bluuebunny/crossref_metadata_2025 huggingface dataset:
Predicting the Strength of Volar Screw Purchase in the Distal Radius: Comparison Between DEXA and a New “Smart” Surgical Tool
Authors: Liddle Kate D. , Marmor Meir , Han Hyun Kyu , Fong Marshall , Chu Thomas , Tai Viva , Mulligan Kathleen , Buckley Jenni M. , Matityahu Amir
Published: July 2013

The distal radius is a common site of fracture with volar plates and screws as the current clinical practice for fracture fixation [1]. Local measurements of bone quality at the sites of screw insertion aid in providing the most stable fixation with the least amount of hardware, minimizing the risk of construct failure and irritation to soft tissue [2, 3]. The clinical standard for pre-operative bone mineral density (BMD) assessment uses dual x-ray absorptiometry (DEXA). However, DEXA scans provide global BMD values and cannot accurately predict variations in BMD within a given anatomical site [4]. Furthermore, patients frequently present without a pre-operative DEXA scan, so intra-operative assessment would be ideal. We developed a simple sensor system that would be appropriate for assessing local BMD intra-operatively. The system consists of a “smart” Weber clamp instrumented with a single uniaxial strain gage that provides real-time feedback regarding the local BMD.
A Computational Technique for Robust Optimization of Cardiovascular Bypass Graft Surgeries
Authors: Sankaran Sethuraman , Marsden Alison L.
Published: July 2013

Bypass graft (BG) surgeries involve surgical construction of a graft over a blocked blood vessel. The graft can either be native tissue of the patient or a synthetic material. Some commonly performed BG surgeries include aorto-bifemoral, femoro-popliteal, femoro-tibial, and coronary artery bypass (CABG). The operative mortality rate for CABG is around 3%. Around 15 to 30% of bypass grafts occlude within the first year of surgery, increasing to over 50% after 10 years. Graft incompatibility, and hemodynamic factors such as blood recirculation, low wall shear stress, and abnormal wall shear stress gradients play an important role in the onset and development of intimal thickening and plaque deposition (atherogenesis).
Quantitative, 3-D Imaging to Co-Localize Bone and Vasculature Tissues During Bone Healing
Authors: Morgan Elise F. , Andre Billy , Hogan Daniel E. , Al-Awadhi Bader A. , Gerstenfeld Louis C.
Published: July 2013

Successful bone repair requires reestablishment of a blood supply at the injury site [1]. However, despite convincing evidence of the close relationship between angiogenesis and osteogenesis during bone healing, little is known about the spatial correspondence between these two processes. This paucity of information hampers understanding of the mechanisms regulating osteogenesis during bone healing and of how molecular communication between endothelial cells and osteoblasts mediates the restoration of mechanical function.
A Comparison of Two Automated Block Placement Methods for Multi-Block Hexahedral Finite Element Meshing
Authors: Ramme Austin J. , Shivanna Kiran H. , Magnotta Vincent A. , Grosland Nicole M.
Published: July 2013

Finite element analysis is a method of continuum mechanics that has been vital to the biomechanics community due to its ability to evaluate structures with complicated geometries. Generation of patient-specific finite element models from medical imaging data requires a series of steps including image segmentation, mesh generation, assignment of material properties, and definition of loading and boundary conditions. Each of these steps can be challenging and time-consuming. Here, we aim to address the challenge of automating the generation of hexahedral meshes.
Experimental Study of Temperature Elevations in Extracted Teeth Using a System B Heating Catheter for Bacterial Disinfection
Authors: Zhu L. , Salloum M. , Feteih S. , Hough J. , Arola D. , Tolba M.
Published: July 2013

Total bacterial disinfection and elimination from the human root canal system are crucial in clinical endodontic procedures [Card et al., 2002; Kakoli et al., 2009]. The current approaches relying on mechanical instrumentation and root canal irrigation and medicaments have demonstrated that eradication of bacteria occurs when the bacteria are in direct contact with the medicaments. However, persistent infection following routine treatments has suggested that bacteria may harbor in the root canal anatomical irregularities and/or deep dentinal tubules, therefore, surface irrigation of medicaments may not be able to reach those regions. Heat treatment has been used for obturation of the root canal in endodontic practice. In this study we hypothesize that as an alternative, surface heating using a System B heating catheter through the root canal surface would be effective for bacterial elimination in the deep dentin. The heat-induced cytotoxic response kills bacteria in the root dentin via heat conduction from the thermal energy incident on the root canal wall. In principle, a high power setting and/or a long heating duration can always achieve sufficient temperature elevations in deep dentin. Yet, the detailed temperature distribution inside the dentin and possible thermal damage to the supporting periodontium are unknown. Therefore, it is of clinical importance to perform and investigate temperature elevations in dentin to provide clinicians with an optimized and effective treatment protocol to minimize unnecessary thermal damage to the surrounding structure.
Mechanical Contribution of Fiber Angular Distribution in Connective Tissue: Comparison of Two Modeling Approaches
Authors: Cortes Daniel H. , Lake Spencer P. , Kadlowec Jennifer A. , Soslowsky Louis J. , Elliott Dawn M.
Published: July 2013

Collagen fibers and their structural arrangement influence tissue tensile stiffness and strength. While a variety of modeling approaches incorporate collagen fibers explicitly as one of the components, due to the complexity of the fiber organization, aligned fibers are usually considered. In the pioneering work of Lanir [1], a constitutive relation for continuous fiber distributions was proposed, where the strain energy and stresses are obtained by angular integration (AI) of infinitesimal fractions of fibers aligned in a given direction. Lanir’s formulation has been successfully used to describe the mechanical behavior of a variety of tissues. In particular, Ateshian et al. [2] showed that large values of the tensile Poisson’s ratio for articular cartilage in tension and the low values observed in compression can be explained using a continuous angular distribution for the fibers. A disadvantage of the AI formulation is the large number of calculations required to evaluate the strains and stresses. On the other hand, Generalized Structure Tensors (GST) have been proposed to model tissues with continuously distributed collagen fibers [3,4]. These tensors are assumed to represent the three-dimensional distribution of the fibers. Once the tensor has been defined, the strain in the fibers can be readily obtained by multiplication with a strain tensor. The advantage of this approach is the small number of calculations required to obtain the strain energy and stresses of the fibers. As a result, this formulation can be efficiently implemented in numerical algorithms like finite elements. However, this approach is limited, as it is valid only when all of the fibers are in tension and when the fiber distribution is small [5]. A numerical comparison is required to quantify when an angular distribution can be considered acceptably small to justify using this more computationally efficient approach. The objective of this study is to numerically compare the AI and GST formulations to determine the range of values of angular distribution for which the GST approach can be accurately used.
The Effects of Radial Core Decompression on Lunate Kinematics
Authors: Smith Andrew , Nowicki Philip , Hefzy Mohamed Samir , Dennis Michael , Mustapha Abdul Azim
Published: July 2013

Kienbock’s disease is an avascular necrosis of the lunate bone in the wrist [1]. Current early-stage treatment techniques include joint leveling procedures, such as radial shortening and ulnar lengthening. These techniques serve to unload the radiolunate joint and redistribute compressive loads to the radioscaphoid joint [2]. Additionally, core decompression of the distal radius and ulna, first introduced by Illarramendi [3], and has been found clinically effective in improving early stage Kienbock’s disease. Clinical studies have since found radial core decompression (RCD) to be as effective as performing the procedure on both forearm bones [4]. However, there have been no biomechanical studies characterizing the changes in wrist kinematics following a RCD. The purpose of this study is to determine the changes in lunate motions following a RCD.
Biomechanical Analysis of Osteotomy Type (OWO, CWO) and Rod Diameter for Treatment of Cervicothoracic Kyphosis
Authors: Scheer Justin K. , Tang Jessica A. , Deviren Vedat , Buckley Jenni M. , Pekmezci Murat , McClellan R. Trigg , Ames Christopher P.
Published: July 2013

Sagittal imbalance of the cervicothoracic spine often causes severe pain and loss of horizontal gaze. Traditionally, C7 opening wedge osteotomy has been classically performed for patients with ankylosing spondylitis. For patients without ankylosing spondylitis closing wedge osteotomy may be considered for more controlled closure. Biomechanical characteristics of the two osteotomy alternatives have not yet been analyzed. The goal of this study is to characterize the structural stability of the two types of cervicothoracic junction osteotomies and the independent effect of rod diameter.
Mechanical Properties of Collagen, Fibrin and Collagen-Fibrin Networks
Authors: Lai Victor K. , Sander Edward A. , Tranquillo Robert T. , Barocas Victor H.
Published: July 2013

The macroscopic mechanical properties of bio-engineered tissues are inextricably linked to their microstructure. Often, their microstructure is a complex arrangement of several different components (e.g. collagen, fibrin) that interact with each other to give a tissue its overall properties. These microstructural complexities are further compounded by the dynamic cell interactions with the extracellular matrix (ECM). Our group [1] uses fibrin as the starting scaffold material for cell seeding and tissue growth; over time, the underlying microstructure undergoes dynamic remodeling as the fibrin network is degraded and gradually replaced with collagen. Currently, we have a modeling framework that incorporates a single-component microstructure network to predict the mechanical properties of the engineered tissue [2]. However, this model is unable to capture the transient intermediate stages of tissue growth, during which the tissue is composed of interpenetrating collagen and fibrin networks at varying compositions. In this work, we have incorporated a second network into our model and compared these modeling results with experimental data obtained from uniaxial tests on acellular collagen-fibrin co-gels. This work represents one step in the progression of our model to capture better the relationships between tissue microstructure and macroscopic mechanical properties, with the ultimate goal of developing a comprehensive model framework for rational design of functional engineered tissues.
Tibiofemoral Alignment for Total Knee Arthroplasty: Differences Between Static and Dynamic Tibial Plateau Loading
Authors: Miller Emily J. , Pagnano Mark W. , Kaufman Kenton R.
Published: July 2013

The surgical goal in total knee arthroplasty (TKA) is to obtain neutral mechanical alignment within three degrees [4]. This has been considered necessary to achieve optimal function, produce balanced medial and lateral loading distributions, and prolong implant longevity [7]. Under static loading, tibial-femoral alignment angle deviations of 3° have been shown to greatly alter the distribution of pressure and load between the medial and lateral tibial plateaus [13]. However, other studies have challenged the practice that coronal tibiofemoral alignment improves implant longevity [9,10]. These studies did not show a statistical difference in the number of revision surgeries between well aligned knees and mechanical alignment outliers (varus/valgus knees). While it has been suggested that accurate alignment allows for improved joint kinematics and improved outcomes in TKA patients [6], no studies have evaluated the effect of tibial-femoral alignment on tibial plateau loading distribution during gait in the TKA population. Therefore, the purpose of this study was to assess tibial plateau loading following TKA.
Disc Biomechanical Response due to Incomplete Length of Collagen Fibers in Various Regions of Annulus Fibrosus: A Finite Element Investigation
Authors: Hussain Mozammil , Gay Ralph E. , An Kai-Nan
Published: July 2013

Collagen fibers in the annulus fibrosus (AF) play a significant role in maintaining the disc mechanical behavior. In healthy discs, AF fibers are concentrically arranged in a zigzag fashion. Tensile loads are transmitted to these fibers when the disc is loaded in compression. As a result, disc bulging occurs. Initiation and progression of mild cervical disc degeneration (DD) has been the subject of clinical concern [1]. The mild DD is associated with structural interruption in laminar organization of fibers in partial AF regions and incomplete length of fibers is a major form of structural interruption in AF fibers [2]. Moreover, a loss of lamellar fiber structure contributes to the progression of spinal deformity [3]. Past research have documented the biomechanical role of complete length of fibers in governing a healthy disc behavior [4]; however, there is a lack of clear understanding as to how incomplete length of fibers in different AF regions affect overall disc biomechanics and how they may play a role in initiating the propagation of DD. The focus of the current study is to investigate the disc biomechanical response due to incomplete length of fibers in outer, middle, and inner AF regions.
Intraocular Pressure Alters Following Altitude Changes in Patients With Gas-Filled Eyes: Theoretical Analysis
Authors: Amini Rouzbeh , Barocas Victor H. , Kavehpour H. Pirouz , Hubschman Jean Pierre
Published: July 2013

Retinal detachment is an eye disorder that, if not treated, can lead to blindness. One of the treatment options is removing all or part of vitreous humor from the vitreous cavity and filling it with a gas bubble. The gas bubble eventually reabsorbs over a few weeks into the systemic circulation.
A New Hexahedral Mesher for a Numerically Efficient Patient Specific Analysis of Arterial Blood Flow and Wall Shear Stress
Authors: De Santis G. , Mortier P. , De Beule M. , Segers P. , Verdonck P. , Verhegghe B.
Published: July 2013

Atherosclerosis depends on systemic risk factors but manifests itself as geometrically focal plaques, which appear in regions of the arterial tree experiencing low and/or oscillating Wall Shear Stress (WSS) such as outer edges of vessels bifurcations and highly curved vessels. Because direct measurements of WSS (differential quantity) in vivo are difficult due to limited spatial resolution offered by current measuring technologies (ultrasound, phase contrast MRI), an indirect approach is often taken, integrating medical imaging techniques (biplane angiography, CT, MRI) with Computational Fluid Dynamics (CFD) for patient specific WSS profiling.
Aerosol Deposition Characteristics in Subject-Specific Tracheobroncheal Airways
Authors: Hyun Sinjae , Hyun Young-Eun , Birchard Katherine , Zhang Zhe , Kleinstreuer Clement
Published: July 2013

The trachea is a tubular structure which serves as the conduit which air travels to the lung. It originates just below the vocal cords, courses inferiorly into the thoracic cavity, then bifurcates into two main bronchi, each of which serve one side of lung. Those main bronchi then branch into smaller airways serving individual lobes of each side of the lung. The trachea is composed of U-shaped cartilaginous rings connected by a posterior membrane. There are several different cross-sectional shapes of the lumen of the trachea including circular, D-shaped, U-shaped, triangular, C-shaped, and elliptical [1]. In some cases, the trachea becomes flaccid and can collapse easily in the presence of positive intrathoracic pressure, which is known as tracheomalacia. This leads to airway obstruction, and may result in wheezing, stridor, and a “seal bark” cough characteristic in patient with tracheamalacia [2–4].
A Three Layered Electrospun Matrix to Mimic Native Arterial Architecture Using Polycaprolactone, Elastin, and Collagen: A Preliminary Study
Authors: McClure Michael J. , Sell Scott A. , Simpson David G. , Walpoth Beat H. , Bowlin Gary L.
Published: July 2013

The architecture of the vascular wall is highly intricate and requires unique biomechanical properties in order to function properly. Native artery is composed of a mix of collagens, elastin, endothelial cells (ECs), smooth muscle cells (SMC), fibroblasts, and proteoglycans arranged into three distinct layers: the intima, media, and adventitia. Throughout artery, collagen and elastin play an important role, providing a mechanical backbone, preventing vessel rupture, and promoting recovery while undergoing pulsatile deformations [1]. The low-strain mechanical response of artery to blood flow is dominated by the elastic behavior, of elastin, which prevents pulsatile energy from being dissipated as heat [2]. A higher amount of energy loss indicates a decrease in recoverability, which could lead to eventual disruption of blood flow. An effective way to quantify recoverability is through hysteresis and compliance measurement. The hypothesis of this study was that the fabrication of a multi-layered electrospun tissue engineering scaffold composed of polycaprolactone (PCL), elastin (ELAS), and collagen (COL) would demonstrate dynamic mechanical properties indicative of a highly elastic material, similar to the three distinct layers of native arterial tissue, while remaining conducive to tissue regeneration. PCL was chosen, in this case, to provide mechanical integrity and elasticity, while elastin and collagen would provide further elasticity and bioactivity [3,4].
Biomechanical Analysis of Knee Cartilage Stress for Individuals With Anterior Cruciate Ligament Reconstruction
Authors: Yang N. H. , Tsai L. C. , Powers C. M.
Published: July 2013

Every year, approximately 80,000 to 150,000 ACL tears occur.[1,2] Post-injury, ACL reconstruction (ACLR) is often recommended to restore functional stability and prevent long-term joint degradation. However, while surgical techniques have improved, individuals with ACLR have been shown to have a higher risk of developing osteoarthritis (OA) and a higher rate of re-injury.[3] The higher incidence and earlier onset of knee OA in individuals who have undergone ACLR may be a result of a post-injury movement strategy that utilizes a higher degree of muscle co-contraction of the hamstrings and the quadriceps muscles during landing to increase joint stability.[4] This increased co-contraction leads to a “stiff” landing pattern, decreases shock absorption, and increases the ground reaction forces. These changes in lower extremity biomechanics also may result in higher forces which likely place the knee cartilage under greater stress and higher risk of OA development and re-injury.
Miniature Transducer for Chordal Force Measurements In Vivo
Authors: Askov J. B. , Jensen M. O. , Hoenge J. L. , Nygaard H. , Hasenkam J. M. , Nielsen S. L.
Published: July 2013

The objective of this study was to develop a miniature force transducer capable of measuring tension in chordae tendineae (CT). The force transducer should be small in size compared with former CT force transducers [1;2] while not compromising implantation, durability and sensitivity.
Multigenerational Interstitial Growth of Biological Tissues
Authors: Ateshian Gerard A. , Ricken Tim
Published: July 2013

The objective of this study is to formulate a theory for multigenerational interstitial growth of biological tissues whereby each generation has a distinct reference configuration determined at the time of its deposition. In this model, the solid matrix of a growing tissue consists of a multiplicity of intermingled bodies, each of which represents a generation, all of which are constrained to move together in the current configuration. This proposed framework builds on the concept of constrained mixtures of solids originally formulated by Humphrey and Rajagopal (2002). The specific aim is to determine the form of constitutive relations for the solid constituents of a multigenerational tissue, and provide simple illustrations of the theory.
Controlling the Mechanical Myofibroblast via SRC: A Potential Drug Discovery Platform
Authors: Merryman W. David , Hutcheson Joshua D.
Published: July 2013

Connective tissue makes up a large portion of our bodies, with collagen constituting ∼30% of the protein of connective tissue. Any tissue that undergoes fibrosis, either due to a genetic mutation or with age or use, typically falls into the ubiquitous category of ‘connective tissue fibrosis’. There are multiple potential contributors to connective tissue fibrosis; however, two dominate the literature — mechanical stress/strain and cytokines. Both stimuli lead to activation of fibroblast cells to a myofibroblast phenotype, the cellular hallmark of fibrotic disease. The myofibroblast phenotype is indicated by the expression of smooth muscle α-actin (αSMA), which associates with myosin to form actin-myosin contractile elements and generates intracellular force that is transduced to the ECM via cell membrane integrins.
Electrostatic Contribution of the Proteoglycans to the In-Plane Shear and Compressive Stiffness of Corneal Stroma
Authors: Hatami-Marbini Hamed , Pinsky Peter M.
Published: July 2013

The extracellular matrix (ECM) is a fibrous structure embedded in an aqueous gel. The mechanical and electrostatic interactions of the ECM constituents, i.e. collagen fibers and proteoglycans (PGs), define the structure and mechanical response of connective tissues (CTs) such as cornea and articular cartilage. Proteoglycans are complex macromolecules consisting of linear chains of repeating gylcosaminoglycans (GAGs) which are covalently attached to a core protein. PGs can be as simple as decorin with a single GAG side chain or as complex as aggrecan with many GAGs. Decorin is the simplest small leucine-rich PG and is the main PG inside the corneal stroma. It has an arch shape and links non-covalently at its concave surface to the collagen fibrils. It has been shown that while collagen fibers inside the extracellular matrix resist the tensile forces, the negatively charged glycosaminoglycans and their interaction with water give compressive stiffness to the tissue. The role of PGs in biomechanical properties of the connective tissues has mainly been studied in order to explore the behavior of articular cartilage [1], which is a CT with large and highly negatively charged PGs, aggrecans. In order to explain the role of PGs in this tissue, it is commonly assumed that their contribution to the CT elasticity is because of both the repulsive forces between negatively charged GAGs and GAG interactions with free mobile charges in the ionic bath. The electrostatic contribution to the shear and compressive stiffness of cartilage is modeled by approximating GAGs as charged rods [1]. The Poisson-Boltzmann equation is used to compute the change in electrical potential and mobile ion distributions which are caused by the macroscopic deformation.
Ankle Injuries During Excessive External Foot Rotation May Depend on Foot Constraint: Development of a Computational Model
Authors: Wei Feng , Powell John W. , Haut Roger C.
Published: July 2013

Numerous studies on the mechanisms of ankle injury deal with injuries to the syndesmosis and anterior ligamentous structures, but previous sectioning and clinical studies also describe the important role of the posterior talofibular ligament (PTaFL) in the ankle’s resistance to external rotation of the foot. Foot constraint may influence subtalar motion and the movement of the bones in the foot, thereby influencing the mode of injury during external rotation [1]. Stiehl et al. [2] constrain the foot with fiberglass cast tape, externally rotate the foot 90°, and produce injury to the deltoid ligament and anterior tibiofibular ligament (ATiFL) with bone fracture. In contrast, Stormont et al. [3] fix the foot in a potting alloy and conclude the primary ligamentous restraints to external rotation are the PTaFL and calcaneofibular ligament (CaFL).
Finite Element Analysis of the Knee: Development of a Failure Locus for the Anterior Cruciate Ligament
Authors: Homyk A. , Orsi A. , Wibby S. , Yang N. H. , Hashemi H. N. , Canavan P. K.
Published: July 2013

A full or partial tear of the anterior cruciate ligament (ACL) is a common and painful injury that has been estimated to occur approximately 250,000 times annually in the U.S. [1]. Articular cartilage and meniscal injuries are also associated with ACL injuries [2]. ACL injuries can often lead to degenerative osteoarthritis of the articular cartilage [2]. An epidemiology study of athletic injuries by Majewski et al. [3] determined that out of 19,530 sports injuries, 20% were ACL injuries and 8% were medial collateral ligament (MCL) injuries.
Propensity for Hip Dislocation in Gait Loading Versus Sit-to-Stand Maneuvers: Implications for Surgical Management of Acetabular Fractures
Authors: McDonald Erik , Marmor Meir , Buckley Jenni M. , Matityahu Amir
Published: July 2013

Acetabular fractures present a clinical challenge due to the complicated anatomy and difficulty of exposure, reduction, and fixation. There are several indications for surgery including any fracture which is displaced more than 2mm, failure to maintain reduction by closed means, or, for transverse fractures, a roof-arc angle less than 45 degrees (1,2). The last indication was determined by a cadaver model that only evaluated hip stability in the single leg stance phase of the gait cycle (3). Kinesiological models have well established that the magnitude and direction of the joint contact force can deviate substantially from the mechanics of gait loading, particularly for such activities of daily living as sit-to-stand maneuvers and climbing stairs (4,5). Thus, the criteria for fracture stability established using gait-only loading conditions may be inadequate for other activities of daily living. Basic engineering principles would dictate that the most conservative estimate of dislocation potential be used in managing these cases clinically; and it is therefore important to re-evaluate fracture management criteria in alternative loading conditions that have a high potential for dislocation.
Probing Nonlinear Cellular Responses to Integrated Mechanical Signals Through Examining Cell Alignment
Authors: Steward Robert L. , Cheng Chao-Min , LeDuc Philip R.
Published: July 2013

Cells are complex systems that continuously receive signals in a variety of forms including both physical and chemical. The ability of cells to integrate these signals and already be hard wired to have coupled responses indicates the complexity at which cells function in terms of signal integration. One of the important areas in signal response is in mechanical stimulation, which has been shown to influence many cellular functions through the cytoskeleton and most often induces various cellular alignment. Most studies generally probe the affects of mechanical stimulation on cell behaviour by one mode of mechanical stimulation, though cells in fact experience multiple modes of mechanical stimulation simultaneously. From this comes the question of how does the cell process these multiple mechanical inputs? In this study we probed the effects of uniaxial stretch and/or shear fluid flow on NIH 3T3 fibroblast behaviour, specifically cell alignment. We used fluorescence microscopy to examine the orientation of the actin cytoskeleton and observed alignment along the direction of force for both uniaxial stretching and shear fluid flow in comparison to cells exposed to both mechanical modes. The cellular response surprisingly revealed an alignment that was neither parallel nor perpendicular to the direction of force. Furthermore, the integration of these 2 modes revealed a nonlinear response to combinations of shear stress and uniaxial stretching. These intriguing results have potential implications in a variety of fields including bioengineering, mechanotransduction, and cell structure.
Fiber Orientation in Porcine Coronaries, as Described by the Holzapfel Model, is Fixed at Physiological Loading
Authors: van der Horst Arjen , van den Broek Chantal N. , Rutten Marcel C. M. , van de Vosse Frans N.
Published: July 2013

Insight into the mechanical properties of the coronary arterial wall can give valuable information concerning atherosclerosis, wall remodeling, and predicting the effects of medical intervention; e.g. balloon angioplasty [1,2]. Furthermore, knowledge of the mechanical properties of the arterial wall is important in modeling the coronary circulation and explaining its hemodynamical functioning.
Effect of Intraluminal Thrombus on Wall Stress and Growth Rate of Abdominal Aneurysms
Authors: Speelman Lambert , Bosboom E. Marielle H. , Schurink Geert Willem H. , Buth Jaap , Breeuwer Marcel , Jacobs Michael J. , van de Vosse Frans N.
Published: July 2013

In the decision for surgical repair of abdominal aortic aneurysms (AAAs), the risk of rupture is weighed carefully against the risk of the surgical procedure. Currently, AAA diameter is the main factor that determines the decision for surgery. However, in rupture risk estimation AAA wall stress has higher sensitivity and specificity than maximum diameter [1]. Moreover, peak wall stress was higher for ruptured than for non-ruptured or asymptomatic AAAs [2, 3].
Characterizing the Maternal Adaptations of Pregnancy and Recovery Following Vaginal Delivery in the Rodent Model
Authors: Feola Andrew , Alperin Marianna , Moalli Pamela , Abramowitch Steven
Published: July 2013

Pelvic organ prolapse and urinary incontinence are common conditions in women that significantly diminish quality of life. Vaginal delivery and maternal birth injury are the number one risk factors for the development of pelvic floor disorders. The goal of this study was to characterize maternal adaptations throughout pregnancy and recovery after vaginal delivery in terms of the passive quasi-static mechanical properties of the vagina using a rodent model.

Virgin (n = 8), mid-pregnant (n = 7, day 15–16), late-pregnant (n = 7, day 20–21), immediate postpartum (n = 8, <2 hours post delivery), and 4 week postpartum (n = 6) Long-Evans female rats were utilized in this study. The mechanical properties (tangent modulus, tensile strength, ultimate strain, and strain energy density) were quantified by testing longitudinal sections of vaginal tissue to failure.

The tangent modulus of virgin animals (25.1±5.1 MPa) was significantly higher compared to mid-pregnant (11.7±7.7 MPa, p = 0.003), late-pregnant (7.9±4.0 MPa, p<0.001), and immediate postpartum (8.5±4.7 MPa, p = 0.001) animals. A similar trend was also observed in the tensile strength, whereas the ultimate strain increased throughout pregnancy until the time of vaginal delivery. Recovery was observed four weeks postpartum as no significant difference was found from virgin animals for any of the parameters.

This study has shown a significant decrease in the tangent modulus and tensile strength along with an increase in the ultimate strain of longitudinal sections of vaginal tissue throughout pregnancy. These maternal adaptations are likely to increase the overall distensibility of the vagina and allow for vagina delivery with minimal injury. This process appears to be effective in the rodent model as the properties recovered to virgin levels by 4 weeks. In the future, we hope to alter these adaptations or exceed them in order to study the risk and impact of birth injury in this model.
The Influence of Wall Stress on AAA Growth and Biomarkers
Authors: Speelman Lambert , Hellenthal Femke A. , Bosboom E. Marielle H. , Buth Jaap , Breeuwer Marcel , Jacobs Michael J. , van de Vosse Frans N. , Schurink Geert Willem H.
Published: July 2013

In the decision for surgical repair of abdominal aortic aneurysms (AAAs), the risk of rupture is weighed carefully against the risk of the surgical procedure. The risk of rupture is estimated based on the maximum diameter and the growth rate of the AAA. Previous studies indicate that AAA growth rate increases with the diameter of the AAA [1, 2]. However, this growth rate is not the same for each AAA, as some AAA’s remain stable over a long period of time, while others show a fast growth or grow discontinuously.
In-Vitro Clot Modeling for the Preclinical Assessment of Mechanical Thrombectomy in Acute Ischemic Stroke
Authors: Chueh Juyu , Silva Christine F. , Wakhloo Ajay K. , Gounis Matthew J.
Published: July 2013

Mechanical thrombectomy devices, such as retrievers or aspiration catheters, have recently received approval from the FDA for the treatment of acute ischemic stroke. There is growing interest in endovascular recanalization procedures due to mounting evidence of favorable clinical outcomes. Several attempts have been made to establish dedicated clot models for in-vitro or in-vivo simulation of thromboembolism [1,2]. However, little is known about the mechanical and structural similarities between experimental clots and human sources of emboli that cause stroke. The goal of this study is to compare the structure and compression behavior of the possible sources of the cerebral emboli extracted from patients and model clots produced in-vitro using human, porcine and bovine donors.
Preferential Vitrification of Water in Small Alginate Microcapsules Significantly Augments Cell Cryopreservation by Vitrification
Authors: Zhang Wujie , Yang Geer , Zhang Aili , Xu Lisa X. , He Xiaoming
Published: July 2013

A major challenge to the eventual success of the emerging cell-based medical technologies such as tissue engineering, regenerative medicine and cell transplantation is the limited availability of the desired cell sources [1]. This challenge can be alleviated by cell microencapsulation to avoid undesired immune response (i.e., immunoisolation) so that non-autologous cells can be used to treat human diseases, and by cell cryopreservation to establish banks of important living cells for wide distribution to end users so that they are readily available when needed in the future [2,3]. Although cell microencapsulation has been investigated since 1960s with promising outcomes, cryopreservation of microencapsulated cells has not been well studied. The major challenges are associated with the cell toxicity of the high concentration (> 4–6 M) of cryoprotectants used for vitrification and the loss of microcapsule integrity due to ice formation during slow freezing [4]. Therefore, it is of great interest to achieve vitrification at a low, nontoxic cryoprotectant concentration for the cryopreservation of microencapsulated cells.
Injury During Early Neonatal Development Leads to a Faster Repair Response When Compared to Later Injury in a Mouse Achilles Tendon
Authors: Ansorge H. L. , Hsu J. E. , Edelstein L. , Birk D. E. , Soslowsky L. J.
Published: July 2013

During neonatal development, tendons undergo a well orchestrated process whereby extensive structural and compositional changes occur in synchrony to produce a normal tissue [1,2]. Similarly, during the repair response to injury, structural and compositional changes occur, but in this case, a mechanically inferior tendon is produced. As a result, the process of development has been postulated as a potential paradigm through which improved tissue healing may occur. By examining injury at distinctly different stages of development, we will obtain vital information into the structure-function relationships in tendon. Although the mouse is an intriguing model system due to the availability of assays and genetically altered animals, due to the small size and fragile nature of neonatal tendons, neonatal tendon injury has not been evaluated. Therefore, the objective of this study is to evaluate the differential healing response in neonatal tendon at two distinct stages of development. We hypothesized that when normalized, maximum stress and modulus will be significantly higher in early neonatal injury when compared to later neonatal injury. Also, when normalized, maximum stress, modulus and percent relaxation will be significantly increased over time in early neonatal injury but will remain low in later neonatal injury.
Stress Concentrations of Vulnerable Plaques With a Composite Variable Core
Authors: Massarwa Eyass , Ze’ev Aronis , Eliasy Rami , Haj-Ali Rami , Einav Shmuel
Published: July 2013

Vulnerable plaques are inflamed, active, and growing lesions which are prone to complications such as rupture, luminal and mural thrombosis, intraplaque hemorrhage, and rapid progression to stenosis. It remains difficult to assess what factors influence the biomechanical stability of vulnerable plaques and promote some of them to rupture while others remain intact. The rupture of thin fibrous cap overlying the necrotic core of a vulnerable plaque is the principal cause of acute coronary syndrome. The mechanism or mechanisms responsible for the sudden conversion of a stable atherosclerotic plaque to a life threatening athero-thrombotic lesion are not fully understood. It has been widely assumed that plaque morphology is the major determinant of clinical outcome [1, 2]. Thin-cap fibroatheroma with a large necrotic core and a fibrous cap of < 65μm was describes as a more specific precursor of plaque rupture due to tissue stress.
Microstructural Modeling of Fiber Kinematics and Biomechanics of the Human Facet Capsular Ligament During Subfailure Loading
Authors: Crosby Nathan D. , Quinn Kyle P. , Winkelstein Beth A.
Published: July 2013

Whiplash and other traumatic neck injuries are a primary cause of chronic neck pain in the United States, with the cervical facet joint and its ligament being a common anatomical source of the pain. During these injuries, the facet capsular ligament undergoes excessive stretching that alters the subsequent mechanical function of the facet joint and can also initiate pain [1,2]. Accordingly, defining the mechanical response of the facet capsule requires understanding its microstructural response during loading. Although the macro-mechanical responses of ligaments for many types of loading and injury scenarios have been studied, the microstructural and fibrillar responses in the facet capsular ligament remain largely undefined.
Pseudo-3D Visualization of Cytoskeletal and Whole-Cell Deformation of MLO-Y4 Osteocytes Under Flow
Authors: Baik Andrew D. , Lu X. Lucas , Hillman Elizabeth M. , Dong Cheng , Guo X. Edward
Published: July 2013

Osteocytes respond to fluid shear loading by activating various biochemical pathways, mediating a dynamic process of bone formation and resorption. Whole-cell [1] and intracellular deformation [2] may be able to directly activate and modulate relevant biochemical pathways. Most studies on cell deformation have focused only on cell deformation in the plane parallel to the substrate surface. However, height-dependent cell deformation has not been well characterized even though it may contribute greatly to mechanotransduction mechanisms. Traditional techniques to obtain this additional height information of a cell-body include confocal and deconvolution microscopy, which require scanning a z-stack of the cell. However, this inherently limits the timescale under which the deformational information can be visualized. To further investigate this behavior at a high temporal resolution, we propose using a “pseudo-3D” microscopy method to better characterize osteocyte cell behavior. In this study, we present a novel technique that is able to image a single cell simultaneously in two orthogonal planes to obtain real-time images of cell at a millisecond timescale. The objectives of this study were to: (1) visualize actin or microtubule networks with the plasma membrane in two orthogonal planes simultaneously under fluid shear; (2) map out the deformations using digital image correlation; and (3) compare the depth-directional deformation of actin and microtubule networks of osteocytes.
High Shear Rate Behavior of Gelatin
Authors: Kwon Jiwoon , Subhash Ghatu
Published: July 2013

Gelatin is popular tissue simulant due to their biocompatibility and hence commonly used as surrogates for soft tissue in biomedical fields. With increased focus on tissue damage from battle field, considerable effort is being placed on modeling the mechanical deformation of soft tissue under high rate loading. Systematic evaluation of properties of such surrogate materials is required at similar strain rates because studies using real tissue are always not practical.
Innocuous Intracellular Ice Formation in Adult Stem Cells in the Presence of Polyvinylpyrollidone
Authors: Guha Avishek , Devireddy Ram V.
Published: July 2013

The objective of this work was to assess the effect of 10% (w/v) polyvinylpyrrolidone (PVP) on the pattern of intracellular ice formation (IIF) in human adipose tissue derived adult stem cells (ASCs) in the absence of serum and other cryoprotective agents (CPAs).
Hemodynamics and Growth of Intracranial Aneurysms
Authors: Sforza Daniel , Putman Christopher , Tateshima Satoshi , Vinuela Fernando , Cebral Juan
Published: July 2013

Understanding the underlying mechanisms responsible for the progression and rupture of cerebral aneurysms is important for improving their evaluation and treatment. Previous studies have identified the main factors involved in these processes: hemodynamics, vascular wall biomechanics and mechano-biology, and contacts with peri-aneurysmal structures [1]. However, little is known about their relative importance and interactions. The goal of our study is to shed light into the mechanisms of aneurysm progression by studying cerebral aneurysms that are followed longitudinally in time. This is a challenging problem because due to the poor prognosis of aneurysm ruptures preventive interventions are considered for most aneurysms. This paper presents preliminary results and observations made on a series of aneurysms followed with non-invasive imaging.
Effect of Cortical Bone Thickness on the Magnitude and Classification of Hill Sachs Lesions Verses Glenoid Lesions
Authors: Rowland Brooklynn P. , Smith Steven M. , Voycheck Carrie A. , Sekiya Jon K. , Debski Richard E.
Published: July 2013

The shoulder is the most dislocated major joint in the body; approximately 2% of the population will dislocate their glenohumeral joint between the ages of 18 and 70 [1]. Hill-Sachs lesions, compression fractures resulting from the impaction of the posteroloateral humeral head against the solid anterior rim of the glenoid, occur in roughly 30–40% of all anterior dislocations. Humeral head defects have been linked to postoperative recurrent dislocations and overall instability of the shoulder following stabilization procedures for the capsule [2]. However, the forces and deformations required to create these lesions during shoulder dislocation should be identified to properly develop injury models and new repair techniques. Therefore, the objective of this study was to determine the forces required to create bony lesions on the humeral head and quantify the size of the resulting lesions. In order to achieve this objective, a repeatable testing protocol was developed to consistently produce Hill Sachs lesions.
Evaluating Relationship Between Passive Knee Envelope and a Dynamically Simulated Walk
Authors: Mane Amit M. , Maletsky Lorin P.
Published: July 2013

The motion patterns of the human knee joint depend on its passive motion characteristics, which are described by the ligamentious and articular constraints. Since active motions, like walking and squatting are believed to fall within a passive envelope, the basis for the understanding of the knee joint kinematics lies in the description of its passive constraint characteristics [1]. The link between the knee passive envelope and the kinematics during various dynamic activities has not been studied. It is unclear how the articular geometry and muscle activations of the knee influence the contribution of ligament constraints during dynamic activities. To explain the relationship between knee passive envelope and dynamic activities completely, new methodology must be developed. The objective of the present study was to estimate the effects of variation in passive knee envelope on the tibiofemoral kinematics during dynamically simulated gait using a multivariate analysis technique, principal component (PC) analysis.
Influence of Surrounding Tissues on Biomechanics of Aortic Wall: A Feasibility Study of Mechanical Homeostasis
Authors: Hunley S. C. , Kwon S. , Baek S.
Published: July 2013

Previous research in cardiovascular mechanics has shown that mechanical factors strongly influence the growth and remodeling of blood vessels, thereby leading the hypothesis of mechanical homeostasis as a mechanism of regulating vascular adaptation [1]. Nevertheless, this assumption is mostly based on stress analysis of an idealized blood vessel. However, for the aorta, its motion is considerably limited by the surrounding tissue during the cardiac cycle, with the thickness of the posterior side significantly thinner than the anterior side (Fig. 1). In this work, we test the possibility of the existence of a homeostatic level of stress in the aorta using a linear plane-strain model that accounts for thickness variations and surrounding tissues. The results of this computational study show that the surrounding tissue, together with thickness variations, homogenizes the stress level of blood vessel under a physiological pressure, which implies that the mechanical homeostasis is still feasible even with thickness variations and the influence of the surrounding tissues in the aorta.
Measurement of the Local Strain of the Porcine Thoracic Aorta During the Inflation Test
Authors: Kim Jungsil , Baek Seungik
Published: July 2013

The aorta is the main artery and plays an important role in the blood circulatory system. Diseases of the aorta such as aortic aneurysm and aortic dissection have high mortality rates, hence the study of the mechanical properties of the aorta has been an active research area. In many previous studies, the aorta has been considered as a straight cylindrical tube undergoing uniform circumferential deformation and therefore uniform strain/stress distribution in the circumferential direction. However, recent biomedical imaging studies show that the aorta has circumferentially nonuniform deformation during the cardiac cycle [1] and the aortic wall distends asymmetrically [2]. Furthermore, it has been shown that the anterior wall displacement is larger than the posterior wall displacement [3]. These in vivo studies have raised yet another question as to whether nonuniform deformation is due to the inhomogeneous properties of the aortic wall or due to surrounding tissues.
Injury Tolerance Criteria for Short-Duration Axial Impulse Loading of the Tibia
Authors: Quenneville Cheryl E. , McLachlin Stewart D. , Greeley Gillian S. , Dunning Cynthia E.
Published: July 2013

Axial loading of the lower leg during short-duration impulsive events, such as ejection seat and parachute landings, or in-vehicle landmine blasts, can cause significant lower limb injuries. To date, most of the research investigating the axial injury tolerance levels of the lower limb has been conducted by the car crash industry [e.g., 1]. The aforementioned short-duration events achieve higher forces over less time than car crashes, and as such, investigation into the applicability of the current injury criterion is required.