bluuebunny/crossref_metadata_2025 huggingface dataset:
Viscous Energy Loss in Aortic Valve Disease Patients
Authors: Barker A. J. , van Ooij P. , Bandi K. , Garcia J. , McCarthy P. , Carr J. , Malaisrie C. , Markl M.
Published: January 2014

Purpose : Aortic valve disease (AVD) in the form of stenosis, insufficiency, or congenital defect will disrupt normal function beyond the valve itself. This includes an increase in cardiac afterload and a drastic alteration in post-valvular 3D blood flow patterns 1, 2. The current AHA/ACC standard-of-care guidelines, however, assess disease severity based on simplified measurements local to the valve, such as: peak velocity, effective orifice area, regurgitation, aortic diameter and transvalvular pressure gradient 3. Paradoxically, it is known that similarly classified AVD patients under these guideline metrics can exhibit radically divergent outcomes — implying an incomplete characterization of the disease 4. For this reason, functional assessment and risk-stratification may benefit from a robust methodology capable of quantifying the energetic load placed on the left ventricle (LV) due to the presence of AVD. The measurement of viscous energy loss, a parameter which is directly responsible for increased cardiac afterload and is independent of pressure recovery effects, is a promising candidate to quantify LV loading. With this in mind, the 4D flow technique (time-resolved 3D phase-contrast MRI with all principal velocity directions encoded) provides the necessary information to calculate this parameter. Therefore, we present a theoretical basis for the use of 4D flow MRI to characterize in-vivo energy loss and apply the technique in a pilot study of patients with aortic valve stenosis (n = 13) or aortic dilation (n = 17) as compared to normal controls (n = 12).
Correlating Knee Characteristics and Dynamic Load to Customize Gait Simulation In Vitro
Authors: Nesbitt Rebecca J. , Bates Nathaniel A. , Schaffner Grant , Hewett Timothy , Shearn Jason T.
Published: January 2014

Anterior cruciate ligament (ACL) tears are one of the most common knee injuries, with estimates reaching approximately 250,000 cases in the US per year [1]. In addition, patients treated with surgical reconstruction, or conservatively through rehabilitation and activity modification, have still been shown to be at increased risk of developing osteoarthritis (OA) earlier in life [2]. Researchers suspect that the failure of current ACL repair techniques is their inability to restore native functionality to the knee after injury.
Experimental Study of Hemodynamics in the Circle of Willis
Authors: Zhu Guangyu , Yuan Qi , Yeo Joon Hock
Published: January 2014

The Circle of Willis (CoW) is a ring like structure located at the base of brain, which is composed of a single anterior communicating artery (ACoA), paired anterior cerebral arteries (ACAs), paired internal carotid arteries (ICAs), paired posterior communicating arteries (PCoAs), paired posterior cerebral arteries (PCAs), paired vertebral arteries (VAs) and a single basilar artery (BA). It is the main cerebral blood perfusion pathway and provides an important collateral channel in patients with severe carotid or vertebral artery disease. Over 50% of stroke cases are related to the stenosis of arteries in the CoW, so the detailed information of the cerebral hemodynamics under different pathology situations is important for a variety of clinical applications. Numerous experimental studies have been performed on this field from different perspectives, include the mechanism of stenosis in the CoW [1], risk assessment of cerebral aneurysm [2] and the impact of pathological variations on the flow distribution [3]. However, none of these researches focus on the influence of ICA stenosis rates on cerebral perfusion and the specific collateral mechanism of the Circle of Willis under such situations. In this paper, an experimental study on cerebral blood perfusion and the collateral mechanism under a series of ICA stenosis rates was carried out.
Fractional Flow Reserve Estimation in Coronary Arteries by Forward Geometrical Modeling
Authors: Schrauwen Jelle T. C. , Wentzel Jolanda J. , van der Steen Anton F. W. , Gijsen Frank J. H.
Published: January 2014

Fractional Flow Reserve (FFR) is an important indicator for the hemodynamic significance of a coronary stenosis [1]. The FFR is defined as the pressure drop over the stenosis under hyperemia. The pressure drop, and thus the FFR, depends on both the geometry and flow. In clinical practice, the FFR is measured with a pressure wire under administration of adenosine and intervention is warranted if the FFR is below 0.8.
The Effect of Creep on Human Lumbar Intervertebral Disc Impact Mechanics
Authors: Jamison David , Marcolongo Michele
Published: January 2014

The intervertebral disc (IVD) is often modeled as a biphasic tissue, with both a solid and a fluid phase [1]. While under a constant compressive load, the IVD responds with continuous creep displacement, resulting in the loss of interstitial fluid from the tissue and increased strain on the annular fibers. The mechanical response of the IVD under impact loading conditions has been previously reported by the authors and others. It is unknown, however, how the loss of interstitial fluid affects disc biomechanics under impact loads. In this study, we investigate the effects of creep on IVD impact mechanics.
Customized Release of Metronidazole From Composite Casted Rings of Poly-Caprolactone/Alginate for Periodontal Drug Delivery
Authors: Starly Binil , Lan Shih-Feng , Schmidtke David
Published: January 2014

Dental implants provide support for dental crowns and bridges by serving as abutments for the replacement of missing teeth. The objective of this study was to demonstrate a novel method of controlled localized delivery of antibacterial agents to an implant site using a custom fabricated ring. The study involved incorporating a model antibacterial agent (metronidazole) into custom designed Poly-ε-Caprolactone/Alginate (PCL/Alginate) composite rings to produce the intended controlled release profile. In vitro release studies indicate that pure (100%) alginate rings exhibited an expected burst release of metronidazole in the first few hours, whereas Alginate/PCL composite rings produced a medium burst release followed by a sustained release for a period greater than 4 weeks. By varying the PCL/Alginate weight ratios, we have shown that we can control the amount of antibacterial agents released to provide the minimal inhibitory concentration needed for adequate protection. The developed system demonstrates a controllable drug release profile and the potential for the ring to inhibit bacterial biofilm growth for the prevention of diseases such as peri-implantitis resulting from bacterial infection at the implant site.
Simulation of the Role of Oscillatory Shear Stress on Mesenchymal Stem Cell Proliferation and Extracellular Matrix Production in Engineered Heart Valve Tissue Formation
Authors: Soares João S. , Le Trung B. , Sotiropoulos Fotis , Sacks Michael S.
Published: January 2014

Living tissue engineered heart valves (TEHV) may circumvent ongoing problems in pediatric valve replacements, offering optimum hemodynamic performance and the potential for growth, remodeling, and self-repair [1]. TEHV have been constructed by seeding vascular-derived autologous cells onto biodegradable scaffolds and exhibited enhanced extracellular matrix (ECM) development when cultured under pulsatile flow conditions in-vitro [2]. After functioning successfully for up to 8 months in the pulmonary circulation of growing lambs, TEHV underwent extensive in vivo remodeling and structural evolution and have demonstrated the feasibility of engineering living heart valves in vitro [3]. The employment of novel cell sources, which are clinically obtainable in principle such as bone marrow-derived mesenchymal stem cells (MSCs), is key to achieve viable clinical application [4].
WPI iCREATE: Graduate Training in Innovative Translation
Authors: Billiar Kristen L. , Gaudette Glenn , Hoy Frank , Camesano Terri Anne
Published: January 2014

Traditional doctoral degree programs in engineering are generally good at teaching “Linear Thinking,” that is the ability to apply existing knowledge to achieve important, but predictable, outcomes (as defined by Stauffer (2005)). However, with few exceptions, the US engineering educational system falls short in enabling the vital attributes of innovation: adaptability, inventiveness, and the confidence to propose new paradigms.
The Effects of Shoe Architecture on Heel Impact Forces During Gait
Authors: Lawson Brie , Aguilar Fernando , Knop Lauren , Goehler Craig M.
Published: January 2014

In the current athletic footwear market, there exists a range of shoe architectures that offer a variety of support and flexibility options. The importance of footwear type has proved to be significant in the prevention of acute injuries due to impact forces [1, 2]. It has been shown that impact forces have most often been implicated in overuse running injuries, such as stress fractures and plantar fasciitis [2]. Additionally, material properties of damping elements, such as shoes, have demonstrated an effect on impact forces. Athletic footwear is categorized by the attribute of flexibility. The natural flex observed in the sole determines the flexibility; a more flexible shoe flexes closer to the mid-foot region, while a shoe designed for stability will flex closer to the ball of the shoe. Prior work has quantified the material stiffness of different shoe architectures with stability shoes possessing higher material stiffness than flexible shoes [3].
Sensing Physiological Tremor in a Hand-Held Microsurgical Instrument
Authors: Saxena Abhijit , Patel Rajni V.
Published: January 2014

Physiological tremor is an involuntary, approximately rhythmic and roughly sinusoidal movement [1]. It is inherent in all humans. The characteristics of physiological tremor are highly dependent on the body parts [2]. For instance, the frequency of tremor in the elbow ranges from 3 to 5 Hz while it ranges from 8 to 12 Hz in the wrist. Physiological tremor is benign for everyday tasks such as walking or eating. However, tasks that require fine muscle control such as microsurgery or military targeting are susceptible to physiological tremor. The imprecision in positioning the tool-tip due to the tremor makes some ophthalmological, neurological and inner ear microsurgeries difficult [3]. Therefore, real-time compensation of physiological tremor would enable surgeons to accurately perform microsurgeries.
Human Annulus Fibrosus Lamellae Generate Significant Multi-Axial Forces and Moments in Biaxial Extension
Authors: Nagel Tina M. , Golman Mikhail , Nuckley David J. , Barocas Victor H.
Published: January 2014

Low back pain is a widespread public health issue affecting about 75% of Americans in their lifetime [1]. In many individuals, the origin remains unknown in spite of decades of research. However, intervertebral disc (IVD) degeneration has been theorized as a major precursor to nonspecific low back pain [2,3].
Prolonged Treatment of Ultra-Low Dose Chondroitinase ABC Improves Matrix Production in Engineered Cartilage
Authors: O’Connell Grace D. , Cui Victoria , Nims Robert J. , Nover Adam B. , Ateshian Gerard A. , Hung Clark T.
Published: January 2014

Articular cartilage is the load bearing soft tissue of diarthrodial joints, and mechanical loading maintains the integrity of the tissue. The predominant extracellular matrix constituents, proteoglycans and collagen, allow cartilage to support the high compressive and tensile loads experienced in diurnal loading. Our laboratory has been successful in cultivating engineered cartilage constructs with a compressive equilibrium modulus and glycosaminglycan (GAG) content near native values [1, 2]. Many approaches to cultivating engineered cartilage have been limited by low collagen production in vitro, an impediment for attaining native functional load-bearing properties [3].
The Biomechanical Properties of Arterial Elastin With Glucose Effect
Authors: Wang Yunjie , Zhang Katherine Yanhang
Published: January 2014

Elastin, as one of the major extracellular matrix (ECM) components, is essential to accommodate physiological deformation and provide elastic support for blood vessels. Elastin is a long-lived ECM protein and it can suffer from cumulative effects of exposure to chemical damage, which can greatly compromise its biomechanical properties. The mechanical properties of elastin are related to its microstructure and the chemical environment. Glucose is an important carbohydrate in human body. The effect of glucose on the mechanical properties of blood vessels is especially magnified in diabetic patients [1]. Glucose can directly condense with amino groups of proteins by nonenzymatic glycation, which is one of the main mechanisms of aging [2].
Modeling Diffusion and Vesiculation in Defective Human Erythrocyte Membrane
Authors: Li He , Lykotrafitis George
Published: January 2014

The hemolytic disorders of hereditary spherocytosis (HS) and hereditary elliptocytosis (HE) affect the lives of millions of individuals worldwide. In HS and HE, connections in the vertical and horizontal directions between components of the RBC membrane (see Fig. 1(a)), are disrupted due to defective proteins, leading to loss of the structural and functional integrity of the membrane (1–2). Moreover, disruptions of either the vertical interactions or horizontal interactions affect the lateral diffusivity of the mobile band 3 proteins, as the motion of band 3 in the RBC membrane is confined by the cytoskeleton (3). Although a number of coarse-grained molecular dynamics (CGMD) RBC membrane models have been developed in the past two decades, very few RBC membrane models have been used to study the disordered band 3 diffusion and membrane vesiculation in HS and HE. The implicit representations of either the lipid bilayer or the cytoskeleton in these membrane models limit their applications in the membrane instability problems in HS and HE. In this extended abstract, we develop a two-component CGMD human RBC membrane model that explicitly comprises both the lipid bilayer and the cytoskeleton. In this way, the interactions between the cytoskeleton and the proteins embedded in the lipid bilayer can be simulated. The proposed model allows us to measure the band 3 lateral mobility and simulate the process of membrane vesiculation in the membrane with protein defects.
Collagen-Hyaluronic Acid Hydrogels Provide Enhanced EMT of Endocardial Cells
Authors: Sewell-Loftin M. K. , DeLaughter Daniel M. , Barnett Joey V. , Merryman W. David
Published: January 2014

A viable tissue engineered heart valve (TEHV) replacement would eliminate disadvantages associated with currently available prosthetics, such as thrombosis and increased risk of valve calcification. Viable TEHVs also are promising in that they can actively remodel and grow, as they would be populated with cells similar to native valves. Valvular interstitial cells (VICs) organize and maintain the complex structure of valves throughout the life of an organism. Considerable effort has been made towards identifying a source of VICs for next generation prosthetic heart valves. Despite this effort, the mechanisms by which VICs are produced in development, via endocardial epithethelial-to-mesenchymal transformation (EMT), are not fully understood. EMT is the critical first step in the formation of heart valve leaflets in utero, and thus a thorough understanding of the biomechanical and signaling environments that regulate EMT could lead to advancements in viable TEHVs.
Combined Microscopy and Hyperelastic Warping for the Measurement of Intranuclear Mechanics in Native 3D Tissue
Authors: Henderson Jonathan T. , Shannon Garrett , Veress Alexander I. , Neu Corey P.
Published: January 2014

The cell nucleus directs the regulation of normal cellular functions as well as the expression of proteins required for adaption to environmental changes. Mechanical forces are an important determinant of gene expression, and yet the measurement of intranuclear mechanics (e.g. strain) in cells embedded within their native tissue in situ remains a challenge.
Steady Flow Preconditioning of Endothelial Outgrowth Cells on Ex Vivo and In Vivo ePTFE Grafts
Authors: Anderson D. E. J. , Glynn J. J. , Hinds M. T.
Published: January 2014

Endothelialization of vascular graft materials is a promising approach for improving the in vivo performance of vascular grafts, particularly for small diameter applications of less than 4 mm. The ability to incorporate a native endothelium onto a graft may reduce the thrombosis and intimal hyperplasia that limits long-term clinical success of these small diameter grafts. Endothelial outgrowth cells (EOCs), which are isolated from whole blood and expand rapidly in vitro, provide an autologous cell source capable of developing into a biologically active endothelial layer. A preconditioning step may enhance EOCs’ performance on vascular grafts. Mature endothelial cells, isolated from vascular walls, are known to decrease expression of pro-thrombotic and pro-inflammatory markers when exposed to steady fluid shear stress, compared to cells under disturbed flow conditions or static culture. This study examined the hypothesis that steady flow preconditioning of EOCs reduces their in vitro markers of thrombosis and inflammation, reduces platelet and fibrin accumulation on EOC–coated ePTFE grafts in an ex vivo shunt, and reduces initial hyperplasia on EOC–coated ePTFE grafts in an in vivo graft implant. This work was performed using well-established, non-human primate models for testing EOC-coated ePTFE grafts ex vivo and in vivo. These conditions represent a clinically-relevant cell source and biomaterial for determining the effects of fluid shear stress preconditioning on graft performance.
Versatility of a Collagen Adaptation Model That Includes Strain-Dependent Degeneration and Cell Traction
Authors: van Donkelaar C. C. , Heck T. A. M. , Wilson W. , Foolen J. , Ito K.
Published: January 2014

The orientation of collagen fibers is essential for tissue mechanical functioning. Tissues are able to adapt this network to changes in the mechanical environment. Two mechanisms for this adaptation that have been proposed are cell-orientation dependent cell-traction (eg (6)), and strain-protected enzymatic collagen degradation (eg (11)). The premise is that these two mechanisms together are able to predict a transient and equilibrium responses of tissue adaptation to mechanical constraints. To evaluate this, they are captured in a numerical model and predictions are corroborated against distinct experimental observations. This abstract overviews the versatility of the model, using already presented (5) and new data.
Changes in Foraminal Geometry With Anterior Decompression Versus Keyhole Foraminotomy in the Cervical Spine: A Biomechanical Investigation
Authors: Chu Bryant , Kuo Calvin , Nguyen Jackie , Leasure Jeremi , Ames Christopher , Kondrashov Dimitriy
Published: January 2014

Cervical spondylosis can be treated with various surgical decompression techniques, notably anterior cervical decompression and fusion (ACDF) and posterior keyhole foraminotomy1. Although each procedure has distinct methods, there is no compelling evidence in the literature to advocate one over the other. Furthermore, subtle differences within the techniques have yet to be examined such as the salvage or resection of uncovertebral joints during ACDF. Systematic reviews2,5 and meta-analyses3 have not elucidated significant differences in pain improvement between ACDF techniques, and no study has compared clinical outcomes for ACDF versus posterior foraminotomy, the two most popular cervical decompression techniques to date. We provide benchtop evidence as to the relative effectiveness of foraminotomy, ACDF with or without resection, and a combination of all surgeries. We hypothesized that ACDF with uncovertebral resection would be most effective to open the neuroforamina. Results of this study inform best practices for cervical decompression surgeries.
Development of a Biodegradable Regenerative Implant for the Treatment of Long Bone Comminuted Fractures
Authors: Bergerson Christie M. , Moreno Michael R.
Published: January 2014

There were approximately 1,620,000 surgical bone graft procedures in the United States in 2005 and 672,000 fracture reductions in 20061. The estimated economic costs for orthopedic injuries to upper and lower extremities collectively account for 17% ($68 billion) of total lifetime costs that originated in 20001. Over the past 15 years, significant efforts have focused on the development of bioactive, load-bearing polymeric materials designed to restore function within critical-sized bone defects. Traditional reconstructive approaches use autografting of the defects, but these approaches have significant limitations2. As a result, transfer of grafts greater than 2 cm are associated with an unacceptably high complication rate. Thus, the optimal skeletal extremity reconstruction would be one in which the reconstruction is performed with material that may be taken “off the shelf” to eliminate donor site morbidity, but is degradable and resorbable affording incorporation into the host.
Cell Shape Dictates Differential Sensitivity of Subcellular Contractile Forces in Response to Directional Substrate Stretch
Authors: Shao Yue , Mann Jennifer M. , Fu Jianping
Published: January 2014

In past decades, it has been well demonstrated that cellular contractile forces against the extracellular matrix (ECM) plays an important role in regulating cellular behaviors such as spreading, adhesion and differentiation [1]. Recent studies have found that focal adhesions (FAs) and subcellular contractile forces mediated by FAs have an intimate connection and form an important feedback loop to control cellular mechanotransduction in response to mechanical cues such as matrix rigidity, cell geometry and external forces [2]. Therefore, understanding how FA-mediated contractile forces are regulated by those factors is critical for our understanding of cellular mechanotransduction and mechano-responsiveness.
Effect of CPA Transmembrane Flux on Cell Volume Change During Freezing and its Application in Biopreservation
Authors: Zhao Gang , Gao Dayong
Published: January 2014

Theoretical models for prediction of cell dehydration during addition/removal of cryoprotective agents (CPAs) or during freezing sprung up like mushrooms. These models are powerful for qualitative analysis of “solution injury” or “osmotic injury”, and furthermore, optimization of the complex processes involved in cryopreservation.
Method for Incorporating Three-Dimensional Residual Stresses Into Patient-Specific Simulations of Arteries
Authors: Pierce David M. , Fastl Thomas E. , Weisbecker Hannah , Holzapfel Gerhard A. , Rodriguez-Vila Borja , Gómez Enrique J. , Verbrugghe Peter , Fourneau Inge , Maleux Geert , Herijgers Paul
Published: January 2014

Through progress in medical imaging, image analysis and finite element (FE) meshing tools it is now possible to extract patient-specific geometries from medical images of, e.g., abdominal aortic aneurysms (AAAs), and thus to study clinically relevant problems via FE simulations. Medical imaging is most often performed in vivo, and hence the reconstructed model geometry in the problem of interest will represent the in vivo state, e.g., the AAA at physiological blood pressure. However, classical continuum mechanics and FE methods assume that constitutive models and the corresponding simulations start from an unloaded, stress-free reference condition.
Effectiveness of Eye Armor During Blast Loading
Authors: Bailoor Shantanu , Soti Atul , Bhardwaj Rajneesh , Nguyen Thao D.
Published: January 2014

Ocular injuries from blast have increased in recent wars, but the effectiveness of eye armor, developed for ballistic and laser protection, in preventing blast injuries remains unknown. The severity of the blast injuries and distance of the tertiary care facility from the injury site means that often patients are unable to recount the injury event, and witnesses are unavailable. These limitations hinder clinical studies of the effectiveness of the armor. The role of the following parameters remains unknown in designing the armor: underwash between the armor and face; clearance between the armor and face; compliance of the armor; angle of incidence of the blast wave; and contact force between the armor and the face. The possibility of the eye armor to fly off, to flex significantly and allow more underwash at a particular incidence angle of the blast wave are some of the open questions to be answered. Furthermore, the influence of these parameters on biomechanical deformation and stresses incurred by the globe due to blast overpressure is unknown.
Biofabrication of Multi-Material 3D Neural Constructs Embedded With Patterned PC12 Neural Cell Lines
Authors: Dreher Rachel , Power Ryan , Starly Binil
Published: January 2014

In Vitro models are being used as a bridge between animal and human studies. Being able to reproduce specific tissue-like structures, functions and responses in a way that is more physiologically relevant allows for huge advantages for tissue engineering, pharmaco-toxicology and food research. These systems are not designed to be directly implanted into patients, but can be used to study human tissue physiology and pathophysiology in vitro. In vitro models are based on human cells, which can capture the responses of the human body, particularly those that are species specific. Models of tissues and organs can give enhanced predictive power, particularly for large-scale screening assays and to understand complex disease pathology.
Flow Diversion in Rabbit Aneurysm Models
Authors: Cebral Juan R. , Mut Fernando , Raschi Marcelo , Kadirvel Ramanathan , Kallmes David
Published: January 2014

Flow diversion treatment of cerebral aneurysms has increasingly been considered, especially for large complex aneurysms with wide necks that are difficult to treat with coils of by clipping. However, the relationship between the hemodynamic environment created immediately after implantation of flow diverters (FD) and the subsequent aneurysm occlusion is poorly understood [1].
Electrical Analog Models to Simulate the Impact of Partial Hepatectomy on Hepatic Hemodynamics
Authors: Debbaut Charlotte , De Wilde David , Casteleyn Christophe , Cornillie Pieter , Dierick Manuel , Van Hoorebeke Luc , Monbaliu Diethard , Fan Ye-Dong , Segers Patrick
Published: January 2014

Due to the growing shortage of donor livers, more patients are waiting for liver transplantation. Efforts to expand the donor pool include the use of living donor liver transplantation (LDLT) and split liver transplantation. LDLT involves a healthy person undergoing a partial hepatectomy to donate a part of his liver to a patient with severe liver failure. Afterwards, the regenerative capacity of the organ allows the livers of both donor and recipient to regrow to normal liver masses. The procedure is not without risk as serious complications may occur (such as cholestasis, ascites, gastrointestinal bleeding and renal impairment). An inadequate liver mass compared to the body mass may result in the small-for-size syndrome (SFSS). In both donor and recipient, LDLT may lead to portal hypertension associated with the elevated intrahepatic resistance of a smaller liver, and an increased portal venous (PV) inflow per gram of liver tissue compared to the total liver before resection. Excessive hyperperfusion and shear stress may damage the sinusoidal endothelial cells and lead to graft dysfunction.
Dependence of Human Lumbar Vertebral Trabecular Bone (HVTB) Mechanical Anisotropy Ratio on QCT–Based Apparent Density
Authors: Aiyangar Ameet , Vivanco Juan , Au Anthony , Anderson Paul , Smith Everett , Ploeg Heidi-Lynn
Published: January 2014

Obtaining bone mechanical properties from clinical resolution quantitative computed tomography (QCT)-derived localized apparent density presents the most attractive, available tool for developing subject-specific finite element (FE) bone models. While QCT density is a good predictor of the mechanical properties of HVTB [1, 2], knowledge of the fabric tensor (anisotropy ratio) can substantially improve prediction [3] and accuracy of CT-based continuum FE models [4]. Unfortunately, resolution of currently available clinical CT scanners is inadequate for mapping the fabric tensor of HVTB, which is known to be at least transversely isotropic [5]. Furthermore, trabecular bone mechanical anisotropy ratio has been shown to vary with density [2].
Characterization of Cardiac Function and Arterial Mechanics During Early Postnatal Development in Fibulin-5 Null Mice
Authors: Le Victoria , Yanagisawa Hiromi , Wagenseil Jessica
Published: January 2014

Fibulin-5 is an extracellular matrix protein that interacts with other proteins during a complex process that results in elastic fiber formation from the elastin precursor, tropoelastin [1]. Elastic fibers are an important component of tissues requiring elasticity, including large arteries, lungs and skin. In mice lacking fibulin-5 ( Fbln5−/−), these tissues contain disorganized elastic fibers and exhibit decreased elasticity [2]. The phenotype of Fbln5−/− mice is similar to that of humans with cutis laxa, a connective tissue disorder characterized by loose skin and narrow arteries with reduced compliance.
Robotically Simulated Clinical Pivot Shift: A Better Tool for Analyzing ACL Reconstructions?
Authors: Colbrunn R. W. , Dumpe J. E. , Bonner T. F. , Kolmodin J. D. , Barsoum W. K. , Saluan P. M.
Published: January 2014

A pivot shift is a useful exam for evaluating anterior cruciate ligament (ACL) reconstruction surgery. A positive result is a perceived “clunk” and is quantified by the kinematics that occur during the tibial reduction phase. In vitro evaluation of ACL reconstruction techniques includes robotic testing of cadaveric knees where the applied loads represent estimated in situ loads. Early understanding of the mechanism of the pivot shift has resulted in a simplified representation where static “rotary loads” (10Nm valgus torque, 5Nm internal tibial torque) are applied at a few discrete flexion angles, and changes in anterior tibial translation (ATT) are compared [1]. Building upon this work, and with advances in technology, we are now able to create a robotic test that is more like the clinical exam. Our hypothesis was that kinematics produced during the robotically simulated pivot shift would be similar to the clinical pivot shift but would be significantly different from the rotary loads method. The ability for a test to produce larger kinematic differences between native and deficient states may suggest a more robust methodology by which to evaluate the efficacy of ACL reconstructions.
Validation of Cerebral Blood Flow in Intracranial Aneurysms: CFD Versus 7 Tesla 4D PC-MRI
Authors: Berg P. , Janiga G. , Stucht D. , Speck O. , Thévenin D.
Published: January 2014

The number of numerical studies predicting blood flow in intracranial aneurysms is rapidly increasing over the last years. Due to a high spatial as well as temporal resolution, computational fluid dynamics (CFD) approaches offer a high potential to investigate flow interaction within the human vascular system. However, state-of-the-art methods still underlie several assumptions, e.g., rigid vessel walls, analytical boundary conditions or the consideration of blood as a single-phase continuous fluid. In consequence, the acceptance of CFD is still limited among a majority of physicians [1]. In order to overcome these reasonable doubts, simulations need to be validated via experiments. Therefore, two patient-specific intracranial aneurysms were measured by means of 7-Tesla magnetic resonance imaging (MRI). Afterwards, highly resolved numerical simulations were carried out and the peak-systolic velocity fields compared in a qualitative manner.
Fluid-Structure Interaction Predictions of Ascending Aorta Hemodynamics Under Tricuspid and Bicuspid Aortic Valve Flows
Authors: Cao Kai , Sucosky Philippe
Published: January 2014

The bicuspid aortic valve (BAV) is the most common congenital cardiac anomaly and is present in 2–3% of the general population. As compared to the normal tricuspid aortic valve (TAV) which consists of three leaflets, the most prevalent type-I BAV morphology forms with two as a result of left-/right-coronary cusp fusion. While the BAV anatomy may not intrinsically hamper valvular function, it is associated with a spectrum of secondary aortopathy such as aortic dilation and subsequent dissection. The dilation and thinning of the ascending aorta downstream of a BAV is marked by structural wall abnormalities including smooth muscle cell depletion, elastic fiber degeneration and abnormal extracellular matrix remodeling, which localize to the convexity of the aortic wall.
Design Analysis: Modular Reverse Total Shoulder Prosthetic Failure Without Proximal Bone Support
Authors: Ansari Farzana , Major Carol , Gunther Stephen B. , Norris Tom R. , Ries Michael , Pruitt Lisa
Published: January 2014

Reverse total shoulder arthroplasty (RSA) serves as an effective alternative to total shoulder arthroplasty (TSA), especially for patients with rotator cuff deficiency [1]. Long-term performance of RSA has been limited by a variety of complications including dislocation, infection, humeral fracture, glenoid loosening, glenoid unscrewing, scapular erosion and polyethylene debris [1–2]. Dissociation between the proximal metaphyseal component and distal humeral prosthetic stem (disaphysis) in modular RSAs has been reported with low frequency (1–2%) [2]; however, cases have led to severe consequences including in vivo disassembly [3]. Most cases of unscrewing have occurred due to insufficient support for the prosthesis resulting from proximal humeral bone deficiency [4–5]. In this study, we evaluate a retrieved RSA that unscrewed and subsequently fractured in vivo in a patient with proximal bone deficiency.
Tensile Properties of the Swine Cardinal Ligament
Authors: Davis Frances M. , Tan Ting , Nicewonder Suzanne , De Vita Raffaella
Published: January 2014

Pelvic floor disorders such as urinary incontinence, fecal incontinence, and pelvic organ prolapse represent a major public health concern in the United States affecting one third of adult women [1]. These disorders are determined by structural and mechanical alterations of the pelvic organs, their supporting muscles and connective tissues that occur mainly during pregnancy, vaginal delivery, and aging [1].
Geometrical and Morphological Assessment of Human Endarterectomy Specimens In Vitro
Authors: Boekhoven Renate W. , Rutten Marcel C. M. , van Sambeek Marc R. H. M. , van de Vosse Frans N. , Lopata Richard G. P.
Published: January 2014

Treatment of rupture-prone carotid atherosclerotic plaques, by means of endarterectomy, is only beneficial for patients with unstable plaques, which comprise only 16% of the patient population [1]. It is therefore of great interest to assess morphology, geometry and mechanical deformation of the plaque and its components, to prevent unnecessary treatment. However, due to the complex geometry of stenotic arteries, 3D information at both high temporal and spatial resolution is required. Besides, assessment of plaque morphology in vivo can still not be routinely performed. Therefore, one has to rely on in vitro methods to obtain morphology and mechanical properties, and thus rupture risk.
Systemic PTH Release During Exercise Enhances Trabecular Bone Architecture
Authors: Gardinier Joseph D. , Mohamed Fatma , Kohn David H.
Published: January 2014

Bone mineral density gained during adolescent years is a significant determinant of bone quality maintained during adult-hood [1]. The ability to enhance the structural integrity of bone at a young age reduces the risk of bone fracture as well as the development of musculoskeletal diseases, such as osteoporosis [1].
Proliferation of Cells From a Mouse Model of Regeneration
Authors: Lynch Kristen , Ahsan Tabassum
Published: January 2014

The ability to induce limb regeneration in humans is of growing interest in the field of regenerative medicine, particularly due to the increased number of amputees among military veterans. Unfortunately, mammals have limited regenerative capabilities as compared to amphibians, which can re-establish complex structures after traumatic injury. There have been a few clinically documented cases of digit regeneration in children [1], indicating that the potential to regenerate is not completely absent in humans. Mammalian models of epimorphic regeneration is primarily limited to the mouse digit, which has a level-specific response in that amputation at the terminal phalangeal element (P3) results in regeneration, but not at the next more proximal joint (P2) (Figure 1). Recently primary stromal cells were isolated from each of these mouse joints (P3 and P2, respectively) [2], which provides a unique opportunity to utilize in vitro techniques to identify differences in one of the phenotypes prevalent at the amputation plane of a regenerating and non-regenerating region.
Lamellar and Interlamellar Shear Compared Across Regions of the Annulus Fibrosus
Authors: Labus K. M. , Hsieh A. H. , Puttlitz C. M.
Published: January 2014

Computational models of the intervertebral disc commonly use continuum descriptions that treat the annulus fibrosus as a single material rather than discretely modeling the lamellae and interlamellar interactions [1,2]. However, modeling the mechanics of individual lamellae and the interlamellar region can aid in the understanding of degenerative disc disease and its treatment. Previous work has demonstrated that fibrous connections between lamellae as well as bridges spanning across layers exist, but the mechanical contributions of these structures have largely remained uncharacterized [3]. Studying interlamellar shear mechanics may provide insights into the structure-function relationships of the annulus. The purpose of this study was to compare the mechanical shear in the interlamellar and lamellar regions, model the stress-stretch relationships of these areas utilizing a hyperelastic strain energy function, and compare the shear properties across multiple locations of the intervertebral disc.
Red Blood Cell Surface Receptor Expression of BCAM/Lu is Regulated by Protein Kinase A Activity
Authors: Maciaszek J. L. , Andemariam B. , Lykotrafitis G.
Published: January 2014

Irregular sickle red blood cells (RBCs) can contribute to the pathogenesis of vasoocclusion and other complications of sickle cell disease (SCD) via abnormal adherence to the vascular endothelium. It has previously been demonstrated that epinephrine enhances SCD RBC adhesion by activating the BCAM/Lu and ICAM-4 surface receptors [1–2]. Epinephrine acts on the RBC β2-adrenergic receptor, thereby activating Gas proteins that stimulate adenylyl cyclase (AC). This enzyme catalyzes the conversion of adenosine triphosphate (ATP) to cyclic adenosine monophosphate (cAMP), leading to protein kinase A (PKA) activation, an intermediate step in the upregulation of BCAM/Lu and ICAM-4 mediated adhesion. The interaction of BCAM/Lu with the α5 chain of laminin may contribute to vaso-occlusive events in SCD due to overexpression of BCAM on SCD RBCs.
Understanding the Mechanical Properties of Microalgae Using Atomic Force Microscopy
Authors: Warren Kristin M. , Mpagazehe Jeremiah , Higgs C. Fred , LeDuc Philip
Published: January 2014

From consumer productions to energy production, algae is used in many industrial processes. Understanding the mechanical behavior of algae is important to optimize these processes. To obtain a better understanding of algae cell response, we mechanically characterized single, dried Scenedesmus dimorphus cells. To accomplish this, we used atomic force microscopy (AFM) to image S. dimorphus cells, which enabled us to map the AFM measurements to a location on the individual cells. We were then able to perform force measurements on the AFM to determine the Young’s modulus of S. dimorphus. These findings enable a more detailed understanding of the mechanical properties of a single S. dimorphus cell, which may be useful in many applications.
Envelopes of Passive Motion in the Intact Tibiofemoral Joint: An
In Vitro Study
Authors: Roth Joshua D. , Howell S. M. , Hull M. L.
Published: January 2014

The kinematics (i.e. passive motions) of the knee are determined and constrained by the articular surfaces and soft tissues of the tibiofemoral joint [1]. Knee kinematics may be characterized by measuring the envelopes of passive motion which are described, for each DOF over a range of flexion, by the positive and negative limits of displacement about a neutral position, under a prescribed load. It is crucial to understand the kinematics of the intact tibiofemoral joint because the envelopes of passive motion could serve as a gold standard for validating computational models of the knee as well as evaluating the effectiveness of innovative and established surgical techniques. Therefore, the objective of this study was to define the envelopes of passive motion for internal-external (I-E) rotation, varus-valgus (V-V) rotation, anterior-posterior translation (A-P), and distraction (D) translation of the intact tibiofemoral joint.
Optimization of Pedicle Screw Depth in the Lumbar Spine
Authors: Buckenmeyer Laura E. , Karami Kristophe J. , Kiapour Ata M. , Goel Vijay K. , Soo Teck M. , Demetropoulos Constantine K.
Published: January 2014

Optimization of pedicle screw insertion depth for ideal fixation and fusion remains a clinical challenge. Improved screw purchase may improve fixation strength 1, which is especially critical in an osteoporotic patient population. Extended screw insertion depths, up to and through the anterior cortex, have yet to be compared to more commonly used shorter pedicle screws in a laboratory controlled series of experiments. The purpose of this study is to evaluate screw purchase in the osteoporotic lumbar spine as a function of insertion depth, which may be used to optimize pedicle screw-rod constructs.
Aortic Valve Sinus Vorticity Dynamics and the Potential Role of Coronary Flow
Authors: Moore Brandon L. , Dasi Lakshmi P.
Published: January 2014

Calcific aortic valve disease affects a wide range of the population in the United States. Each year there are approximately 50,000 valve replacements due to this disease [(Freeman & Otto, 2005)]. While it is unclear what the exact causes of CAVD are, it does appear to be correlated to local hemodynamic conditions particularly related to the complex spatio-temporal nature of fluid wall shear stress dynamics that the aortic side of the leaflets experience.
The Effect of Press Fit and Viscoelasticity on the Seating of a Percutaneous Endoprosthesis
Authors: Noble Garrett J. , Allen Matthew J. , Fitzpatrick Noel , Hart Richard T.
Published: January 2014

Problems with the current, stump-socket method of prosthetic attachment for amputees include general discomfort, rashes, sores, and pain in the residual limb [1]. To alleviate these and other problems with prosthetic attachment, methods of securing a prosthetic to a skeletally-anchored percutaneous endoprosthesis are currently being developed [2]. These skeletally-anchored prosthetics provide a more direct transfer of load between a prosthetic limb and the residual limb, preventing bone resorption. This method allows patients to better sense and control their prosthesis [3, 4] and alleviates problems inherent to a prosthetic that attaches to the skin. Because the endoprosthetic device penetrates the skin, this method could also allow the direct attachment of nervous tissue to the implant which could be an important step in the future development of neuronal prosthesis control. Human clinical trials are currently underway in Sweden and the UK to test these devices in both human and animal patients.
Postnatal Time Course of Arterial Mechanics in a Mouse Model of Pathological Remodeling due to Decreased Elastin Amounts
Authors: Cheng Jeffrey K. , Mecham Robert P. , Wagenseil Jessica E.
Published: January 2014

Properly developed large elastic arteries serve as reservoirs that store stroke volume during systole and damp downstream blood pressure fluctuations. This function is enabled by the extracellular matrix (ECM) protein elastin. Mouse gene expression data reveals that elastin expression begins during embryonic development and peaks around postnatal day (P) 14. Expression then decreases to low levels for the remainder of adult life, indicating that elastin production during development is critical for a properly functioning vessel [1]. Reduced elastin in humans due to genetic mutations is associated with a congenital narrowing of the ascending aorta, known as supravalvular aortic stenosis, and chronic hypertension [2].
Calcium Signaling is a Key Regulator of Mesenchymal Stem Cell Response to Hydrostatic Pressure
Authors: Steward A. J. , Kelly D. J. , Wagner D. R.
Published: January 2014

Fluid pressurization is the dominant load-bearing mechanism of the in vivo joint environment, supporting up to 90% of compressive loads in cartilage[1]. In accordance with its prominence in cartilaginous tissues, hydrostatic pressure (HP) significantly enhances the chondrogenic differentiation of mesenchymal stem cells (MSCs) [2,3]. However, surprisingly little is known about the mechanisms by which cells sense HP and translate it into a biochemical signal. This is partly due to the fact that HP generates a state of stress with little deformation, as hydrated tissues and cells are nearly incompressible. Because of this, it has been assumed that HP mechanotransduction differs from that of other mechanical loads which deform the cells [4]. Recently, we demonstrated that integrin binding to the pericellular matrix (PCM) regulates the cytoskeletal organization of MSCs, and this in turn determines their response to HP [5]. Another proposed mechanism of HP mechanotransduction is fluctuations in intracellular ion concentrations, which are altered by the application of HP [6–8]. In particular, calcium signaling has been implicated as a key regulator of cellular response in other mechanical loading modalities, yet no studies have examined the role of calcium in the response of MSCs to HP. Therefore the objective of this study was to examine the cellular proliferation and chondrogenic matrix accumulation of MSCs in response to HP in the presence of pharmacological inhibitors of calcium ion mobility in order to elucidate the role of calcium signaling in the mechanotransduction of HP.
Nonlinear Derating of High-Intensity Therapeutic Ultrasound Beams Using Gaussian Modal Sums
Authors: Dibaji Seyed Ahmad Reza , Myers Matthew R. , Soneson Joshua E. , Banerjee Rupak K.
Published: January 2014

High intensity focused ultrasound (HIFU) is a noninvasive medical procedure during which a large amount of energy is deposited in a short duration which causes sudden localized rise in tissue temperature, and ultimately, cell necrosis. In assessing the influence of HIFU on biological tissue, semi-empirical mathematical models can be useful for predicting thermal effects. These models require values of the pressure amplitude in the tissue of interest, which can be difficult to obtain experimentally. One common method for estimating the pressure amplitude in tissue is to operate the HIFU transducer in water, measure the pressure amplitude, then multiply by a scaling factor that accounts for the difference in attenuation between water and tissue. This procedure can be accurate when the ultrasound amplitude is low, and the pressure trace in tissue is proportional to that in water. Because of this proportionality, the procedure for reducing the amplitude from water to tissue is called linear derating. At higher intensities, however, harmonics of the fundamental frequency are generated due to nonlinear propagation effects. Higher harmonics are attenuated differently in water and tissue (Hamilton and Blackstock [1]), and the pressure waves in water and tissue are no longer proportional to one another. Techniques for nonlinearly transforming pressure amplitudes measured in water to values appropriate for tissue are therefore desirable when bioeffects of higher intensity procedures are being studied. These techniques are labeled “nonlinear derating”.