bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of the In Vivo Forces on the Sternum in Pigs
Authors: Pai Shruti , Dunn Raymond M. , Pins George D. , Billiar Kristen L.
Published: March 2014

Approximately 15,000 Americans suffer complications associated with inadequate sternal fixation after open-heart surgery each year [1]. Although alternative fixation methods exist, limitations of current device evaluation systems have led to uncertainty about the relative increase in stability that these novel devices provide, thereby diminishing their widespread clinical use. Sternal closure techniques are typically evaluated in situ where estimated sternal forces (180–400N) are applied to an intact chest [2] or in vitro on isolated sternal models [3]. The mechanical stability afforded by each technique is quantified as the resultant separation along the bisected sternal midline. This displacement is assumed to reflect micro-motion that would occur at the wound site under physiological loading, a critical factor during bony healing [4]. However, the loading in these studies is hardly physiological; it is generally simplified to a single direction and applied quasistatically to only a few discrete locations along the sternum without regard for the in vivo distribution of forces. It is also unclear whether the transfer of loads from sternum to fixation device during in situ tests [5](cadavers) accurately reflects loading in vivo due to the potential effects of rigor mortis and/or embalming. To improve the accuracy of current in situ and in vitro sternal fixation test methods it is essential to advance our knowledge of in vivo dynamic multi-directional sternal loading.
Grasping Contact Analysis of Tissues With Semi-Cylindrical Teeth Grasper for Minimally Invasive Surgery Applications
Authors: Bonakdar Ali , Molavi Marjan , Dargahi Javad , Bhat Rama
Published: March 2014

This study presents both numerical and analytical methods to determine the contact pressure on the surface of tissues being grasped by an endoscopic grasper with semi-cylindrical teeth, in Minimally Invasive Surgery (MIS). It is highly important to avoid damage to the tissues during grasping and manipulation by endoscopes. Therefore, it is essential to determine the exact contact pressure on the surface of the tissue.
Accelerated Bone Growth Remotely Induced by Magnetic Fields and Smart Materials
Authors: Hart Stephen A. , Dapino Marcelo J.
Published: March 2014

Bone structure is exquisitely matched to its physical loading environment. From the cartilaginous skeletal framework formed in the embryo to the aging skeleton, bone architecture is directly related to function. Bone is a dynamic system, constantly remodeling itself by absorbing old tissue and forming new tissue. This capability allows bone architecture to become optimized to the loading environment. Julius Wolff [1] first postulated that bone structure adapts to changing stress environments in 1892. Exact understanding of the process of mechanotransduction, however, has remained elusive. In addition to normal remodeling, bone growth has been shown to occur along the diaphysis, or shaft portion, of long bones such as the femur when placed in dynamic bending. Bone in this region is dense and is known as cortical bone. A bending moment placed on a long bone will cause the bone to curve creating a region of tension on one side and a region of compression on the opposing side. As the bending moment is cycled, fluid within the bone will flow from the region of compression to the region of tension creating fluid shear on cell walls within the bone which promotes the anabolic response of growth [2]. Growth from such stimuli is thought to be mediated by fluid flow around quiescent bone cells, osteocytes, and their canalicular process coursing through the bone structure [3]. Growth in this manner is directed in a latitudinal direction creating a thicker and stronger diaphysis.
Measurement of Erythrocyte Motions in Microchannels by Using a Confocal Micro-PTV System
Authors: Lima Rui , Ishikawa Takuji , Takeda Motohiro , Tanaka Shuji , Imai Yo-suke , Tsubota Ken-ichi , Wada Shigeo , Yamaguchi Takami
Published: March 2014

Detailed knowledge on the motion of individual red blood cells (RBCs) flowing in microchannels is essential to provide a better understanding on the blood rheological properties and disorders in microvessels. Several studies on both individual and concentrated RBCs have already been performed in the past [1, 2]. However, all studies used conventional microscopes and also ghost cells to obtain visible trace RBCs through the microchannel. Recently, considerable progress in the development of confocal microscopy and consequent advantages of this microscope over the conventional microscopes have led to a new technique known as confocal micro-PIV [3, 4]. This technique combines the conventional PIV system with a spinning disk confocal microscope (SDCM). Due to its outstanding spatial filtering technique together with the multiple point light illumination system, this kind of microscope has the ability to obtain in-focus images with optical thickness less than 1 μm, a task extremely difficult to be achieved by using a conventional microscope.
Ischemic Factors and Deformation Influence Metabolism of Engineered Skeletal Muscle
Authors: Oomens Cees W. J. , Gawlitta Debby , Bouten Carlijn V. C. , Baaijens Frank P. T.
Published: March 2014

Tissue compression may induce collapse of blood vessels resulting in tissue ischemia (insufficient blood flow). In addition, cellular deformation due to tissue compression may initiate tissue degeneration. These are two of the hypotheses that have been proposed to explain the development of (deep) pressure ulcers. Skeletal muscle tissue, in particular, is susceptible to compression induced breakdown. A model system was developed to investigate the relative contributions of deformation and ischemic factors to compromising tissue viability or metabolism. A theoretical model, describing the relationship between glucose consumption, lactate production and cell death was developed.
Measurement of In-Vivo Pulmonary Vascular Impedance in Two Animal Models of Pulmonary Hypertension
Authors: Hunter Kendall S. , Lanning Craig J. , Albietz Joseph A. , Oka Masahiko , Fagan Karen A. , Stenmark Kurt R. , Shandas Robin
Published: March 2014

Pulmonary vascular input impedance has been increasingly promoted as an important diagnostic for pulmonary arterial hypertension (PAH) [1,2]. The gold-standard clinical diagnostic for the disease, pulmonary vascular resistance (PVR), quantifies only the mean resistance to flow but ignores the impact of vascular stiffness and flow pulsatility, which in PAH can represent up to 40% of the total load presented to the right ventricle. PVR has also been found to be only a moderate predictor of PAH outcomes [3]. The first of these deficiencies is not present in impedance; clinical studies have found the sum of its 1st and 2nd harmonic moduli to have good correlation (r2 = 0.812) with global pulmonary vascular stiffness (PVS) [2], a hemodynamically-measured quantifier of vascular stiffness. Additionally, the 0th harmonic modulus of impedance has excellent correlation to PVR (r2 = 0.974); thus, it also quantifies the resistive load. Moreover, because PVS has recently been found as a valuable determinant of mortality in PAH [4], we believe that impedance, as a combined measure of PVR and PVS, might be an excellent predictor of disease outcomes.
Mesenchymal Progenitor Cells Differentially Respond to Mechanical Stimulation: Morphology, Proliferation, Gene and Protein Expression
Authors: Maul Timothy M. , Chew Douglas W. , Nieponice Alejandro , Vorp David A.
Published: March 2014

Mechanical stimulation has been shown to regulate gene and protein expression in many cell types, including stem cells. Cyclic strain has been previously shown by our laboratory and others [1, 2] to regulate smooth muscle gene and protein expression in mesenchymal progenitor cells (MPCs). From these and other results [3], we hypothesize that the differentiated phenotype of MPCs may be controlled by the appropriate type, magnitude, and frequency of mechanical stimulation. We describe here the differential response of MPCs to three mechanical stimuli — cyclic strain, cyclic hydrostatic pressure, and laminar shear stress — over a range of magnitudes and frequencies that are consistent with the cardiovascular system.
Image- and Numerics-Based Analysis of Constitutive Properties of Cellular Structures
Authors: Gladilin Evgeny , Eils Roland
Published: March 2014

External forces, cell adhesion and soluble signaling molecules influence fundamental functions of cells like shape, migration, proliferation or differentiation. Thus, investigating how mechanical forces affect 3D cell structure and function is of crucial significance in order to gain a better understanding healthy and malignant cell behavior during embryogenesis, regeneration or malignancy [1]. Micromanipulation of cells in a controlled environment is a widely used approach for understanding cellular responses with respect to external mechanical forces. While experimental data provide optical information about the overall cell shape, the 3D deformation state of intracellular structures is not accessible by direct observations and measurements. However, the continuous description of the intracellular deformation state can be calculated as a numerical solution of the boundary value problem given by the partial differential equations of structural mechanics, including a set of canonic material constants (stiffness, compressibility), and the boundary conditions derived from time series of images, e.g. change of visible cell contours. The main idea of our approach is to reformulate the problem of finding optimal modeling parameters as an image registration problem. That is the optimal set of modeling parameters corresponds to the minimum of a suitable similarity measure between computationally predicted and experimentally observed deformations. In this article, we focus on the numerical analysis of uniaxial stretching of a rat embryonic fibroblast 52 (REF 52) based on a series of 2D images reflecting the successive alteration of cell contours during deformation. The goal of this study consists in finding an optimal set of material constants within a non-linear hyperelastic material law, which is able to reproduce results of experimental observations.
Transitional Stiffness Intramedullary Stems to Reduce Periprosthetic Pain
Authors: Crowninshield R. D. , Wentz D. , Paprosky W. , Rosenberg A. , Stoller A.
Published: March 2014

The intramedullary canal presence of a stemmed prosthetic component can be expected to change the distribution of stress from the joint loading to the adjacent skeleton. The reconstructed skeletal stiffening that results for relatively rigid prosthetic components can result in periprosthetic stress shielding. The abrupt change in reconstruction stiffness that can occur at the implant stem terminus can be associated with periprosthetic pain. A stem end “clothes pin” slot, intended to make a stem end more flexible, produces a substantially asymmetric and abrupt alteration of stem stiffness. The present work is directed to analyzing ways that the structural stiffness of the terminus region of a prosthetic stem can be controlled to provide a symmetrical transitional region of controllable load transfer to the surrounding bone. It is hypothesized that through implant design, prosthesis-to-bone interface pressure and periprosthetic bone stress levels at a prosthetic stem terminus can be reduced and that this will be associated with a reduced occurrence and severity of “end of stem pain” in a variety of prosthetic applications.
Development of Carbon Nanotube Field Emitters for X-Ray Source
Authors: Calderón-Colón Xiomara , Zhou Otto
Published: March 2014

Carbon Nanotubes (CNTs) have been shown excellent field emission emitters due to their unique properties. CNTs are a stable form of carbon; a graphite sheet rolls up forming a cylindrical shape with high aspect ratio, low turn-on field, high current density, high strength (1) and can generate quality x-ray radiation (2). These properties make carbon nanotubes very attractive for field emission applications. Field emission cathodes are the central part of field emission displays (FED) and carbon nanotubes field emission x-ray source. FED is a new flat panel display technology; this technology enables much thinner, lighter, and highest resolution displays than the cathode ray tubes (CRT). CNTs field emission x-ray source technology has applications in medical imaging and homeland security (2–7). The current thermionic cathodes have several disadvantages over CNT based field emission x-ray source such as slow response time, high power consumption, high operation temperature that reduces the lifetime of the x-ray tube (4) and large device size (3). Also CNT based field emission x-ray source offers improvement in high temporal resolution and capabilities for spatial and temporal modulation (7). CNT field emission x-ray source technology is available in single- and multi-beam imaging system. Multi-beam imaging system offers image of an object from multiple projection angles without mechanical motion (7).
The Role of IL-1 in Meniscal Tissue Breakdown Following Simulated Partial Meniscectomy
Authors: Zielinska B. , Gupta T. , Haut Donahue T. L.
Published: March 2014

In a healthy meniscus, the compressive strains are approximately 2–10%. [1] When 30% or more of the tissue is removed during partial meniscectomy, strains increase to approximately 18%. [1] We have previously shown that dynamic compressive strains of 20% to meniscal explants results in an increase in proteoglycan (PG) breakdown, nitric oxide (NO) production, metalloproteinases 1, 3, and 13 (MMP-1, MMP-3, and MMP-13) compared to 0, 5, and 10% compressive strain. [2,3,4] The objective of this study was to determine if interruption of the IL-1 pathway would alter this biochemical response to dynamic mechanical compression.
MRI Measurement of Surface Strain Due to Growth in the Developing Ferret Brain
Authors: Knutsen Andrew K. , Kroenke Christopher D. , Taber Larry A. , Neil Jeffrey J. , Bayly Philip V.
Published: March 2014

The human cerebral cortex undergoes folding from the 5th fetal month into the first post-natal year. Disturbances of folding have serious and lasting consequences, but the mechanism is not well understood. Van Essen [1] has hypothesized that axonal tension between strongly interconnected regions draws them together and induces outward folds. However, no direct measurements have confirmed this theory. Experimental data are needed, beginning with a quantitative description of the kinematics of cortical growth during folding.
A Study of Collagen Crimp Pattern in the Bovine Anterior and Posterior Medial Meniscal Horn Attachments
Authors: Villegas Diego , Dehlin William , Haut Donahue Tammy L.
Published: March 2014

Menisci are fibrocartilagenous structures located between the femoral condyles and tibial plateau that aid in joint lubrication and stability in the knee joint. Previous experimental and theoretical studies have shown that the meniscal horn attachments, which serve as the transition from mensical fibrocartilage into subchondral bone, are important for proper meniscal function [1–3]. Meniscal attachments did not show significant differences in surface mechanical properties such as ultimate strain or moduli, however, there were significant differences in overall behavior of the anterior versus posterior attachments [4]. No significant differences in creep or stress relaxation properties were found between the different meniscal attachments [5].
Remodeling of Fracture Callus in Mice Can Be Explained by Mechanical Loading
Authors: Isaksson Hanna , Wilson Wouter , van Rietbergen Bert , van Donkelaar Corrinus , Huiskes Rik , Ito Keita
Published: March 2014

Bone fracture repair is a complex process which is divided into an inflammatory, reparative, and remodeling phase. Only few studies focus on the remodeling phase of healing. However, behavior during the remodeling phase is important because that is when strength of bone returns and chance of re-fracture decreases.
Progressive Increase in Platelet Activation With Smoke Exposure: Human Subject and In-Vitro Studies
Authors: Girdhar Gaurav , Xu Sulan , Jesty Jolyon , Bluestein Danny
Published: March 2014

Second hand cigarette smoke (SHS) is one of the major risk factors for cardiovascular disease (CVD) and has been shown to substantiate platelet activation and aggregation in several studies [1, 2]. Most of these studies, under chronic or acute exposure conditions or over prolonged exposure, do not represent the initiation of a disease state or hematological damage under normal levels of cigarette smoke. These above studies of platelet activation with SHS together with our previous in-vitro studies demonstrating cardio-protective effects of nicotine [3], have motivated the present investigation of physiological levels of SHS exposure on human subjects and within an in-vitro endothelial cell-platelet system, with cigarettes (or smoke extracts) of varying nicotine content to confirm analogous cardio-protective effects of nicotine.
Effects of Compression on Distributions of Oxygen and Lactate in Intervertebral Disc
Authors: Huang Chun-Yuh , Gu Wei Yong
Published: March 2014

Since the intervertebral disc (IVD) is the largest avascular cartilaginous structure in the human body, poor nutrient supply has been suggested as a potential mechanism for disc degeneration. The previous theoretical studies have shown that the distributions of nutrients and metabolites (e.g., oxygen, glucose, and lactate) within the IVD depended on tissue diffusivities, nutrient supply, cellular metabolic rates, and coupling effects between nutrient and metabolite [1,2]. Our recent theoretical study suggested that dynamic compression can promote transport of neutral solute in the anisotropic cartilaginous tissue by enhancing both diffusive and convective solute fluxes [3]. However, the effect of compression on distributions of nutrients and metabolites in the IVD has not been studied. The objective of this study was to examine the effects of compression on distributions of oxygen and lactate in the IVD under static and dynamic unconfined compression using a new formulation of the triphasic theory.
Finite Element Method to Evaluate Effects of Hip Implant Geometry on Bone Cement Stress Distribution
Authors: Son Yang W. , Wentz Douglas H. , Levine Danny L. , Johnson Todd S.
Published: March 2014

Loosening of cemented hip prostheses has been reported on occasion. Although a few laboratory experiments have replicated clinical failure modes, the methods appear to be very complicated and time consuming. In this analysis, the Finite Element Method was utilized to evaluate the stress distribution in a cement layer. Two distinct hip implant designs with and without grooves in the anterior/posterior surfaces were investigated. The results indicate that the features of the multiple grooves in these cemented hip implants may improve the rotational stability and reduce the cement stress at the implant-cement interface.
The Effect of Red Cell Dynamics on Platelet Spatial Distribution in Sudden Expansion
Authors: Zhao Rui , Marhefka Joie , Kameneva Marina , Antaki James
Published: March 2014

Thrombosis is a common complication associated with blood contacting devices [1]. Platelets often (or preferably) deposit in specific regions which contain complex flow featuring separations, recirculation zones and stagnation points [2, 3].
Fluid and Particle Transport in an In-Vitro Model of an Expanding/Contracting Human Alveolus
Authors: Chhabra Sudhaker , Prasad Ajay K.
Published: March 2014

Inhaled particulate matter from the environment can produce adverse health effects on the human respiratory system. Conversely, inhalable therapeutics can be delivered to the respiratory tract to treat local and systemic ailments. Both of these fields of study require the accurate prediction of particle transport and deposition in the lung, particularly in the acinar region. A necessary first step to predict particle trajectories is to characterize the airflow in which the particles are suspended. Only particles smaller than 5 μm reach the acinar region [1], hence it can be assumed that such particles will closely follow the fluid streamlines. The current work focuses on the fluid mechanics of the acinar region of the lung to infer particle transport and deposition.
Addition of Particle Tracking Techniques to Improve Two-Dimensional Echo PIV for Opaque Flow Measurement
Authors: Zhang Fuxing , Liu Lingli , Zheng Hairong , Shandas Robin
Published: March 2014

The ability to measure multi-component velocity vectors in opaque flows, especially in blood flows, would have a number of important benefits. Over the last few years, we have developed a new technique, echo particle imaging velocimetry (echo PIV), based on the synthesis of two technologies: PIV and digital brightness-mode (B-mode) ultrasound contrast imaging. Recently-reported results using a custom-developed Echo PIV system [1] showed the utility of this technique in accurately measuring two-dimensional velocity vectors in a variety of opaque flows.
CFD Modeling of Transient Flow Phenomena in an Axial Flow VAD
Authors: Untaroiu Alexandrina , Throckmorton Amy L. , Wood Houston G. , Allaire Paul E.
Published: March 2014

A ventricular assist device (VAD) effectively relieves the workload from a native heart, which has been weakened by disease, and increases blood flow supplied to the body to maintain normal physiologic function. The device must be able to operate over a wide range of conditions. Designed to operate at a single, best-efficiency operating point, it must frequently perform at off-design conditions due to a fluctuating flow rate demanded by the human body and a time varying flow within the pump, due to the beating of the native heart. The design and optimization of a blood pump is a challenging and complex process. Pump design equations are used to estimate the initial dimensions of the pump regions. Computational fluid dynamics (CFD) analyses are then performed to optimize the blood flow path according to specific design criteria under steady flow conditions [1].
Estimation of Corrective Changes in Muscle Activation Patterns for Stroke Patients During FES Intervention
Authors: Shao Qi , Bassett Daniel N. , Manal Kurt , Buchanan Thomas S.
Published: March 2014

Functional electrical stimulation (FES) has been used in the rehabilitation of stroke patients. It is important to know how to stimulate the muscles when using FES. Many control methods have been used to derive the required electrical stimulation patterns. However, these models were not developed based on biomechanical model of human neuromuscular system, thus can not account for sophisticated neurological control strategies during human movements. Based on our developed electromyography (EMG) driven model, we have created a biomechanical model to estimate the corrective increases in muscle activation patterns needed for a person following stroke to walk with an improved normal gait.
Development of a Finite Element Model to Predict Gap Displacement at Fracture Bridged Using Distal Femur Periarticular Locking Plate
Authors: Dharia Mehul A. , Fryman J. Craig , Keith Michael , Kincaid Brian L. , Levine Danny L.
Published: March 2014

Mechanical motion at a fracture site is known to affect the course of fracture healing. Perren’s interfragmentary strain theory assumes that the strain magnitudes in the fracture gap determine the subsequent differentiation of fracture gap tissue [1]. Gap strain is defined as the relative displacement of the fracture gap ends divided by the initial fracture gap width.
Does Lift-Off Occur During Deep Squat?
Authors: Abbasi Ali , Hefzy Mohamed Samir
Published: March 2014

Kneeling, deep squatting, crouching, and gardening represent activities that require flexing the knee maximally. Yet, the present-state-of-the-art of knee mechanics does not provide an accurate understanding of how this joint functions in deep flexion in normal individuals as indicated by Kurosaka, et al. [1]. This limited understanding of the complex 3-D dynamic tibio-femoral and patello-femoral motions past 130° of knee flexion hinders the development of a prosthesis that would provide for full flexion of the knee. One of the questions that is being presently debated is whether lift-off occurs during deep squat or not [2, 3]. The purpose of this paper is to provide an answer to this question by determining the kinematics of the knee while it is maximally flexed, past 155 degrees of flexion.
Effects of Local Mechanical Stimulation on Cellular Behavior
Authors: Cheng Chao-Min , LeDuc Philip R.
Published: March 2014

Cell response to mechanical stimulation is a controlled and complex set of events that has been investigated by numerous groups. Understanding the behavior of cells from a localized perspective is even more challenging due to the integrated responses that play significant roles. After investigating the effect of local mechanical stimulation with respect to cell apoptosis, we find that the resulting ratio of apoptotic cells with respect to the deformation of the cells through using soft pyramid shaped microstructure versus rectangular microstructures is increased by 200% percent. These results may also have implications in understanding cell behaviors such as cell-cell communication under the mechanical stimulation and mechanotransduction.
Viscoelastic Finite-Element Modelling of Cell Deformation in an Optical Stretcher
Authors: Teo Soo Kng , Parker Kim , Chiam K.-H.
Published: March 2014

In this paper, we discuss the results arising from using a finite-element model [1] of cell deformation to study the optical stretching [2,3] of normal and malignantly transformed fibroblast cells. The key feature of our model is the use of a constitutive viscoelastic fluid element [4] whose parameters are both spatially and temporally varying so as to mimic the experimentally-observed spatiotemporal heterogeneity of cellular material properties. First, we show that normal fibroblast cells can undergo active cellular response by increasing their cellular viscosity when optically stretched for loading times of between 0.2s and 2.5s. Second, we show that, under similar optical conditions, cells of a smaller radius will experience more stretching compared to cells of a larger radius. This may explain why malignantly transformed cells experience higher strains than normal cells. Third, we compute the extent of the propagation of stress in the cytoplasm, and show that, for malignantly transformed cells, the maximal stress does propagate into the nuclear region whereas for normal cells, the maximal stress does not. We discuss how this may impact the transduction of cancer signalling pathways.
3D Coculture of Human Endothelial Cells and Myofibroblasts for Vascular Tissue Engineering
Authors: Pullens Rolf A. A. , Stekelenburg Maria , Bouten Carlijn V. C. , Baaijens Frank P. T. , Post Mark J.
Published: March 2014

Cardiovascular disease is still the number one cause of death in the industrialized world. Diseased small diameter blood vessels are frequently replaced by native grafts. However, these vessels have a limited life time [1], for example the patency at 10 year after coronary artery bypass grafting of saphenous vein grafts is 57% [2]. Tissue engineering (TE) of small diameter blood vessels seems a promising approach to overcome these shortcomings or address the increasing need for substitutes during follow up surgery. Mechanical conditioning of myofibroblast (MFs) seeded constructs appears to be beneficial for functional tissue properties, such as cell proliferation, ECM production and mechanical strength [3,4]. Without a functional endothelial cell (ECs) layer however, patency may be compromised by thrombogenecity. Construction of an EC layer might on the other hand affect the tissue composition during culture, as was shown for bovine ECs, which influenced proliferation and ECM production of smooth muscle cells [5].
Cytokine and Chemokine Release Upon Sustained Mechanical Loading of the Epidermis
Authors: Bronneberg Debbie , Cornelissen Lisette H. , Oomens Cees W. J. , Baaijens Frank P. T. , Bouten Carlijn V. C.
Published: March 2014

Pressure ulcers are areas of soft tissue breakdown resulting from sustained mechanical loading of the skin and underlying tissues. These ulcers are painful, difficult to treat, and represent a burden to the community in terms of health care and money. Currently, pressure ulcer risk assessment is dominated by subjective measures and does not predict pressure ulcer development satisfactorily [1]. Objective measures are therefore needed for early, non-invasive detection.
A Simulation Study on the Growth of Cerebral Aneurysms
Authors: Shimogonya Y. , Imai Y. , Ishikawa T. , Yamaguchi T.
Published: March 2014

Cerebral aneurysm is a cerebrovascular disease characterized by the local balloon-shaped expansion of the arterial wall. It is an extremely important disease on the clinical medicine, because the rupture of the cerebral aneurysm causes serious pathologic conditions such as the subarachnoid hemorrhage.
Simulation of the Coupling of Cell Contractility and Focal Adhesion Formation
Authors: Pathak Amit , Deshpande Vikram S. , McMeeking Robert M. , Evans Anthony G.
Published: March 2014

The remodeling of the cytoskeleton and focal adhesion distributions for cells on substrates with micro-patterned ligand patches is investigated using a bio-chemo-mechanical model. All the cells have approximately the same area and we investigate the effect of ligand pattern shape on the cytoskeletal arrangements and focal adhesion distributions. The model for the cytoskeleton accounts for the dynamic rearrangement of the actin/myosin stress fibers and entails the highly non-linear interactions between signaling, the kinetics of tension-dependent stress-fiber formation/dissolution and stress dependent contractility. This model is coupled with a focal adhesion (FA) model that accounts for the mechano-sensitivity of the adhesions from thermodynamic considerations. This coupled stress fiber and focal adhesion model is shown to capture a variety of key experimental observations including: (i) the formation of high stress fiber and focal adhesion concentrations at the periphery of circular and triangular, convex–shaped ligand patterns; (ii) the development of high focal adhesion concentrations along the edges of the V, T, Y and U shaped concave ligand patterns; and (iii) the formation of highly aligned stress fibers along the un-adhered edges of cells on the concave ligand patterns. When appropriately calibrated, the model also accurately predicts the radii of curvature of the un-adhered edges of cells on the concave-shaped ligand patterns.
Bottom-Up Mesoscale Model of Microtubule
Authors: Deriu Marco A. , Enemark Søren , Votta Emiliano , Montevecchi Franco M. , Redaelli Alberto , Soncini Monica
Published: March 2014

Microtubules (MTs) are fundamental structural elements in the cytoskeleton of all eukaryotic cells. The MTs are hollow cylinder-shaped biopolymers with inner and outer diameter of about 18 and 30 nm respectively and length ranging from 1 to 10 μm. They are constituted by αβ-tubulins arranged in protofilaments with head-to-tail motif. The protofilaments bind together laterally along the MT’s long axis with a slight shift generating a spiral with a pitch of 2, 3 or 4 monomers’ length [1]. The building-block of the MT, αβ-tubulin, is a hetero-dimer made of two globular monomers, α- and β-tubulin. α- and β-tubulin monomers consists of about 450 residues and shows a high degree of similarity from the primary to the tertiary structure level. However, one important difference is that the α-monomer binds a GTP molecule while the β-monomer binds a GDP molecule [2].
Structural Properties of Human Cerebral Arteries as Assessed by a Constituent-Based Biomechanical Model
Authors: Fonck E. , Feigl G. , Augsburger L. , Rüfenacht D. A. , Stergiopulos N.
Published: March 2014

Human cerebral arteries may develop aneurysms, as a result of geometrical and structural modifications in the arterial wall resulting from a variety of genetic, epigenetic and biomechanical factors. Aneurysms exhibit a markedly different wall composition and structure, characterized by relatively low elastin content as shown in Figure 1.
A Structural Strain Energy Function for Vascular Tissue Considering Elastin Anisotropy
Authors: Rezakhaniha Rana , Stergiopulos Nikos
Published: March 2014

The vessel wall exhibits relatively strong nonlinear properties and undergoes a wide range of deformations. Identification of a strain energy function (SEF) is the preferred method to describe the complex nonlinear elastic properties of the vascular tissue. Once the strain energy function is known, constitutive equations can be obtained.
Effects of Reduced Compliance on Endothelial Functionality With Regards to Inflammation and Adhesion
Authors: Thacher Tyler N. , Gambillara Veronica , da Silva Rafaela , Silacci Paolo , Stergiopulos Nikos
Published: March 2014

Among other things, the aging process is associated with a stiffening of the arteries, initiating the development of systolic hypertension and a significant increase in pulse pressure. Amplified pulse pressure has been linked to problems causing arterial dysfunction. In this study we focused on how reduced wall compliance induces pulse pressure-mediated changes in endothelial function with regards to inflammation and adhesion.
An Experimental and Numerical Investigation Into the Deformation Profiles of Mock Arteries
Authors: Quinn Niamh M. , Ivankovic Alojz , Karac Aleksandar
Published: March 2014

Atherosclerosis is a chronic medical condition in which thickening and loss in the elasticity of the artery wall leads to impaired blood circulation[1]. Cholesterols and other proliferating cells accumulate at localized regions within the artery wall. This has the effect of stiffening and thickening the wall at that point. The presence of an emerging plaque should effect the deformation of and stresses generated within the artery wall sufficiently so to make it possible to detect this disease whilst still in its early stages. The hypothesis under investigation in this work is that an altered deformation profile, because of stiffening and thickening of the artery wall is an early indicator of the existence of this disease.
A Finite Element Prediction of Cellular Strain in a GAG-Scaffold
Authors: Stops A. J. F. , McMahon L. A. , O’Mahoney D. , McHugh P. E. , Prendergast P. J.
Published: March 2014

Tissue engineering is an emerging area in bioengineering engaging biomaterials, biology and biomechanics. Current in-vitro studies have shown mesenchymal differentiation into specific cellular lineages when using osteoinductive factors [1], though the quantitative understanding of the load transfer process within a cell-seeded scaffold is still relatively unknown. Here, this paper presents a finite element simulation of the cellular-scaffold interaction so that cellular strain and the corresponding strain mechanisms can be evaluated.
Surface Strains in the Looping Embryonic Chick Heart Measured Using Optical Coherence Tomography
Authors: Filas Benjamen A. , Taber Larry A.
Published: March 2014

The heart is the first functional organ in the vertebrate embryo. In the chick embryo, the heart begins beating at Hamburger and Hamilton [1] stage 10 (approximately 35 hours of a 21-day incubation period). The initially straight heart tube bends and twists into a c-shaped tube before reaching stage 12 (approximately 48 hours incubation). This process, known as c-looping, marks one of the first visible signs of left-right asymmetry in the embryo. Incorrect looping is one cause of congenital heart defects, where significant malformations occur in roughly 1% of human live births [2]. Understanding the mechanisms that drive c-looping could lend insight into the processes causing some of these defects.
Does the Difference in Realistic Waveform Before and After Stenting Affect Hemodynamics in Stenosed Coronary Artery?
Authors: Torii Ryo , Wood Nigel B. , Hadjiloizou Nearchos , Wright Andrew , Hughes Alun D. , Thom Simon A. M. , Xu X. Yun
Published: March 2014

Vascular hemodynamic forces influence the focal development of atherosclerosis. Atherogenesis has been linked to low and oscillating wall shear stress (WSS) driven by the pulsatile nature of blood flow [1, 2]. Strong evidence has emerged that time-averaged WSS (TAWSS) and oscillating shear index (OSI) are important measures of the atherogenic nature of blood flow. Recently it was reported that the phase-angle between oscillating WSS and circumferential strain in arterial wall (stress phase angle: SPA) may also influence endothelial cell function and contribute to atherosclerosis [3]. In stenosed, curved or bifurcated arteries, the blood flow pattern is complex because of flow separation, which is highly sensitive to the local velocity waveform [4]. Although the effects of waveform on coronary blood flow has been studied by comparing physiological and idealised waveforms [5], the effects of variation in physiological waveforms and their impact on SPA are still unclear. In this study we investigated computationally the influence of physiological flow velocity and pressure waveforms on coronary hemodynamic parameters (e.g. TAWSS, OSI and SPA) using waveforms acquired before and after coronary artery stenting.
Increases in the Elastic Modulus of Trabeucular Bone Tissue Leads to More Rapid Perforation of Trabeculae in Osteoporotic Bone
Authors: Mulvihill Brianne M. , McNamara Laoise M. , Prendergast Patrick J.
Published: March 2014

Osteoporosis is a bone disease which manifests itself in the perforation and subsequent resorption of individual trabeculae [1]. Bone mass is consequently reduced leading to a mechanically weakened structure which is prone to fractures. These fractures have serious health and social implications for sufferers of osteoporosis.
The Effect of Flow Characteristics on Thrombus Formation Rate and Deposition
Authors: Raz S. , Enbal A. , Rubinshi M. , Einav S.
Published: March 2014

Embolism is defined as the obstruction of a blood vessel by a clump of material, such as a broken-off piece of plaque, a blood clot or air bubble, travels through the bloodstream and becomes lodged in a blood vessel. Depending on the size of the embolism and which blood vessel it is obstructing, the result can range from no symptoms whatsoever to a life-threatening emergency.
An Assessment of Primary Blast Injury in Human Brains: A Numerical Simulation
Authors: Sotudehchafi Mahdi , Karami Ghodrat , Ziejewski Mariusz
Published: March 2014

Most blast-related injuries happen as a result of complex pressure waves generated by the explosion. In this paper, we model the explosion from detonation and examine the blast propagation in air using Arbitrary Lagrangian–Eulerian (ALE) finite element formulation. The results of the simulation agree well with those of physical data obtained from blast wave experiments. Such results set the circumstances necessary for an examination of brain injury exposed to such situations. Thus the model will be coupled with a Fluid/Structure Interaction (FSI) algorithm to implicitly examine the blast wave interactions with a human head and to study the creation of high regions of biomechanics pressure and stress gradients.
A Confined Compression Technique for Hydraulic Conductivity Measurement in Soft Tissues
Authors: O’Neill Brian E. , Quinn Timothy P. , Li King C. P.
Published: March 2014

Multiphasic tissue models have been used extensively to predict the behavior of cartilaginous tissues [1]. Their application to other soft tissues, however, has often been overlooked. Unlike the more commonly used continuum model of the viscoelastic solid [2], multiphasic models allow us to infer the behaviors and properties of tissue subcomponents by observing the behavior of the tissue whole. As a great deal of tissue function and structure is related to the control and transport of fluids and fluid-borne agents, there is clearly a need for this insight in all tissues. For example, there has been a great deal of interest recently in the possibility of modifying the flow properties of solid tumors and other tissues to allow the targeted delivery of large molecular weight drugs, such as chemotherapeutic or genetic agents [3–4]. It is well known that the high interstitial fluid pressures, confused vasculature, and lack of a lymphatic system prevent the effective distribution of directly injected or systemically administered drugs into tumors [3]. Increasing the effective permeability of these tumors can ameliorate these issues and allow for more effective treatment. A handful of studies have found that the biphasic model, along with some basic experimental tools, can reasonably represent the flow properties of tumors [4–5]. In this paper, we describe a technique using a simple confined compression experiment with the biphasic model to measure the hydraulic conductivity of samples of cardiac tissue.
Investigation of Osteoclast Resorption Mechanisms in a Hybrid Cellular Automaton Model of Bone Remodeling
Authors: Penninger Charles L. , Roeder Ryan K. , Niebur Glen L. , Renaud John E.
Published: March 2014

Bone is a living tissue which is continually adapting to its biological environment via continuous formation and resorption. It is generally accepted that bone remodeling occurs in response to daily mechanical loading. The remodeling process enables various functions, such as damage repair, adaptation to mechanical loads, and mineral homeostasis [1]. The cells that are responsible for the bone remodeling process are the bone resorbing osteoclasts and the bone forming osteoblasts. These cells closely coordinate their actions in a basic multicellular unit to renew “packets” of bone.
The Mechanical and Viscoelastic Properties of the Healing Rabbit Patellar Tendon
Authors: Abramowitch Steven D. , Fisher Matthew B. , Karaoglu Sinan , Woo Savio L.-Y.
Published: March 2014

Central third bone-patellar tendon-bone (BPTB) autografts are commonly used for anterior cruciate ligament (ACL) reconstructions. Following surgery, complications arise at the donor site, including extension deficits and anterior knee pain [1]. These complications are partially caused by inadequate healing of the patellar tendon (PT) as well as adhesions in the anterior interval. Recent clinical data have suggested these are contributing factors in the early development of osteoarthrosis following ACL reconstruction [2]. Thus, it is necessary to understand the changes in mechanical and viscoelastic behavior in the healing PT.
Development of Quantum Dot-Embedded Nanoparticles for Biothermal Imaging
Authors: Hanson Willard L. , Michael Nancy L. , Kim Choong-Un , Han Bumsoo
Published: March 2014

Recent surgical management of cancer tends toward minimally invasive surgical techniques since tumors can be detected smaller than ever due to the advance of cancer diagnostic technologies. Many of these surgical procedures are thermal therapies where a localized freezing or heating zone (i.e. thermal lesion) is created to destroy tumors without damaging adjacent normal tissues. The outcomes of these innovative and less invasive surgeries, however, are significantly impaired by the limited image-guidance of the thermal lesion during the procedures. Since the primary clinical objective of these surgeries is to eradicate diseased tissues while sparing the adjacent normal tissue, accurate intra-operative monitoring of the thermal lesion is critical. Moreover, in many surgical situations, sparing adjacent tissue is not only desired, but imperative since major blood vessels, nerve bundles and surrounding organs are susceptible to thermal injury. However, currently available monitoring techniques have limited accuracy or accessibility, and/or are not capable of monitoring the lesion in real-time during the procedure. In our recent study [1], we demonstrated the feasibility of non-invasive thermometry using quantum dot (QD) as temperature probe. Although its feasibility was demonstrated, several limitations should be addressed before more rigorous clinical applications. Especially the lower quantum yield of core/shell QDs should be significantly improved for deeper tissue imaging. In the present study, QD-embedded nano-composite particles were developed for deeper tissue imaging and its temperature dependent fluorescence was characterized.
Concurrent Simulations of Musculoskeletal Movements and Tissue Deformations
Authors: van den Bogert Antonie J. , Erdemir Ahmet
Published: March 2014

In computational biomechanics, there are two well-developed but separate modeling domains: multibody (MB) dynamics for body movements, and finite element (FE) modeling or tissue deformations. State of the art movement simulations make use of accurate musculoskeletal models and allow prediction of resultant forces in joints and muscles. These simulations, however, do not explicitly represent the distribution of mechanical loads within these anatomical structures. One approach to overcome this limitation is to use these resultant loads as input for a finite element model which is then used for postprocessing at specific instants in time.
Next Generation Knee Replacements: A New Approach to Replicate the Function of the ACL
Authors: Yildirim Gokce , Walker Peter S. , Sussman-Fort Jonathan , Boyer Jason
Published: March 2014

Current total knee replacements solve the problem of arthritic knee joints, but the evidence is that normal patterns of knee motions are not restored (1) In addition; paradoxical anterior sliding of the femur on the tibia can occur in the first half of the flexion range (2). Achieving natural motion is likely to be important for daily activities which involve higher angles of flexion, in terms of restoring normal soft tissue lengths and patello-femoral mechanics. Studies have shown the damaging effects of anterior femoral slide on the tibia affecting both the patella and the patellar tendon (3). Our paper examines new knee replacement designs which incorporate geometrical features to regain anatomical knee motion.
Electrospinning of Photopolymerizable Poly(β-Amino Ester) Networks for Fibrous Tissue Engineering
Authors: Tan Andrea R. , Ifkovits Jamie L. , Baker Brendon M. , Mauck Robert L. , Burdick Jason A.
Published: March 2014

Fiber-reinforced tissues of the musculoskeletal system, including tendon, ligament, intervertebral disc, and the knee meniscus function to transmit the high mechanical forces that arise with locomotion. As these tissues operate under demanding mechanical regimes, their structure and composition are optimized to enable these activities and to resist damage with repeated use. Hallmarks of these dense fibrous tissues include a high collagen content organized along a prevailing fiber direction that is generally coincident with the principal loading direction, as well as a lack of vascularity after skeletal maturation. While these characteristics enable function, they also predispose these tissues to a poor healing response subsequent to injury.
Effects of Fluid Shear Stress on Endothelial Cell Invasion Into Three-Dimensional Matrices
Authors: Kang Hojin , Bayless Kayla J. , Kaunas Roland
Published: March 2014

We have previously developed a cell culture model to study the effects of angiogenic factors, such as sphingosine-1-phosphate (S1P), on the invasion of endothelial cells into the underlying extracellular matrix. In addition to biochemical stimuli, vascular endothelial cells are subjected to fluid shear stress due to blood flow. The present study is aimed at determining the effects of fluid shear stress on endothelial cell invasion into collagen gels. A device was constructed to apply well-defined fluid shear stresses to confluent human umbilical vein endothelial cells (HUVECs) seeded on collagen gels. Fluid shear stress induced significant increases in cell invasion with a maximal induction at ∼5 dyn/cm2. These results provide evidence that fluid shear stress is a significant stimulus for endothelial cell invasion and may play a role in regulating angiogenesis.