bluuebunny/crossref_metadata_2025 huggingface dataset:
3D In Vivo IVUS-Based Anisotropic FSI Models With Cyclic Bending for Human Coronary Atherosclerotic Plaque Mechanical Analysis
Authors: Tang Dalin , Yang Chun , Zheng Jie , Woodard Pamela K. , Billiar Kristen , Teng Zhongzhao , Bach Richard
Published: July 2013

Assessing atherosclerotic plaque vulnerability based on limited in vivo patient data has been a major challenge in cardiovascular research and clinical practice. Considerable advances in medical imaging technology have been made in recent years to identify vulnerable atherosclerotic carotid plaques in vivo with information about plaque components including lipid-rich necrotic pools, calcification, intraplaque hemorrhage, loose matrix, thrombosis, and ulcers, subject to resolution limitations of current technology [1]. Image-based computational models have also been developed which combine mechanical analysis with image technology aiming for more accurate assessment of plaque vulnerability and better diagnostic and treatment decisions [2]. However, 3D models with fluid-structure interactions (FSI), cyclic bending and anisotropic properties based on in vivo IVUS images for human coronary atherosclerotic plaques are lacking in the current literature. In this paper, we introduce 3D FSI models based on in vivo IVUS images to perform mechanical analysis for human coronary plaques. Cyclic bending is included to represent deformation caused by cardiac motion. An anisotropic material model was used for the vessel so that the models would be more realistic for more accurate computational flow and stress/strain predictions.
Atherosclerotic Carotid Plaques With Prior Rupture Are Associated With Higher Structural Stresses: In Vivo MRI-Based 3D FSI Studies
Authors: Teng Zhongzhao , Petruccelli Joseph D. , Huang Xueying , Yang Chun , Liao Zijie , Yuan Chun , Hatsukami Thomas , Canton Gador , Ferguson Marina , Zheng Jie , Woodard Pamela K. , Tang Dalin
Published: July 2013

Atherosclerotic plaque vulnerability assessment and the ability to predict possible future rupture are of vital importance for early diagnosis, prevention and treatment of cardiovascular diseases related to atherosclerosis. It has been hypothesized that critical stress conditions in the plaque may be closely related to plaque rupture and can be combined with current image-based assessment techniques for more accurate plaque evaluation. A major challenge for all available plaque assessment schemes is the lack of gold standard based on in vivo patient data where both ruptured and non-ruptured plaques were compared and analyzed. In vivo patient image data showing rupture verified by histological information (current gold standard) provided by excised specimens data will help to establish in vivo benchmark for image-based and/or stress-based assessment schemes.
Effects of Mechanical Strain on Structural and Actin-Binding Proteins in Neuroblasts
Authors: Chou Szu-Yuan , Cheng Chao-Min , Lin Yi-Wen , Chen Chih-Cheng , LeDuc Philip R.
Published: July 2013

Mechanical stimulation affects the functioning and outgrowth of neurons and has the potential capacity for regeneration. Mechanoreceptors in sensory neurons act as a conduit to respond to pain and touch while neurites experience mechanical stimulation during the process of animal growth. To understand mechanotransduction in neural outgrowth, we used a custom fabricated device to investigate the effects of static mechanical stretching while examining molecular connections such as advillin and actin. Our results have the potential of providing greater understanding of mechanotransduction in neuroblasts, as well as providing insight into mechanical approaches that might be used in increasing neural outgrowth.
Towards the Optimal Placement of Inferior Vena Cava Filters: Modeling the Impact of Renal Inflow
Authors: Singer Michael A. , Henshaw William D. , Wang Stephen L.
Published: July 2013

The endovascular deployment of inferior vena cava (IVC) filters is a clinical treatment for the prevention of pulmonary embolism due to deep vein thrombosis. In addition, IVC filters are used routinely for prophylactic purposes in patients who are at high risk of developing pulmonary embolism, e.g., trauma patients. There are approximately eight IVC filters available in the U.S., each with a unique design.
Structure Prediction and Nanomechanical Properties of Human Vimentin Intermediate Filament Dimers
Authors: Buehler Markus J. , Qin Zhao
Published: July 2013

Intermediate filaments (IFs), in addition to microtubules (MTs) and microfilaments (MFs), are one of the three major components of the cytoskeleton in eukaryotic cells. As the basic building block of IFs, the properties of the IF dimmer re crucial to fully understand the molecular basis for the properties of the IF network in cells. However, the structure of IF dimers remains unknown, which has thus far prevented the elucidation of its nanomechanical properties, in particular molecular-level mechanisms of deformation. Here we present the development of a full atomistic molecular model of the vimentin dimmer, a coiled-coil structure consisting of four alpha-helixes (AHs). The structure is found to be stable in molecular dynamics simulation after an extensive equilibration process. After careful structure prediction, the behavior of the IF dimer under mechanical stress is investigated; including studies of changing the pulling velocity and a detailed analysis of the associated deformation and rupture mechanisms. Most notably, we observe a transition of AHs to beta-sheets (BSs) under mechanical deformation, as has been observed indirectly in earlier experimental studies. Our result helps to better understand the structure and fracture mechanism of this important protein filament.
A Basic Theory of Artery Buckling Under Internal Pressure
Authors: Han Hai Chao
Published: July 2013

The stability of blood vessels under the lumen blood pressure load is essential to the maintenance of normal arterial function. It has been well documented that arteries and veins collapse when the internal lumen pressure is too low and/or the external pressure become higher than the internal pressure [1–3]. It has been demonstrated recently that arteries and veins also buckle (bend) due to hypertensive pressure or a reduced axial stretch ratio [4]. Buckling equations have been established recently for linear and nonlinear elastic artery and vein models based on assumed sinusoidal mode shapes [4–6]. However, the theoretical base for the assumption is lacking. It is necessary to determine whether arteries can bifurcate into the buckled shape under internal pressure.
Effects of Edge-to-Edge Repair on Chordal Tension of Prolapsed Mitral Valve
Authors: He Zhaoming , Emmadi Suveen , Bhattacharya Shamik
Published: July 2013

Edge-to-edge repair (ETER) was introduced to correct mitral valve (MV) regurgitation and has demonstrated efficacy in a spectrum of MV diseases [1], especially MV prolapse. This technique changes MV geometric configuration by suturing the anterior and posterior leaflets at central or commissural edges (depending on lesion), and consequently alters MV mechanics. MV prolapse is the most common heart valve abnormality in the United States. It is mainly caused by chordal rupture or elongation in which imbalanced chordal lengths protrude MV anterior and/or posterior leaflets. Chordal repair or leaflet resection are common surgical procedures in an open heart surgery. ETER is also effective in treatment of MV prolapse and preferred because of potential percutaneous application of the similar procedure. However, ETER restore leaflet coaptation from a prolapsed MV and may alter leaflet stress and chordal tension distribution. Our hypothesis is that ETER changes leaflet and chord special configuration of a prolapsed MV and thus chordal tensions as compared with normal and prolapsed MVs. The aim of the current study was to investigate tensions of marginal, strut chordae of anterior leaflet, and of marginal, intermediate chordae of posterior leaflet during systole before and after ETER on the MV with a prolapsed posterior leaflet. Hypothesis is tested by comparison of chordal tension change.
Design of a Polycarbonate-Urethane Meniscal Implant: Finite Element Approach
Authors: Linder-Ganz Eran , Elsner Jonathan J. , Danino Amir , Zur Gal , Guilak Farshid , Shterling Avi
Published: July 2013

The medial meniscus plays an important role in the knee joint [1]. Meniscus dysfunction due to tear is a common knee injury which leads to degenerative arthritis, attributed primarily to the changes in knee load distribution [2]. Clearly, there is a substantial need to protect the articular cartilage by either repairing or replacing the menisci. A “floating” Polycarbonate-Urethane (PCU) meniscal implant (Fig. 1a) is proposed as a solution for restoring the function of the missing meniscus and for the reduction of pain, through improved tibial and femoral pressure distribution. The implant is composed of PCU embedded with polyethylene reinforcement fibers (“Dyneema®”, DSM), and its design is based on the geometry of the articulating surfaces of the femur and tibia. Our goal was to develop an optimal meniscal implant design (in terms of composition and geometry), whose contact pressure with the tibial plateau (TP) would be similar to that of the natural meniscus and be able resist mechanical failure of any of its components. We hereby present one aspect of the implant bench-tests, finite element (FE) analyses of the implant in the medial knee under physiological relevant loading conditions.
Characterizing Lapine Meniscal Tissue: A Regional Comparison Between Normal Medial and Lateral Menisci
Authors: Lepinski Nicole M. , Killian Megan L. , Isaac Daniel I. , Haut Roger C. , Haut Donahue Tammy L.
Published: July 2013

The meniscus is comprised of two semilunar disks resting between the articular surface of the tibial plateaus and femoral condyles within the knee joint of each leg [1–3]. Both the medial and lateral menisci play a vital role in maintaining the joint’s integrity by distributing loads, stabilizing and lubricating the joint, and proprioceptive functions [2,3]. While the meniscus is found in many animals, morphological variations are present between species, indicating differences in the biomechanics of the joint [1,2]. These anatomical variations have not been quantified and, thus, remain unlinked to further structural changes that occur with injury. The goals of this study were aimed towards characterizing the normal lapine meniscal tissue using regional comparisons for tissue area and cell density measurements. The preliminary data from this research will be used as a comparison against future animal injury models. It was hypothesized that a difference would be observed between anterior, central, and posterior divisions in the normal lapine meniscus.
An Improved Splint Design for Boutonniere Deformity
Authors: Macdonald Scott A. , Rentschler Mark E.
Published: July 2013

Boutonniere deformities are a common injury to the extensor mechanism of the finger. The deformity results in fixed contraction in the medial finger joint, and is severely debilitating to functionality. Due to the complexity of the mechanism, surgical procedures are difficult, expensive, and often unsuccessful. However, nonsurgical treatment of the deformity has not changed in many years and remains time consuming and mostly ineffective. The goal of this work is to develop an improved mechanical brace, to correct the deformity, by utilizing unconventional materials such as Nitinol and proven therapeutic techniques such as heat and motion to increase blood flow to the damaged tissue.
Cervical Spine Tolerance to Catastrophic Injury in Rollover Crash Environments
Authors: Burke Donald S. , Bidez Martha W. , Mergl Kathryn
Published: July 2013

According to the National Highway Traffic Safety Administration (NHTSA) rollovers have a higher fatality rate than all other kinds of crash modes. Of the 6,159,287 police reported crashes in 2005 in the United States, only 4.1% involved a rollover. Yet, rollovers accounted for 34.4% (10,816) of all passenger vehicle fatalities and another 149,406 individuals sustained serious injuries in rollover crashes in 2005 [5].
Material and Mechanical Properties of Tricalcium Phosphate-Based (TCP) Scaffolds
Authors: Vivanco Juan , García-Rodríguez Sylvana , Smith Everett L. , Ploeg Heidi-Lynn
Published: July 2013

Bioactive ceramic materials like tricalcium phosphates (TCP) have been emerging as alternative and valid approaches to the current therapies of bone scaffolding to target major diseases such as fracture healing, osteoporosis, and osteoarthritis [1]. These scaffolds can induce bone formation by acting as carriers or guides for enhanced bone regeneration by cell migration, proliferation, and differentiation. Previous studies have shown that both material and architectural characteristics influence the mechanical strength of bone scaffolds and their biological functionality [2]. In this study, the physical and mechanical properties of three sets of TCP scaffolds were analyzed. The physical properties that were evaluated included volume, mass, density and porosity. The scaffold compressive mechanical properties were evaluated in air at room temperature and in saline at 37°C.
Biomechanical Analysis of a Serious Pressure Ulcer Case in a Real-World Scenario
Authors: Linder-Ganz Eran , Shabshin Nogah , Gefen Amit
Published: July 2013

Deep tissue injury (DTI) is a serious pressure ulcer, characterized by necrotic tissue mass under intact skin. There is evidence that elevated tissue strains/stresses over prolonged times cause DTI, via paths of physical damage to cells, ischemia and impaired diffusion. Skeletal muscle is considered less tolerable to mechanical loads, likely because of higher metabolic demand and denser vascularization. When damaged in compression, muscle tissue stiffens up to ∼3-fold, depending on the magnitude and duration of loading [1]. Cell-death thresholds for loaded muscle, that are a Boltzmann-type downward-step sigmoid function of the magnitude of compression strain/stress and time, were developed based on meta-analysis of animal experiments [2]. These cell-death thresholds allow extrapolation of biological damage trends from computational stress analyses of muscle in load bearing postures.
Visualization of CFD Results in a Virtual Reality Environment
Authors: Gundert Timothy J. , Hayden Paul , Migrino Raymond Q. , LaDisa John F.
Published: July 2013

Imaging modalities such as computed tomography, 3D ultrasound and magnetic resonance imaging (MRI) facilitate detailed viewing of vascular geometries [1], but lack the ability to directly measure important hemodynamic parameters associated with the onset and progression of cardiovascular disease (i.e. pressure, wall shear stress) [2]. Computational fluid dynamics (CFD) is a noninvasive tool to quantify these indices in vessels reconstructed from imaging data. Although image-based CFD can be used to relate altered hemodynamics to vascular disease, a disjunction exists between information gathered from 4-D CFD (3 spatial dimensions and time) and the 2-D screens where results are typically displayed. In contrast, 3D virtual reality environments can be used to visualize CFD results in a comprehensive manner.
Differential Regulation of Articular Cartilage Biomechanical and Biochemical Properties by IGF-1 and TGF-β1 During In Vitro Growth
Authors: Stender Michael E. , Flores Christian R. , Dills Kristin J. , Williams Gregory M. , Stewart Kevin M. , Hazelwood Scott , Chen Albert C. , Sah Robert L. , Klisch Stephen M.
Published: July 2013

Articular cartilage (AC) is a load bearing material that provides a low friction wear resistant interface in synovial joints. Naturally-occurring and stimulated intrinsic repair of damaged AC is ineffective. Thus, there is a desire to engineer effective replacement tissue that could be used for AC repair. Previous studies [1] have shown that culture of immature cartilage with medium including TGF-β1 will result in a more mature tissue than culture with IGF-1. Detailed characterization of tissue mechanical properties would be helpful for development of cartilage growth models [2].
The Effect of Cement Line Properties and Crack Orientation on Crack Propagation in Cortical Bone
Authors: Mischinski Susan , Ural Ani
Published: July 2013

Microstructural features such as osteons and cement lines are considered to play an important role in determining the crack growth behavior in cortical bone. Cracks that penetrate the osteons may lead to complete failure of the bone [1]. On the other hand, the cracks that are deflected into the cement line slow down the crack propagation and increase the crack resistance of the bone. Although various factors were reported in the literature [1–4], the underlying mechanisms of crack propagation behavior in cortical bone have not been completely understood.
The Characterization and Comparison of Human Cortical Bone and Teeth Structural Changes by Low Field NMR
Authors: Ni Qingwen , Chen Shuo
Published: July 2013

It is known that NMR proton spin-spin (T2) or spin-lattice (T1) relaxation time measurements and analytical processing techniques have been used to determine microstructural characteristics of various types of fluid filled porous materials with characteristic pore sizes ranging from sub-micron to sub-millimeter. Currently this method has been developed and applied to quantify the porosity, pore size distribution and microdamage in human cortical bone [1–3]. The observed proton NMR relaxation signals are a convolution of the relaxation of fluid in the pores throughout the observed system with the longer relaxation time corresponding to larger pore sizes. Thus, regions within the bone matrix in which fluid may accumulate can effectively be treated as a “pore” and will be manifest as a change in the relaxation signal. Deconvolution of the relaxation signal can provide quantitative information about the relaxation distributions of fluid inside bone, i.e., the distribution of water within bone tissue. Since teeth are comprised of fluid-filled porous materials, and dentin is like bone, we also applied this rapid, non-destructive and non-invasive technique to detect and quantify age-related teeth structural changes particularly for both dentin and pulp based on broadline pulsed NMR.
Hemodynamics in Abdominal Aortic Aneurysms at Rest and Graded Levels of Exercise
Authors: Suh Ga-Young K. , Tenforde Adam , Shadden Shawn , Spilker Ryan , Cheng Christopher P. , Herfkens Robert J. , Dalman Ronald L. , Taylor Charles A.
Published: July 2013

Abdominal aortic aneurysms (AAA) are characterized by a permanent, localized dilation of the abdominal aorta. As AAA grow in size, the risk of rupture increases and open surgery or endovascular repair may be required. We hypothesize that increased flow resulting from exercise may alter the hemodynamics in the abdominal aorta, reduce the inflammatory burden on the vessel wall and slow the growth of small AAA thereby avoiding the need for endovascular or surgical intervention [1]. The purpose of this study is to quantify hemodynamic conditions in the abdominal aorta at rest, mild exercise and moderate exercise states in individual patients using computational fluid dynamics techniques based on magnetic resonance angiography (MRA) anatomic data and cine phase contrast magnetic resonance imaging (cine PC-MRI) flow data obtained at rest and during upright exercise on an MR-compatible exercise cycle.
Repeated Heat Shocks Enhance Procollagen III Expression in Dermal Fibroblasts
Authors: Dams Susanne D. , de Liefde Moniek , Nuijs Tom , Oomens Cees W. , Baaijens Frank P.
Published: July 2013

Aging of the skin is a universal process. Well-known characteristics are the development of fine lines and wrinkles, but also changes in skin tone, skin texture, thickness and moisture content are aspects of aging [1,2]. The aging process can be divided into intrinsic aging, such as changes in e.g. dermal components like collagen, elastic fibers, glucosaminogycans and fibroblasts, and extrinsic aging, which is caused by external factors e.g. damage by UV-radiation [3]. Rejuvenation of the skin aims at reversing the intrinsic and extrinsic signs of skin aging and can be established in the epidermis as well as in the dermis.
Relationships Between Stiffness of Human Distal Tibia, Distal Radius, Proximal Femur, and Vertebral Body Assessed by HR-pQCT and cQCT Based Finite Element Analyses
Authors: Liu X. Sherry , Cohen Adi , Yin Perry T. , Lappe Joan M. , Recker Robert R. , Shane Elizabeth , Guo X. Edward
Published: July 2013

High-resolution peripheral quantitative computed tomography (HR-pQCT) is a promising clinical tool that permits separate measurements of trabecular and cortical bone compartments at the distal radius and tibia. It has an isotropic voxel size of 82 μm, which is high enough to assess the fine microstructural details of trabecular architecture. HR-pQCT images can also be used for building microstructural finite element (μFE) models to estimate the mechanical competence of whole bone segments. Melton et al. showed that derived bone strength parameters (axial rigidity and fall load to failure load ratio) are additional to BMD and bone geometry and microstructure as determinants of forearm fracture risk prediction [1]. Boutroy et al. found that the proportion of the load carried by trabecular bone versus cortical bone is associated with wrist fracture independently of BMD and microarchitecture [2]. These clinical studies demonstrate that HR-pQCT based μFE analyses can provide measurements of mechanical properties that independently associate with fracture risk. However, microstructure of one skeletal site may be different from that of another site. It is unclear whether and to what extent these peripheral measurements reflect the bone strength of the proximal femur and vertebral bodies, the sites of frequent osteoporotic fractures. Currently, central quantitative computed tomography (cQCT) is the most commonly used clinical imaging modality to quantify the structural and mechanical properties of the proximal femur and lumbar spine. We therefore evaluated relationships between the stiffness of the distal radius and tibia estimated by HR-pQCT-based FEA with that of the proximal femur and lumbar spine which was estimated from cQCT-based FEA in the same human subjects.
Targeted Brain Hypothermia Induced by an Interstitial Cooling Device in Human Neck: An Experimental Study
Authors: Attaluri Anilchandra , Zhu Liang , Huang Zhongping
Published: July 2013

In recent years, mild or moderate hypothermia during which brain temperature is reduced to 30–35°C, has been proposed for clinical use as an adjunct for achieving protection from cerebral ischemia during cardiac bypass injury [Nussmeier 2002], carotid endarterectomy [Jamieson et al., 2003] and resection of extra-cranial aneurysm [Wagner and Zuccarello 2005], as well as stroke and traumatic brain injury [Marion et al., 1996; Marion 1997]. It has been shown that a reduction in brain temperature as small as 2°C substantially reduced ischemic cell damage [Clark et al., 1996], or improved significantly post-ischemic regional histopathology [Wass et al., 1995]. Most of the currently used clinical studies have examined only systemic hypothermia by whole body cooling. The major methodological drawback of this approach is slow cooling rate (∼0.5°/hour) due to the large volume of the human body and arteriovenous shunt vasoconstriction [Krieger et al., 2001; Marion et al., 1997; Schwab et al., 1998]. Whole body cooling does induce systemic complications. The systemic risks may outweigh the beneficial effects of neuro-hypothermia in the current clinical practice. Selective brain cooling which keeps the rest of body at normal temperature, on the other hand, can be used to maximize the neuroprotection of hypothermia.
An In-Vitro Experiment to Study Sustained Torque on the Spine
Authors: Rizza Robert , Liu Xue-Cheng , Mahinfalah Mohammad , Wang Yu , Thometz John , Lyon Roger , Tassone Channing
Published: July 2013

In adolescent scoliosis patients, as the vicious cycle hypothesis proposed by Dr. Stokes suggests [1], a lateral spinal curvature produces asymmetrical loading of the skeletally immature spine, which in turn causes asymmetrical growth and therefore progressive wedging deformity. Numerous studies have been done to evaluate the effect of sustained compression or tension loading on the spinal bone growth [2,3]. However, in scoliosis patients, there is not only the asymmetrical axial loading which will worsen the curve progression, but also constant shear force in the transverse plane that may affect the bone growth. So far, no in vivo experiment has been done to study the effect of shear force on the spine. The goal of this study is to design an in vitro experiment that will provide incessant torques in the calves’ tails, and determine the relationship between the magnitude of the torque and change of stress between tail segments.
Posterior Total Joint Replacement, a Novel Alternative to Lumbar Anterior Disc Arthroplasty: A Computational and Vitro Study
Authors: Kiapour Ali , Goel Vijay K. , Krishna Manoj , Koruprolu Sarath
Published: July 2013

Total lumbar disc replacements (TDRs) are designed to restore kinematics of a degenerated segment [1]. Compared to the fusion of the segment, disc replacements may prevent adjacent segment degeneration. Various designs have been proposed for lumbar TDR; however most of these require an anterior surgical intervention for placement. Post-surgery facet pain and degeneration are shown to occur. Complicated surgical procedure and difficulty in revision are other deficiencies of anterior discs concept. Posterior disc designs are novel alternatives for restoring kinematics across the implanted spine and posses the ability to overcome the limitations of anterior lumbar arthroplasty.
Semi-Automated Patient Specific Hexahedral Mesh Generation of Articular Cartilage
Authors: Tadepalli Srinivas C. , Shivanna Kiran H. , Magnotta Vincent A. , Grosland Nicole M.
Published: July 2013

Articular cartilage is a critical component in the movement of one bone against another. It possesses unique chemical properties allowing it to serve as a bearing surface, capable of transferring loads from one bone to another while simultaneously allowing the load bearing surfaces to articulate with low friction. Patient-specific finite element (FE) models incorporating articular cartilage provide insight into articular joint mechanics [1, 2]. To date, the methods/tools available to create accurate FE mesh definitions of the articular cartilage are limited. Semi-automated morphing methods have been developed, but many intermediate steps have to be performed to get the final cartilage mesh definition [3]. Commercially available software [4] is capable of generating tetrahedral/shell/pyramid element based meshes of the cartilage from the underlying bony surface, but hexahedral meshes are preferred over tetrahedral meshes [5]. IA-FEMesh currently provides the ability to project a pre-defined set of elements a uniform distance [6]. This technique has been adopted in several models [1, 2]. Cartilage does not necessarily exist as such; rather the thickness of the cartilage is non-uniform and varies over the surface. Consequently an accurate representation of the articular cartilage is crucial for an accurate contact FE analysis. The goal of this study was to develop an algorithm that will aid in the generation of anatomically accurate cartilage FE mesh definitions in a reliable manner based on patient-specific image data.
Mechanical Study on Tumor Microvessel Damage Induced by Alternate Cooling and Heating Treatment
Authors: Shen Yuanyuan , Zhang Aili , Xu Lisa X.
Published: July 2013

Temperatures lower or higher than the body temperature have been used to treat diseases for therapeutic purposes based on thermal effects on biological tissues, i.e. cryosurgery, hyperthermia or high temperature ablation. New treatment modality by combining cryotherapy with hyperthermia or high temperature ablation has been proposed for better therapeutic outcome [1]. Using nude mice dorsal skin fold tumor chamber, our previous experimental study found that vasculature damage caused by the alternate treatment (cooling at −10°C for 1/2 hour followed by heating at 42°C for another 1/2 hour) was much more serious as compared to that of cooling or heating alone. The structure of tumor microvessels was mostly ruptured and blood supply shut down. Fractures caused by thermal stresses were frequently found in arteries or tissues during cooling and thawing processes because of the temperature gradients and heterogeneous properties of the biological materials such as the thermal expansion coefficient, elasticity, etc. Thermal stresses in both freezing and heating were expected to be major factors that caused the vessel rupture. During the subsequent heating, blood reperfusion occurred in the vessels and blood flow rates increased evidently. The pressure gradient driven blood flow yielded stress on the vessel wall, which was often used as a rupture indicator. In the alternate cooling and heating treatment, mechanical stresses on microvessel wall resulted from blood flow may be another important factor causing vascular damage.
Direct Validation of Active Solute Transport Induced by Dynamic Loading of Porous Hydrated Media
Authors: Albro Michael B. , Li Roland , Banerjee Rajan E. , Hung Clark T. , Ateshian Gerard A.
Published: July 2013

Transport pathways play a key role in maintaining cellular metabolic activity in biological tissues. Efforts to maintain or enhance the transport of nutrients may prove beneficial to the maintenance of native or development of engineered tissue. Various studies have investigated the potential of dynamic mechanical loading to increase the uptake and desorption rates of solutes in articular cartilage [1, 2]. Recently, a novel concept has been theoretically suggested that such dynamic loading of porous deformable media may additionally yield higher steady state concentrations of solutes, beyond those achieved by passive diffusion [3]. The first experimental evidence that dynamic loading can significantly enhance solute uptake over passive diffusion was recently reported for a model system of dextran in agarose hydrogels [4]. The results of this experimental study [4] were interpreted in the context of the earlier theoretical predictions [3], though a direct validation of theory with experiments has not yet been attempted. Therefore, the current study focuses on directly validating the theoretical framework by independently measuring the mechanical and transport properties of agarose hydrogels and dextran solutions experimentally, and substituting these values into the theory to evaluate the predicted solute uptake. These predictions are then compared to the previously reported experimental measurements of uptake of dextran in agarose under dynamic loading [4], for several gel concentrations and solute molecular weights.
Calcium Signaling in Bone Cell Networks Induced by Fluid Flow
Authors: Lu X. Lucas , Huo Bo , Baik Andrew D. , Guo X. Edward
Published: July 2013

Mechanical stimuli such as fluid flow can induce robust multiple intracellular calcium ([Ca2+]i) peaks in connected bone cell networks [1]. This fluid flow induced oscillation of [Ca2+]i can come from two sources: intracellular Ca2+ stores (e.g., endoplasmic reticulum, ER) and the extracellular environment. Moreover, [Ca2+]i signaling is mediated by various molecular pathways, such as IP3, ATP, PGE2, and NO. Osteocytes are believed to comprise a sensory network in bone tissue that monitors in vivo mechanical loading and triggers appropriate adaptive responses from osteoblasts and osteoclasts [2]. It is also well recognized that osteoblasts, the cells responsible for bone formation, can directly sense and respond to mechanical stimulation (e.g., fluid flow). In the present study, two types of cell networks were constructed in vitro with osteocyte-like and osteoblast-like cells, respectively, by using microcontact printing and self assembled monolayer (SAM) technologies. The calcium responses of the two types of cell networks to fluid flow were recorded, quantitatively analyzed, and compared. Then we examined how the [Ca2+]i response in the osteocyte cell network was influenced by gap junctions, intra/extracellular calcium sources, and other various molecular pathways.
Translational and Rotational Head Kinematics in Side Impact
Authors: Zhang Jiangyue , Yoganandan Narayan , Pintar Frank A.
Published: July 2013

Regulatory tests use translational head accelerations and its derived variable HIC (head injury criterion) as the criteria for automotive vehicle crashworthiness evaluation. The FMVSS standard sets HIC36 of 1000 as the threshold for frontal impact protection. On the other hand, rotational head kinematics, such as rotational accelerations and velocities, has been attributed to brain injury in the motor vehicle environment for more than six decades [1–5]. As documented in recent real-world case studies, severe brain injuries without skull fracture, such as diffuse axonal injury, can result from rotational head motions in side impacts even at low change in impact velocity [6, 7]. Because the HIC only accounts for the translational head accelerations, there is no clear evidence showing there is a direct correlation between translational and rotational head acceleration. Therefore, it is important to quantify the correlation between head translational and rotational accelerations and HIC, in side impacts. Consequently, the current research was designed with this purpose.
Flow Reduction in Jailed Arteries After Stenting of Cerebral Aneurysms
Authors: Cebral Juan R. , Mut Fernando , Appanaboyina Sunil , Löhner Rainald , Scrivano Esteban , Lylyk Pedro , Putman Christopher
Published: July 2013

Recently, there has been increased interest in the use of flow divertion endovascular devices such as stents [1–3] to treat unruptured cerebral aneurysms. The goal of these devices is to deviate the blood flow away from the aneurysm and promote its thrombosis and exclusion from the circulation. However, one of the major concerns with these devices is the possibility of occluding a small arterial branch or perforating artery that may be jailed by the stent mesh. This could result in an ischemic stroke. The goal of this study was to assess the reduction in the flow rate in jailed side branches after stenting of cerebral aneurysms.
Influence of Parent Artery Motion on the Hemodynamics of Basilar Tip Aneurysms
Authors: Sforza Daniel M. , Putman Christopher , Cebral Juan R.
Published: July 2013

The pathogenesis, progression and rupture of cerebral aneurysms are multi-factorial mechanisms that involve arterial hemodynamics, wall biomechanics, wall mechano-transduction or mechano-biology, and peri-aneurysmal environmental effects [1].
Multiphoton Microscopy of Healthy and Aneurismal Human Ascending Aorta
Authors: Meadley Stacey L. , Tripathy Umakanta , Wiseman Paul W. , Leask Richard L.
Published: July 2013

The ascending aorta (AA) is the largest artery in the human body. It is responsible for transporting blood between the heart and the rest of the body. The structure of the AA allows it to withstand the resulting blood flow forces. This unique structure is due primarily to the proteins collagen and elastin. Collagen accounts for the strength of the aorta while the mechanical properties of the tissue, under healthy physiological conditions, is dominated by the elastin. Aneurysms are the primary disease associated with the AA, where the diameter of the vessel increases over 1.5 times its original size. Aneurysms can result in severe blood flow disturbances or rupture of the AA and almost always require surgical intervention. The development of an aneurysm is due to a weakening of the aortic wall, specifically the degradation of the structural proteins. This study examines the changes that occur to collagen and elastin in the ascending aorta with aneurysms using multiphoton microscopy. Specifically, the orientation of collagen fibers and the morphology of the fenestrations in the elastic lamina are compared between healthy and dilated human ascending aortas.
Prediction of Shear Induced Platelet Activation in Prosthetic Heart Valves by Integrating Fluid–Structure Interaction Approach and Lagrangian-Based Blood Damage Model
Authors: Morbiducci Umberto , Ponzini Raffaele , Nobili Matteo , Massai Diana , Montevecchi Franco M. , Bluestein Danny , Redaelli Alberto
Published: July 2013

Altered haemodynamics are implicated in the blood cells damage that leads to thromboembolic complications in presence of prosthetic cardiovascular devices, with platelet activation being the underlying mechanism for cardioemboli formation in blood flow past mechanical heart valves (MHVs). Platelet activation can be initiated and maintained by flow patterns arising from blood flowing through the MHV, and can lead to an enhancement in the aggregation of platelets, increasing the risk for thromboemboli formation. Hellums and colleagues compiled numerous experimental results to depict a locus of incipient shear related platelet activation on a shear stress – exposure time plane, commonly used as a standard for platelet activation threshold [1]. However, platelet activation and aggregation is significantly greater under pulsatile or dynamic condition relative to exposure to constant shear stress [2]. Previous studies do not allow to determine the relationship existing between the measured effect — the activation of a platelet, and the cause — the time-varying mechanical loading, and the time of exposure to it as might be expected in vivo when blood flows through the valve. The optimization of the thrombogenic performance of MHVs could be facilitated by formulating a robust numerical methodology with predictive capabilities of flow-induced platelet activation. To achieve this objective, it is essential (i) to quantify the link between realistic valve induced haemodynamics and platelet activation, and (ii) to integrate theoretical, numerical, and experimental approaches that allow for the estimation of the thrombogenic risk associated with a specific geometry and/or working conditions of the implantable device. In this work, a comprehensive analysis of the Lagrangian systolic dynamics of platelet trajectories and their shear histories in the flow through a bileaflet MHV is presented. This study uses information extracted from the numerical simulations performed to resolve the flow field through a realistic model of MHV by means of an experimentally validated fluid-structure interaction approach [3]. The potency of the device to mechanically induce activation/damage of platelets is evaluated using a Lagrangian-based blood damage cumulative model recently identified using in vitro platelet activity measurements [4,5].
TRID Cervical Analysis During Rear Impact Simulation With MADYMO
Authors: Meyer Andrew R. , Fritz Jessica M. , Harris Gerald F.
Published: July 2013

The ability to determine cervical Injury Assessment Reference Values (IARVs) is the result of contributions extending over the past several decades [1–7]. These studies confirm that lower speed impact analyses require careful assessment of mechanical and biomechanical parameters in order to examine body segmental effects. Mechanical and biomechanical metrics are included in an analysis to account for complexities of occupant and vehicle coupling. The purpose of this work is to describe the IARV results of a series of controlled lower speed rear impacts applied to a restrained, 50th percentile TRID male occupant.
Tuning a Multiscale Model of Abdominal Aortic Hemodynamics to Incorporate Patient-Specific Features of Flow and Pressure Waveforms
Authors: Spilker Ryan L. , Taylor Charles A.
Published: July 2013

Computational models enable the calculation of quantities that are impractical or impossible to measure and the prediction of physiological changes due to interventions. In order to be useful, cardiovascular models must be both rooted in physical principles and designed such that measured or otherwise desired features of the cardiovascular system are reproduced. The former requirement has motivated the development of image-based anatomic models, patient-specific inflow boundary conditions, deformable vascular walls, outflow boundary conditions that represent the influence of the downstream circulation, and multiscale models. The development of approaches to address the latter requirement, reproducing desired features of the circulation, is a critical area of modeling research that has received comparatively little attention.
Validation of a Finite Element Model of Passive Force and Pressure in Skeletal Muscle
Authors: Morrow Duane A. , Haut Donahue Tammy L. , Odegard Gregory M. , Kaufman Kenton R.
Published: July 2013

Intramuscular pressure (IMP) has been put forth as a surrogate measure for muscle force. As technological advancements have lead to the creation of smaller IMP microsensors, obtaining IMP readings in the clinic has come closer to becoming a minimally-invasive reality. However, appropriate use of data from these sensors relies upon an understanding of the mechanism of pressure changes within skeletal muscle. To that end, a constitutive model, representing muscle as a transversely isotropic, hyperelastic, and isovolumetric was created [1] for implementation in a finite element simulation. The purpose of this study was to validate this constitutive muscle model with passive elongation tests of skeletal muscle tissue from New Zealand White (NZW) rabbits. Reaction forces and hydrostatic pressures resulting from applied deformations were determined with the finite element modeling (FEM) approach and were compared with previously published experimental data [2].
Age Dependent Mechanical Properties of the Infant Porcine Parietal Bone and a Correlation to the Human
Authors: Baumer Timothy G. , Powell Brian J. , Fenton Todd W. , Haut Roger C.
Published: July 2013

An infant less than 18 months of age with a skull fracture has a 1 in 3 chance of abuse [1]. While the parietal bone is most often the site of fracture, an abusive situation is difficult to diagnose based on characteristics of the fracture alone [2]. Age of the child is one important factor in determining abuse. Injury biomechanics are often used in the investigation of cases suspected to involve child abuse [3]. In addition to case-based investigations, computer modeling, and test dummies, animal model studies can aid in these investigations. While the relationship between animal studies and human pediatric patients is yet unclear, some animal models have emerged in the current literature. A study by Margulies and Thibault [4] made an attempt to correlate the mechanical behavior of human infant cranial bone to porcine infant cranial bone. The study suggests that weeks of pig age may correlate to months in the human. Yet, an 18 week old pig is considered to be in adolescence. The current study was conducted to determine the mechanical properties of parietal bone and coronal suture in porcine infants of a younger age than previous studies and correlate the bending properties of the bone to existing human data.
Three-Dimensional Simulations of Blood Flow With Systemic Arterial Baroreflex
Authors: Kim H. J. , Taylor C. A.
Published: July 2013

The systemic arterial baroreflex controls the systemic arterial pressure to maintain homeostasis. The carotid sinus and aortic arch are the major systemic arterial baroreceptors, and they respond to distention of the carotid and aortic walls causing compensatory mechanisms, which regulate heart rate, cardiac contractility, peripheral arterial resistance, venous compliance, and venous unstressed volume [1]. In this study, we connect a feedback control loop, which represents the systemic arterial baroreflex, to the closed loop system we developed in a previous study [2]. The three-dimensional finite element model of the aorta and the closed loop system enable us to obtain not only the physiologic flow rate and pressure fields of the finite element model but also the global characteristics of the cardiovascular system from the closed loop model. We study the autoregulatory mechanisms occurring due to the systemic arterial baroreflex by considering the interactions between the heart and the systemic and pulmonary circulations.
Symmetric Itakura Distance as an EEG Signal Feature for Sleep Depth Determination
Authors: Estrada Edson , Nazeran Homer , Ebrahimi Farideh , Mikaeili Mohammad
Published: July 2013

Sleep is a natural periodic state of rest for the body, in which the eyes are usually closed and consciousness is completely or partially lost. Consequently, there is a decrease in bodily movements and responsiveness to external stimuli. In this pilot study, we performed power spectral estimation of EEG signals by Autoregressive (AR) modeling, and then used Itakura Distance to measure the degree of similarity between an EEG baseline and EEG epochs for the entire sleep study. Sleep data from twenty-five subjects (21 males and 4 females, age: 50 ± 10 years, range 28–68 years) from Physionet database were used. We found that Itakura Distance was the smallest for sleep stages similar to the baseline. We intend to deploy this feature as an important element in automatic classification of sleep stages. Results show that trends provided by this feature could discern between sleep stages with a very high level of statistical significance p<0.01.
Performance While Crossing Obstacles in Patients With Total Hip Replacement: Comparing Pre-Operation and Post-Operation Performance
Authors: Chang Susan , Lee Shiuann Sheng , Chen Hsieh Ching , Chern Jen Suh , Chen Shih Shan
Published: July 2013

This study investigated the performance the patients with total hip replacement (THR) and healthy adult whiling crossing obstacles. By using a 3D motion analysis system and force plates, we measured the parameters of: (1) toe-obstacle clearance, (2) heel-obstacle clearance, (3) distance between toe and obstacle before crossing, and (4) between heel and obstacle after crossing. In the healthy adult, the results revealed that except the TD of the trailing leg (p = 0.001), other parameters were no significant difference in every crossing condition. Although the THR-patient also showed insignificant different before operation, but in the phase of 2 weeks after the operation, he could only execute the 10 cm crossing condition because of the self-perceived range of motion limitation of the hip surgery, and the performance was unsatisfied. Until the recovery stage in 6 weeks after the operation, the subject could execute all crossing activities, and there was significant difference in toe-obstacle clearance (p = 0.006) while the obstacle height changed, but the other parameters did not show difference significant, and the performances were almost near the healthy adult, with a stable crossing pattern. This study was the initial study on THR-patient, we hope that we can understand the recovery stage of these groups, and base on these results to set up better rehabilitation program after operation, and finally prevent fall in daily life.
Tissue Engineered Heart Valves Develop Native-Like Collagen Architecture
Authors: Cox Martijn A. J. , Kortsmit Jeroen , Bouten Carlijn V. C. , Baaijens Frank P. T.
Published: July 2013

Over the last few years, research interest in tissue engineering as an alternative for current treatment and replacement strategies for cardiovascular and heart valve diseases has significantly increased. For a tissue engineered heart valve to be functional, it should be able to withstand the high pressures and flows that occur in vivo. Nature’s solution for this challenge can be found in the complex collagen fiber architecture of the native aortic valve (Fig. 1).