matched diameter in the decision-critical regime of approx. 55mm. For this purpose diameter matched groups of asymptomatic and ruptured/symptomatic AAA are examined and significance of computational rupture risk predictors is studied.
Endothelial Cell Migration in Patient-Specific Models of Intracranial Aneurysm
Authors: Jou Liang-Der
Published: July 2013

Effects of wall shear stress on atherosclerotic disease are widely studied, but its effects on intracranial aneurysms are less clear. In vitro studies have demonstrated that endothelial cells (EC) go through morphological changes under abnormal wall shear stress, and these studies have also shown that abnormal wall shear stresses lead to a non-uniform EC distributions [1, 2]. Since endothelial cells play a critical role in mechanotransduction, a sub-optimal distribution of EC may affect remodeling of vessel wall.
Developing Brain and Heart Cells Respond Similarly to Altered Mechanical Loads
Authors: Filas Benjamen A. , Bayly Philip V. , Taber Larry A.
Published: July 2013

Past studies have shown that the mechanical environment plays a critical role in regulating tissue development and function. For example, in the embryonic heart abnormal internal pressures cause morphological adaptation leading to aberrant morphogenesis [1]. Similarly, increasing luminal pressure in the early brain results in hyper-proliferation of the neuroepithelium [2]. Less is known, however, about how embryonic precursor cells quantitatively adapt to changes in loading, especially in vivo and across tissue types. These data would be valuable in determining the role of altered mechanical loads in congenital defects.
A Coupled Particle-Continuum Model of Nanoparticle Targeted Delivery Under Vascular Flow With Experimental Validation
Authors: Liu Yaling , Nguyen Kytai , Mariyappa Manohara , Kona Soujanya , Tan Jifu
Published: July 2013

Nanomedicine poses a new frontier in medical technology with the advantages of targeted delivery and patient specific design. In applications of nanoparticle targeted drug delivery, the delivery efficiency is controlled by the physical properties of the nanoparticle such as its size, shape, ligand density, as well as external environmental conditions such as flow rate and blood vessel diameter. Proper drug dosage choice relies on determination of the attachment and detachment rates of the nanoparticles at the active region and the understanding of the complex process of targeted drug delivery. A few particulate models have been proposed to study the adhesion individual spherical or non-spherical nanoparticles on receptor coated wall. Meanwhile, continuum convection-diffusion-reaction models have been widely used to calculate the drug concentration under various conditions, which usually assumes specific binding and de-binding constants. In reality, these binding and de-binding rates largely vary with physical properties of the particles and local flow conditions. However, there has not been any study that links the particulate level nanoparticle size and shape information to the system level bounded particle concentration. A hybrid particle binding dynamics and continuum convection-diffusion-reaction model is presented to study the effect of shear flow rate and particle size on binding efficiency. The simulated concentration of bounded nanoparticles agrees well with experimental results in flow chamber studies.
Modeling of Red Blood Cell Dynamics Using Fluid Structure Interaction (FSI) Technique
Authors: AlMomani T. D. , Vigmostad S. C. , Udaykumar H. S. , Chandran K. B.
Published: July 2013

Red blood cells (RBCs) or erythrocytes are biconcave disks with diameter of 8μm and thickness of 2 μm. RBC can be considered as a nucleus free deformable capsule enclosed by a flexible membrane and consisting of an incompressible viscous fluid [8, 9]. The deformation of RBCs is thought to play a major role in both RBC dynamics and functionality. Previous studies have indicated that two important characteristics related to deformation of the RBC [1]: i) the interior of the RBC is a liquid state that surrounded by an elastic membrane, ii) the biconcave shape of the RBC enables it to deform into a wide varieties of shapes without inducing any stresses in the cell membrane.
Biceps Tendon Changes Along Its Length, and With Altered Loading, in the Presence of Rotator Cuff Tears in a Rat Model
Authors: Peltz Cathryn D. , Hsu Jason E. , Glaser David L. , Soslowsky Louis J.
Published: July 2013

Biceps tendon pathology is commonly seen in the presence of rotator cuff tears and is often identified as a source of shoulder pain. However, the contribution of the biceps tendon to shoulder function is controversial and therefore the etiology of this pathology and its optimal treatment are unknown. Degeneration, inflammation and altered loading have all been hypothesized as possible mechanisms for biceps tendon pathologies. A previous study began to investigate the contribution of altered loading to these pathologies and showed that 4 weeks of increased loading resulted in decreased mechanical properties along the entire length of the tendon while decreased loading resulted in increased stiffness at the insertion site but decreased properties elsewhere [1]. Building on this study, the objective of the present study was to determine the effects of a longer period of altered loading along the length of the biceps tendon in order to determine where biceps tendon pathology originates following rotator cuff tears in a rat model. We hypothesized that: 1) increased loading would result in decreased mechanical and histological properties and decreased loading would result in increased mechanical properties and organization and 2) modulus and organization would increase along the length of the biceps tendon.
Reversed Correlations Between Atherosclerotic Carotid Plaque Progression and Flow Shear Stress/Plaque Wall Stress Based on Past and Current Scan Data: In Vivo MRI-Based 3D FSI Studies
Authors: Yang Chun , Canton Gador , Yuan Chun , Hatsukami Thomas , Tang Dalin
Published: July 2013

It has been well accepted that low and oscillating blood flow shear stresses (LFSS) correlate positively with intimal thickening and atherosclerosis initiation [1,2]. However, the LFSS hypothesis cannot explain why advanced plaques continue to grow under elevated high flow shear stress conditions [3]. For patient tracking studies, plaque progression is often measured by the difference of plaque geometries between two scans (“past” and “current” scans) when medical imaging is used. Mechanical flow shear stress (FSS) and plaque wall stress (PWS) conditions from the two scans may have different correlations with plaque progression. Using 2D structure models based on in vivo magnetic resonance imaging (MRI) human carotid plaques, Tang et al. showed that 18 out of 21 patients had significant negative correlation between plaque progression measured by wall thickness increase (WTI) and plaque wall stress from current scan [3]. The correlation was reversed when plaque wall stress from past scan was used. In this paper, 3D fluid-structure interactions (FSI) models for 32 matched “past-current” scan pairs of human atherosclerotic carotid plaques based on in vivo MRI data were solved and plaque wall stress (PWS) and flow shear stress (FSS) data were obtained to quantify their correlations with plaque progression measured by WTI.
Does Spontaneous Blinking Increase Iris-Lens Contact?
Authors: Amini Rouzbeh , Barocas Victor H.
Published: July 2013

The constant flow of aqueous humor (AH) in the anterior eye provides avascular tissues, notably the lens and cornea, with oxygen and nutrients (Fig. 1a). The hydrodynamics of AH and the iris contour are directly related to each other and abnormality of one may cause abnormal behavior in the other one. For example, in primary angle closure glaucoma, the abnormal anteriorly-located iris blocks the outflow pathway of AH. Increased AH pressure, in return, may push the iris more towards the anterior and worsen the blockage.
Non-Specific Endothelial Cell Interactions With the Substrate Result in Cell Activation and Angiogenesis In Vitro
Authors: Cho Hongkwan , Sheikh Abdul , Narmoneva Daria A.
Published: July 2013

Vascularization is critical for success of tissue engineering applications. Previous studies by us and others have shown that self-assembling peptide nanoscaffold RAD16-II promotes de novo capillary formation (angiogenesis) in vitro and neovascularization in vivo, and is a promising material for tissue engineering applications [1, 2]. However, the molecular mechanisms for cell interactions with this material are not known. Angiogenesis is mediated via interactions between integrins, which are expressed on the surface of activated endothelial cells (ECs), and extracellular matrix proteins. Among several integrins, αvβ3 is the most abundant and influential receptor regulating angiogenesis [3]. The αvβ3 integrin binds to its ligands via Arg-Gly-Asp (RGD) biding motif. However, there are no RGD motifs on RAD 16-II peptide. Instead, it contains three RAD motifs. Studies have shown that non-specific binding of αvβ3 with RAD can be retained through R and D sides [4]. The objective of this study, therefore, is to elucidate the underlying molecular mechanisms of RAD16-II nanoscaffold interactions with microvascular endothelial cells. We hypothesize that non-specific interactions between RAD16-II peptide nanoscaffold and αvβ3 integrin result in phosphorylations of β3 cytoplasmic domain, which then activate downstream angiogenic signaling pathways and promote angiogenesis.
Validation of Finite Element Models for Plantar Pressure in an Orthotic for Clubfoot
Authors: Rizza Robert , Liu Xue-Cheng , Thometz John , Lyon Roger , Tassone Channing , Van Valin Scott
Published: July 2013

Ponseti’s method, which implements a series of castings, has become popular in the treatment of clubfoot. Although this non-surgical procedure has found wide clinical use and there are significant improvement of clubfoot deformities and foot function, residual clubfoot deformities with a range of 11% to 47% still occur [1].
Effect of Needle Puncture Injury on Human Intervertebral Disc Mechanics
Authors: Natarajan Raghu N. , Espinoza Alejandro , Andersson Gunnar B. J.
Published: July 2013

Diagnosis, repair and regeneration of the disc often necessitate needle injection to the nucleus pulposus through the annulus. Discography in which a radio opaque material is injected into the nucleus and electrothermal treatment involving inserting a catheter into the disc requires disruption of the annulus through needle puncture. Annulus puncture may also be required during placement of nucleus implants. Needle puncture is also used to inject growth factors, gene and cell therapy for regeneration of the disc. In animal models, disc degeneration is induced over time by needle puncture of the annulus. The severity of the degeneration depends on the magnitude of the annulus needle puncture. One thing that is not clear is how much of the observed changes in the disc biomechanics and biochemical changes are due to nucleus treatment and how much is due to annular disruption through needle puncture. Animal model studies have shown that significant changes in disc mechanics were noticed within 1 week of needle puncture with a large-gauge needle. Another in-vitro animal study showed that biomechanical changes were observed in the disc when the ratio of needle diameter to disc height is greater than 40%. All these studies were focused on the effect of small number of needle diameters and addressed using animal cadaver models. How these needle puncture injury studies on small and large animal models can be extrapolated to human conditions is still not known. Thus there is need to evaluate effect of range of needle puncture diameters in human lumbar disc biomechanics. The purpose of this study is, with the help of a finite element models, quantify the biomechanical effect due to varying size of needle punctures in a human lumbar intervertebral disc.
Congruency of Scapula Locking Plates: Implications for Implant Design
Authors: Nguyen Thuc-Quyen D. , Park Andrew Y. , DiStefano James Guido , Buckley Jenni M. , Montgomery William H. , Grimsrud Christopher D.
Published: July 2013

While often treated non-operatively, certain displaced scapular fractures have shown improved clinical results with open reduction and internal fixation [1, 2]. Common methods of internal fixation for fractures of the scapula include non-locking and locking fracture plates. Locking scapula plate designs have several advantages over other repair techniques. First, they are site-specific and pre-contoured, which reduces soft-tissue irritation. Soft-tissue irritation is a common patient complaint, ultimately resulting in revision surgery in 7.1% of all scapular fracture cases [3]. A second advantage of locking plate designs is that the fixed angle design also helps create a more stable construct in thin cortical bone. Lastly, the anatomical fit of the locking scapula plates allows for reconstruction of comminuted fractures.
Finite Element Model of Multi Level Cervical Laminoplasty
Authors: Kode Swathi , Kallemeyn Nicole A. , Smucker Joseph D. , Grosland Nicole M.
Published: July 2013

Cervical spinal stenosis is a medical condition caused by the narrowing of the spinal canal, possibly leading to the compression of the spinal cord or other nerve roots [1]. Surgical options include an anterior approach involving decompression and fusion or a posterior approach involving laminectomy and fusion or laminoplasty. Laminoplasty, considered an alternative to laminectomy, is a procedure intended to relieve pressure on the spinal cord while maintaining the stabilizing effects of the posterior elements of the vertebrae.
Inclined Direct Shear Testing Device: A New Tool for Bone Mechanics and Osteoporosis Research
Authors: Abousleiman Younane N. , Hoang Son K. , Tran Minh H.
Published: July 2013

Shear properties and strength are crucial for osteoporotic hip and wrist fracture risk assessment. This paper presents the design of a newly developed testing device for bone mechanical properties under circulation of different fluids. The device will ultimately be used to actively modify bone mineral content and porosity to simulate different stages of osteoporosis and directly measure the corresponding changes in mechanical properties. Preliminary results on intact bovine cancellous bones without fluid circulation showed excellent agreement with published literature data.
Head Impact Response: Pressure Analysis Simulation
Authors: Young P. G. , Pearce C. W. , Walker B. , Beldie L. , Cotton R.
Published: July 2013

A new approach to generating physical and numerical models of the human head is presented. In this study, analytical, numerical and experimental models were used in parallel to explore the pressure response of the human head as a result of low velocity impact.
Modeling of Gait Adaptations to Minimize Plantar Tissue Strain During Walking
Authors: Halloran J. P. , Ackermann M. , Erdemir A. , van den Bogert A. J.
Published: July 2013

Computational models often represent the most cost-effective approach to predict the behavior of musculoskeletal systems. Historically, dynamic musculoskeletal simulations have simplified representations of soft tissue structures, which makes it impossible to investigate the relationship between neuromuscular control and tissue loading. It is possible to overcome this limiting assumption by coupling a finite element model, e.g. of a foot, directly with a musculoskeletal model, e.g. of the lower extremity [1]. The goal of the current study was to apply this concept to the control of human gait and demonstrate that it is possible to have a gait pattern that minimizes internal foot deformation while satisfying an overall movement goal, e.g. minimal deviations from normal gait. Successful implementation will have wide-ranging implications such as finding therapeutic and rehabilitative movement patterns that relieve localized tissue loading.
Finite Element Algorithm for Frictionless Contact of Porous Permeable Media Under Finite Deformation and Sliding
Authors: Ateshian Gerard A. , Maas Steve , Weiss Jeffrey A.
Published: July 2013

Contact problems are fundamental to the study of biological tissues, especially in the area of diarthrodial joint biomechanics. Finite element formulations and implementations of the contact mechanics of porous media remain challenging, and only a limited number of studies have proposed solution schemes for these types of problems [1–3]. Unfortunately, finite element codes using these formulations are not generally available to the public. A commonly used commercial finite element implementation of porous media contact is provided by Abaqus FEA (www.simulia.com), which has been used for studying articular contact mechanics [4–6]. This implementation is also able to analyze large sliding and finite deformations. The Abaqus implementation allows the application of a ‘drainage-only-flow’ boundary condition that is inconsistent with conservation of mass across the contact interface. Furthermore, it does not automatically enforce free-draining conditions outside of the contact region while enforcing continuity of the contact traction and fluid flux across the contact interface.
Comparison of Experimental and Affine-Predicted Fiber Kinematics in Human Supraspinatus Tendon
Authors: Lake Spencer P. , Cortes Daniel H. , Kadlowec Jennifer A. , Elliott Dawn M. , Soslowsky Louis J.
Published: July 2013

Mathematical modeling approaches are frequently used to characterize and predict the mechanics of biological soft tissues. Structurally-based continuum models, which describe the relationship of the constituents’ properties (i.e., collagen fibers, matrix) to overall tissue properties, require knowledge of the relationship between microscopic (fiber) and macroscopic (tissue) deformation. The most common and straightforward approach is the use of an affine model, which assumes that local fiber kinematics follow the global tissue deformation. Although the affine assumption is often used in constitutive modeling, several studies have reported non-affine fiber behavior in soft tissue testing [1–2]. Our recent work has quantified the anisotropic and inhomogeneous mechanical and organizational properties of human supraspinatus tendon (SST) [3–4]. We have also utilized a fiber dispersion model to examine SST [5]; however the relationship between macroscopic and microscopic deformation in this tendon remains unknown. Therefore, the purpose of this study was to examine the affine assumption in human SST fiber kinematics by comparing experimentally-measured fiber alignment to the affine model prediction.
Experimental Measurement of the Migration Force at the Proximal End of an Aortic Endograft
Authors: Corbett Timothy J. , Callanan Anthony , McGloughlin Tim M.
Published: July 2013

Endovascular AAA repair has evolved since its inception in the late 1980s to become an accepted alternative to open surgery. This minimally invasive approach involves inserting a collapsed stent-graft through the vasculature to the AAA location and allowing it to expand to form a new conduit for blood flow [1]. EVAR carries lower operative risk than the traditional method and recovery times are significantly lower. It has been performed with considerable success in octogenarians and patients with significant comorbidities [1].
Aneurysm Rupture After Treatment With Flow Diverting Stent
Authors: Cebral Juan , Mut Fernando , Scrivano Esteban , Lylyk Pedro , Putman Christopher
Published: July 2013

Recently there has been increased interest in the use of flow diverting devices to treat intracranial aneurysms. The goal is to deviate the blood flow away from the aneurysm and promote its thrombosis and exclusion from the circulation. This therapy is mostly considered for large, geometrically complex, wide necked, unruptured aneurysms that are difficult or impossible to coil or clip. Recent trials using flow diverting stents have shown promising results [1]. However, little is known about the possible complications of these procedures. This paper presents a hemodynamic study of a cerebral aneurysm that was treated with a flow diverting stent and ruptured a few days later.
Hemodynamics of Ruptured and Unruptured Cerebral Aneurysms
Authors: Cebral Juan , Mut Fernando , Putman Christopher
Published: July 2013

Because the prognosis of subarachnoid hemorrhage due to the rupture of a cerebral aneurysm is very poor, preventive surgery or endovascular interventions are performed on most aneurysms. However, the risk of the interventions can outweigh the natural risk of rupture of unruptured aneurysms. Therefore, it would be highly beneficial if the risk of rupture of cerebral aneurysms could be reliably determined in order to treat only those aneurysms at higher risk. Current assessment of aneurysm rupture risk is based on geometric parameters such as size and aspect ratio. But, it is known that small aneurysms also rupture. Previous studies have suggested the use of computational models to identify hemodynamic characteristics that could be used to better assess the rupture risk of cerebral aneurysms [1]. The current study extends these previous analyses to a larger population sample and quantitative hemodynamic variables.
Mechanical Properties of the Glenohumeral Capsule Change With Simulated Injury
Authors: Voycheck Carrie A. , McMahon Patrick J. , Debski Richard E.
Published: July 2013

The glenohumeral joint suffers more dislocations than any other joint, most of which occur in the anterior direction. The anterior band of the inferior glenohumeral ligament (AB-IGHL) is the primary restraint to these dislocations and as a result experiences the highest strains during these events. [1] Injuries to the capsule following dislocation include permanent tissue deformation that increases joint mobility and contributes to recurrent instability. [2] This deformation can be quantified by measuring nonrecoverable strain. [3] Simulated injury of the capsule results in permanently elongated tissue and nonrecoverable strain. Current surgical repair techniques are subjective and may not fully address all capsular tissue pathologies resulting from dislocation. Surgeons typically repair the injured capsule by plicating the stretched-out tissue; however, these techniques are inadequate with 23% of patients needing an additional repair. [4] Quantitative data on the changes in the biomechanical properties of the capsule following dislocation may help to predict the amount of capsular tissue to plicate for restoring normal stability. Therefore, the objectives of this study were to quantify changes in stiffness and material properties of the AB-IGHL tissue sample following simulated injury (creation of nonrecoverable strain).
Histological Determination of Murine Plaque Mechanics and Implications for Plaque Rupture
Authors: Campbell Ian C. , Weiss Daiana , Oshinski John N. , Taylor W. Robert
Published: July 2013

Among the most common models in atherosclerosis research is the atherosclerosis-prone mouse. Genetically manipulated mouse strains such as the ApoE−/− mouse will reliably form plaques under certain conditions, and these lesions have been noted to exhibit morphological and biochemical similarities with human atherosclerotic plaques. Unlike plaques in humans, however, murine plaques are not observed to rupture and form occlusive thrombi [1]. As atherosclerosis and its complications are the leading cause of death in the modern world, a comprehensive understanding of the mechanisms of plaque disruption is essential to develop diagnostic and interventional techniques. Although the mouse model is frequently employed to study plaque formation, its validity for studying plaque disruption events such as rupture or erosion has been questioned.
Experimental and Probabilistic Finite Element Analysis of Distal Femoral Fractures: A Comparison of Locking Plate Versus Intramedullary Nail Fixation
Authors: Salas Christina , Mercer Deana , DeCoster Thomas A. , Reda Taha Mahmoud M.
Published: July 2013

In the treatment of unstable, distal, metaphyseal femoral fractures, surgeons have multiple implant options for fixation. Biomechanical studies of intramedullary nailing systems and locking plates have shown that both systems achieve stable fixation of the fracture to allow healing.1–3 These systems are indicated for comminuted fractures, non-unions, and osteoporotic bone where distal femur fractures are associated with a 20% mortality rate in elderly individuals.4 Though capable of achieving stable fixation, both locking and non-locking plates have been associated with periprosthetic fractures in osteoporotic and normal bone.4–6 A recent clinical study reported a 2.6% incidence of periprosthetic fractures at the locking plate end.7
Determination of In Situ Articular Cartilage Pericellular Matrix Properties via Inverse BEM Analysis of Chondron Deformation
Authors: Kim Eunjung , Guilak Farshid , Haider Mansoor A.
Published: July 2013

The pericellular matrix (PCM) of articular cartilage is the narrow tissue region surrounding all chondrocytes. Together, the chondrocyte and its surrounding PCM have been termed the chondron. In normal cartilage, the presence of type VI collagen is exclusive to the PCM, and the PCM is believed to play a critical role in regulating biomechanical cell-matrix interactions. Since the PCM is stiffer than the chondrocyte, it has been hypothesized to play a critical role in protecting the cell while, simultaneously, facilitating the transmission of mechanical signals to the cell. Previous studies that represent the cell, PCM and extracellular matrix (ECM) as linear biphasic materials have supported this hypothesized role for the PCM [1–4]. Previous in vitro micropipette studies of isolated chondrons [5–7] have shown that the PCM Young’s modulus ranges between 25–70kPa in middle and deep zone cartilage, separating it by an order of magnitude from both the chondrocyte stiffness (∼1kPa) and ECM stiffness (∼1MPa). In recent years, Choi et al. [8] measured changes in the three-dimensional morphology of the chondron, in situ within the ECM, under equilibrium unconfined compression of porcine cartilage explants subjected to 10–50% compressive strain (Fig. 1). Their study employed a novel 3D confocal microscopy technique, based on immunolabeling of type VI collagen, that yielded ellipsoidal approximations of undeformed and deformed chondron shapes in the superficial, middle and deep zones of the explant. In this study, an efficient computational model, based on the boundary element method (BEM), was developed and used to estimate cartilage PCM linear elastic properties based on the data reported in Choi et al. [8] for the case of middle zone cartilage under 10% compressive strain.
Effects of Fluid Shear Stress on Endothelial Cell Invasion Into Three-Dimensional Matrices
Authors: Kang Hojin , Kwak Hyeong-Il , Kaunas Roland , Bayless Kayla J.
Published: July 2013

Angiogenesis, the formation of new blood vessels from pre-existing structures, is a key step in development, wound healing and pathological events (1). ECs in the vascular system must continually sense and respond to both biochemical and mechanical stimuli to appropriately initiate angiogenesis. Therefore, studying the combined influences of fluid wall shear stress (WSS) and pro-angiogenic biochemical factors on ECs on 3D matrices is critical to precisely define the signals that initiate sprouting angiogenesis, where normally quiescent ECs must transition into an invading phenotype. Sphingosine-1-phosphate (S1P) is a potent pro-angiogenic factor that we previously reported to be critical for EC invasion (2).
The Adaptive Response of Endothelial Transcription to Increased Shear Stress In Vitro
Authors: Zhang Ji , Friedman Morton H.
Published: July 2013

Previous studies have shown a substantial effect of shear stress on endothelial phenotype and functions such as production of nitric oxide, secretion of growth factors, inflammatory responses, production of reactive oxygen species, permeability to macromolecules and cytoskeletal remodeling [1–3]. However, the dynamics of the endothelial adaptive response to changes in shear stress are largely unknown. The response of vascular endothelial cells to alterations in shear stress is an essential component of normal endothelial physiology, since local shear stress can be altered in vivo by the global hemodynamic changes that are caused by daily activities such as exercise, sleep, smoking and stress. The duration of these changes ranges from minutes to hours. When adapting to the altered shear stress, endothelial cells undergo a series of structural remodeling and morphological changes, and a transient alteration of endothelial phenotype will be induced. An understanding of the transient regulation of endothelial phenotype will not only improve our knowledge of normal endothelial physiology but also yield insights into mechanisms underlying atherogenesis.
Patient-Specific Finite Element Analysis of Carotid Artery Stenting
Authors: Conti Michele , Auricchio Ferdinando , De Santis Gianluca , De Beule Matthieu , Verhegghe Benedict
Published: July 2013

At present, the clinical trend to treat peripheral atherosclerotic vessels, such as the carotid or the superficial femoral artery, is to apply percutaneous techniques using Nitinol self-expanding stents.
Effect of Solvent on Electrospun PLLA Fiber Mechanical Characteristics and Ligament Fibroblast Responses
Authors: Liu Chun-Yuan , Chang Wei-Ren , Tsai Wei-Bor , Chao Pen-Hsiu Grace
Published: July 2013

Due to the poor healing ability of anterior cruciate ligaments (ACL), surgical interventions with graft materials are often needed to reconstruct the knee joint. Electrospinning is widely utilized to manufacture highly aligned fibrous materials. When cultured on such substrates, ligament fibroblasts are known to exhibit elongation and enhanced collagen production [1, 2]. Poly-L-lactic-acid (PLLA) is a popular biocompatible material with high mechanical strength, and is most often used in electrospinning with chloroform as solvent. Hexafluoropropanol (HFP), another solvent, generates more uniform and consistent electrospun PLLA fibers. In this study, we investigated the effects of electrospun PLLA fiber scaffolds using different solvent on ligament tissue engineering. PLLA fibers electrospun with chloroform or HFP were compared for their structure and mechanical characteristics. We also investigated their effects on ligament cell morphology and proliferation. Further analysis of composite fiber bilayers were also performed [3].
The Geometry of Connective Tissue Planes Accentuates the Biophysical Response to Traditional Acupuncture: An In Vitro Study
Authors: Julias Margaret , Buettner Helen M. , Shreiber David I.
Published: July 2013

In traditional acupuncture, fine needles are inserted and rotated at defined points that correspond to specific therapeutic effects, which can occur locally or at a distance from the needling point. The majority of acupuncture points co-align with fascial planes under the skin, which present more subcutaneous loose connective tissue [1] (Fig 1 – black dot). Needle rotation induces this connective tissue specifically to couple to and wind around the needle, forming a whorl of alignment and generating measurable force on the needle that is significantly higher at fascial planes in comparison to insertion above a muscle (Fig 1A – black dot) [2, 3]. At these planes, the loose connective tissue is bounded on two sides by skeletal muscle and generally becomes narrower with increasing depth, presenting distinct geometry and boundary conditions compared to locations above a muscle, which resembles an infinite plane (Fig 1B&C).
Bilateral Laminar Hook Placements Reduces Pedicle Screw Pull Outs in Long Pedicle Screw Fixation
Authors: Kiapour A. , Sairyo K. , Terai T. , Goel V. K. , Ebraheim N. A.
Published: July 2013

The pedicle screw (PS) system has been widely used for the spinal reconstruction. Even for the osteoporotic spine, PS system has been the first choice for the instrumentation. However, the usage of PS in the porotic spine seems to be challenging. When the PS is inserted in the osteoporotic vertebrae, the PS is sometimes loosened; eventually, it shows back out, because the PS cannot hold bones with osteoporosis efficiently [1,2].
Moduli and Stress Patterns Determined From Heterogeneous MRI-Based Strains
Authors: Butz Kent D. , Chan Deva D. , Nauman Eric A. , Neu Corey P.
Published: July 2013

Characterization of stress and strain patterns in load-bearing tissue such as articular cartilage is key to developing successful treatment strategies for osteoarthritis, a degenerative disease affecting 27 million people in the United States alone [1]. Moreover, knowledge of the stress and mechanical properties of cartilage provides a more comprehensive characterization of tissue integrity during tissue degeneration or repair.
Regulation of Articular Cartilage Volumetric and Compressive Properties by Sequential Application of IGF-1 and TGF-β1 During In Vitro Growth
Authors: Dills Kristin J. , Van Donk Jennifer R. , Williams Gregory M. , Smith Stephanie A. , Chen Albert C. , Raub Christopher B. , Hazelwood Scott J. , Sah Robert L. , Klisch Stephen M.
Published: July 2013

Articular cartilage (AC) is a load bearing material that provides a low friction wear resistant interface in synovial joints. Naturally-occurring and stimulated intrinsic repair of damaged AC is challenging [1]. Thus, there is a need to guide the formation of tissue of specific size and mechanical properties for AC repair. Previous studies [2,3] with immature cartilage have shown that culture with medium containing TGF-β1 results in enhanced mechanical integrity while culture with IGF-1 results in diminished mechanical integrity. Conversely, culture with medium containing IGF-1 results in substantial volumetric growth while culture with TGF-β 1 results in little or no volumetric growth.
The Effect of Impeller Position on CFD Calculations of Blood Flow in Magnetically Levitated Centrifugal Blood Pumps
Authors: Fraser Katharine H. , Taskin M. Ertan , Zhang Tao , Richardson J. Scott , Gellman Barry , Dasse Kurt , Griffith Bartley P. , Wu Zhongjun J.
Published: July 2013

Cardiovascular disease is the leading cause of mortality globally. Among various forms of cardiovascular disease, heart failure (HF) affects 5.7 million patients in the United States with about 670,000 new patients diagnosed for the first time annually (1). The fatality rate for HF is high, with one in five people dying within 1 year (1). The number of deaths has increased (1) despite advances in surgical treatment and new pharmaceutical therapies. Many therapies are available to treat patients with HF, including lifestyle changes, medications, transcatheter interventions and surgery. However, despite optimal medical and surgical therapies, some patients still do not improve and the available therapies fail to control their symptoms; for them, cardiac transplantation may be the only treatment option. However, only approximately 2300 donor hearts become available each year resulting in around 2200 transplants (1), or only about 6% of the estimated 35,000 US patients who would benefit from a heart actually receiving a transplant. To address the need to support the circulation in patients with end-stage HF a wide variety of mechanical circulatory support devices (MCSDs) have been developed over the past four decades. These MCSDs have been developed as a bridge to transplant, a bridge to recovery, and as an end stage treatment. They can be implanted as a ventricular assist device (VAD) to support the left ventricle (LVAD) or the right ventricle (RVAD) or two devices are used to support both left and right ventricles (Bi-VAD).
Improvements in Rupture Prediction of Abdominal Aortic Aneurysms Using Local Mechanical Property Estimation Obtained From ECG-Gated Computed Tomography
Authors: Tierney Áine , Callanan Anthony , McGloughlin Tim M.
Published: July 2013

Cardiovascular disease concerns any disease which affects the heart or blood vessels. Aneurysms account for a significant portion of these cardiovascular diseases. The most common type of aneurysm is abdominal aortic aneurysm (AAA) which affects up to 5% of the population over the age of 55. AAA is a focal balloon like dilation of the terminal aorta that occurs gradually over a span of years [1]. There are approximately 200,000 patients in the US and 500,000 patients worldwide diagnosed with AAA each year [2]. The incidences of AAA’s has increased largely during the past two decades due in part to the aging demographic, the rise in the number of smokers, the introduction of screening programmes and improved diagnostic tools [3].
A Fluid Structure Interaction Simulation of the Cerebrospinal Fluid, Spinal Cord, and Spinal Stenosis Present in Syringomyelia
Authors: Liu Yifei , Martin Bryn A. , Royston Thomas J. , Loth Francis
Published: July 2013

Syringomyelia (SM) is a neurological disease in which a fluid-filled cystic cavity, or syrinx, forms in the spinal cord (SC) resulting in progressive loss of sensory, motor functions, and/or pain in the patient. It has been hypothesized that abnormal cerebrospinal fluid (CSF) pressure distribution and absorption in the subarachnoid space (SAS), resulting from a CSF flow blockage (stenosis), could be a key etiological factor for syrinx pathogenesis. In particular, the magnitude of the abrupt SAS pressure waves produced during coughing has been correlated with headache and pain in the patient.

To better understand the influence of coughing on the spinal SAS, four axisymmetric fluid-structure interaction (FSI) in silico models representative of various conditions associated with SM were constructed. Each of the models was subjected to a cough-like CSF pressure pulse.

The CSF flow stenosis was shown to attenuate and decelerate the CSF wave propagation in the SAS. The spinal SAS distensibility was also shown to have significant influence on the wave propagation. The in silico pressure results were found to be in agreement with a set of similar in vitro experiments [1].
Finite Element Analysis of Ox-Tail Segments With Intervertebral Pressure and Torque Applied
Authors: Cihlar Steven M.
Published: July 2013

Dr. Stokes [1] has proposed a vicious cycle hypothesis which relates the asymmetrical loaded spine of scoliotic adolescents to a progressive discal and vertebral wedging deformity. This hypothesis is mainly significant to the study of lateral spinal deformity (scoliosis), but can be related to the curvature experienced as a result of kyphosis (spinal curvature in the sagittal plane, which is the plane separating the body in left and right portions). The asymmetrical tissue remodeling causes a wedging effect that can gradually increase spinal curvature can, in some cases, be non-progressive. The effect of torsional loading to this specific spinal curvature could indicate that strategically applied muscular approaches to spinal activation could help prevent further curvature in less severe cases of spinal abnormalities.
Spatial Heterogenity of Iris Elasticity Measured by Indentation
Authors: Whitcomb Julie E. , Jouzdani Sara , Barocas Victor H.
Published: July 2013

Angle-closure glaucoma, pigment dispersion syndrome, and intraoperative floppy iris syndrome (IFIS) are all ocular disorders that involve abnormal morphologies of the iris. In angle-closure glaucoma, for example, the iris bows anteriorly and impedes the natural flow of the fluid (aqueous humor), which then increases the intraocular pressure (IOP) leading to vision loss. The iris contour is determined by a combination of external stresses arising from the flow of the aqueous humor [1] and internal stresses due to the passive and active components of the constituent tissues. We have previously shown that the iris has a mechanical asymmetry [2] and that posterior positioning of the dilator muscle within the iris contributes to the anterior bowing during dilation [3]; however, the relative contributions of the individual components of the iris are unknown.
Transverse Mechanical Properties of Human Lateral Meniscal Attachments
Authors: Moyer John T. , Abraham Adam C. , Killian Megan L. , Haut Donahue Tammy L.
Published: July 2013

The human knee joint bends during gait, running or similar dynamic activity. During such activity the ligaments and menisci provide joint stability. It is well know that the collagen fibers in knee ligaments are aligned parallel to the primary loading direction. In the knee meniscus, the fibers are aligned specifically to assist in the in vivo loading conditions. The human menisci are firmly attached to the tibia by means of ligamentous structures known as meniscal attachments [1]. Meniscal attachments are best modeled as fiber composite materials where the matrix is the ground substance and the collagen fibers are the reinforcement. The load is primarily transferred to the insertion sites which are designed to reduce the stress concentrations caused by the load transfer across the attachment-bone interface [1]. Determination of the transverse properties of human meniscal attachments will aid in the development of three dimensional knee joint models in which the attachments are treated as transversely isotropic, hyperelastic [2].
Anatomic Variation in the Elastic Inhomogeneity and Anisotropy of Cortical Bone Tissue is Consistent Across Multiple Donors
Authors: Rudy David J. , Deuerling Justin M. , Espinoza Oríaz Alejandro A. , Roeder Ryan K.
Published: July 2013

Elastic inhomogeneity in cortical bone tissue is commonly accounted for by power-law scaling relationships with apparent tissue density, mineral density, or porosity [1–4], but limited data exists for anatomic variation in elastic anisotropy [5]. Experimental investigations of the elastic inhomogeneity and anisotropy of cortical bone tissue have typically used specimens excised from the femoral mid-diaphysis due to expediency. However, the proximal and distal ends of the diaphysis are more clinically relevant to common orthopaedic procedures and interesting mechanobiology.
Role of Collagen Content and Cross-Linking in Large Pulmonary Arterial Stiffening During Hypoxic Pulmonary Hypertension
Authors: Wang Zhijie , Chesler Naomi C.
Published: July 2013

Chronic hypoxic pulmonary hypertension (HPH) is associated with large, conduit pulmonary arterial (PA) remodeling, which is characterized by morphological changes such as accumulation of collagen and elastin and wall thickening1–4. It is estimated that large PA stiffening accounts for over a third of the right ventricular workload increase in pulmonary arterial hypertension5. In this disease state, conduit PA stiffness is a strong predictor of mortality6, 7.
Cellular Uptake of Carbon Nanotubes Conjugated to Semiconductor Quantum Dots for Breast Cancer Imaging and Treatment Applications
Authors: Zimmermann Kristen A. , Zhang Jianfei , Dorn Harry , Rylander Christopher , Rylander Marissa Nichole
Published: July 2013

Carbon nanotubes (CNTs) are attractive materials for early detection, treatment, and imaging of cancer malignancies; however, they are limited by their inability to be monitored in vitro and in vivo [1]. Unlabeled CNTs are difficult to distinguish using elemental analysis because they are composed entirely of carbon, which is also characteristic of cellular membranes. Although some single walled nanotubes (SWNT) have been found to exhibit fluorescent properties, not all particles in a single batch fluoresce [2]. Additionally, these emissions may be too weak to be detected using conventional imaging modalities [3]. Incorporating fluorescent markers, such as fluorescent proteins or quantum dots, allows the non-fluorescent particles to be visualized. Previously, fluorophores, such as green fluorescent protein (GFP) or red fluorescent protein (RFP), have been used to visualize and track cells or other particles in biological environments, but their low quantum yield and tendency to photobleach generate limitations for their use in such applications.
Cell Death Assessment in Thermal Therapies of Human Tonsils
Authors: Suryadevara Suchil Kumar , Jimenez-Rios Jorge L. , Bhowmick Sankha
Published: July 2013

According to a survey by Harris Interactive on behalf of the American Academy of Otolaryngology – Head and Neck Surgery (AAO-HNS), approximately 600,000 tonsillectomies are performed every year. Post-operative pain and risks were found to be the major concerns of 90% of parents of children undergoing this procedure. Various technologies to completely or partially remove the infected tonsils have been developed over the years; the most common of which is the Dissection and snare method, in which the tissue is removed using forceps and scissors. Among other methods is the ablation of tissue by heating it using a CO2 Laser. There is, however, room for improvement on the effectiveness of the treatment in terms of post-operative care and cost. In order to address these issues, a laser-based heating device is proposed by Gradiant Research, LLC, (Concord, MA) which will heat the tonsil tissue using two opposing light-emitting, temperature-controlled surfaces that are pressed against the tonsils to create near-uniform temperature distribution on the bulk tissue. This work presents ex-vivo, thermal treatment experiments on freshly excised tonsil tissues to assess the corresponding cellular damage and support the development of the proposed method. An Arrhenius model uses the obtained results to determine the necessary exposure times.