bluuebunny/crossref_metadata_2025 huggingface dataset:
Collagen Fiber Re-Alignment and Mechanical Properties in a Mouse Supraspinatus Tendon Model: Examining Changes With Age and Location
Authors: Miller Kristin S. , Connizzo Brianne K. , Feeney Elizabeth , Soslowsky Louis J.
Published: July 2013

One postulated mechanism of tendon structural response to mechanical load is collagen fiber re-alignment. Recently, where collagen fiber re-alignment occurs during a tensile mechanical test has been shown to vary by tendon age and location in a postnatal developmental mouse supraspinatus tendon (SST) model [1]. It is thought that as the tendon matures and its collagen fibril network, collagen cross-links and collagen-matrix interactions develop, its ability to respond quickly to mechanical stimuli hastens [1]. Additionally, the insertion site and midsubstance of postnatal SST may develop differently and at different rates, providing a potential explanation for differences in fiber re-alignment behaviors at the insertion site and midsubstance at postnatal developmental time points [1]. However, collagen fiber re-alignment behavior, in response to mechanical load at a mature age and in comparison to developmental ages, have not been examined. Therefore, the objectives of this study are to locally measure: 1) fiber re-alignment during preconditioning and tensile mechanical testing and 2) to compare local differences in collagen fiber alignment and corresponding mechanical properties to address tissue response to mechanical load in the mature and postnatal developmental mouse SST. We hypothesize that 1) 90 day tendons will demonstrate the largest shift in fiber re-alignment during preconditioning, but will also re-align during the toe- and linear-regions. Additionally, we hypothesize that 2) mechanical properties and initial collagen fiber alignment will be greater in the midsubstance of the tendon compared to the tendon-to-bone insertion site at 90 days, 3) that mechanical properties will increase with age, and that 4) collagen fiber organization at the insertion site will decrease with age.
Biomechanical Effect of Annular Tears in Healthy and Degenerated Lumbar Discs
Authors: Natarajan Raghu N. , An Howard S. , Andersson Gunnar B. J.
Published: July 2013

Structural alterations in the disc are accompanied by changes in disc tissue structure and composition during degeneration processes. As the lumbar disc degenerates, the disc height decreases. At the same time due to the development of fissures and cracks in the annulus, its material behavior changes. The degeneration process also includes cleft formation in the nucleus and reduction in water content in the nucleus and annulus. Porosity and drained modulus of the disc tissues are also affected by disc degeneration. The clear demarcation between nucleus and surrounding annulus slowly disappear as the disc degeneration progresses thus increasing the annulus volume while reducing the nucleus volume. Both in-vitro and finite element studies exist in literature which deals with the biomechanical effect of disc degeneration. The changes in biomechanical behavior due to degeneration are a combined effect of change in geometrical parameters of the disc, change in material characteristics of the disc components and presence of annular tears. It is not known how much of the change in disc biomechanics is due to change in disc tissue composition and due to additional tears present within the degenerated disc. The current study is thus related to the effect of such progressive changes on lumbar disc biomechanics.
Development of a Numerical Model for Micro-Scale Blood Flow Simulation Using GPGPU
Authors: Takeishi Naoki , Imai Yohsuke , Nakaaki Keita , Ishikawa Takuji , Yamaguchi Takami
Published: July 2013

Computational fluid dynamics (CFD) study of the behavior of red blood cells (RBCs) in flow provides us informative insight into the mechanics of blood flow in microvessels. However, the size of computational domain is limited due to computational expense. Recently, we proposed a graphics processing unit (GPU) computing method for patient-specific pulmonary airflow simulations (Miki et al., in press). In this study, we extend this method to micro-scale blood flow simulations, where a lattice Boltzmann method (LBM) of fluid mechanics is coupled with a finite element method (FEM) of membrane mechanics by an immersed boundary method (IBM). We also present validation and performance of our method for micro-scale blood flow simulations.
CFD Challenge: Solutions Using Open Source Flow Solver Caffa3d.MBRi With Immersed Boundary Condition
Authors: Usera Gabriel , Mendina Mariana
Published: July 2013

Open source flow solver caffa3d.MBRi is applied in this work to solve the cases proposed in the SBC2012 CFD Challenge, offering an overall very cost effective solution. It is found that cycle-averaged pressure drops are well represented by correspoding stationary cases, while peak systole pressure drop values are widly overestimated by corresponding stationary cases.
Development of an In Vitro Cartilage Degradation Model to Emulate Early-Stage Osteoarthritis
Authors: Grenier Stephanie , Torzilli Peter A. , Bhargava Madhu
Published: July 2013

Osteoarthritis (OA) is a disease characterized by the degeneration of articular cartilage. Disease progression is associated with the irreversible cleavage of the collagen network, surface fibrillation and loss of proteoglycans from the extracellular matrix.1, 2 These matrix changes increase surface porosity and matrix permeability, which diminish the cartilage’s ability to resist joint compressive loading. In this study, we developed an in vitro degradation model to emulate the damage that occurs in early OA in order to study how damage affects the tissue’s biomechanical function.
Finite Element Modelling of In Vitro Articular Cartilage Wear in the Patellofemoral Joint
Authors: Li Lingmin , Patil Shantanu , Steklov Nick , Bae Won , D’Lima Darryl D. , Sah Robert L. , Fregly Benjamin J.
Published: July 2013

The mechanism by which altered knee joint motions and loads (e.g., following anterior cruciate ligament (ACL) injury) contribute to the development of knee osteoarthritis (OA) is not well understood. One mechanobiological hypothesis is that articular cartilage degradation is initiated when altered knee kinematics increase loading on certain regions of the articular surfaces and decrease loading on other regions [1]. If homeostatic loading conditions vary from region to region, then load changes induced by altered kinematics could initiate cartilage degradation in a site-specific manner. This hypothesis is attractive from a computational simulation perspective since it is based on mechanical factors that lend themselves well to physical modeling. If computational simulations could predict the knee OA development process, then they could potentially be used to facilitate the design of new or improved treatments for the disease.
Basic Principles of Translational Research
Authors: Rubinsky Boris
Published: July 2013

Translational research turns fundamental new science and innovations into a product that has value to the public. The process is difficult because it combines a variety of diverse disciplines and skills from basic science, clinical medicine, engineering, business, public health, laws and regulations. These areas are so wide apart that it is very difficult to combine. The author has engaged in translational research since the early 1980’s and will describe the processes, pitfalls and rewards through typical examples from his projects that include: development of imaging monitored cryosurgery from concept to treatment of hundreds of thousands of patients, transgenes in food engineering from basic science to a twenty year wait for FDA approval, microelectroporation from basic concept to incorporation of the technology by numerous companies and non-thermal irreversible electroporation from basic concept to current clinical use in over 50 hospitals and over thousand treated patients.
Which Muscles Power the Human Running Stride?
Authors: Dorn Tim W. , Lin Yi-Chung , Schache Anthony G. , Pandy Marcus G.
Published: July 2013

Running is a physically demanding activity that requires explosive delivery of muscle power to the ground during stance, and precise, yet rapid limb coordination during swing. In particular, as running speed increases, greater metabolic energy in the form of muscle mechanical work is required to power the motion of: i) the center-of-mass (i.e., external power); and ii) the individual limb segments (i.e., internal power) [1,2]. The purpose of this study was to quantify the contributions that individual muscles make to the external and internal power of the body across a range of running speeds so as to identify the key muscle groups in coordinating a full running stride.
Calculation of Carotid Artery Flow Rates Using Doppler Ultrasound: Implications of Velocity Profile Skewing
Authors: Mynard Jonathan P. , Steinman David A.
Published: July 2013

Doppler ultrasound (DUS) is a non-invasive means of obtaining patient-specific flow boundary conditions in computational modelling studies [1] or estimating volumetric flow in clinical studies [2, 3]. To convert velocity information to a flow waveform, three related assumptions are often applied, 1) that the peak velocity lies in the centre of a cylindrical vessel, 2) that a centrally-located sample volume will thus detect the peak velocity, and 3) that the velocity profile is fully-developed and axisymmetric, being well-approximated by a parabolic (Poiseuille) or Womersley profile. These assumptions may not always be valid, however, even for nominally straight vessels like the common carotid artery (CCA) [4, 5]. While one might expect that flow estimated from DUS would become increasingly inaccurate as the profile becomes less axisymmetric, the scale of such errors and their relation to the true profile shape have not been quantified for the CCA. Moreover, for a heavily skewed velocity profile, the peak velocity may not lie within the DUS sample volume, and hence the choice of sample volume or beam-vessel orientation may also affect the accuracy of flow calculations. In this study, we investigate these issues by performing an idealized virtual DUS on data from image-based computational models of the carotid bifurcation.
Change in Mechanical Response of Arterial Elastin due to Glycation
Authors: Stephen Beth , Good Theresa A. , Topoleski L. D. Timmie
Published: July 2013

Collagen and elastin are the primary load-bearing components of arteries. Elastin is a low strength, highly elastic, fibrous material and collagen is a stiffer material, generally present as wavy fibers when unstretched. Together, they account for the material response of arteries under tensile load. Arteries, and other soft tissues, exhibit a two-part material response to tensile load. There is an initial low stiffness response at low stretch followed by a high stiffness response at higher stretch. It has been proposed that the low stiffness response is dominated by the elastin in the material and the high stiffness response is dominated by collagen [1]. The elastin accounts for the initial low stiffness response of the material, until the wavy collagen fibers straighten and become engaged, at which point the material transitions to its higher stiffness response. It is important to understand the role of the individual collagen and elastin components and how they contribute to the overall mechanical response of the arteries. Further, it is important to understand how specific biochemical processes that occur with age and disease affect the mechanical response of the individual collagen and elastin components and consequently the overall mechanical response of the arteries. This knowledge will increase our understanding of arterial mechanical response and how this response changes arterial function in health and disease.
Effect of Severity of Rod Contour on Posterior Rod Failure in Setting of Lumbar Pedicle Subtraction Osteotomy (PSO): A Biomechanical Study
Authors: Tang Jessica A. , Leasure Jeremi M. , Buckley Jenni M. , Kondrashov Dimitriy , Ames Christopher P.
Published: July 2013

Pedicle subtraction osteotomy (PSO) is a powerful technique to correct flat back deformity in the lumbar spine. Because corrections as great as 30–40 degrees can be achieved with this technique, contouring of the fusion rods can be quite extreme in PSO constructs. Rod failure (Figure 1) during the late post-operative period (<1 year) has been reported clinically and is commonly associated with pseudoarthrosis. In fact, instrumentation failure following PSO occurs frequently enough that several studies have reported and investigated revision strategies.
Stiffness Dependent Separation of Cells in a Microfluidic Device
Authors: Wang Gonghao , Mao Wenbin , Henegar Caitlin , Alexeev Alexander , Sulchek Todd
Published: July 2013

Rapidly sorting and separating cells are critical for detecting diseases such as cancers and infections and can enable a great number of applications in bio-related science and technology. While a variety of techniques demonstrate separation by physical parameters such as size[1] and mass[2], inexpensive and easy to use methods are needed to separate cells by mechanical compliance. A number of pathophysiological states of individual cells result in drastic changes in stiffness in comparison with healthy counterparts. Mechanical stiffness has been utilized to identify abnormal cell populations in detecting cancer[3–5] and identifying infectious disease[4, 6]. Recently, microfluidic methods were developed to classify and enrich cell populations utilizing mechanical stiffness[7–9]. We demonstrate a new strategy to continuously and non-destructively separate cells into subpopulations of soft and stiff cells. In our microfluidic separation method, we employ a microchannel with the top wall decorated by a periodic array of rigid diagonal ridges (Fig. 1). The gap between the ridges and the bottom channel wall is smaller than the cell diameter, thus the cells are periodically compressed by the ridges. The difference in mechanical resistance to compression of cells gives rise to a stiffness-dependent force associated with cell passage through narrow constrictions formed by the consecutive channel ridges. This elastic force is directed normal to the compressive diagonal ridges and, therefore, deflects cells propelled by the flow in the lateral direction with a rate proportional to their compliance. In this paper, we employ this principle to separate modified lymphoblastic cells with dissimilar mechanical stiffness in high-throughput.
The Effect of Anterior Dislocation on the Mechanical Properties of the Inferior Glenohumeral Ligament
Authors: Browe Daniel P. , Rainis Carrie A. , McMahon Patrick J. , Debski Richard E.
Published: July 2013

The glenohumeral joint is the most frequently dislocated major joint in the body with about 2% of the population dislocating their shoulders between the ages of 18 and 70 [1]. Instability due to permanent deformation of the glenohumeral capsule is commonly associated with dislocation [2]. Current surgical repair techniques for shoulder dislocations typically consist of plication of the glenohumeral capsule, or folding the tissue over on itself, to reduce redundancy in the capsule and restore stability to the shoulder. Up to 25% of patients who undergo surgery for a shoulder dislocation still experience pain, instability, and recurrent dislocation after surgery [3]. It is hypothesized that the mechanical properties of the glenohumeral capsule change in response to dislocation. In addition, the magnitude and location of these changes may have implications for the ideal location and extent of plication. Therefore, the objective of this study was to quantify the mechanical properties of the axillary pouch of the glenohumeral capsule in tension and shear after anterior dislocation.
Effect of Age on Performance of Tasks With Spatial Conflict
Authors: Patterson Rita M. , Longnecker Robert , Collins DeRaan , Knebl Janice , Bugnariu Nicoleta
Published: July 2013

Attentional selection has an important adaptive role in individuals’ interactions with the environment. Orienting attention over a scene and selecting the object or location to attend to, is necessary for carrying out desired actions. The cognitive processes range from correctly perceiving and interpreting information from different body sensors to planning and coordinating the effectors to produce the desired movement1.
Contributions of Elastin to the Quasi-Static Tensile Mechanics of Medial Collateral Ligament
Authors: Henninger Heath B. , Underwood Clayton J. , Weiss Jeffrey A.
Published: July 2013

Elastin is a highly crosslinked, chemically stable protein that provides resilience to tissues, but its contribution to the mechanics of ligament is not fully understood. In highly extensible tissues like artery, heart valves and nuchal ligament that can consist of up to 75% elastin [8], disruption of the elastin network has been shown to decrease the stiffness and resilience in these tissues [2,10,11].
Impact Pressure Increases Permeability of Cultured Human Endothelial Cells
Authors: Nakadate H. , Akanuma S. , Aomura S. , Kakuta A.
Published: July 2013

Traumatic brain injury (TBI) is well known to trigger multiple brain parenchymal and vascular responses. The immediate and prolonged opening of blood-brain barrier (BBB) is a hallmark of TBI pathophysiology, and results in extravasation of blood components, including red blood cells, plasma proteins and water (vasogenic edema) [1]. On the other hand, Studies in impact biomechanics have demonstrated a number of brain injury mechanisms [2]. These mechanisms include positive pressures at the impact site, negative pressure at the site opposite of impact. Recently, Hardy et al. demonstrated the presences of transient pressure pulses with impact conditions. Coup pressures measured within a pressurized cadaver head after impact ranged from 34 to 160 kPa, and the contrecoup pressures ranged from −2 to −48 kPa [3]. Pamela et al. tested the effect of overpressure from positive pressure to negative pressure on astrocytes. Pressure wave generated by the barochamber, with high amplitude and short duration in the first pulse [4]. However, there is a lack of information with regards to the effect of impact pressure on endothelial cells in vitro, which are the components of BBB.
Pre-Strain and Integrity of Mineral Crystals in Human Cortical Bone Under Tensile and Compressive Loads
Authors: Wang Xiaodu , Giri Bijay , Almer Jonathan
Published: July 2013

In this study, the pre-strain status and structural integrity of mineral crystals in bone was investigated using synchrotron X-ray scattering techniques. By measuring the pre-strain status, the interaction of mineral crystals with the surrounding matrix was determined. In addition, the load-induced changes in the lattice integrity of mineral crystallites were assessed using the value of the full-width-at-half-magnitude (FWHM). With increasing load, it was observed that the pre-strain in mineral crystals was relaxed in both tension and compression, whereas the lattice integrity of mineral crystallites was sustained until the failure of bone irrespective of loading modes.
The Complementary Effect of Mechanical and Chemical Stimuli on the Neural Differentiation of Mesenchymal Stem Cells
Authors: Liu Chun , Baek Seungik , Chan Christina
Published: July 2013

Mesenchymal stem cells (MSCs), derived from bone marrow stroma, are a promising source for tissue repair and regeneration, due to their excellent abilities for proliferation and multipotent differentiation. While accumulated evidences during the past decade have shown that MSCs are able to differentiate into osteoblasts, chondrocytes, myoblasts and adipocytes, more recent research suggest their potential in neuronal differentiation [1]. Chemical stimuli, including growth factors, hormones, and other regulatory molecules, are used traditionally to direct MSC differentiation. Our group has previously shown that the intracellular second messenger, cAMP, is able to initiate early phase neuron-like morphology changes and late phase neural differentiation in MSCs [2]. Studies using chemical stimuli alone, however, have shown limited success in differentiating MSCs to mature neurons, thereby suggesting other factors are necessary for this process. In recent years, interest has grown on the impact of mechanical stimulation, such as stiffness, surface topography, and mechanical stretching, on cell fate decision [3].
Pure Moment Testing for Spinal Biomechanics Applications: Fixed Versus 3D Floating Ring Cable-Driven Test Designs
Authors: Tang Jessica A. , Scheer Justin K. , Ames Christopher P. , Buckley Jenni M.
Published: July 2013

For spine biomechanical tests, the cable-driven system in particular has been widely used to apply pure bending moments. The advantages to pure moment testing lie in its consistency as an accepted standard protocol across previous literature and its ability to ensure uniform loading across all levels of the spinal column. Of the methods used for pure moment testing, cable-driven set-ups are popular due to their low requirements and simple design. Crawford et al [1] were the first to employ this method, but prior work by our group indicated a discrepancy between applied and intended moment for this system in flexion-extension only [2]. We hypothesize that this discrepancy can be observed in other bending modes and minimized with a second-generation floating ring design to eliminate off-axis loads.
A Mathematical Model for Shear-Induced Platelet Activation in Response to Time Dependent Shear Stress Histories
Authors: Soares João S. , Sheriff Jawaad , Bluestein Danny
Published: July 2013

The advent of blood recirculating devices and cardiovascular implants (e.g. ventricular assist devices and prosthetic heart valves) has motivated research efforts towards a better understanding of blood damage, hemolysis, and chronic platelet activation that these devices induce. Because of the latter, patients with these classes of implants still develop thromboembolic complications that expose them to a greater risk of cardioembolic stroke and mandate life-long anticoagulant drug regimen with its inherent risks.
Microchamber System to Experiment Mechanotransduction in the Organ of Corti
Authors: Narr Paul , Ringo Alex , Marnell Daniel , Nam Jong-Hoon
Published: July 2013

The mammalian cochlea is an acoustic spectrum analyzer and pressure transducer with a remarkable operating range, both in frequency and amplitude (Fettiplace & Hackney, 2006). A young healthy human ear can capture sounds of 40 to 20,000 Hz in frequency and 20 μPa to 20 Pa (0 to 120 dB sound pressure level) in amplitude. In research on the cochlea, one of the most significant achievements in decades is the identification of the cochlear amplifier. Tiny acoustic vibrations are amplified in the organ of Corti (OC)—sensori-eptithelium in the cochlea. Mechano-transducer receptors in the OC, called the outer hair cells, have been identified as the cellular actuators that provide energy to boost small pressure waves. However, how the amplification is achieved is still unclear.
Measurement of Bond Strength of Direct Heat Tissue Fusion in Arteries
Authors: Cezo James D. , Ferguson Virginia L. , Taylor Kenneth D. , Rentschler Mark E.
Published: July 2013

Tissue fusion is a method of joining tissue using heat and pressure. Several surgical tool companies have developed devices which perform tissue fusion on blood vessels in order to perform ligation of the vessel [1]. The success or failure of these devices is contingent upon the strength of the bond it creates between opposing sides of the blood vessel lumen, yet little characterization has been done to measure the strength of this interface. Previous studies have examined the strength of tissue fusion using clinically relevant metrics such as burst pressure or tearing strength, but none have explored metrics more appropriate for determining the mechanics of the actual bond, such as peel strength or shear strength [2–3]. These clinical metrics are susceptible to large variations due to tissue composition and geometry. The goal of this study is to measure the bond’s modulus and strength using standard engineering methods. The motivation of the present work is to develop a method for quantitatively measuring the strength of the bond made during tissue fusion. This method can then be applied to quantify the strength of the fusion interface between arterial tissue using other devices and aid in future evaluation and development of tissue fusion devices to maximize the bond strength.
Surgical Variability of Resection Parameters During Total Knee Arthroplasty
Authors: Dai Yifei , Henderson Adam , Seebeck Joern , Bischoff Jeffrey E.
Published: July 2013

There is intrinsic surgical variability in the practice of total knee arthroplasty (TKA), and thus computational analyses of TKA should account for this variability to ensure clinical applicability and robustness of results. Statistical inputs within computational analyses have been used to assess the biomechanical characteristics of TKA implants [1], and such methodologies are promising when applied to morphological analysis of TKA in order to motivate component design, assess current designs, and improve the understanding of surgical outcomes. Analyses to date either directly use actual TKA component placement or bone resection data [2], or assume a single set of parameters for placement and resection across the entire specimen group that was investigated [3], and thus do not account for surgical variability. This could be due to a lack of available data to quantify clinical variability in TKA component placement.
Strains in Stratified Agarose Constructs as Determined by Displacement-Encoded MRI
Authors: Griebel Adam , van Donkelaar C. C. , Neu Corey P.
Published: July 2013

Osteoarthritis (OA) is a debilitating disease for which no satisfactory treatment exists. Tissue engineering-based strategies have shown considerable potential for repair. Agarose is frequently used as a scaffold material, as chondrocytes maintain their phenotype and cells remain responsive to mechanical stimuli. To improve the mechanical quality of tissue engineered cartilage, recent studies aimed to reproduce the depth-dependent structure of healthy cartilage. One approach to achieve this is by applying depth-dependent mechanical stimuli via cyclically sliding a glass cylinder over the cell-seeded agarose construct [1,2]. The different strains applied to the surface and the deeper regions are expected to induce stratified matrix synthesis and therefore stratified tissue stiffness. Consequently, with the same external stimuli, the internal strain distribution may alter with ongoing tissue development. Such effect is important to understand in order to optimize mechanical loading regimes for cartilage tissue engineering.
Stress Relaxation of Cartilage Under Simple Shear and Compression: Experiments and Finite Element Analyses
Authors: Chung Chen-Yuan , Motavalli Mostafa , Mansour Joseph M.
Published: July 2013

Articular cartilage is a hydrated connective tissue consisting of a relatively small number of chondrocytes surrounded by a saturated extracellular matrix comprised mainly of type-II collagen fibrils and proteoglycans. As a deformable fluid saturated material, cartilage is most often modeled using biphasic or poroelastic theories [1,2]. The ultimate goal of this work is to evaluate biomechanical properties of native and tissue engineered cartilage under combined compression and shear. The purpose of this investigation was to determine stress and deformation fields in cartilage under compression and simple shear and relate these to measured results.
A Continuous Shear Deflection Function for Articular Cartilage
Authors: Motavalli Mostafa , Chung Chen-Yuan , Schluchter Mark , Mansour Joseph M.
Published: July 2013

Articular cartilage (AC) covers the articulating bones within synovial joints. Mechanically, it provides a bearing surface with low friction and wear properties, and it lowers surface stress by deforming and increasing the contact area. Cartilage mechanics has received much attention, but until recently most investigations have focused on average properties of full thickness tissue. However, given depth dependent variations in composition and structure, there is a growing appreciation of the tissue’s inhomogeneity and its relationship to mechanical behavior [1–4]. Determining the depth-dependent mechanical properties plays an important role in understanding the relationship between function and structure of native, diseased and tissue-engineered cartilage.
A Polymer-Free Drug-Eluting Stent: In Vitro and In Vivo Analysis
Authors: Yazdani Saami K. , Cheng Qi , Dutta Debashis , Kolodgie Frank D. , Virmani Renu
Published: July 2013

Drug-eluting stents (DES) have significantly improved restenosis rates as compared to bare metal stents (BMS), however, an increased risk in late stent thrombosis (LST) has been observed due to delayed healing and incomplete endothelialization. These adverse events have been associated to the high level of anti-proliferative drugs eluted from 1st generation DES, as well as non-erodible polymers that remain intact. The purpose of this study was to fist determine optimal surface modification in vitro and to then assess trends in endothelial coverage and recovery of the modified non-polymeric DES in a rabbit iliac stent model.
In Vivo Imaging of Dynamic Shear Modulus of Rodent Mammary Tumors Using Ultrasound
Authors: Wang Yue , Insana Michael
Published: July 2013

Biomechanical properties of living tissue are very important in maintaining normal tissue function, cellular and extracellular structural integrity. Therefore, the quantitative determination of biomechanical properties of breast tissue, especially in vivo, serves an important role in clinical diagnosis.
Assessing the Accuracy of Non-Invasive Measuring Methods of Pulse Wave Velocity: An Analysis Based on Fluid-Structure Interaction Simulations in the Carotid Artery
Authors: Swillens Abigail , Taelman Liesbeth , Degroote Joris , Vierendeels Jan , Segers Patrick
Published: July 2013

Pulse wave velocity (PWV) is the propagation speed of pressure and flow waves in the arterial system induced by the contracting left ventricle. PWV is a measure of arterial stiffness, and has been shown to predict cardiovascular events. In a clinical setting, PWV is usually associated with carotid-femoral PWV, reflecting the propagation speed over the aorta. It is, however, also possible to assess local PWV at a given measuring location, which reflects the stiffness of the artery under investigation at that particular location. When locally assessing PWV, single-location techniques are commonly used, which rely on the fact that in uniform elastic tubes, the relationship between a change in pressure (dP) and velocity (dU) is constant in the absence of wave reflections. As such, when plotting the pressure P as a function of the velocity U in an artery, a PU-loop is obtained, where reflection-free instants emerge as a straight line (typically during early systole), with a slope given by ρPWV (ρ = blood density). The original method relied on pressure and velocity data (PU-method), but alternative methods have been introduced based on cross-sectional area (A) and flow (Q) (QA-method), or diameter (D) and velocity (U) (ln(D)U-method).
Comparison of Different Radial Basis Functions in Developing Subject-Specific Infant Head Finite Element Models for Injury Biomechanics Study
Authors: Li Zhigang , Hu Jingwen , Zhang Jinhuan
Published: July 2013

Developing a subject-specific finite element (FE) model, especially with only high quality hexahedral solid elements and quadrilateral shell elements, is very time-consuming. Recently, template-based mesh morphing method has become popular to construct subject-specific FE models, in which a baseline FE mesh can be morphed into a FE model with subject-specific geometry. Because the mesh morphing algorithm could be programmed and run automatically, it is a very promising method for future applications of subject-specific FE models in injury biomechanics studies. Radial Basis Function (RBF) as a powerful spatial interpolation method has already been used as a mesh morphing method (1). The types of RBFs can affect the morphed mesh quality and geometry accuracy in the RBF method. However, to date, no previous study has tried to compare the differences generated by different RBFs. Therefore, in this study, different RBFs were used to morph a baseline infant head FE model into 10 different subject-specific infant head FE models based on CT images from 10 children aged from 0 to 3 months. The mesh quality and geometry accuracy of the subject-specific models generated by different RBFs were compared using statistic analysis.
Hemodynamic Environment and Occlusion Time of Tandem Intracranial Aneurysms Treated With Flow Diverters
Authors: Mut Fernando , Scrivano Esteban , Lylyk Pedro , Cebral Juan R.
Published: July 2013

The use of flow diverting devices to treat complex intracranial aneurysms difficult to treat with coils and clips has recently received substantial attention. Initial experiences with increasing numbers of patients have been carried out with promising results [1]. However, it is still difficult to predict the outcome and/or the aneurysm occlusion time after treatment with flow diverters. The purpose of this work was to relate the hemodynamic environment created immediately after treatment and the occlusion period of a pair of tandem aneurysms.
Airway Inflammation Induced by Mechanical Ventilation Through Multiscale Modeling
Authors: Pidaparti Ramana M. , Ward Kevin R.
Published: July 2013

Inflammation has been recognized as a major integral component for most of the acute and chronic diseases. Inflammation can be initiated within the body as an innate process or by external factors such as infections and trauma. Inflammation is a complex and dynamic process, and involves nonlinearity and stochasticity. Without the inflammation, the harmful stimuli cannot be removed and the healing process cannot occur. However, an over-expression or under-expression of inflammatory responses can lead to severe consequences, such as Multiple Organ Dysfunction Syndrome (MODS), which is characterized by sequential organ failure. Acute lung injury (ALI) is typically one of the first manifestation of MODS. It can be triggered by external stimuli such as pathogens or from inflammatory mediators produced from various other processes ranging from other damaged organs or to blood transfusions to even the biomechanical forces of mechanical ventilation itself.
An Implantable Device Design Concept for Ocular Drug Delivery
Authors: Lee Jae-Hwan , Pidaparti Ramana M.
Published: July 2013

New drugs for curing eye diseases have been developing for a decade and are very unique for each eye diseases such as glaucoma, cataracts, and age-related macular degeneration (AMD). It is estimated that 1.6 million adults in the US over the age of 50 and above suffer from age-related macular degeneration and about 200,000 cases are diagnosed annually. Worldwide, about 500,000 cases are diagnosed annually [1]. Drugs currently utilized for AMD are delivered via repeated intravitreal injections of the drug into the eye. Risks of repeated intravitreal injections can include intraocular infections (endophthalmitis), intraocular hemorrhage, and retinal detachment. Also, reducing the frequency of dosing will clearly benefit the patient by reducing the need for risky intravitreal injections and improving the pharmacokinetics of the drug in the eye. The eye disease of posterior segment (Dry and Wet) has limits to deliver the drug to retina region using typical eye drop. The drug injection using a needle with syringe can deliver but it barely provide right amount of doses, or over doses that may cause more severe problem such as swelling, fatigue, and damaging photoreceptor molecules. Furthermore, most drugs run away in a month so that repeated injection is necessary. Developing an implantable drug delivery device will help reduce the costs and risks associated with frequent injections and facilitate delivering the drug in a controlled manner and in the required amounts, and improve therapeutic efficacy and safety of drugs. This study focuses on the design, simulation and development of the implantable ocular drug delivery device.
Use of Regional Mechanical Properties of Abdominal Aortic Aneurysms to Advance Finite Element Modeling of Rupture Risk
Authors: Tierney Áine P. , Callanan Anthony , McGloughlin Timothy M.
Published: July 2013

AAA rupture represents a catastrophic failure of the degenerated aortic tissue when the aneurysm wall can no longer withstand the stresses on it. Understanding the stress distribution in the aneurysm, along with its material properties, is an essential step toward predicting the rupture of an AAA. FE analysis is a computer-based method of solving complex structural problems for which the stress distribution can be easily studied. In analyzing AAA behavior with FE models, realistic aortic anatomies with patient-specific physiological and mechanical properties have been used in recent years. Data for these anatomies have typically come from computed tomography (CT) scans.
The Effect of Pulmonary Hypertension on Tricuspid Valve Coaptation in Normal and Pathologic Valve Geometries: An In Vitro Study
Authors: Dolensky Joseph R. , Casa Lauren D. C. , Yoganathan Ajit P.
Published: July 2013

Pulmonary hypertension (PHTN) is a pathological condition defined as a mean pulmonary artery pressure (mPAP) greater than 25 mmHg. PHTN can result from a number of lung and heart pathologies, including abnormalities of the pulmonary vasculature, left heart disease, chronic lung disease, and chronic thrombotic disease [1]. Regardless of the cause, the increased afterload on the right heart results in right ventricle (RV) hypertrophy and dilatation and tricuspid regurgitation (TR) [2]. RV dilatation is thought to result in the displacement of the tricuspid valve (TV) papillary muscles (PM) and dilatation of the TV annulus, negatively impacting TV function.
Thrombogenicity Comparison of Axial Ventricular Assist Devices by DTE Methodology: MicroMed HeartAssist 5 and Thoratec Heartmate II
Authors: Chiu Wei-Che , Xenos Michalis , Alemu Yared , Girdhar Gaurav , Lynch Bryan , Jesty Jolyon , Slepian Marvin , Einav Shmuel , Bluestein Danny
Published: July 2013

Mechanical circulatory devices, such as ventricular assist devices (VADs), have become the life-saving alternative for the patients who suffered from severe heart failure (1). These devices were utilized as the bridge-transplant devices; however, due to the fast growing population of cardiovascular diseases and the eligible organ donations are very limited, these devices have been considered for the application of life-long implantation. The continuous-flow VADs offer better hemodynamic performance than the first generations pulsatile flow VADs, its compact design offers surgical advantage; however, due to the non-physiological blood flow past constricted geometrics where platelets are exposed to elevated wall shear stress (2), VADs are burdened with high incidence of thromboembolic events, mandating anticoagulation therapies for its recipients (3).
A Finite Element Model for Estimating Axonal Damage in Traumatic Brain Injury
Authors: Wright Rika M. , Ramesh K. T.
Published: July 2013

There has been an ongoing effort to reduce the occurrence of sports-related traumatic brain injury. These injuries are caused by an impact to the head and often lead to the damage of neural axons in the brain. This type of damage is classified as diffuse axonal injury (DAI) or traumatic axonal injury (TAI) [1]. One of the difficulties in studying the progression of axonal injury is that the structural signature of DAI cannot be readily visualized with conventional medical imaging modalities since the damage occurs at the cellular level [2]. This also makes the injury difficult to diagnose. Many researchers have turned to finite element (FE) models to study the development of diffuse axonal injury. FE models provide a means for observing the mechanical process of injury development from the loads to the head at the macroscale to the damage that results at the cellular level. However, for a finite element model to be a viable tool for studying DAI, the model must be able to accurately represent the behavior of the brain tissue, and it must be able to accurately predict injury. In this work, we address both of these issues in an effort to improve the material models and injury criteria used in current FE models of TBI. We represent the white matter with an anisotropic, hyper-viscoelastic constitutive model, incorporate the microstructure of the white matter through the use of diffusion tensor imaging (DTI), and estimate injury using an axonal strain injury (ASI) criterion (Figure 1). We also develop a novel method to quantify the degree of axonal damage in the fiber tracts of the brain.
A Microfabricated Platform to Measure and Manipulate the Mechanics of Engineered Cardiac Microtissues
Authors: Boudou Thomas , Legant Wesley R. , Mu Anbin , Borochin Michael A. , Thavandiran Nimalan , Radisic Milica , Zandstra Peter W. , Epstein Jonathan A. , Margulies Kenneth B. , Chen Christopher S.
Published: July 2013

Cardiac tissue engineering is currently limited by the incapacity to test the wide range of parameters that might impact the engineered tissue in a high throughput and combinatorial manner. Here we used microelectromechanical systems (MEMS) technology to generate arrays of cardiac microtissues (CMTs) embedded within three-dimensional micropatterned matrices. Microcantilevers constrain CMT contraction and report generated forces. We demonstrate the ability to routinely produce ∼200 CMTs per million cardiac cells whose spontaneous contraction frequency, duration, and forces can be tracked. Independently varying the mechanical stiffness of the cantilevers and collagen matrix revealed that the CMT contractility increased with boundary or matrix rigidity. We also show that the combination of electrical stimulation and auxotonic load strongly improve both the structure and the function of the CMTs. Finally, we demonstrate the suitability of our technique for high throughput monitoring of drug-induced changes in spontaneous frequency or contractility in CMTs.
Polyelectrolyte Multilayer Nanoshells With Hydrophobic Nanodomains for Delivery of Paclitaxel
Authors: Boudou Thomas , Kharkar Prathamesh , Jing Jing , Guillot Raphael , Pignot-Paintrand Isabelle , Auzely-Velty Rachel , Picart Catherine
Published: July 2013

Delivery of poorly water-soluble drug molecules, which constitute a large part of commercially available drugs, is a major challenge. Several drugs including paclitaxel (PTX) that are used for cancer treatment are hydrophobic and need to be delivered using an appropriate carrier. Here we engineered PTX-loaded polyelectrolyte films and microcapsules by pre-complexing PTX with alkylamino hydrazide derivatives of HA, and subsequent assembly with either poly(L-lysine) (PLL) or quaternized chitosan (QCHI) as polycations. The PTX loading capacity of the films was found to be dependent on the number of layers in the films as well as on the initial concentration of PTX pre-complexed to hydrophobic HA, with a loading capacity up to 5000-fold the initial PTX concentration. The films were stable in physiological medium and were degraded in the presence of hyaluronidase. The PTX-loaded microcapsules were found to decrease the viability and proliferation of MDA-MB-231 breast cancer cells, while unloaded microcapsules did not impact cell viability. All together, our results highlight the potential of hyaluronan-based assemblies for hydrophobic drug delivery.
Encapsulation of Mammalian Cells in Nanoporous Silica Gels: Interactions at the Biointerface
Authors: Reátegui Eduardo , Kasinkas Lisa , Aksan Alptekin
Published: July 2013

Encapsulation of cells in nanoporous silica gels has shown great potential for the development of biotechnology applications such as biosensors, biocatalysis, bioremediation, energy conversion systems, and cellular therapies [1]. However, even though the inorganic matrix confers improved mechanical properties, chemical and thermal stability, and is resistant to microbial attacks, long-term viability and function after encapsulation remains as one of the principal setbacks of this technology [2].
Development of a Novel Magnetic-Driven Micropillar Substrate for Mechanical Stimulation at Individual Focal Adhesions of Cells
Authors: Nagayama Kazuaki , Hamada Yasuhiro , Inoue Takuya , Matsumoto Takeo
Published: July 2013

Traction force generated at focal adhesions (FAs) of cells plays an essential role in regulating various cellular functions. The force can be measured by plating cells on a flexible substrate to observe local displacement of the substrate caused by the forces (1–100 nN) [1]. Approaches employing this method include using microfabricated arrays of poly(dimethylsiloxane) (PDMS) micropillars that bend by cellular traction forces [2]. If you could apply forces to individual FAs independently by actively moving micropillars, it should become a powerful tool to delineate the cellular mechanotransduction mechanisms.
Varying Degrees of Nonlinear Mechanical Behavior Arising From Geometric Differences of Urogynecological Meshes
Authors: Feola Andrew , Pal Siladitya , Moalli Pamela , Maiti Spandan , Abramowitch Steven
Published: July 2013

In the field of urogynecology, synthetic polypropylene (PP) meshes have seen an increase in use over the last decade. These devices are implanted in over 200,000 women annually and are designed to restore pelvic organ support for women suffering from pelvic organ prolapse (1). Because they are essentially modified abdominal hernia meshes, their use in the field urogynecology has undergone little oversight. With more patients experiencing morbidity, the FDA has released two Public Health Notifications in 2009 and 2011 informing the public about the potential complications associated with urogynecological mesh implantation.
A Computationally Efficient Muscle Model
Authors: Millard Matthew , Delp Scott
Published: July 2013

Modern biomechanical models often include many degrees of freedom, complex joint geometry, and hundreds of muscles [1]. Such complex models may provide realistic representations of musculoskeletal dynamics, but they require a great deal of time to simulate. The state equations of the muscles are frequently the stiffest numerical element in a biomechanical model and determine the simulation time. Here we introduce a muscle model that generates similar forces as a conventional muscle model, but requires fewer explicit integration steps.
The Relative Contributions of Muscle Deformation and Ischemia to Pressure Ulcer Development
Authors: Loerakker Sandra , Strijkers Gustav J. , Nicolay Klaas , Baaijens Frank P. T. , Bader Dan L. , Oomens Cees W. J.
Published: July 2013

Sustained mechanical loading of soft tissues covering bony prominences may lead to degeneration of skeletal muscle tissue. This can result in a condition termed deep tissue injury (DTI), a severe kind of pressure ulcer that initiates in deep tissue layers, and progresses towards the skin. Previously, we have provided evidence that in a controlled animal model, deformation is the main trigger for damage within a 2 h loading period [1,2]. Recently, we also showed that ischemia and reperfusion may contribute to the damage process during prolonged loading [3]. In the present study, we investigated the relative effects of deformation, ischemia, and reperfusion on the temporal and spatial damage process of skeletal muscle tissue during a 6 h period using magnetic resonance imaging (MRI) techniques.