bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of Mechanical Feedback in Restoration of Normal Cardiac C-Looping Following Perturbed Loading
Authors: Ramasubramanian Ashok , Nerurkar Nandan L. , Achtien Kate H. , Taber Larry A.
Published: March 2014

Cardiac c-looping is an important developmental phase, as the initially straight heart tube (HT) is transformed into a c-shaped tube. Looping consists of two distinct processes: ventral bending, which is likely driven by actin polymerization, and dextral torsion, which is likely due to external forces. These forces are applied by a membrane enveloping the ventral side of the heart, the splanchnopleure (SPL, Fig. 2A) and a pair of atria that flank the caudal end of the heart tube (HT, Fig 1A). In particular, the atria provide the initial push, biasing the HT towards the right while the SPL applies a ventrally directed force, which causes the HT to rotate using the dorsal mesocardium (DM, Fig. 2A) as a pivot (the DM attaches the dorsal length of the heart to the body of the embryo).
Anatomically Correct Right Coronary Artery Model
Authors: Lentzakis Helen , Farcas Monica , Rouleau Leonie , Leask Richard L.
Published: March 2014

Upon clinical analysis, regions such as curvatures and bifurcations have been characterized as high prone regions where atherosclerotic plaques were more likely to occur. Biological studies have linked this phenomenon to the localized response of the endothelial cells to mechanical blood flow forces such as fluid shear stress. Present common in vitro flow cell culture models such as parallel-plate flow chambers and cone and plate viscometers used to study endothelial cell response depict a simplified geometry and thus, unrealistic in vivo conditions. The aim of this project was to develop a more realistic in vitro cell culture model by using an anatomically correct right coronary artery model and a more physiologic flow environment for dynamic endothelial cell culture experiments.
Predicting the Stresses and Displacements in Femoral Intramedullary Nails and Screws Using a Finite Element Model
Authors: Kralovic Barbara J. , Fryman J. Craig , Longsworth Serene
Published: March 2014

A femoral intramedullary nail is a metal rod which is inserted into the femoral canal to stabilize fractures of the long bone. The retrograde femoral nail is a type of intramedullary nail which is inserted at the distal end of the long bone and is typically used for distal femur fractures. While the success rates are high, some complications still exist, including failure of the nail through the screw holes, failure or loosening of screws, and bone fracture [1]. There are many design variables that affect clinical performance including the implant material, nail and screw diameters, the number of screws, and the nail and screw position and orientation. To help determine the most suitable design for a given fracture the effect of the above variables on the stresses and displacements in the nail, screws, and bone may be important to consider.
Mechanical Properties of Polyurethane Foam Compared With Values for Normal and Osteoporotic Human Cancellous Bone
Authors: Patel Purvi S. D. , Shepherd Duncan E. T. , Hukins David W. L.
Published: March 2014

Rigid polyurethane (PU) foam is widely used as a test medium for mimicking human cancellous bone e.g. for investigating fixation of bone screws [1,2]. Whilst the solid and higher density PU foams are used as standard test materials [3], very little work has been carried out to date on modelling human osteoporotic bone. Osteoporosis (OP) is a bone disease in which bone resorption exceeds bone deposition, resulting in bone loss. Various low density, open cell rigid PU foams are available for use as OP bone models, but none of these has been standardised or universally accepted as a test material. In this study the objective was to determine whether low density PU foam might be suitable for mimicking human osteoporotic bone.
Two Methods of Determining [3H]Dexamethasone Distribution in Rat Subcutaneous Tissue
Authors: Dungel Paul , Moussy Yvonne , Hersh Lawrence
Published: March 2014

Several recent reports suggest that controlled local release of dexamethasone may be useful for preventing inflammation around an implantable glucose sensor [1,2]. This decrease in inflammation is expected to increase glucose sensor function and lifetime. Local delivery of dexamethasone would permit high interstitial drug concentrations at the site of glucose sensor implantation without producing high systemic drug levels. Although dexamethasone is a commonly used anti-inflammatory agent, its local concentration, diffusion coefficient and rate of elimination have not been reported following subcutaneous release. The ability of dexamethasone to penetrate subcutaneous tissue can be measured and quantified by comparison to mathematical models [3]. This method allows a reliable estimate of the drug concentration in the tissue near the implanted glucose sensor.
Phospholipid Encapsulation and Surface Functionalization of Superparamagnetic Iron Oxide Nanoparticles for Molecular Magnetic Resonance Imaging: Effects on Spin-Spin Proton Relaxation
Authors: Larsen Brian A. , Haag Michael A. , Stoldt Conrad R.
Published: March 2014

Superparamagnetic iron oxide (SPIO) nanoparticles are prevalent as nanoprobes for molecular magnetic resonance imaging (MRI), providing negative contrast by locally affecting the spin-spin (T2) proton relaxation of water. SPIO nanoparticles are typically Fe3O4 nanocrystals and are commonly used as a negative MRI contrast agent, implementing various surface functionalization techniques to provide molecular targeting to biological macromolecules. The authors recently demonstrated molecular MRI (Figure 1) of epidermal growth factor receptor (EGFR), an extensively studied oncoprotein, in human prostate and head-and-neck cancer cell lines using monoclonal antibodies covalently conjugated to phospholipid micelle encapsulated 12 nm single crystalline SPIO nanoparticles, demonstrating molecular targeting capabilities via surface functionalization [1].
Surfactant Spreading on a Thin Film Is Sensitive to Film Thickness: Implications for In Vivo Pulmonary Systems Versus In Vitro Scenarios
Authors: Siebert Trina A. , Rugonyi Sandra
Published: March 2014

The role of pulmonary surfactant is critical to the mechanics of the lung. Pulmonary surfactant forms a monolayer film at the air-liquid interface of a thin film of fluid lining the alveoli. Without surfactant, the air-liquid surface tension would be too high and the lungs would collapse during exhalation, as is the case with premature babies who develop respiratory distress syndrome (RDS) because they lack a sufficient amount of pulmonary surfactant [1]. Because an increase in surfactant surface concentration correlates with a decrease in surface tension, the surface tension gradients resulting when a monolayer of surfactant is deposited on a thin fluid film cause the surfactant to spread. This self-spreading phenomenon is of interest for applications such as surfactant replacement therapy in infants suffering from RDS and for drug delivery [1,2].
Specimen Specific Multiscale Model for the Anisotropic Elastic Properties of Human Cortical Bone Tissue
Authors: Deuerling Justin M. , Yue Weimin , Espinoza Alejandro A. , Roeder Ryan K.
Published: March 2014

The elastic constants of cortical bone are orthotropic or transversely isotropic depending on the anatomic origin of the tissue. Micromechanical models have been developed to predict anisotropic elastic properties from structural information. Many have utilized microstructural features such as osteons, cement lines and Haversian canals to model the tissue properties [1]. Others have utilized nanoscale features to model the mineralized collagen fibril [2]. Quantitative texture analysis using x-ray diffraction techniques has shown that elongated apatite crystals exhibit a preferred orientation in the longitudinal axis of the bone [3]. The orientation distribution of apatite crystals provides fundamental information influencing the anisotropy of the extracellular matrix (ECM) but has not been utilized in existing micromechanical models.
Tibial Tuberosity Realignment Decreases Pressure Applied to Patellofemoral Cartilage
Authors: Elias John J. , Walden David L. , Weinstein David M.
Published: March 2014

For patients with unrelenting patellofemoral pain, tibial tuberosity realignment procedures are commonly performed to improve patellofemoral alignment and decrease the pressure applied to patellofemoral cartilage. Because malalignment is typically attributed to an excessive lateral force applied to the patella by the quadriceps muscles and the patella tendon, the tibial tuberosity is commonly osteotomized and transferred medially to decrease the lateral force applied by the patella tendon. The tibial tuberosity can also be anteriorized to increase the extensor moment arm of the patella tendon, which decreases the forces applied by the quadriceps muscles during function and subsequently decreases joint compression. Anteriorization and medialization of the tibial tuberosity can also be combined in a single procedure. The goal of the current study was to characterize how medialization, anteriorization and anteromedialization of the tibial tuberosity influence the patellofemoral force and pressure distributions within symptomatic knees. The authors hypothesize that all three realignment techniques decrease the pressure applied to patellofemoral cartilage, but that anteromedialization produces the largest pressure decrease.
Numerical Simulation of a Suspension of Swimming Micro-Organisms
Authors: Ishikawa Takuji , Pedley T. J. , Yamaguchi Takami
Published: March 2014

The size of individual micro-organisms is often much smaller than that of the flow field of interest, in an oceanic plankton bloom for instance. In such cases, the suspension of micro-organisms is modelled as a continuum in which the variables are volume-averaged quantities. Continuum models for suspensions of swimming micro-organisms have been proposed for the analysis of phenomena such as bioconvection. However, the continuum models proposed so far are restricted to dilute suspensions, in which cell-cell interactions are negligible. If one wishes to analyze larger cell concentrations, it will be necessary to consider the interactions between micro-organisms. Then the particle stress tensor, the velocities of the micro-organisms and the diffusion tensor in the continuum model will need to be replaced by improved expressions. In this study, we compute the motion of interacting swimming model micro-organisms in periodic suspensions in a fluid otherwise at rest, and discuss the microstructure constructed by micro-organisms.
Dynamic Simulation of Red Blood Cells/Platelet Interaction in Arteriolar Blood Flow
Authors: AlMomani T. , Udaykumar H. S. , Marshall J. , Chandran K. B.
Published: March 2014

Hemodynamic forces have been proposed as a major factor in thrombosis (thrombus formation) in the human cardiovascular system [1]. It has been suggested that platelet activation, aggregation and adhesion to the surface of the implants result in the formation of the mural thrombi [2]. Red blood cells (RBCs) are thought to play a significant role in the dynamics and the activation of the platelets and hence thrombus formation in the human arterial system. Previous experimental works indicate that RBCs cause platelets to migrate and move toward the vessel walls [3]. Thrombus formation has also been shown to increase as the hematocrit (Hct) increases [4]. In order to simulate the platelet dynamics requires the computational analysis of the transport and collision of the formed elements under physiological flow. In the present study, a two-dimensional (2D) simulation of the RBC/platelet dynamics in the arterioles is described.
Entropy Based Phase Aberration Correction Technique in Ultrasound Imaging
Authors: Mahmoud Ahmed M. , Mukdadi Osama , Kadah Yasser M.
Published: March 2014

Ultrasound technology has been widely used in medical imaging. Techniques using phased array transducers use an array of transducer elements to transmit a focused beam into the body, and each element then becomes a receiver to collect the echoes. The received echoes from each element are dynamically focused to form an image. These systems assume a constant acoustic velocity in the tissue of 1540 m/s while steering and focusing the beam. However, soft tissues have a range of acoustic velocities that vary from 1470 m/s for fat to 1665 m/s for collagen [1]. The acoustic wavefront propagation through a region with locally different acoustic velocities will be phase shifted relative to the rest of the wavefront. This effect is known as phase aberration. The effects of phase aberration include broadening of the system point spread function that deteriorate the image resolution, and increasing the off-axis response leading to multiple images for the target [2].
Determination of Real Time In-Vivo Cartilage Contact Deformation in the Ankle Joint
Authors: Li Guoan , Wan Lu , Kozanek Michal
Published: March 2014

Knowledge of in-vivo articular cartilage contact deformation is critical for understanding normal cartilage function and the etiology of osteoarthritis (2,8). This knowledge is also instrumental for design of ex-vivo experiment to investigate the chondrocyte mechanotransductions under physiological loading conditions (7). Further, in-vivo cartilage contact data is necessary for validation of 3D computational models used to predict biomechanical responses of the articular joints (1,5). However, due to the complexity of in-vivo joint loading conditions as well as the complicated joint geometry, little information is available on in-vivo cartilage deformation in literature (9). In-vivo cartilage deformation as a function of loading history has not been delineated.
The Effects of Varying Frictional Contact Boundary Conditions in Finite Element Analysis of Mandibular Parasymphyseal Fracture
Authors: Caraveo Victor , Lovald Scott , Khraishi Tariq , Wagner Jon , Baack Brett
Published: March 2014

FE modeling of biological tissues and physiological behavior is now becoming common practice with the improvement in finite element analysis (FEA) software and the significant increase in capability of computing resources. There are many uses for FEA of this nature, one of which has been simulating the mechanical behavior of implant devices for fracture repair. FE analysis offers insight into the mechanistic behavior of fixation plates used in rigid internal fixation and, if modeled carefully, could eventually become an accurate design tool.
Extended Two Compartmental Swelling Stress Model and Isotropic Cauchy Stress Equation for Articular Cartilage Proteoglycans
Authors: Oungoulian Sevan R. , Chen Silvia S. , Davol Andrew , Sah Robert L. , Klisch Stephen M.
Published: March 2014

Proteoglycans (PGs), a constituent of cartilaginous tissues, have a negative fixed charge (FC) that causes an intratissue swelling stress [1]. This swelling stress is thought to balance tensile stress in the collagen network and contribute to the aggregate modulus of articular cartilage (AC) [1]. Stress constitutive equations that accurately characterize mechanical behavior of individual tissue constituents are crucial for the development of accurate total tissue models. The goal of this study is to extend the range of an existing two compartmental model for PG swelling stress by Basser et al. [1], and develop a continuum level equation for PG Cauchy stress. Specifically, the first aim is to increase the accuracy of the two compartmental model proposed in [1], to a lower range of FC density (FCD) typically found in bovine calf AC. The second aim is to use the extended model to develop a continuum level strain energy function and associated isotropic PG Cauchy stress constitutive equation.
Fluid Structure Interactions in the Eustachain Tube Under Normal and Pathological Conditions
Authors: Warrick Amanda E. , Swarts J. Douglas , Ghadiali Samir N.
Published: March 2014

Cleft Palate is a craniofacial syndrome in which the two plates that form the hard palate are not completely joined. As a result, the soft tissue anatomy of the Eustachian Tube (ET) is altered. The ET is a collapsible tube which connects the middle ear (ME) with the nasopharynx (NP). The ET must be periodically opened to equalize ME and NP pressures and drain ME fluids. In healthy adults, ET openings occur during swallowing, where muscle contraction deforms the surrounding soft tissue. However, changes in tissue anatomy may lead to ET dysfunction (i.e. closure during swallowing) and the development of ME disorders such as Otitis Media (OM)[1]. These disorders are especially problematic in infants with cleft palate as they hinder speech, hearing and psychosocial development. Although surgical procedures can be used to repair a cleft palate, these procedures do not typically account the possible development of ET dysfunction and/or OM.
Kinetic and Biomechanical Testing of Two-Level Cervical Disc Replacement
Authors: McGilvray Kirk C. , Lyons Amy S. , Turner A. Simon , Patel Vikas V. , Puttlitz Christian M.
Published: March 2014

Cervical disc replacement has become an increasingly common practice in Europe and several disc designs are currently being evaluated via clinical trial for regulatory approval in the United States. The majority of these procedures have been performed at one level in the absence of adjacent level fusion. However, recent conference proceedings have reported on multi-level implantations of these devices. Numerous literature accounts have reported on the in vitro kinetics and kinematics of these devices that have generally shown motion equivalence to the intact spine when implanted at one level. The current study seeks to build upon this previous work by investigating the kinetics associated with two-level disc replacement. In addition, we investigated the implications of a minimally invasive two-level salvage procedure that would involve direct plating over an implanted disc prosthesis while maintaining the disc replacement at an adjacent level.
Maximum Principal Strains in the Glenohumeral Capsule During a Clinical Exam: A Validated Finite Element Model
Authors: Drury Nicholas J. , Ellis Benjamin J. , Moore Susan M. , Weiss Jeffrey A. , Debski Richard E.
Published: March 2014

The shoulder is the most frequently dislocated joint in the body, with 80% of dislocations occurring in the anterior direction [1]. One of the primary contributors to anterior shoulder stability is the glenohumeral capsule. Up to 23% of repaired shoulders redislocate following arthroscopic surgical techniques [2], and the function of the capsule in response to external loading remains unclear. Information on the strain distribution throughout the capsule during joint motion can help lead to more effective pre- and post-surgical diagnostics for capsular pathologies. One common diagnostic examination is the apprehension test, in which anterior loading is applied to the humerus at 60° of glenohumeral abduction with varying amounts of external rotation. The inferior glenohumeral ligament (IGHL), composed of three regions, the anterior band (AB-IGHL), axillary pouch, and posterior band (PB-IGHL), has been shown to be the primary region of the capsule to provide stability in this joint position [3]. The objective of this study was to determine the maximum principal strains in each region of the IGHL during an apprehension test at 0, 30, and 60° of external rotation, using a validated subject-specific model of the glenohumeral joint. The strain distribution may help elucidate the function of these regions in providing stability and transferring load between the humerus and scapula.
Magnetic Resonance Elastography of the Mouse Brain In Vivo
Authors: Atay Stefan M. , Bayly Philip V.
Published: March 2014

In the current study we apply the magnetic resonance elastography (MRE) technique to estimate the dynamic shear modulus of mouse brain tissue in vivo. The frequency used (1200 Hz) is well above those reported previously [1]. Estimates of dynamic shear modulus range from 12,600–14,800 N/m2 at 1200 Hz. These data are strictly relevant only to small oscillations at this specific frequency, but these values are obtained at high frequencies (and thus high deformation rates) and non-invasively throughout the brain. These data complement measurements of nonlinear viscoelastic properties obtained by others at slower rates, either ex vivo or invasively.
Intermolecular Multiple Quantum MR Thermography
Authors: Galiana Gigi , Branca Rosa T. , Jenista Elizabeth R. , Warren Warren S.
Published: March 2014

An accurate method for noninvasive temperature monitoring in vivo would be invaluable for hyperthermic cancer treatments [1]. These therapies selectively heat tumors with RF or microwave radiation, thereby bringing about enhanced drug delivery (up to 30-fold), inhibited cell repair, and even cell death [2]. Unfortunately, this promising treatment has been stymied by the inadequacy of current methods to map temperature in vivo. Conventional magnetic resonance (MR) temperature maps are easily distorted, and provide only a relative measurement of the temperature. Instead we propose a physically different method based on the detection of water-fat iZQCs (intermolecular Zero Quantum Coherences) which produce an absolute temperature map and are insensitive to other distorting factors [3]. Novel but simple modifications to the pulse sequence allow us to isolate the relevant signal, and early applications demonstrate an order of magnitude improvement of temperature accuracy, both in vitro and in vivo.
Mechanical and Biochemical Comparison of Cell-Derived Matrix, Collagen Gels, and Fibrin Gels for Tissue Engineering Applications
Authors: Ahlfors Jan-Eric W. , Billiar Kristen L.
Published: March 2014

Cell-seeded collagen and fibrin gels have been used extensively as in vitro wound healing models and for studying tissue remodeling. The have also been utilized as replacements for lost or damaged connective tissue [1]. The major drawback of these gel-based living tissue equivalents (LTEs) for tissue engineering applications is that they are not completely synthesized and arranged by the cells themselves, thus they are weak relative to native connective tissue.
Sequence Specific Role of Water in Spontaneous Local Unwinding of Collagen
Authors: M. Ravikumar Krishnakumar , Hwang Wonmuk
Published: March 2014

Collagen is one of the most abundant proteins in the human body. Due to its biological significance and omnipresence, it has been intensely studied for several decades both at the molecular and at the tissue level. A single collagen molecule is a rope like super helix of three α-chains. Collagen molecules self assemble in an orderly fashion to form different suprastructures such as fibrils and networks, providing mechanical strength to the tissue. Collagen density and suprastructural organization determines the local mechanical tension in a particular region of the tissue. Cells sense the tension and in turn trigger a controlled process of growth and remodeling of tissues through secretion or degradation of extracellular components including collagen. Tissue homeostasis is a complex process and adding to such complexity, a single collagen molecule is unstable at body temperature [1], but its stability increases after self-assembly and cross-linking.
Mode Changes in the Post-Yield Behavior of Bone
Authors: Wang Xiaodu , Nyman Jeffry , Reyes Michael
Published: March 2014

A number of factors across multiple length scales (Table 1) may contribute to the mechanical competence of bone (i.e., the resistance to fracture). This structural complexity hinders a complete mechanistic explanation (model) for elderly bone fragility. Although age-related loss of bone mass has been viewed as the reason for the rising incidence of bone fractures in the elderly,(2) bone quality is more meaningful to provide insights into why individuals with ‘normal’ bone mineral density (BMD) suffer fractures. Bone is a hierarchical and hydrated composite of mineral and collagen phases,(3, 4) showing a rather complex response to the mechanical loading.(5, 6) While previous research has investigated the resistance of bone to crack propagation,(7, 8) fatigue behavior,(9–11) and mechanical changes to load-induced damage,(12–14) little is known about the mechanical behavior of bone as a function of progressive deformation (strain). In this study, by employing a previously developed progressive loading scheme,(15) we intend to investigate the progressive stress-strain behavior of bone with increasing strain levels, so as to gain more information on the underlying mechanisms for post-yield behavior of bone. It is hypothesized that the post-yield behavior of bone varies with the increasing strain, which plays a significant role in sustaining the toughness or quality of bone.
A Fluid Dynamics Study Focusing on Wall Shear Rates Within the Penn State 12 cc Pulsatile Pediatric Ventricular Assist Device: A Comparison of Mechanical Heart Valve Types
Authors: Cooper Benjamin T. , Roszelle Breigh N. , Long Tobias C. , Deutsch Steven , Manning Keefe B.
Published: March 2014

Previous studies have shown that the interrelated flow characteristics necessary for the prevention of thrombosis in a pulsatile ventricular assist device (VAD) are a strong inlet jet, a late diastolic recirculating flow, and adequate wall washing (greater than 500 s−1). Particle image velocimetry was used to compare the flow fields in the chamber of the 12 cc Penn State pediatric pulsatile VAD using two valves: Björk-Shiley Monostrut (BSM) tilting-disc valves at the inlet and outlet and Carbomedics (CM) bi-leaflet valves at the inlet and outlet. In conjunction with the flow evaluation, wall shear data were calculated and analyzed to help to quantify wall washing. The major orifice inlet jet of the device containing BSM valves was more intense which led to better circulation and wall washing than the three jets produced by the CM valves Regurgitation through the CM valve was observed and served as a significant hindrance to the development of the rotational flow.
Cyclic Bending of Coronary Plaques Leads to Much Higher Stress Variations: A Major Factor Contributing to Plaque Rupture Risk
Authors: Tang Dalin , Yang Chun , Zheng Jie , Kobayashi Shunichi , Sicard Gregorio A. , Woodard Pamela K. , Ku David N.
Published: March 2014

Mechanical forces play an important role in the complicated process of atherosclerotic plaque rupture which often leads to serious clinical events such as stroke and heart attack [4]. Factors causing the vulnerable plaque cap to fracture are important clinically [2–7]. It is known that coronary plaques are more likely to rupture compared to carotid plaques under comparable conditions (such as stenosis severity at about 50% by diameter). One possible reason is that coronary arteries are under cyclic bending caused by heart motions and compressions. We hypothesize that cyclic bending of coronary atherosclerotic plaques may be a major contributor to critical stress variations in the plaque leading to increased plaque rupture risk. We have developed MRI-based 3D multi-component models with fluid-structure interactions (FSI) in order to perform flow and stress/strain analysis for atherosclerotic plaques and identify possible mechanical and morphological indices for accurate plaque vulnerability assessment [6–7].
The Impact of an Abdominal Aortic Aneurysm on Aortic Wave Reflection
Authors: Swillens Abigail , Lanoye Lieve , De Backer Julie , Stergiopulos Nikos , Vermassen Frank , Verdonck Pascal , Segers Patrick
Published: March 2014

The economical growth and increased welfare in the Western world have a reverse side, with an increased death toll due to cardiovascular diseases. Among these, aortic aneurysms (a local dilation) are particularly lethal as they may grow unnoticed until rupture occurs. In this study, we assessed the impact of the presence of an abdominal aortic aneurysm on arterial hemodynamics and wave reflection in particular. Experimental and numerical methods were applied. Linear wave separation was used to quantify the reflections; wave intensity analysis was applied to assess the nature of the reflected waves. In both the experimental and numerical models, negative reflections were found in the upper aorta corresponding to a backward expansion wave caused by the sudden expansion of the aorta. A numerical parameter study demonstrated that larger diameters and more compliant aneurysms generate stronger negative reflections.
Methods for Quantifying Vessel Deformation Due to Pulsatile and Non-Pulsatile Forces
Authors: Choi Gilwoo , Cheng Christopher P. , Wilson Nathan M. , Taylor Charles A.
Published: March 2014

Despite the significant effort expended by the medical device industry to design and manufacture stents and stent grafts, vascular stent fractures have been reported in almost every implanted location including the aortic, iliac, popliteal, subclavian, renal, coronary, carotid, and superficial femoral arteries.
Contralateral Boundary Conditions Affect the Biomechanical Response of the Pubic Symphysis During Pelvic Side Impacts
Authors: Li Zuoping , Kim Jong-Eun , Alonso Jorge E. , Davidson James S. , Eberhardt Alan W.
Published: March 2014

Clearer understanding of the biomechanics of the pubic symphysis in lateral pelvic impact tests may serve to elucidate the mechanisms of injury in automotive side impacts. While numerous experimental and computational studies have been conducted on the human pelvis, stresses and deformations of the symphysis were never measured, and the role of the boundary conditions supporting the pelvis was not emphasized. The objective of the present study was to develop a biofidelic FE model to investigate the deformations and stresses experienced by the pubic ligaments and interpubic disc under side impact conditions simulating both drop tower experiments and automotive side impacts.
The Influence of Age on the Forces Produced During Normal Seat Belt Buckling
Authors: Scher Irving S. , Young Douglas E. , Trachtman Doris
Published: March 2014

Historically, the observed seat belt usage rate for occupants has varied across a number of factors (e.g., primary or secondary use law, seat location, etc.). Of these factors, the age of the driver or occupant has been consistently noted as an important characteristic that is linked to the use of the seat belt. For example, the seat belt use rate for drivers and front seat passengers in the U.S. in 2002 was estimated to be over 70% for adults [1] but over 10% less for pre-teens [2] and teenagers [3], which are generally less than 60%. This discrepancy between younger age groups and adults has been reported in several states across the country [2–5]. Eby et al. [4] reported that individuals 4–15 years old, seated in the second and third rows, wore seat belts about 50% of the time in the left and right positions. In a separate four-state observational study of teenage and older occupants by Womack et al. [6], teen seat belt use in the back seats was only 10.9%. Together, these studies indicate pre-teen and teenagers wear seat belts less frequently than comparable adult cohorts, and that they will be even less likely to wear a seat belt when they are located in the back seat positions.
Using 3D FSI RV/LV Models Based on Patient-Specific MRI Data to Predict Outcome of PVI and RV Volume Reduction Surgeries
Authors: Tang Dalin , Yang Chun , Geva Tal , Del Nido Pedro J.
Published: March 2014

Right ventricular (RV) dysfunction is a common cause of heart failure in patients with congenital heart defects and often leads to impaired functional capacity and premature death. Computational heart models have been developed to understand the complex blood flow and cardiac mechanical behaviors [2,4]. However, clinic-oriented patient-specific models with fluid-structure interactions which can be used to make accurate predictions for potential surgical outcome are still lacking in the literature and clinical practices. A novel modeling procedure is proposed to test the hypotheses that a) patient-specific computational RV/LV combination model based on pre-operation MRI data can provide accurate assessment of RV cardiac functions (measured by RV ejection fraction and stroke volume) and that b) the RV/LV model validated by pre-operation data can be used as the base model to perform virtual pulmonary valve insertion (PVI) and RV volume reduction surgery to optimize post-operative RV morphology and patch design prior to the actual operation and that this procedure will lead to improved recovery of RV functions. With validation, this modeling process could replace empirical and often risky clinical experimentation to examine the efficiency and suitability of various reconstructive procedures in diseased hearts.
Supramolecular Structure and Stability of the GNNQQNY β-Sheet Bilayer Filament: A Computational Study
Authors: Park Jiyong , Kahng Byungnam , Hwang Wonmuk
Published: March 2014

Self-assembly of β-sheet forming peptides into filaments has drawn great interests in biomedical applications [1,2]; Hydrogels formed by filaments self-assembled from de novo designed peptides possess potential applications for cell culture scaffolds [3]. On the other hand, peptides derived from amyloidogenic proteins in neurodegenerative diseases such as Alzheimer’s and Parkinson’s also form similar β-sheet filaments in vitro. They share little sequence homology, yet filaments formed by these self-assembling peptides commonly have the cross-β structure, the key signature of the amyloid fibril. Detailed structural information of the self-assembled β-sheet filaments has been limited partly due to the difficulty in preparing ordered filament samples, and it has been only recently that solid-state nuclear magnetic resonance and x-ray techniques have revealed their molecular structure at the atomic level [4,5]. Although molecular structures of amyloid fibrils are becoming available, physical principles governing their self-assembly and the properties of the filaments are not well-understood, for which computational as well as theoretical approaches are desirable [6].
A Novel In Vivo Measurement of Three-Dimensional Lumbar Facet Joint Orientation and Area
Authors: Otsuka Yoshihisa , An Howard S. , Williams Jamie R. , Ochia Ruth S. , Yamaguchi Kazuyoshi , Andersson Gunnar B. J. , Inoue Nozomu
Published: March 2014

Changes in load transmission through facet and facet orientation have been considered as an important factor in intervertebral disc degeneration and osteoarthritic changes of the facet joint. (1)(2)(3) Facet joint surface area and orientation of the facets play key roles in load transmission. Their information is important for designing implants of the spine. They have been 2-dimentionally measured using CT and MRI. (4)(5) The purpose of the current study was to establish a three-dimensional (3D) technique for measuring lumbar facet joint area and orientation in vivo.
Validation of an MRI-Based Method for Measuring the Deformation of the Brain During Angular Acceleration
Authors: Sabet Arash A. , Christoforou Eftyxios , Zatlin Benjamin , Genin Guy M. , Bayly Philip V.
Published: March 2014

A magnetic resonance (MR) method for measuring the deformation of the brain during angular acceleration was validated in a simple model system. Experimentally-derived shear strain patterns in a cylindrical gel “phantom” under angular acceleration were compared to analogous strain fields predicted by finite element simulation.
Two-Dimensional Simulation of Platelet Activation in the Hinge Region of a Mechanical Heart Valve
Authors: Govindarajan V. , Udaykumar H. S. , Chandran K. B.
Published: March 2014

The proper functioning of the leaflets of a bi-leaflet mechanical valve requires the use of the hinge mechanism which lets the leaflets pivot to the valve housing and lets it rotate at a specified angle. It has been pointed that the hinge design directly affects the durability of the valve [1]. In Bi-leaflet valves the thrombus formation is mostly observed in the hinge region and also on the valve housing [2]. This may be due to the complex geometry presented by the hinge region, which makes the flow complex making the hinge region a potential site for thrombus formation and accumulation which could pose a threat to the efficient functioning of the valve itself. It was hypothesized that the flow fields with in the hinge region played a major role in thrombus accumulation in the Medtronic parallel valve [3]. Studies have demonstrated that fluid dynamics in the vicinity of valve leaflet and housing at the instant of valve closure may lead to large negative pressure transients across the leaflets [4]. These large pressure gradients present for a small duration of time induces very high velocity squeezed flow through the clearance region between the valve housing and the leaflet tip and through the gaps in the hinge region which has been provided for rotation of the leaflet and washout. The wall shear stress in these regions can be relatively high during the closure phase resulting in platelet activation. This study will focus on the flow through the hinge region and its effect on the platelet activation during the valve closure under Mitral conditions which is the harshest environment for a valve.
Inverse Characterization of Nonlinear Anisotropic Mechanical Properties of Engineered Cardiovascular Tissues Using a Spherical Indentation Test
Authors: Cox M. A. J. , Boerboom R. A. , Bouten C. V. C. , Driessen N. J. B. , Baaijens F. P. T.
Published: March 2014

Over the last few years, research interest in tissue engineering as an alternative for e.g. current treatment and replacement strategies for cardiovascular and heart valve diseaes has significantly increased. In vitro mechanical conditioning is an essential tool for engineering strong implantable tissues [1]. Detailed knowledge of the mechanical properties of the native tissue as well as the properties of the developing engineered constructs is vital for a better understanding and control of the mechanical conditioning process. The typical highly nonlinear and anisotropic behavior of soft tissues puts high demands on their mechanical characterization. Current standards in mechanical testing of soft tissues include (multiaxial) tensile testing and indentation tests. Uniaxial tensile tests do not provide sufficient information for characterizing the full anisotropic material behavior, while biaxial tensile tests are difficult to perform, and boundary effects limit the test region to a small central portion of the tissue. In addition, characterization of the local tissue properties from a tensile test is non-trivial. Indentation tests may be used to overcome some of these limitations. Indentation tests are easy to perform and when indenter size is small relative to the tissue dimensions, local characterization is possible. Therefore, we propose a spherical indentation test using finite deformations.
Mechanical Stimulation Increases Collagen Type I and Collagen Type III Gene Expression of Stem Cell: Collagen Sponge Constructs for Patellar Tendon Repair
Authors: Juncosa-Melvin Natalia , Matlin Karl S. , Holdcraft Robert W. , Nirmalanandhan Victor S. , Butler David L.
Published: March 2014

Tendons (rotator cuff, Achilles and patellar tendons) are among the most commonly injured soft tissues [1]. Many repairs/reconstructions have been attempted using sutures, resorbable biomaterials, autografts, and allografts, but with varying success. A tissue engineered repair using mesenchymal stem cells (MSCs) is attractive [2–4] but often lacks initial stiffness and strength [5].
Effect of Mechanical Stimulation on the Biomechanics of Stem Cell: Collagen Sponge Constructs for Patellar Tendon Repair
Authors: Juncosa-Melvin Natalia , Shearn Jason T. , Galloway Marc T. , Boivin Gregory P. , Gooch Cynthia , Butler David L.
Published: March 2014

Tendons (rotator cuff, Achilles and patellar tendons) are among the most commonly injured soft tissues [1]. Many techniques for repair/reconstruction have been attempted (e.g. sutures, resorbable biomaterials, autografts, and allografts) with varying success. A tissue engineered repair using mesenchymal stem cells (MSCs) is and attractive option [2–4] but the stiffness and strength of currently available constructs are insufficient for clinical use [6].
Nonlinear Material Parameter Estimation Using Inverse Finite Element Analysis
Authors: Bischoff Jeffrey E.
Published: March 2014

Constitutive parameters for biological materials are ideally regressed against data from well-designed experiments in which the loading and boundary conditions give rise to a homogeneous region of deformation. Such conditions may exist for healthy tissue within the context of in vitro tests, but rarely are met when attempting to measure parameters physiologically or noninvasively, due to complex boundary conditions or heterogeneous material structure and properties. The ability to estimate parameters in these situations is essential in many clinically relevant studies, including determination of tendon/ligament parameters in whole knee studies, non-destructive evaluation of evolving material parameters in laboratory studies, and estimation of heterogeneous parameters due to local normal or pathologic disruptions in tissue microstructure. In such cases, computational algorithms must be used to regress material parameters for a given constitutive model against the available data, in which the experimental conditions are modeled as accurately as possible without significant regard to complexity. The work presented here is focused on development of an iterative, inverse finite element (FE) algorithm for estimation of material parameters from experimental data obtained from tests with nonlinear complexities from contact, large deformations, and constitutive models.
Advanced Material Modeling of UHMWPE for Orthopaedic Implant Design
Authors: Bischoff Jeffrey E. , Dharia Mehul A. , Levine Danny L.
Published: March 2014

Ultra-high molecular weight polyethylene (UHMWPE) is extensively used in orthopaedic implants, and recent constitutive modeling efforts have endeavored to rigorously capture the nonlinear, quasi-static, inelastic properties of the material. In particular, the “hybrid model” developed by Bergstrom et al. has been shown to accurately characterize the response of UHMWPE to various loading protocols including uniaxial tension to failure, cyclic uniaxial tension/compression, and small punch testing [1–2].
Feasibility of Measuring the Effect of Knee Injury Prevention Training on Dynamic ACL Length During Jump Landing
Authors: Bishop Jennifer L. , Tashman Scott , Zauel Roger , Demps Erinn L. , Waters Gwynne , Koralewski Kelly
Published: March 2014

Anterior cruciate ligament (ACL) injuries are very common, causing pain, loss of function, and medical expense. Women sustain ACL injuries more often than men. Most of these injuries (70%) are non-contact for women [1], occurring during pivoting or sudden deceleration [2]. Training programs have been developed to try to prevent these injuries in women. These programs are designed to improve strength, muscle balance, and knee control. Evaluating the effectiveness of training programs is difficult. To date, these evaluations have only assessed factors such as muscle activation and joint angles that are not directly related to ACL strain and ACL injury risk.
Prediction of Mechanical Properties of Vertebral Trabecular Bone Using Microstructural Finite Element Models
Authors: Dai Yifei , Ryan Jordan , Niebur Glen L.
Published: March 2014

Finite element models of the spine provide a means to assess fracture susceptibility [3] or to evaluate devices [5]. Such models require accurate estimates of the mechanical properties of the trabecular bone within the vertebral body. Properties can be estimated using density measures from quantitative computed tomography [1]. Cellular solid analysis suggest the importance of incorporating microstructure in determining trabecular bone mechanics [4]. But it is difficult to classify the structure of real trabecular bone morphology in terms of the idealized models. Instead, statistical measures of morphology, such as the fabric tensor are usually employed [6].
Different Strains of Mice Exhibit Different Aortic Arch Geometry and Plaque Distribution: A Fluid Dynamic Effect
Authors: Zhu Hui , Shih Jessica , Long David S. , Hagaman John R. , Maeda Nobuyo , Friedman Morton H.
Published: March 2014

In earlier work, we observed different patterns of disease distribution in the aortic arches of apolipoprotien E (apoE)-deficient C57BL/6 (B6) and 129/SvEv (129) mouse strains [1]. In the relatively young mice (6 mo old), fatty plaques are seen mainly in the aortic root area, extending into the right innominate artery (RIA), with very little plaque in the more distal aortic arch in the B6 strain. However, in the 129 strain, plaques are found more in the inner curvature of the aortic arch but less in the sinus area than in B6 strain (Fig. 1).
Synergistic Moments at the Hip and Knee Joints Are Altered in Post-Stroke Hemiplegic Gait
Authors: Nessler Jeff A. , Lin Winsean , Dhaher Yasin
Published: March 2014

Following stroke, many patients are unable to adequately bend their knee during the swing phase of gait [1,2]. This loss of functional control may be related to an abnormal muscle synergy or torque couple in the lower limb, similar to those reported for the upper extremity [3–5]. For example, several investigators have described a flexor synergy that couples shoulder abduction torque and elbow flexion torque under static, isometric conditions [3–4]. This couple is typically altered following stroke [3–4]. In the lower extremity, hip kinetics in the frontal plane appear to be coupled with knee kinetics in the sagittal plane for static, isometric conditions [6]. It is unknown, however, whether the same relationship holds for hip and knee kinetics under dynamic conditions, such as during the swing phase of gait.
Interaction Between Bone Cement Cracking and Non-Slip Implant Interfaces
Authors: Park Pan Gi , Sudak Leszek J.
Published: March 2014

According to National Hospital Discharge Survey 2003, approximately 217,000 and 402,000 patients in the U.S. underwent Total Hip Replacement (THR) and Total Knee Replacement (TKR) operations, respectively and $24.7 billion dollars were spent in hospitalization related to these replacement surgeries. In addition, there were 36,000 revision hip replacements and 33,000 revision knee replacements. To decrease the revision surgeries and increase the performance of the implants, many researchers have provided new techniques for better implant fixation and mechanisms of debonding around implants. With respect to fixation, performance of cemented prosthesis is reported to be better than those of cementless ones. Moreover, surgery with cemented implants has been among the most popular and widely performed.
Fluid Mechanical Analysis at Closure of the On-X Mechanical Heart Valve
Authors: Haggerty Christopher M. , Herbertson Luke H. , Deutsch Steven , Manning Keefe B.
Published: March 2014

Three-dimensional laser Doppler velocimetry (LDV) was used to characterize the flow created by the On-X bileaflet mechanical heart valve (MHV) manufactured by Medical Carbon Research Institute (MCRI), Inc. (Austin, TX). The valve was mounted into a pneumatically driven single-shot chamber in the mitral position such that only the closure dynamics were simulated. Measurements taken 2 mm proximal to the valve housing showed a peak velocity of 1.8 m/s and maximum Reynolds Shear Stresses (RSS) of 17,500 dynes/cm2, which were found along the centerline of the valve in the hinge region 2 ms after valve closure. The large velocity and RSS gradients denote the presence of complex flow structures. These results provide an initial basis for understanding the impact of valve geometry on hemolysis and thrombosis associated with the On-X MHV.