bluuebunny/crossref_metadata_2025 huggingface dataset:
The Characterization of Age-Related Human Cortical Bone Porosity, Water Distribution Changes by Nuclear Magnetic Resonance
Authors: Ni Qingwen , Nyman Juffry S. , Wang Xiaodu , Nicolella Daniel P.
Published: March 2014

Previous studies have shown that bone fracture toughness is also significantly correlated to changes in porosity, microarchitecture, osteonal morphology, collagen integrity, microdamage, and the interactions of water with collagen and mineral phases, all of which are measures of bone quality. Currently, the influence of water removal on the strength and toughness of cortical bone has studied by Nyman et al [1]. The results have shown that loss of water in the collagen phase decreases the toughness of bone, whereas loss of water associated with the mineral phase decreases both bone strength and toughness. However, in that paper the loss of water was used the dehydration method for such mechanism studies. Here, we hypothesize that the NMR relaxation technique can non-destructively and non-invasively assess the porosity, bound water (water bound to collage and mineral phases) and mobile water (water within the pores).
Characterization of Cell Association and Heat Treatment Using Iron Oxide Magnetic Nanoparticles
Authors: Kalambur Venkat S. , Longmire Ellen , Bischof John C.
Published: March 2014

Magnetic iron oxide nanoparticles (NPs) have intrinsic advantages over other NPs for various biomedical applications. These advantages include visualization under Magnetic Resonance Imaging (MRI), heating with Radiofrequency (RF), and movement in a magnetic field. There are now numerous efforts to expand the applications of these particles for non-invasive drug and adjuvant delivery, cellular imaging and in vitro cell sorting and purification. In the present study, we describe methods to (i) assess and quantify NP cell association (ii) facilitate NP heat destruction of cells after association with RF and laser. First, we show that (i) the cell association of iron oxide NPs is dependent on the surface coating (surfactant greater than dextran), time, cell-type and extracellular NP concentrations (saturation with concentration and time). Furthermore, the association fits a simple enzyme Michealis-Menten model. Second, (ii) improved heat destruction of cells can be achieved after laser irradiation compared to traditional RF treatment for similar NP associations. These results and assays show promise for cell sorting and purification applications.
Image Based CFD Modeling of Coronary Artery Wall Shear Stress and Importance of Patient-Specific Velocity Boundary Conditions
Authors: Johnson Kevin R. , Oshinski John N.
Published: March 2014

Low and oscillatory arterial wall shear stress (WSS) have been shown to have an effect on many factors implicated in atherosclerotic lesion development. The majority of studies on the relationship between low or oscillating WSS and sites of intimal thickening and early atherosclerotic lesion development are based on in-vitro model studies of flow and WSS distribution. These models are based on average vessel geometries with average flow conditions and compared to average pathology distribution of lesions that may obscure the true relationship between WSS and lesion distribution[1]. Recent techniques have been developed using coronary MR angiography to create patient-specific 3D models along with velocity measurements of blood flow using phase contrast magnetic resonance (PCMR). However, these models may lack adequate spatial resolution for accurate, localized calculation of WSS[2]. Current, state-of-art multidetector CT scanners offer improvements in spatial resolution over MRI for creation of 3D vessel models.
Influence of Nutrient Channels on Development of Engineered Cartilage Properties
Authors: Bian Liming , Ng Kenneth W. , Lima Eric G. , Ateshian Gerard A. , Hung Clark T.
Published: March 2014

It has been shown that chondrocyte-seeded agarose constructs of large dimensions develop spatially inhomogeneous material properties with stiffer outer edges and a softer central core [1]. This axial (depth-dependent) inhomogeneity was observed for constructs with relatively large diameter (4mm) and thickness (2.3mm) and suggests nutrient diffusion limitations to the central region of the constructs. Our previous study also showed that by reducing the thickness of the agarose construct (to 1mm) more homogenous construct properties can be obtained as a result of the reduced diffusion distance [2]. In this study we hypothesized that more homogeneous constructs of better mechanical properties could be achieved by creating channels running through the depth of the thick constructs (2.3mm), thereby facilitating nutrient diffusion into the central region of the constructs.
A Semi-Empirical Constitutive Model for Post Yield Behavior of Bone in Tension
Authors: Leng Huijie , Nyman Jeffry S. , Dong Xuanliang , Reyes Michael J. , Wang Xiaodu
Published: March 2014

Among the material properties that can be assessed through mechanical testing, toughness quantifies the energy required for failure and is therefore most suited for characterizing bone quality. As much of the toughness of bone occurs after yielding, post yield behavior of bone is attracting more and more attention [1, 2]. Although a lot of experimental studies have been conducted on post yield behavior of bone, little efforts have been made to develop constitutive relation for post yield behavior of bone tissues. Elucidating the underlying mechanism of post-yield behavior of bone is critical for further development of clinical strategies to predict and prevent age and disease related bone fractures. In addition, such understanding could help bridge the gap between biology and mechanics of bone since cellular activities are directly related to the ultrastructural architecture and composition of the tissue. Moreover, an accurate constitutive model is always required in numerical modeling and simulating the mechanical behavior of bone under different loading conditions. Based on the results reported in the literature and obtained in our laboratory, this study intends to develop and verify a semi-empirical constitutive model of the post-yield and failure behavior of the cortical bone tissue in tension.
Thermal Damage Distribution in Human Cornea Following Thermal Keratoplasty: An FTIR Study
Authors: Zhang Li , Wolkers Willem F. , Aksan Alptekin
Published: March 2014

Hyperopia (farsightedness) and presbyopia are two common eye diseases, especially seen in the elderly. In both cases, eyes lose the ability to focus on nearby objects due to change in the cornea shape or stiffening of the lens. In recent years, thermal treatment of cornea in the form of Conductive Keratoplasty (CK) procedures has been successfully utilized to reshape the cornea. In the CK treatment, a thin radiofrequency (RF) probe is inserted into the cornea and heat is delivered into the stroma [1]. The heat treatment causes collagen denaturation and mechanical shrinkage of the collagen fibers. In the CK treated region, the collagen fibers are aligned in a circular fashion. Therefore, the shrinkage of these fibers steepens the curvature of the cornea. The amount of heat delivered to the stroma during CK treatment can be controlled either by changing the applied RF power or the heating time. In this study, we utilized Fourier Transform Infrared Spectroscopy (FTIR) to map the thermal damage distribution in the human cornea tissue following simulated CK treatment.
Zinc Superparamagnetic Iron Oxide Nanoparticles for Use as MRI Contrast Agents
Authors: Bárcena Carlos , Khemtong Chalermchai , Chaubey Girija S. , Kessinger Chase W. , Liu J. Ping , Gao Jinming
Published: March 2014

Molecular imaging has become a rapidly evolving field used in various applications to target macromolecules and biological process [1,2]. Various imaging systems, such as single photon emission computed tomography (SPECT), positron emission tomography (PET), computerized tomography (CT), and magnetic resonance imaging (MRI), use non-invasive techniques that provide disease-specific information through diagnostic imaging. Early detection of disease demonstrates the potential benefit of these systems.
Quantification of Heterogeneity in Desiccating Droplets
Authors: Ragoonanan Vishard , Aksan Alptekin
Published: March 2014

Desiccated state biostabilization aims at stopping molecular motions and biochemical processes to halt degradation and to preserve functionality. Preservation by desiccation typically involves drying the biological material or the organism in a preservation solution, which typically contains non-reducing sugars (trehalose, sucrose, etc.) and salts [1]. Typically, preservation solutions (containing the biological material to be preserved) in the form of sessile droplets are deposited and dried on a surface in a controlled environment.
The Effect of Nonlinear Scleral Properties on Optic Nerve Head Biomechanics
Authors: Eilaghi Armin , Sigal Ian A. , Olesen Christian G. , Tertinegg Inka , Flanagan John G. , Brodland G. Wayne , Ethier C. Ross
Published: March 2014

Glaucoma is a group of potentially blinding ocular diseases caused by gradual and progressive damage to the optic nerve, and is usually associated with elevated intraocular pressure (IOP) [1]. This damage occurs at the optic nerve head (ONH), the site where the optic nerve axons leave the posterior eye. IOP-related biomechanical factors are hypothesized to play a key role in the pathogenesis of glaucomatous damage [2].
Phenomenological Test Method to Assess of Material Symmetry in Thick Soft Tissues
Authors: Raghavan Madhavan L. , Kratzberg Jarin A. , Ben-Abraham Ephraim I.
Published: March 2014

Characterizing the material symmetry of a biological soft tissue can aid in understanding and modeling its mechanics. Optical methods have been reported for identification of structural fiber orientations in thin tissues such as heart valve leaflets [1], but not in thick tissues such as arteries because optical methods are not as effective with thick tissues. Besides fiber architecture, effective transmural material symmetry of a planar tissue needs to be known a priori in order to perform and interpret common testing methods such as planar biaxial testing or inflation testing (for cylindrical specimens). Nielsen et al. [2] reported on planar radial testing to study inhomogeneous properties of elastic membranes. We submit that planar radial extension testing (PRET) of a thick circular soft tissue specimen will reveal the underlying material symmetry. We performed numerical simulations of planar radial extension testing and assessed its feasibility using a simple custom-fabricated device.
Coronary Artery Wall Strain Estimation From Clinical IVUS Images
Authors: Liang Yun , Zhu Hui , Gehrig Thomas , Friedman Morton H.
Published: March 2014

Atherosclerotic plaque rupture is responsible for the majority of acute coronary syndromes and myocardial infarctions. Intravascular ultrasound (IVUS) imaging is a widely available clinical technique providing real time cross-sectional images of the vessel wall and plaque morphometry. However, IVUS echo images have limited ability to predict the vulnerability of the plaque. The mechanical behavior of the plaque is consistent with its underlying components, suggesting that measurements of plaque mechanical response can be used to assess the likelihood of plaque rupture [1]. Arterial wall strain in response to luminal pressure change is such a measurable quantity. IVUS elastography has been developed to measure the radial strain through correlation analysis of the IVUS radiofrequency (RF) signal [2]. Due to the movements of IVUS catheter caused by cardiac motion and the nonlinearity of tissue deformation, reliable strain is obtained by elastography only when the tissue motion is aligned with the RF direction and the RF traces correspond to the same axial location. This is difficult to achieve in vivo. We have developed a strain estimation method based on IVUS image registration. This 2D processing method has the ability to overcome in-plane catheter movement and heterogeneous tissue deformation, thereby increasing its accuracy. Using retrospectively retrieved cardiac phase information, we propose a practical method to estimate cross-sectional coronary arterial wall strain distribution from clinically acquired images during a conventional IVUS procedure.
Influence of Early Ovariohysterectomy on the Mechanical Properties of Rabbit Medial Collateral Ligament
Authors: Thornton Gail M. , Bailey Soraya J. , Shao Xinxin , Morck Douglas , Hart David A. , Achari Yamini
Published: March 2014

Female athletes have significantly higher incidence of anterior cruciate ligament (ACL) injuries than males participating in similar sports [1]. To date, no clear explanation has emerged for this disparity. However, hormonal differences may provide an explanation because some ACL injuries have been linked to physiologic fluctuations in estrogen levels over the menstrual cycle [2]. Receptors for estrogen have been identified in rabbit and human ACLs and medial collateral ligaments (MCLs) [3]. Increased estrogen levels caused decreased fibroblast proliferation and collagen synthesis in cell cultures from human and rabbit ACLs [4]. Since fibroblasts maintain collagen production and degradation in ligaments and collagen is the major load-bearing component of ligaments, estrogen may affect knee ligament mechanical properties.
Effect of Pulse Pressure on the Vasomotor Function of Arteries
Authors: Hayman Danika M. , Han Hai-Chao
Published: March 2014

Arteries are subjected to a pulsatile pressure centered on a constant mean pressure in vivo. This oscillating pressure is disrupted by treatments for cardiovascular disease, which include the use of cardiopulmonary bypass machines and ventricular assist devices.
Micromechanical Analysis of Tissues: The Effect of Cell Adhesion to Extra Cellular Matrix
Authors: Abolfathi N. , Karami G. , Ziejewski M.
Published: March 2014

Modeling of interactions between cell and extra cellular matrix (ECM) is essential in a cell and tissue injury study. Several studies have been conducted to realize the role of mechanical property of a cell and ECM in a tissue exposed to an external loading. In this study we have used a micromechanical approach by assuming two representative volume elements (RVE) with different packing of cell inside the matrix to characterize the mechanical property of the composite formed by the cell and the ECM in a tissue. In the micromechanical modeling procedure, the cell-ECM adhesion will be studied in detail. The results will clarify the role of cell adhesion in load transferring characteristics inside the cell – ECM composite.
Desiccation Response of Geobacter sulfurreducens
Authors: Malsam Jason A. , Ragoonanan Vishard , Bond Daniel R. , Aksan Alptekin
Published: March 2014

Geobacter sulfurreducens is an electricity producing bacteria. It is used in bacterial fuel cells, microbial-based sensors, and catalytic surfaces for bioremediation. Further development of such applications requires stabilization and preservation of the bacteria as thin films on surfaces. This research investigated G.sulfurreducens response to desiccation to explore the feasibility of room temperature preservation. Room temperature preservation involves drying and storing bacteria at ambient conditions. Dried bacteria can be revived on demand by the addition of water.
Development of 4-D High-Resolution CT for Measurement of Airway Deformation
Authors: Sera Toshihiro , Yokota Hideo , Fujisaki Kazuhiro , Fukasaku Kazuaki , Uesugi Kentaro , Yagi Naoto , Himeno Ryutaro
Published: March 2014

Airway consists of a number of various compliant tubes from trachea to alveolus, and the airway geometry deforms dramatically during respiration. This morphometric deformation is very important factors in pulmonary dynamics (flow structure, particle deposition, surfactant transport and so on). Previously, we reported the small airway deformations of euthanized animals using micro-CT and synchrotron radiation-CT.
Numerical and Theoretical Analysis of the Ion Transport Around a Completely Polarizable Electrode Under AC for Use in Microfluidics
Authors: Suh Yong Kweon , Heo Seong Gyu
Published: March 2014

It is well known that a solid surface when in contact with an electrolyte shows accumulation of ions (usually anions) at the interface due to some reason. Because of this, the counter ions (cations, in the usual cases) in the electrolyte are attracted to the region very close to the interface between the solid and liquid constituting the EDL (electric double layer). Distribution of ions within EDL depends on the amount of ions adhered on the surface and also the nature of the electrolyte, such as PH and ion concentrations, etc. Figure 1 illustrates the concept sketch of this classical phenomenon.
Evaluation of Hemodynamic Efficiency in a New “Y-Graft” Design for the Fontan Operation
Authors: Bernstein Adam J. , Marsden Alison L. , Spilker Ryan L. , Reddy V. Mohan , Taylor Charles A. , Feinstein Jeffrey A.
Published: March 2014

Hypoplastic left heart syndrome is a congenital heart defect that occurs in 20 per 100,000 live births. Patients are born with severe underdevelopment of the left side of the heart which, if left untreated, is uniformly fatal. A series of operations is performed, including a cavopulmonary (Glenn) shunt and total cavopulmonary connection (Fontan procedure), which connect the superior (SVC) and inferior vena cavae (IVC) respectively in an end-to-side fashion to the left (LPA) and right pulmonary arteries (RPA), resulting in a T-shaped junction. This bypasses the heart on the venous side as blood flows from the IVC and SVC directly into the pulmonary arteries. Early survival rates following the Fontan are as high as 90%. However, these figures drop to 60% survival after 10 years [1], and most patients exhibit diminished exercise capacity.
Vulnerable Plaque Rupture Due to Stress Concentration Around Microcalcifications in the Thin Fibrous Cap
Authors: Vengrenyuk Yuliya , Cardoso Landa Luis , Carlier Stéphane , Einav Shmuel , Weinbaum Sheldon
Published: March 2014

More than half of the 500,000 coronary artery disease deaths every year are due to the sudden rupture of vulnerable plaque. Several pathological studies of ruptured plaques have provided morphological descriptions of the high-risk, or vulnerable, coronary plaque that is prone to rupture or erosion as a positively remodeled lesion rich in vasa-vasorum, containing a lipid-rich core with an overlying thin fibrous cap infiltrated by macrophages. Virmani et al. [1] described thin-cap fibroatheroma with a large necrotic core and a fibrous cap < 65 μm as a more specific precursor of plaque rupture due to tissue stress. Despite the above observations, the mechanism of vulnerable plaque rupture has remained a mystery since ruptures often occur in regions where computational finite element (FEM) and fluid structure interaction (FSI) models do not predict maximal stress. Forty percent of ruptures occur in the central part of the cap rather than regions of high curvature at the shoulders of the lipid core where FEM models predict maximum tissue stresses [2]. Similarly, the latest study by Tang et al. [3] predicts that maximal stress often appears at healthy parts of the vessel where the vessel wall is thinner than the wall on the diseased plaque side or where vessel wall curvature is large.
Anisotropic Strain Effects on Vascular Smooth Muscle Cell Physiology
Authors: Tsvankin Vadim , Belchenko Dmitry , Scott Devon , Tan Wei
Published: March 2014

Biological development is a complex and highly-regulated process, a significant part of which is controlled by mechanostimulus, or the strain imparted on a cell by its environment. Mechanostimulus is important for stem cell differentiation, from cytoskeletal assembly to cell-cell and cell-matrix adhesion [1]. The mechanics of cells and tissues play a critical role in organisms, under both physiological and pathological conditions; abnormal mechanotransduction — the mechanism by which cells sense and respond to strain — has been implicated in a wide range of clinical pathologies [2,3].
PIV Experiments to Measure the Velocity Field Just Downstream of an Oscillating Collapsible Tube
Authors: Bertram Christopher D. , Truong Nicholas K. , Hall Stephen D.
Published: March 2014

Almost all vascular conduits in the human body, being flexible, collapse elastically to a non-circular cross-section when the external pressure sufficiently exceeds the internal. Examples include the brachial artery (sphygmomanometry), veins (everyday manoeuvres), pulmonary airways (forced expiration), pulmonary capillaries (zones 1 and 2), and the urethra (micturition). Venous collapse is involved in regulation of venous return, which in turn regulates cardiac output.
Strain Induced Bladder Smooth Muscle Remodeling
Authors: Long Rebecca A. , Parekh Aron , Sacks Michael S.
Published: March 2014

Multiple urinary bladder wall (UBW) pathologies, such as overactive bladder, bladder outlet obstruction, spinal cord injury (SCI) and related neurogenic disorders, and diabetes result in tissue remodeling marked by hypertrophic bladder smooth muscle cells (BSMC) and altered extra-cellular matrix components. This remodeling results in changes in UBW biomechanical properties leading to altered bladder function. Our previous studies have revealed that during the initial areflexic phase of SCI the UBW undergoes profound remodeling that appears to be a compensatory mechanism for the increased wall stretch resulting from over-distension [1, 2]. Remodeling in the bladder wall results in changes in biomechanics and ultimately the ability of the organ to normally fill and void [3]. The stimuli and precise mechanisms that are responsible for bladder remodeling in SCI and the aforementioned pathologies remain unknown. The objective of the present study is to determine the effects of varied in vitro strain on ECM production in the ex vivo rat bladder as a first step toward understanding tissue remodeling in response to strain.
Substrate Stiffness Affects Laminin-332 Matrix Deposition in Cultured Keretinocytes
Authors: Thangawng Abel L. , Ruoff Rodney S. , Jones Jonathan C. , Glucksberg Matthew R.
Published: March 2014

It has been reported that the mechanical properties of a substrate influence cell motility, morphology, and adhesion [1–3]. This work is an attempt to move a step further beyond cells’ sensing the mechanical properties of their environment, by determining whether the secretion and assembly of laminin extracellular matrix is regulated by the mechanical environment in which the cell is placed. We hypothesize that this matrix then influences the behavior of the cell, particularly with regard to its motility.
Evaluation of a Novel Scaffold Material for Tendon Tissue Engineering
Authors: Nirmalanandhan Victor S. , Kinneberg Kirsten R. C. , Juncosa-Melvin Natalia , Powell Heather M. , Rao Marepalli , Boyce Steven T. , Butler David L.
Published: March 2014

Tissue engineering offers an attractive alternative to direct repair or reconstruction of soft tissue injuries. Tissue engineered constructs containing mesenchymal stem cells (MSCs) seeded in commercially available type I collagen sponges (P1076, Kensey Nash Corporation, Exton, PA) are currently being used within our laboratory to repair tendon injuries in rabbit models [1]. When introduced into the wound site, mechanically stimulated stem cell-collagen sponge constructs exhibit 50% greater maximum force and stiffness at 12 weeks compared to values for static controls [1]. However, these constructs often lack the maximum force sufficient to resist the peak in vivo forces acting on the repair site [2, 3]. Insufficient repair biomechanics can be attributed to the poor initial mechanical resistance provided by the collagen sponges to replace the function of the lost tendon before its degradation and replacement with new extracellular matrix. This current study seeks to identify a biologically-derived scaffold with improved mechanical integrity that could be used in stem cell-based tissue engineered constructs for tendon repair.
Measurement of Endovascular Stent Mechanical Properties
Authors: Johnston Clifton R. , Flewitt Jacqueline , Moore Randy , Thornton Gail M. , Dobson Gary
Published: March 2014

Endovascular stents are used to treat aneurysms, dissections and acute traumatic disruptions of the thoracic aorta. While stents are certainly a much less invasive treatment option, the behaviour of stents in the aorta is still not well understood. Six Gianturco stents were tested and found to exhibit nonlinear force-displacement relationships.
Morphological Variations of the Femural Head and Acetabulum: Femoro-Acetabular Impingement and Dysplasia as Possible Initiators of Cartilage Degeneration
Authors: Chegini Salman , Beck Martin , Ferguson Stephen J.
Published: March 2014

Morphological deviations of the acetabulum and femoral head may lead to hip dysplasia or femoro-acetabular impingement. Hip dysplasia and femoro-acetabular impingement (FAI), a pathological contact of the femoral neck with the acetabular rim during motion, have been proposed as potential factors in the development of hip osteoarthritis. The effects of these two kinds of disorders on the mechanical environment of the hip joint are analyzed and compared. One of the morphological measures of the acetabulum is the angle of Wiberg (CE angle), which defines dysplastic, normal or over-covered joints. The morphological measure defined for femoral head deviations in orthopedic literature is the alpha (α) angle [1]. A three-dimensional finite element model of the hip joint has been developed. Changing the CE angle, and alpha angle, normal and pathological joint geometries have been simulated with idealized CAD-generated models, and the results of finite element analyses have been compared for different load and motion cases. Internal contact pressures and cartilage stresses were calculated for each case. The results provide an understanding of normal and pathological joint function, as well as a scientific basis for the corrective operations which are already being utilized. Also, this study verifies femoro-acetabular impingement as one of the potential initiators of cartilage degeneration in the hip.
Temperature Measurement of Advanced Murine Atherosclerotic Plaques
Authors: Gijsen Frank , Ten Have Anna , Wentzel Jolanda , Van Der Steen Antonius
Published: March 2014

Ischaemic heart disease is most frequently caused by coronary atherosclerosis, of which the vulnerable plaque is one of the developmental stages. Rupture of a vulnerable plaque with superimposed thrombosis frequently leads to acute coronary syndromes. The major components of a vulnerable plaque are a lipid-rich, atheromatous core, and a thin fibrous cap with macrophage and macrophage infiltration (Schaar et al., 2004). After the first paper suggesting the possibility of thermographic detection of vulnerable plaques (Casscells et al., 1996), intracoronary thermography as a vulnerable plaque detection technique has been investigated. Increased metabolic activity of macrophages is suggested as the main reasons for the increased temperatures (ten Have et al., 2005).
Stability of Stepping Movements in the Frontal Plain: A Biomechanical Model
Authors: Karg Sonja A.
Published: March 2014

Walking is a complex task influenced by many factors. It is still not well understood how single parts as mechanics, sensor feedback and according control components are integrated to the very robust and adaptive task ‘walking’. So one possible way to address this task is to look at single components, as passive mechanics, and analyze their abilities for walking [1,2]. Or rhythmic movement mechanisms in vertebrates are analyzed, like central pattern generator mechanisms, to produce muscle activation patterns [3]. The combination of mechanics and rhythmic actuation leads to more robust walkers [4]. In the following a new biomechanical model for stepping movements in the frontal plain is introduced. This model bases on passive dynamics actuated by a neural oscillator network. It concentrates on low level generation of basic movement patterns which allow different stepping tasks as stepping in place, stepping up and down or stepping to the side. For the case stepping in place, it is shown that there exist periodic movements which are stable in the sense of a limit cycle, though the movement is varied in frequency and amplitude.
Strain Distribution Over Plaques in Human Coronary Arteries Relates to Shear Stress
Authors: Gijsen Frank J. H. , Wentzel Jolanda J. , Schuurbiers Johan C. H. , van der Steen Antonius F. W. , Serruys Patrick W.
Published: March 2014

It is well established that atherosclerotic plaques generally develop in low shear stress regions, including curved arterial segments and bifurcations. Once these plaques intrude into the lumen, the shear stress they are exposed to alters with hitherto unknown consequences. We hypothesize that in the more advanced stages of the disease, shear stress has an important impact on plaque composition in such a way that high shear stress enhances plaque vulnerability through its biological impact on the endothelium. We investigated this hypothesis by studying the relationship between shear stress and strain, a marker for plaque composition, in human coronary arteries.
A New Non-Invasive Method for Assessing the Intrinsic Active Strength of Human Left Ventricular Tissue
Authors: Claessens Tom E. , Rietzschel Ernst R. , De Buyzere Marc L. , De Bacquer Dirk , De Backer Guy , Gillebert Thierry C. , Van Ransbeeck Peter , Verdonck Pascal R. , Segers Patrick
Published: March 2014

The contractile state of the human left ventricle (LV) is often assessed by its end-systolic elastance (Ees) [1]. This index is calculated as the slope of the linear end-systolic pressure-volume relationship (ESPVR), which connects the upper left corners of pressure-volume loops obtained under various loading conditions (figure 1).
Evaluation of the Dynamics of a Bileaflet Heart Valve: Physical and Numerical Experiments
Authors: Conti Carlo , Morbiducci Umberto , Nobili Matteo , Passoni Giuseppe , Del Gaudio Costantino , Balducci Antonio , Grigioni Mauro , Redaelli Alberto
Published: March 2014

Clinical reports indicate that mechanical heart valves are still unable to eliminate problems mainly related to a non physiological fluid dynamics like thrombosis and coagulation complications [1]. Advanced experimental technique such as laser doppler anemometry (LDA) and particle image velocimetry (PIV), used to investigate the fluid dynamics of these devices, suffer from some intrinsic limitations (eg. access difficulties, light reflection, low resolution) [2]. In parallel with the increased performance at computing, the use of computational fluid dynamics has gained relevance as a powerful tool able to provide meaningful information of clinical and design aspects [3]. Key parameters in the assessment of blood damage potency (velocity patterns and turbulence, among them) are related to the behaviour of the valve in the flow field. The application of fluid structure interaction (FSI) models moves in the direction of greater accuracy in the reproduction of realistic flow condition in order to reach more in-depth insight into the hemodynamic of the virtual prototypes. The aim of this study is the investigation, in silico, of the bileaflet mechanical valve dynamics during the whole systolic phase. A 3D direct numerical simulation (DNS) was performed and an implicit fluid structure interaction model was used [4,5]. The results of the dynamics of the valve were validated with an experimental counterpart.
Three Dimensional Fluid Mechanics of the Sinus of Valsalva With a Bileaflet Mechanical Heart Valve
Authors: Yagi Takanobu , Ishikawa Daisuke , Sudo Hiroyuki , Wakasa Shotaro , Yang William , Iwasaki Kiyotaka , Umezu Mitsuo
Published: March 2014

Fluid mechanics of the sinus of Valsalva is an underlying basis of aortic surgery. Bellhouse and Talbot first reported the closure mechanism of the human aortic valve in vitro, and found that a vortex motion in the sinus facilitates the initial closing response, thus minimizing the regurgitation [1]. Since their early study, a variety of researches have been conducted to gain systematic understanding of the flow in the sinus of Valsalva. Phase-contrast MRI technique in vivo and computational fluid dynamics in vitro are modern flow diagnostic tools, both of which potentially has a capability of characterizing the three-dimensional flow. However, the flow in reality is strongly affected by the opening and closing dynamics of the aortic valve, and vice versa. This fluid-structure coupling has yet to be understood systematically. This study aims to clarify the mechanism of the coupling in vitro with a bileaflet mechanical heart valve by means of 2D PIV and 3D Stereo PIV technique [2]. An emphasis is placed on the geometrical effect of the sinus of Valsalva, where three geometries, namely the Anatomical, Neosinus and Straight models, are compared on the flow dynamics and valve closing dynamics.
Finite Element Stent Design: Parametric Modeling of Braided Wirestents Using PyFormex
Authors: De Beule Matthieu , Verhegghe Benedict , Mortier Peter , Van Loo Kim , Van Impe Rudy , Verdonck Pascal
Published: March 2014

Selfexpandable stent(graft)s are supporting tubular mesh devices used for the treatment of occlusive diseases and for the ‘exclusion’ of aneurysms. Wirestents are a class of flexible stents braided from a set of ultra fine wires and currently manufactured in a wide range of materials (e.g. phynox, nitinol, polymers) and compositions (single or multilayer). For design purposes as well as for studying the mechanical behavior of such a device by finite element simulations, a geometrical model using 1D elements will usually be appropriate. However, the computer model will contain a very large number of such elements, and building the geometrical model using classical CAD methodologies may become laborious. Consequently, literature dedicated to the mechanical behavior of braided wirestents is (very) scarce and the stent(graft)s are simplified as virtual single sheets [1].
Development of a New Device for In-Vitro Simulation of Upper Extremity Fractures
Authors: Sheridan Danna R. , Livesay Glen A. , Rogge Renee D.
Published: March 2014

Upper extremity fractures are common among all age groups, and distal radius fractures are the most prevalent type of fracture among individuals younger than 75 [1]. In 1999 the US Consumer Product Safety Commission estimated that approximately 117,000 emergency room visits were the result of a fall event at a playground [2]. The increased popularity of activities such as inline skating, snowboarding and skateboarding in the aging population has been correlated with increased numbers of upper extremity fractures, as these activities have a high fracture risk [3]. While personal protective equipment such as wrist guards and elbow pads may alter fracture risk, little is known about fall biomechanics and the effects of a fall arrest on the upper extremity.
Intra- and Extrafibrillar Fluid Exchange in the Disc
Authors: Schroeder Y. , Sivan S. , Wilson W. , Huyghe J. M. , Maroudas A. , Baaijens F. P. T.
Published: March 2014

The mechanical properties of the intervertebral disc are regulated by its biochemical composition. With ageing and degeneration the water content of the disc decreases which highly influences the mechanical properties. The disc is subjected to a combination of elastic, viscous and osmotic forces. Osmotic forces are shown to have a major impact on crack opening and propagation [1] and on cellular responses [2]. In particular, osmosis provides an understanding on why fissures in the degenerating disc are so poorly related to external mechanical load [3].
A Poroviscoelastic Model of Intraluminal Thrombus From Abdominal Aortic Aneurysms
Authors: Boschetti Federica , Di Martino Elena , Gioda Giancarlo
Published: March 2014

Computational models, developed to study abdominal aortic aneurysm (AAA) biomechanics, demonstrated that the presence of an intraluminal thrombus (ILT) can significantly alter the wall stress distribution in the degenerated vessel wall [1,2]. ILT is a soft hydrated tissue constituted of 90% of water. The solid porous matrix is made of a fibrin lattice entrapping solid aggregates, mostly platelets [3].. Although the ILT is subjected to compression in vivo, up to now ILT constitutive models have been based on parameters derived from tensile testing of ILT specimens [1]. The aim of this study was to define the biomechanical properties of ILT under compressive loads, using a combined experimental-numerical approach. ILT samples were tested for unconfined compression and permeation. A poroviscoelastic model was implemented to interpret the experimental data.
Effects of Gender on the Mechanical Properties of the Glenohumeral Capsule: Implications for Surgical Repair Techniques
Authors: Rainis Eric J. , Voycheck Carrie A. , Timcho Elizabeth A. , McMahon Patrick J. , Debski Richard E.
Published: March 2014

The glenohumeral joint is the most dislocated major joint in the body and the axillary pouch of the glenohumeral capsule is the primary stabilizer at the extreme ranges of external rotation. [1] Procedures to repair the capsule following dislocation result in 12–25% of patients still experiencing pain and instability. [2] Studies performing clinical exams have found inconsistent data on differences between males and females. Increased laxity in the glenohumeral joint of females has been found as well as overall hypermobility when compared to males. [3,4] However, others have found no differences in overall joint stiffness between genders. [5] These findings suggest that a difference in the mechanical properties might exist between genders. Therefore, the objective of this study was to determine the effects of gender on the mechanical properties of the axillary pouch during tensile loading. A combined experimental and computational approach was used to evaluate the properties of the tissue. This data could potentially be utilized to improve surgical procedures and necessitate gender-specific repair techniques.
Determination of Diffuse Brain Injury Thresholds Using Retrospective Analysis
Authors: Fijalkowski Ronald J. , Stemper Brian D. , Pintar Frank A. , Yoganandan Narayan , Gennarelli Thomas A.
Published: March 2014

Diffuse brain injury (DBI) severity can be clinically diagnosed as concussion or diffuse axonal injury (DAI). Concussion the least severe DBI, is associated with neurological deficit limited to disorientation and unconsciousness lasting minutes to hours [1–4]. In contrast, DAI, a severe injury, commonly results in death or permanent vegetation [1]. It is generally accepted that injury severity is modulated by increased mechanical measures such as rotational acceleration and velocity [5–11].
Magnetic Vascular Positioner for Automatic Coronary Artery Bypass Grafting Does Not Significantly Increase the Risk of Failure Related to Local Fluid Dynamics: A Numeric Study
Authors: Morbiducci Umberto , Ponzini Raffaele , Nobili Matteo , Redaelli Alberto
Published: March 2014

Anastomotic devices have been recently introduced in cardiac surgery, in order to make the anastomosis procedure more quick, automatic and efficient. The Ventrica magnetic vascular positioner (MVP) constitutes an attractive anastomotic option that significantly shortens the ischemic time when creating the coronary anastomosis on the beating heart [1]. However, the implantation of the MVP connector modifies the graft configuration, consistently affecting the hemodynamics usually found in the traditional anastomosis. As local fluid dynamics could play a significant role on the onset of vessels’ wall pathologies, in this study a computational approach was designed to investigate the flow patterns in presence of the MVP. To do this, a model of standard hand-sewn anastomosis and a model of automated anastomosis were constructed, and CFD was used to simulate realistic graft hemodynamics. Synthetic analytical methods were calculated and compared for the quantitative assessment of the role played by the fluid dynamics in the activation of mechanotransduction pathways at the vessel wall, i.e., time-averaged wall shear stress (TAWSS), oscillating shear index (OSI) [2], and the very recent helical flow index HFI [3, 4]. This allowed to evaluate if the use of the MVP design increases the risks of failure related to the local bypass fluid dynamics.
Dynamics of Arterial Remodeling in Response to a Sustained Step Change in Blood Flow Using a Constituent-Based Model
Authors: Tsamis Alkiviadis , Stergiopulos Nikos
Published: March 2014

The arterial wall undergoes substantial remodeling whenever the local blood flow changes for more than a few days [1]. An increase in flow causes an increase in inner radius, which occurs in two phases and tends to restore the baseline levels of intimal shear stress [2]. Firstly, an acute dilation of the artery occurs due to relaxation of vascular smooth muscle (VSM) cells [3]. Secondly, a long-term media reconstruction takes place, during which VSM cells migrate and proliferate circumferentially causing an increase in undeformed lumen. Moreover, arterial wall thickens to restore the altered wall stress [4].
Non Invasive Measurement of Blood Flow in the Human Lower Extremity
Authors: Zhou Hehe , Novotny John E. , Wang Liyun
Published: March 2014

Stress fracture in lower extremities occurs commonly among military recruits and athletes during intensive physical training. This injury has a marked impact on the health of military personnel and imposes a significant financial burden [1]. Despites advances in stress fracture studies, its pathogeneses remains poorly understood and early diagnostic tools are lacking. Focal ischemia is a potential initiator of site-specific bone remodeling and may cause stress fractures in human lower extremity [2, 3]. We hypothesize that intensive repetitive loading impairs intramedullary blood flow due to pressurization of the bone marrow cavity, leading to focal ischemia and eventual development of stress fractures. To begin to test our hypothesis, we developed and validated a quantitative, non-invasive method to measure blood flow in vivo. The approach was based on Cine Phase Contrast MRI (CPC-MRI), a dynamic motion measurement and visualization modality that was originally designed for cardiovascular studies. By measuring the phase shift that is induced by pulsatile blood flows in the magnetic resonance signal, cross-sectional images and velocity maps are acquired of the moving fluid. This technique has been adapted to study blood flows in skeletal muscles [4], intracranial flows [5], and muscle mechanics and joint kinematics [6]]. We first performed a flow phantom study to validate the reliability and accuracy of CPC-MRI in measuring flow velocity. We then quantified the effects of brief exercise on blood flows in the lower extremities of human subjects. These non-invasive measurements will help us better understand the interplay between vasculature and skeletal system in various physiological and pathological conditions.
Simulation-Guided Stimulation for Paretic Ankle Muscles During Stroke Gait
Authors: Higginson J. , Kesar T. , Perumal R. , Binder-Macleod S.
Published: March 2014

Stroke is the leading cause of long-term adult disability in the U.S. Neuronal damage in the brain results in impaired muscle coordination which induces asymmetric and abnormal walking patterns. Muscle-actuated forward dynamic simulation of walking patterns of healthy young adults has elucidated unique and synergistic roles of the uniarticular and biarticular plantarflexors. Neptune and colleagues (2001) reported that soleus delivers energy to the trunk, gastrocnemius accelerates the leg forward, and both contribute significantly to vertical support of the center of mass [1]. In a simulation of post-stroke hemiparetic gait, Higginson et al. (2006) observed that non-paretic muscles mimicked the function of healthy muscles, while paretic ankle plantarflexor function was limited and required supplemental effort by hip and knee extensors [2].
Virtual Assessment of the Performance of an Inhalation Drug Delivery Device
Authors: Dufour Françoise , Davies Gavin
Published: March 2014

Inhalation therapies are gaining popularity for both respiratory and non-respiratory therapies. However the challenge remains to achieve optimal drug delivery because of the complex interaction between inhaler devices, drug formulations along with patients’ coordination and physiology. In order to lower R&D costs and efforts, and understand better the mechanics of pharmaceutical aerosols, system designers are looking for comprehensive tools enabling them to reproduce virtual inhalation processes. Computational fluid dynamics (CFD) techniques represent a non-invasive way of predicting the fate of inhaled medication from oral or nasal delivery devices. The object of this work is to apply CFD methodology to model the full inhalation mechanism, from the drug dispersion inside the device and delivery to the patient, to its journey within the respiratory tract.
A Molecular Modelling Approach for Designing Bioartificial Membranes for Clinical Use With Tailored Transport Properties
Authors: Ionita Mariana , Gautieri Alfonso , Votta Emiliano , Redaelli Alberto
Published: March 2014

There has been a demand for hemodialysis membranes with better biocompatibility, the use of which would reduce the incidence of complications in patients who have been under long hemodialysis treatment. Recently, highly biocompatible membranes have been obtained by blending synthetic and polymers [1]. Specifically, poly(vinyl-alcohol) (PVA) and poly(acrylic acid) (PAA) have been combined with chitosan (Chi) and dextran (Dex) to create a biomaterials with excellent biocompatibility and mechanical properties. In this work we present a computational method based on molecular mechanics (MM) and dynamics (MD) techniques have been combined with an experimental studies, with the aim of designing and forecasting the permeability and diffusion properties of these membranes to small molecules, as a function of their composition.
Left Ventricular Assist Device Evaluation With a Model-Controlled Mock Circulation
Authors: Vaes Mark , Rutten Marcel , van de Molengraft René , van de Vosse Frans
Published: March 2014

Left-ventricular assist devices (LVADs) have evolved from being a bridge to total heart transplant to forming a bridge to recovery of the heart. With this development, the process of weaning has become more important, and consequently, the operation and control of the LVADs during this process is more important as well. To evaluate the function and the assist properties of LVADs, a mock circulation, featuring the properties of the (diseased) heart and the systemic circulation may prove to be a valuable tool.
Effect of Parenchymal Tethering on the Steady Propagation of a Liquid Plug in a Flexible Airway Model
Authors: Fujioka Hideki , Halpern David , Grotberg James B.
Published: March 2014

Surface tension on an air-liquid interface induces liquid flows, which may cause the lung’s airways to close due to the formation of a liquid plug as a result of drainage of the liquid lining coating the airways. Formation of the plug occurs more frequently when lung-surfactant availability is reduced. [1] Mechanical stresses due to fluid motion cause pulmonary epithelial cells to be damaged. [2, 3] Our previous studies for plug propagation in a rigid wall channel show that mechanical stresses are significantly large in the front transition region of the plug compared to the rear transition region. [7, 8] Pulmonary airways are flexible tubes which are surrounded by elastic parenchyma. In this study, the steady propagation of a liquid plug in a flexible tube is investigated numerically and mechanical stresses acting on the epithelial cells are estimated.