bluuebunny/crossref_metadata_2025 huggingface dataset:
High Throughput Characterization of Cryoprotective Agent Mixtures Using an EWOD-Based Digital Microfluidic Device
Authors: Park Sinwook , Kunchala Praveen , Moon Hyejin , Han Bumsoo
Published: July 2013

One of the most challenging issues in cryopreservation is to identify new and improved cryoprotective agents (CPAs) or CPA mixtures beyond widely used dimethyl sulfoxide (DMSO). In order to address this challenge, numerous combinations of CPA mixtures need to be prepared, characterized, and screened. The characterization includes thermal properties and phase change behavior during freezing and thawing. For an example, Han et al. [1] performed analysis of the phase change behavior and the thermal properties of phosphate buffers saline (PBS) with various chemical additives (CPAs, AFPs, excess salts) using a differential scanning calorimeter and a cryo-microscope. Considering the number of possible compositions and concentration of CPA mixtures, a high throughput (HTP) screening platform capable of preparing and characterizing array of CPA mixtures is highly desired.
The Effects of Cryoprotective Agent on Spatiotemporal Deformation of Engineered Tissues During Freezing
Authors: Teo Ka Yaw , Dutton J. Craig , Han Bumsoo
Published: July 2013

Maintaining tissue functionality is crucial for successful cryopreservation. However, current understanding of the effects of cryopreservation including those of cryoprotective agents (CPAs) on post-thaw tissue functionality is still very limited. In numerous cryopreservation protocols, CPAs such as dimethyl sulfoxide (DMSO) are commonly used. Different concentrations and combinations of CPAs have been reported to be advantageous in maintaining post-thaw tissue functionality, but the determination of their optimum composition often requires extensive experimental studies due to the lack of understanding of their effects on the biophysics of the tissues during freezing.
Sliding Contact Loading Improves the Tensile Properties of MSC-Based Engineered Cartilage
Authors: Huang Alice H. , Baker Brendon M. , Ateshian Gerard A. , Mauck Robert L.
Published: July 2013

Articular cartilage is a load-bearing surface whose mechanical function arises from its unique properties. The structural and mechanical properties of mature cartilage are inhomogeneous through the depth and anisotropic. Tissue maturation is directed by mechanical forces; loading induces remodeling of the immature matrix, leading to increases in compressive and tensile properties and the development of tissue anisotropy [1, 2]. Limitations in cartilage repair strategies have engendered numerous efforts to engineer functional replacements. As mesenchymal stem cells (MSCs) undergo chondrogenesis in 3D culture, this cell type has been increasingly utilized in these efforts [3]. Despite their initial promise however, generating MSC-based constructs with the mechanical complexity and integrity of cartilage remains a challenge; the properties of MSC-seeded hydrogels are consistently lower than those of the native tissue [4, 5]. As mechanical stimulation is critical to cartilage development and maturation, bioreactor systems that simulate the native mechanical environment of cartilage may bridge these functional disparities. Indeed, dynamic axial compression enhances the compressive properties of both chondrocyte- and MSC-based engineered cartilage, though collagen content remains low [6, 7]. While promising, these studies were not designed to generate either depth-dependence or constructs with improved tensile properties. We therefore developed a new sliding contact bioreactor system that can better recapitulate the mechanical stimuli arising from joint motion (two contacting cartilage layers). In previous experiments using this system, we demonstrated improved expression of chondrogenic genes with short-term sliding contact of MSC-seeded agarose; these changes in gene expression were dependent on both axial strain and TGF-β supplementation [8]. Furthermore, FEM analysis of sliding contact showed that tensile strains (parallel to the sliding direction) and fluid efflux/influx were depth-dependent and highest in the region closest to the construct surface [8]. In the current study, we applied long-term sliding contact to MSC-seeded agarose constructs using the optimized parameters previously determined. We hypothesized that sliding contact would improve tensile properties and direct depth-dependent matrix remodeling.
Effect of ACL Reconstruction Graft Material on Joint Force Loss During Cyclic Fatigue Testing Using a 6-DOF Motion
Authors: Boguszewski Daniel V. , Shearn Jason T. , Wagner Christopher T. , Butler David L.
Published: July 2013

As many as 250,000 people suffer anterior cruciate ligament (ACL) injury annually [1]. As the primary ligamentous restraint to anterior tibial translation [2–3], the ACL is surgically reconstructed in an attempt to restore knee stability. However, up to 10–25% of reconstructions still fail [4]. While reconstructions restore antero-posterior kinematics, abnormal kinematics persist in other directions [5], leading to a shift in cartilage contact and poor adaptation to altered load [5]. With or without reconstruction, the likely prognosis after ACL injury is long-term osteoarthritis [6]. Improving this outcome requires assessment of the limitations of ACL graft reconstruction compared to normal ACL forces during simulated activities of daily living (ADLs). Our objective in this study was to evaluate the magnitude and temporal changes in force for the intact versus ACL-reconstructed knee over 2000 cycles of a simulated ADL.
Location of Plaque Ulceration in Human Coronary Arteries is Related to Shear Stress
Authors: van der Giessen Alina , Wentzel Jolanda , Groen Harald , de Feyter Pim , van de Vosse Frans , van der Steen Anton , Gijsen Frank
Published: July 2013

Vulnerable plaques are characterized by the presence of a large lipid pool, which is separated from the lumen by a thin fibrous cap. Rupture of this fibrous cap is generally regarded as one of the main underlying causes of cardiovascular events (1). The composition of the plaque plays a crucial role in the rupture process: it determines how blood pressure is translated into stresses in the wall, and composition also determines the strength of the tissue.
Depth Dependent In-Plane Shear Properties of the Corneal Stroma
Authors: Petsche Steven , Pinsky Peter , Chernyak Dimitri , Martiz Jaime
Published: July 2013

The popularity of refractive surgery to correct the vision of individuals with hyperopia or myopia is increasing. These procedures alter the tissue of the human cornea to cause a change in curvature (refractive power) of the cornea. Radial keratotomy, photorefractive keratectomy, LASIK, and LASEK are all types of refractive surgery. The outcomes of refractive surgical procedures must depend significantly on the biomechanical response of the tissue and therefore on the biomechanical properties of the cornea, or more specifically the corneal stroma which makes up 90% of the tissue. The missing link between computer models of these procedures and predicting patient outcomes is the biomechanical properties of the tissue, including shear modulus. This study aims to characterize the in-plane shear modulus of the corneal stroma through the depth by mechanical testing. Scant data, if any, exists about the shear stiffness and no data includes depth dependence. The stroma consists of sheets of collagenous lamellae in which fibrils are maintained at uniform spacing by glycoaminoglycan molecules. Studies have shown increased interweaving of the lamellae in the anterior third of the stroma compared to the central and posterior thirds [1]. Figure 1 shows the distinct interweaving in the anterior third [2]. It is hypothesized that more interweaving lamellae increases the in-plane shear stiffness. The shear modulus of the full cornea, as well as individual thirds, is examined in this study.
Patient-Specific Model of Iris Mechanics
Authors: Jouzdani Sara , Amini Rouzbeh , Barocas Victor H.
Published: July 2013

Over 2 million Americans suffer from glaucoma [1]. Certain types of glaucoma are directly related to the iris contour. For example, some cases of primary angle-closure glaucoma (PACG) involved with pupillary block, which the iris is abnormally positioned towards the anterior [2]. Generally, the iris contour is determined by two factors: external stresses arising from the flow of the aqueous humor (AH) and internal stresses due to the passive and active components of the constituent tissues.
In Vivo Hemodynamic Performance of Wild-Type vs. Mutant Zebrafish Embryos Using High-Speed Confocal Micro-PIV
Authors: Chen Chia-Yuan , Patrick Michael J. , Corti Paola , Frakes David , Roman Beth L. , Pekkan Kerem
Published: July 2013

In developing cardiovascular systems, definite performance comparison between disease and healthy hemodynamics requires quantitative tools to support advanced microscopy. Mutations in the activin receptor-like kinase 1 (ALK1) gene are responsible for the autosomal dominant vascular disease, hereditary hemorrhagic telangiectasia type 2 (HHT2), characterized by high flow arteriovenous malformations (AVMs) [1]. Recent studies show that the zebrafish mutant violet beauregrade (vbg), which harbors a mutation in alk1, develops an abnormal circulation with dilated cranial vessels and AVMs [2]. Quantitative understanding of mechanical influences on the alk1 mutant phenotype will aid treatment of HHT2 patients. Inspired by earlier studies that demonstrate the capability of using confocal micro-PIV technique to quantify biofluid dynamics in vivo [3], primarily in major vessels (dorsal aorta, vitelline veins), the present study focused on secondary branching great vessels of zebrafish embryos where microcirculation flow regimes are different. Furthermore, confocal microscopy, essentially being an imaging modality, requires rigorous validation efforts with respect to the gold standard measurement protocols (such as PIV) and synthetic scan data. Another objective of this work was to document the intra-species differences of wall shear stress (WSS) and flow physics during embryonic development in aortic arch systems of zebrafish [4].
Effects of Friction Coefficient and Receptor Number on Cell-Substrate Interactions During Migration
Authors: Wong Henry C. , Tang William C.
Published: July 2013

Biological tissues are composed of cells that adhere to the extracellular matrix (ECM) via cell-surface integrin receptors that bind to specific proteins, such as fibronectin, embedded in the matrix. In this manner, the ECM functions as a structural support for the attached cells, and mechanical forces are able to be transmitted from the cell to the ECM and vice versa [1]. Cell migration, a process that is highly dependent on these mechanical interactions, is important for many normal biological processes and diseases that occur in the human body, which include embryonic development, immune response, would healing, and cancer invasion [2]. Though many continuum models of cell migration have been proposed, there is still a need for a model that can be used to quantitatively understand the mechanical factors that can influence the movement of a cell on a substrate. This would be invaluable to the research areas of tissue engineering as well as cancer metastasis. We utilized a finite element model to elucidate the mechanism of cell-substrate interactions for a cell that consistently migrates in a single direction. Our model follows the approach taken by Gracheva and Othmer [2], but we extended their model to describe two-dimensional plane strain behavior.
Pressure and Flow Characterization for Different Idealized Models of Stenotic Coronary Arteries
Authors: Chen Jenny , Coogan Jessica S. , Kim Hyun Jin , Taylor Charles A.
Published: July 2013

Coronary artery disease is one of the leading causes of death worldwide. This year, an estimated 785,000 Americans will have a new coronary attack [1]. Treatment of coronary artery disease varies from medication alone to cardiovascular surgery. Treatment regimens depend on the number and hemodynamic significance of stenoses present. In this study, we created idealized models of stenotic coronary arteries with varying geometric properties and simulated flow and pressure in coronary stenoses using a novel computational method including a three-dimensional model of an idealized coronary artery coupled to a lumped parameter model of the heart at the inlet and a lumped parameter model of the distal coronary vasculature at the outlet.
The Nanostructure and Nanomechanics of a Novel Black Widow Spider Silk Assessed Using Atomic Force Microscopy
Authors: Tang Simon Y. , Hsia Yang , Vierra Craig
Published: July 2013

The black widow spider produces numerous silk types that serve unique biological and mechanical functions. Recently, a novel member of the spider silk family, Pyroform Spidroin 1 (PySp1), was identified from the attachment discs of black widow spiders. Here we investigate the nanostructure and the nanoscale material behavior of native PySp1 silks using atomic force microscopy.
Measurement of Biting Force Over Dental Implant
Authors: Biswas B. K. , Bag S. , Pal S.
Published: July 2013

Measurement of biting or chewing force is important as very little data regarding this is available in the literature. The biting force is generated by the action of the associated musculature of mandible and maxilla, ultimately transmitted through the teeth on the material which is being bitten or chewed. The objective was to find the range of magnitude of the force for each pair teeth. Biting force measurement was performed over dental implant to observe its biofunctionality. In this work, a load cell was used along with a newly developed transduction device for measuring force. The biting force was measured for ten subjects with dental implant and compared with normal subjects without any dental disease. Result showed our design of screw-root dental implant is comparable to normal tooth.
The Strain in the Medial Ulnar Collateral Ligament is Localized in Both the Anterior and Posterior Bands of the Anterior Bundle
Authors: Mohaghegh Motlagh Amin , Cook Harold A. , Kim Sunghwan , Kuxhaus Laurel , Brogdon Mandy , DeMeo Patrick J. , Miller Mark Carl
Published: July 2013

The multi-bundle structure of the medial ulnar collateral ligament (mUCL) has been documented [1]. Mechanically, the anterior bundle of the mUCL is the primary restraint to valgus stress of the elbow [2] and research has indicated that the anterior band of this bundle becomes taut in extension while the posterior band becomes taut in flexion [3]. Injury of the mUCL in throwing athletes due to overuse or extreme valgus load can require surgical repair. In order to achieve a successful surgical reconstruction of the UCL, one can expect the appropriate tension during graft placement to be an important variable. The strain in the ligament is known to vary with flexion angle. Therefore, the in situ strains of the mUCL are potentially vital information and determination of a flexion angle at which the native ligament has no strain may guide the repair. To determine the slack length, i.e., the reference length with no strain, previous work examined the particular regions of the anterior and posterior bands [3]. The slack length was readily determined, but all regions did not behave in the same way. The purpose of the current work was to determine whether a consistent behavior was apparent in each of the bands, that is, to determine if bands could be identified by consistent strains along their lengths.
Plaque Progression in a Human Coronary Artery is Associated With Low Wall Shear Stress and Extended Particle Residence Time
Authors: Suo Jin , McDaniel Michael , Eshtehardi Parham , Dhawan Saurabh , Avati Nanjundappa Ravi Prasad , King Andrew , Taylor Robert W. , Samady Habib , Giddens Don
Published: July 2013

Intravascular ultrasound (IVUS) evaluation was performed in the coronary arteries of a 45-year-old patient with stable angina during vigorous physical activity. Concurrent angiography demonstrated a mild plaque in the proximal left anterior descending artery (LAD), with obvious lumen dilatation immediately distal to the plaque. Blood velocity was measured by a catheter Doppler transducer at proximal and distal segments of the left coronary artery, and the left main artery (LM) and LAD were reconstructed using a 3D-IVUS reconstruction technique based on biplanar angiography and IVUS images, enabling simulation of the flow field in the artery employing computational fluid dynamics (CFD). Wall shear stress (WSS) and particle path lines were determined from the CFD studies. The patient returned for a follow up evaluation after 6 months, and plaque progression during this period was evaluated from the IVUS data. Results showed that low WSS, less than 5 dynes/cm2, which occurs in the region immediately distal to the plaque, correlates with localized progression of the lesion over the 6 month interval. The path line tracking computations showed that particles near the vessel surface where plaque progression was observed resided near the artery wall longer than one complete cardiac cycle, whereas in other areas particles were flushed through the region of interest rapidly. These observations in a specific individual are consistent with the hypothesis that plaque progression is related to low WSS and relatively long residence time of atherogenic blood-borne substances.
Wall Shear Stress in an MRI-Based Subject-Specific Human Aorta Using Fluid-Structure Interaction
Authors: Lantz Jonas , Renner Johan , Karlsson Matts
Published: July 2013

Wall shear stress (WSS) is well established as an indicator of increased risk for development of atherosclerotic plaques, platelet activation and thrombus formation [1]. Prediction and simulation of the sites of wall shear stresses that are deemed dangerous before intervention would be of great aid to the surgeon. However, the geometries used for these types of simulations are often approximated to be rigid. To more accurately capture the flow and arterial wall response of a realistic human aorta, fluid-structure interaction (FSI) which allows movement of the wall, is needed. Hence, the pressure wave and its effect on the wall motion are resolved and enables a more physiological model as compared to a rigid wall case.
Compression Testing of 3D Polymer Fabrics for Use as Cartilage Scaffolds
Authors: Rodts Timothy W. , Schmid Steven R.
Published: July 2013

The onset of osteoarthritis is characterized by damage to articular cartilage. Current treatments include pharmaceutical therapies and arthroplasty procedures. Work on a new type of device that uses orthogonal woven polymer scaffolds as a structure for tissue engineering of cartilage has been cited in the literature [1].
Individual Muscle Contributions to Whole-Body Angular Momentum During Normal Walking
Authors: Neptune Richard R. , McGowan Craig P.
Published: July 2013

Walking is a complex dynamic task that requires the generation of whole-body angular momentum to maintain dynamic balance and perform a wide range of locomotor tasks. Previous studies have shown that controlling angular momentum is essential to maintaining dynamic balance and preventing falls during walking [1] and recovering from a trip [2]. Others have suggested that angular momentum is highly regulated by the central nervous system [3] and that control synergies may be used to provide this regulation [4].
Effect of Pedicle Lengthening Screw on Biomechanics of Lumbar Spine
Authors: Kiapour A. , Goel V. K.
Published: July 2013

Lumbar spinal canal stenosis is a common cause of back and leg pain which occurs as the lumbar spinal canal narrows. The current surgical treatment for many patients with spinal stenosis is surgical decompression and spinal fusion with instrumentation. However there are several drawbacks associated with fusion surgeries including degenerative effect at segments adjacent to the fusion in long run [1,2]. Pedicle lengthening device is a new technology which is designed to be applied for treatment of spinal stenosis and replace the traditional fusion techniques.
Engineering Tools for Studying the Interplay Between Mechanics and Biology in Lymphatic Lipid Transport
Authors: Dixon J. Brandon
Published: July 2013

The lymphatic vasculature extends through most tissues of the body and plays an essential role in maintaining fluid balance, immune cell trafficking, and lipid transport. Nearly all dietary lipid is transported from the intestine to the circulation via the lymphatic system in the form of triglyceride-rich lipoproteins called chylomicrons. This process can be described through two different mechanisms: 1) entry of the chylomicron into the initial lymphatic vessels of the small intestine, known as lacteals, and 2) the transport of these chylomicrons through the larger collecting lymphatics by a complex and coordinated system of individual contracting vessel units (lymphangions) and valve leaflets. We describe here a set of in vitro and in vivo tools we have developed to study the mechanisms that modulate lipid transport under these two different paradigms and show how these tools are uncovering important biological features involved in these mechanisms. Lymphatic pump function is known to be sensitive to the mechanical load on the vessel as the contractility of isolated vessels has been shown to be both shear and stretch sensitive [1], yet whether these mechanisms are important in regulating contractile function in vivo remains uncertain.
Sub-Axial Cervical Spine Instability Following Unilateral Facet Injury: A Biomechanical Analysis
Authors: McLachlin Stewart D. , Rasoulinejad Parham , Gurr Kevin R. , Bailey Stewart I. , Bailey Chris S. , Dunning Cynthia E.
Published: July 2013

Unilateral facet injuries are relatively common in the sub-axial cervical spine. Facet fractures, capsular disruptions, and posterior ligament tears can all contribute to this type of injury resulting in a range of instability spanning undisplaced fractures to complete unilateral dislocations [1]. For a particular injury pattern, considerable variability exists in the choice of treatment, and the modality selected is frequently based on surgeon preference [2]. This is due, in part, to a lack of biomechanical studies focused on increasing the understanding of changes in spinal stability that occur following cervical spine injury.
Comparative Assessment of Sacral Screw Loosening Augmented With PMMA Versus a Calcium Triglyceride Bone Cement
Authors: McLachlin Stewart D. , Al Saleh Khalid , Gurr Kevin R. , Bailey Stewart I. , Bailey Chris S. , Dunning Cynthia E.
Published: July 2013

Instrumentation failure in the S1 pedicles as a result of the screw loosening created by large cyclic bending loads is well documented. Biomechanical studies have shown that pedicle screw augmentation with Polymethylmethacrylate (PMMA) can result in improved screw-bone interface strength [1].
Single Cell Mechanosensitivity to Cyclic Compression Using a Combined Atomic Force Microscope-Confocal System
Authors: Weafer Paul , Jarvis Suzi P. , McGarry Patrick J.
Published: July 2013

The experimental measurement of contractile forces generated by cells seeded in scaffolds subjected to cyclic stretching reveals a force-strain relationship that cannot be predicted by passive viscoelastic models. It was demonstrated that cells subjected to higher strain rates were shown to exhibit lower peak forces and lower stiffness than cells subjected to low strain rates [1]. It is hypothesized that this pattern results from increased stress fiber dissociation at high unloading strain rates. However, this hypothesis can only be fully validated by performing single cell experiments with live imaging of cytoskeletal dynamics.
Hexahedral Meshing of Subject-Specific Anatomic Structures Using Registered Building Blocks
Authors: Natarajan Amla , Magnotta Vincent A. , Grosland Nicole M.
Published: July 2013

Generating high quality, subject-specific, 3D finite element anatomic models with minimal user-intervention remains a challenge. Numerous automated tetrahedral mesh generators are available, but hexahedral meshes are preferred due to their higher accuracy and faster computational time over tetrahedral meshes. Historically, the generation of hexahedral meshes for analysis is a tedious and time-consuming task. Therefore, the utilization of hexahedral meshes is often limited to baseline models that are powerful, but not patient-specific. Once a high quality mesh has been created, it would be ideal if it can be used to create meshes of similar surfaces from different subjects, without disrupting mesh quality.
Robotic Simulation of the Effects of Surgical Placement of the ProDisc-L on Motion Segment Mechanics: An In Vitro Human Cadaveric Lumbar Model
Authors: Dhillon Braham K. , Wido Daniel M. , DiAngelo Denis J. , Bertagnoli Rudolph , Kelly Brian P.
Published: July 2013

A variety of lumbar total disc replacement (TDR) designs exist for the treatment of disc pathologies and several of which have undergone clinical trials. A key design parameter for a constrained ball and socket type device is a fixed center of rotation (CoR). A previous study [1] demonstrated that the lumbar motion segment unit (MSU) was highly sensitive to the anatomical location of the sagittal plane rotational axis. Malalignment between the implant CoR and the inherent rotational axis of the MSU may lead to an overloaded or over-constrained condition.
A Novel Trilayered Polymer Scaffold Mimicking Native Aortic Valve Leaflet
Authors: Chen Joseph , Wang Feng , Williams Lakiesha , Guan Jianjun , Liao Jun
Published: July 2013

The most common surgical therapy for heart valve disease is heart valve replacement via mechanical or bioprosthetic valves. These valves succeed in restoring blood hemodynamics but fail in the repairing/remodeling aspect that is essential for the pediatric population. Tissue engineered heart valves (TEHV) aim to solve this issue by implanting a functional living tissue with the ability to grow and remodel with the heart. Current efforts in the fabrication of synthetic scaffolds for TE heart valves have been lacking in structural consideration, treating it as a uniform mass. In this study, we addressed the leaflet mechanical integrity and structural characteristics. By utilizing electrospinning, we have generated a three layered polymer scaffold mimicking the trilayered structure in the aortic valve: fibrosa, spongiosa, and ventricularis. (Figure 1)
Quasistatic and Dynamic Compressive Behavior of Gelatin
Authors: Kwon Jiwoon , Subhash Ghatu
Published: July 2013

Gelatin has been extensively used as a tissue stimulant. Determination of properties and tits constitutive behavior is crucial to successful use of gelatin in these applications. In this study, ballistic gelatin was used because the recipe to prepare the gelatin and its quasi-static strength (250 bloom) of this particular type of gelatin is well known [1]. Although the study for high rate deformation is important to understand the damage from blast impact, majority of the currently available material property data is in quasi-static range [2,3]. Generally, polymeric materials (including human tissue) exhibit highly rate sensitive response [4]. Therefore, the understanding of the constitutive behavior for these materials at high rate loading is essential. This study will provide the rate sensitivity of gelatin by comparing the response under quasi-static and dynamic loading. In order to investigate the dynamic behavior of gelatin, the split Hopkinson pressure bar (SHPB) was used in this study. Because use of a solid metallic bar to test such soft materials does not provide an adequate transmitted signal, a polymer split Hopkinson pressure bar (PSHPB) was used to reduce the impedance mismatch between bar and soft gelatin specimen. The nature of dispersion and attenuation was corrected using an iterative scheme developed earlier [5].
Biomechanics of the Mitral Valve in Ischemic Heart Disease: Translating From the Bench to the Operating Room
Authors: Padala Muralidhar , Yoganathan Ajit P.
Published: July 2013

The Mitral Valve (MV) is the left atrioventricular valve that controls blood flow between the left atrium and the left ventricle (Fig 1A-B). It has four main components: (i) the mitral annulus — a fibromuscular ring at the base of the left atrium and the ventricle; (ii) two collagenous planar leaflets — anterior and posterior; (iii) web of chordae and (iv) two papillary muscles (PM) that are part of the left ventricle (LV). Normal function of the mitral valve involves a delicate force balance between different components of the valve.
Differential Osteogenic Marker Expression by Human Vascular and Valvular Cells in Tissue-Engineered Collagen Constructs
Authors: Ferdous Zannatul , Jo Hanjoong , Nerem Robert M.
Published: July 2013

Atherosclerosis and aortic stenosis are two of the most prevalent cardiovascular disorders and a major cause of death in elderly population. In atherosclerosis, plaques and calcium deposits build up inside major arteries, which lead to narrowing of the vessel lumens and limits or completely blocks blood flow. Similarly, in calcific aortic stenosis, calcium deposits on valve cusps and valve ring result in narrowing of valve lumen, eventually leading to impaired function and even valve failure. As the disease progresses, both diseases thus require expensive replacement/repair surgeries in most patients. However, in spite of the high prevalence, the causes and mechanisms of these diseases are still not clearly understood. Due to the similarities in diseased tissue pathology, atherosclerosis and aortic stenosis have been suggested to be continuum of the same disease [1] and mainly have been investigated for atherosclerosis. However, the prevalence of both diseases is not concurrent in most patients. Likewise, valvular interstitial cells (VICs) were thought to behave in a similar manner as smooth muscle cells (SMCs), but some recent studies suggest differences between the two cell types [2]. Therefore, unique mechanisms might be involved in how VICs and SMCs respond to an osteogenic environment.
Propagation of Liquid Plugs With Yield Stress in Human Airways
Authors: Zamankhan Parsa , Takayama Shuichi , Grotberg James B.
Published: July 2013

The airway closure due to the capillary instability [1] occurs in lung diseases such as asthma, cystic fibrosis, or emphysema. The reopening process involves with displacement of plugs constituted from mucus, a non-Newtonian fluid with a yield stress, in the airways. In this work the steady propagation of mucus plugs in a 2D channel is studied numerically, assuming that the mucus is a Bingham fluid. The governing equations are solved by a mixed-discontinuous finite element formulation and the free surface is resolved with the method of spines. The constitutive equation for Bingham fluid is implemented through a regularized constitutive equation. According to the numerical results, the yield stress behavior of the plug modifies the plug shape, the pattern of the streamlines and the distribution of stresses in the plug domain and along the walls in a significant way. The distribution along the walls is a major factor in studying cell injuries.
Influence of Stent Configuration on Cerebral Aneurysm Fluid Dynamics
Authors: Babiker Haithem , Gonzalez L. Fernando , Albuquerque Felipe , Collins Daniel , Elvikis Arius , Frakes David H.
Published: July 2013

Treatment options for cerebral aneurysms have drastically evolved in the last decade. In the past, surgical clipping through craniotomy was the predominant treatment option for cerebral aneurysms. Presently, endovascular coiling, a minimally invasive technique, has superseded clipping in many centers [1]. However, the coiling of wide-neck aneurysms is still a challenge [2]. Complete aneurysmal occlusion is often impossible [3]. Recently, stand-alone stents have been explored as an alternative treatment option for wide-neck aneurysms [4].
Effect of Head Rotation at the Prone Position on the Geometric Features of the Healthy Carotid Bifurcation
Authors: Aristokleous Nicolas , Seimenis Ioannis , Papaharilaou Yannis , Georgiou Georgios , Brott Brigitta C. , Anayiotos Andreas S.
Published: July 2013

The influence of posture change on the geometry and hemodynamics of the carotid bifurcation has not been thoroughly studied [1,2,3]. Such changes may alter the hemodynamic variables that are generally associated with the development of atherosclerosis, such as low oscillating wall shear stress (WSS) and particle residence times. Glor et al. (2004) had reported changes in the right carotid bifurcation geometry with leftward rotation of the head. We have previously reported that geometric differences in the right and left carotid bifurcation occur with a rightward rotation of the head [3].
Closed-Loop Lumped Parameter Cardiovascular Model of Infarct Border Zone Pacing
Authors: Pilla James J. , Koomalsingh Kevin , Gorman Robert C.
Published: July 2013

The border zone (BZ) region has been classified as a unique form of dysfunctional myocardium adjacent to an infarct that is normally perfused but has an abnormal systolic strain pattern (1). This abnormal strain has been theorized to result in a proliferation of the hypocontractility region to extend to involve progressively more normally functioning myocardium, resulting in ventricular dilatation and heart failure (2,3). It has been theorized that contracting the BZ prior to the remote myocardium can normalize strain distribution, which could improve cardiac function and mitigate remodeling. This study developed a closed-loop lumped parameter cardiovascular model to evaluate the effect of BZ pacing on cardiovascular hemodynamics and function.
Hemodynamic Simulation of an Arterial Bypass Graft: A Longitudinal Study of Remodeling
Authors: McGah Patrick M. , Riley James J. , Aliseda Alberto
Published: July 2013

Arterial bypass grafting is the most common surgical procedure to alleviate critical ischemia and intermittent claudication in patients with peripheral arterial disease. However, the failure rate of bypass grafting remains high; up to 20% within the first year of implantation and up to 50% within five years [1, 2]. The failure of the graft is usually due to occlusion by intimal hyperplasia (IH) followed by thrombosis. Although the exact mechanisms of IH remain unclear, the focal distribution of stenotic lessions suggest that the hemodynamic conditions within the graft are intimately related to the remodelling process [3].
Shock Induced Deformation and Damage in Rat Brain Slices
Authors: Kwon Jiwoon , Lee Sung J. , Subhash Ghatu , King Michael , Sarntinoranont Malisa
Published: July 2013

Shock-induced traumatic brain injury (TBI) and post traumatic stress disorder (PTSD) have received increasing attention because many soldiers returning from Iraq and Afghanistan suffer from these disorders. The shock loading duration is typically on the order of few hundred microseconds and hence the strain rate of deformation is very high. Therefore, in the current study, high-rate loading experiments were conducted on brain tissue slices which mimic loading durations encountered in shock loading [1]. The polymer split Hopkinson pressure bar (PSHPB) was used to generate high rate loading as a high speed digital camera captured the deformation of brain tissue. To further clarify initial injury events, post-test damage was assessed through histological studies. This experimental model provides the opportunity for time-resolved visualization of actual tissue deformation thus allowing improved ability to isolate damage-sensitive tissue regions.
Variations in Tracheobronchial Airway Morphology for Different Age Groups
Authors: Ryans Jason , Welch Bennett , Hyun Sinjae , Zhang Zhe , Kleinstreuer Clement
Published: July 2013

Knowledge of the geometric characteristics of actual human tracheobronchial (TB) airways is crucial for realistic and accurate computer simulations and experimental studies. An area of particular interest is drug delivery in the respiratory system to combat various diseases, such as COPD/asthma, diabetes and certain cancers. Deposition in the upper TB region is significant because it may be related to clearance of deposited particulate matters (PM) [1] and drug-aerosol treatment for upper airway asthma such as bronchodilators and corticosteroids [2,3]. The air flow characteristics, which affect particle deposition in the lung, depend strongly upon the morphology of the respiratory system and the breathing pattern of the subject. Therefore, an accurate understanding of the lung airway morphology is a crucial first step for an accurate analysis of inhaled particle trajectories as well as local and regional deposition of PM due to the irregular and asymmetric branching pattern [4]. In this paper, the age group variations of TB morphology are evaluated using lung airway morphology data from the literature and PET/CT images of two adolescents, 4 adults, and 4 seniors.
Comparison of Aneurismal Hemodynamics Between 4-D Accelerated Phase-Contrast MR Angiography and Computational Fluid Dynamics Simulations: Initial Experience in a Canine Aneurysm Model
Authors: Jiang Jingfeng , Johnson Kevin , Valen-Sendstad Kristian , Mardal Kent-Andre , Consigny Dan , Wieben Oliver , Strother Charles
Published: July 2013

The etiology and progression of intracranial aneurysms (IAs) are closely associated with complex patterns of disturbed blood flow. [1] Consequently, blood flow imaging [2] and CFD simulations in realistic geometries [3, 4] are of clinical interests because flow information obtained by such techniques can provide insight not only into the development and progression of IAs but also into their responses to therapeutic interventions (e.g. coil embolization and stent deployment).
Correlation of Nanomechanical and Mineral Properties of Human Osteoarthritic Meniscal Attachments
Authors: Abraham Adam C. , Killian Megan L. , Haut Donahue Tammy L.
Published: July 2013

Meniscal horns attach the meniscus to the underlying subchondral bone. Successful meniscal replacements must maintain horn attachments of the menisci, hence recent studies have been aimed at characterizing the material properties of the ligamentous horn attachments. In order to mimic material properties in tissue engineered meniscal replacements, we must understand how these properties are influenced by mineral and matrix constituents. Additionally, understanding how osteoarthritis alters the meniscal horn attachments may elucidate appropriate design considerations of such tissue engineered replacements. Therefore, this study investigated the relationship between mechanical and mineral properties of osteoarthritic meniscal attachments.
Co-Culture of a Chondrocyte Monolayer With Engineered Cartilage Constructs Immediately Increases Tissue Properties
Authors: Tan Andrea R. , Dong Elizabeth Y. , Rho Byunghwi , Sampat Sonal R. , Bulinski J. Chloe , Ateshian Gerard A. , Hung Clark T.
Published: July 2013

Engineered cartilage comprised of chondrocytes encapsulated in agarose gel is capable of attaining a Young’s modulus and glycosaminoglycan (GAG) content comparable to native tissue within 8 weeks of culture [1]. Expediting this growth, especially early in culture when pericellular matrices are first forming, may be critical to optimizing functional properties of the tissue as well as increasing their impact and use in cartilage repair strategies. Recently, we have been exploring the concept of a feeder layer, typically associated with culturing embryonic stem cells, for tissue engineering of cartilage.
Differential Chondrogenic Potential of Human and Bovine Mesenchymal Stem Cells in Agarose and Photocrosslinked Hyaluronic Acid Hydrogels
Authors: Kim Minwook , Erickson Isaac E. , Burdick Jason A. , Dodge George R. , Mauck Robert L.
Published: July 2013

Articular cartilage has a limited regenerative capacity, and there exist no methodologies to restore structure and function after damage or degeneration. This has focused intense work on cell-based therapies for cartilage repair, with considerable literature demonstrating that chondrocytes in vitro and in vivo can generate cartilage-like tissue replacements. However, use of primary cells is limited by the amount and quality of autologous donor cells and tissue. Multipotential mesenchymal stem cells (MSCs) derived from bone marrow offer an alternative cell source for cartilage tissue engineering. MSCs are easily accessible and expandable in culture, and differentiate towards a chondrocyte-like phenotype with exposure to TGF-β [1]. For example, we have shown that bovine MSCs undergo chondrogenic differentiation and mechanical maturation in agarose, self-assembling peptide, and photocrosslinkable hyaluronic acid (HA) hydrogels [2]. HA hydrogels are particularly advantageous as they are biologically relevant and easily modified to generate a range of hydrogel properties [3]. Indeed, bovine MSCs show a strong dependence of functional outcomes on the macromer density of the HA gel [4]. To further the clinical application of this material, the purpose of this study was to investigate functional chondrogenesis of human MSCs in HA compared to agarose hydrogels. To carry out this study, juvenile bovine and human MSCs were encapsulated and cultured in vitro in HA and agarose hydrogels, and cell viability, biochemical, biomechanical, and histological properties were evaluated over 4 weeks of culture.
Functional Endoluminal Paving (FELP): Thermoforming, Biodegradation, and Mechanical Properties of a Novel Polymer Graft for Abdominal Aortic Aneurysms
Authors: Ashton John H. , Mertz James A. M. , Alexander Megan J. , Slepian Marvin J. , Mills Joseph L. , Vande Geest Jonathan P.
Published: July 2013

The preferred method to treat abdominal aortic aneurysms (AAAs) is endovascular repair with a stent-graft (EVAR). Although EVAR is fairly successful, there are several challenges to address, which include patient ineligibility due to complex anatomy and long-term failure due to migration and endoleak. Drug treatments that reduce or halt AAA growth are also currently under investigation [1].
Correspondence of the Effect of Shear Stress Magnitude on Endothelial Cell Alignment and Heparan Sulfate Expression
Authors: Wallace Charles S. , Hasenberg Tobias , Friedman Morton H.
Published: July 2013

The endothelial glycocalyx is believed to play a crucial role in many endothelial functions, including mechanotransduction [1,2], modulation of vascular permeability, and interaction with blood components [3]. A principal constituent of the glycocalyx, thought to sense shearing forces and convey this signal into the cell, is the glycosaminoglycan heparan sulfate (HS). Previous in vitro studies have shown that batch removal of 60% of the heparan sulfate within the glycocalyx inhibits the steady shear-induced production of nitric oxide [4], cell alignment, cell migration, suppression of cell proliferation, and accumulation of vascular endothelial cadherin in cell-cell junctions [5].
Large Eddy Simulation of Steady and Pulsating Flow in Asymmetric Stenosed Pipe
Authors: Gårdhagen Roland , Carlsson Fredrik , Karlsson Matts
Published: July 2013

Local hemodynamics and its impact on the development of cardiovascular disease and the blood itself have gained increasing attention during the last decades. Regions with low and/or oscillatory Wall Shear Stress (WSS) have been correlated with increased risk for development of atherosclerosis [1]; and turbulence in the cardio vascular system is suggested to increase the risk for hemolysis as well as platelet activation and thrombus formation [2, 3]. Furthermore, turbulent flows are inherently oscillatory with large spatial as well as temporal fluctuation, and hence possibly a risk for atherosclerosis development per se.
Tissue Optical Clearing Devices: Effects of Water Content on the Hyperelastic Mechanical Properties of Ex Vivo Porcine Skin
Authors: Vogt William , Izquierdo-Roman Alondra , Rylander Christopher G.
Published: July 2013

Skin is a highly anisotropic and heterogeneous material composed of water, proteins, and various cells arranged in several different layers. Because of this complex structure, there is a large mismatch in index of refraction between the tissue constituents, creating a highly scattering medium for near-infrared and visible light. “Tissue optical clearing” methods can improve light transmission through tissues, potentially improving optical imaging techniques and photoirradiative treatments [1]. Dehydration has been suggested as a possible mechanism of optical clearing [2], and previous work has demonstrated mechanical loading as a method of creating reversible localized water displacement in skin using novel tissue optical clearing devices (TOCDs) [3–4]. These TOCDs were hypothesized to increase light transmission by displacing water locally in the tissue, causing local dehydration. A model of the mechanical behavior of skin will enable improvement of current TOCDs that utilize local mechanical compression.
A Structural Continuum Constitutive Model for a Two-Phase Soft Tissue
Authors: Wognum Silvia , Sacks Michael S.
Published: July 2013

Due to the complexity in determining multi-constituent tissue properties, most structural constitutive models for soft tissues focus on a single constituent. However, many tissues contain multiple load-bearing constituents, such as collagen fibers and smooth muscle (SM) cells. Moreover, to elucidate how observed changes in tissue components are related to altered net mechanical behavior at the tissue level, structural constitutive models require physiological relevant model parameters and formulations for changes in referential configuration when one component is physically removed. As an excellent example application that underscores these issues, we have examined the urinary bladder wall (UBW), which undergoes large deformations and exhibits highly nonlinear and anisotropic mechanical behavior [1,2]. Moreover, it undergoes profound remodeling in response to different pathologies such as spinal cord injury (SCI) [1,2].
Wall Motion Influences Flow Pattern in the Outflow Tract of the Chick Embryonic Heart Tube
Authors: Liu Aiping , Wang Ruikang , Thornburg Kent , Rugonyi Sandra
Published: July 2013

The outflow tract (OFT) of the chick embryonic heart offers a good model system to study the association between blood flow dynamics and cardiac morphogenesis in early heart development. At early stages, the chick heart is a looped tube without valves. The OFT, the distal region of the heart, functions as a primitive valve [1]. The OFT is a slightly curved tube with three-layered wall (Fig. 1 (A) and (B)): the myocardium, an external muscle layer that actively contracts; the endocardium, an inner endothelial layer that directly contacts blood; in between the cardiac jelly, an extracellular matrix layer. The OFT undergoes complex morphogenesis, eventually leading to the development of semilunar valves, and this morphogenesis is sensitive to blood flow dynamics.
Elasticity of the Lens Capsule as Measured by Osmotic Swelling
Authors: Powell Tracy A. , Amini Rouzbeh , Oltean Alina , Barnett Vincent A. , Dorfman Kevin D. , Segal Yoav , Barocas Victor H.
Published: July 2013

Basement membranes are planar extracellular matrices ubiquitous within tissues and serve roles in the organization, support and regulation of resident cell populations. The ocular lens capsule is experimentally accessible accounting for its wide use as a model in studies of basement membrane mechanics [1–3]. Optical tracking of passive osmotic swelling, unlike previously employed methods of determining the elasticity of the lens capsule, involves minimal manipulation of the lens, which is desirable when using smaller animal models, such as the mouse.
Demonstration of a Multiscale Biaxial Tensile Testing Device: Simultaneous Mechanical and Microstructural Response of Porcine Coronary Artery
Authors: Keyes Joseph T. , Borowicz Stacy , Rader Jacob , Utzinger Urs , Vande Geest Jonathan P.
Published: July 2013

It has been shown that the mechanical properties of tissue change significantly with age and under different disease states [1]. Specifically, blood vessels have shown that modified mechanical properties can be a predictor of impending disease such as advanced atherosclerosis or aneurysm [2].