bluuebunny/crossref_metadata_2025 huggingface dataset:
A Method for Determining the Strain-Time Endurance of Cells in Planar Tissue-Engineered Constructs Subjected to Large Compressive Deformations
Authors: Gefen Amit , van Nierop Bastiaan , Bader Dan L. , Oomens Cees W.
Published: March 2014

The mechanical environment of cells influences their normal growth and function, and may also affect the development of diseases and chronic injuries. Accordingly, there is substantial interest in determining the endurance of cells subjected to controlled mechanical strains for given time periods. A standardized, generic experimental method for determining strain-time thresholds for cell death is so far missing in the literature. In this study, a new experimental method was developed to measure strain-time thresholds of cells in planar tissue-engineered constructs subjected to large compressive strains. The method was applied to measure a strain-time threshold for differentiated C2C12 murine skeletal muscle cells in tissue-engineered bio-artificial muscle (BAM) constructs.
Mathematical Optimization of Mechanical Testing to Study Periprosthetic Fracture Following Femoral Trochanteric Nail Fixation
Authors: Schenk Andrew T. , Horowitz Kevin S. , Bucchi Paul F. , Wiater Patrick J. , Demetropoulos Constantine K.
Published: March 2014

Understanding the biomechanics of periprosthetic fractures is especially important in today’s aging population. As the prevalence of osteoporosis continues to climb, fracture risk, especially in proximity of an orthopaedic implant, is of great concern. In a study designed to investigate the mechanism of such fractures, the authors have chosen to test human cadaveric specimens implanted with short Synthes Titanium Trochanteric Fixation Nails. However, the exact loading conditions that elicit fracture are not known.
Exploring Cellular Tensegrity: Physical Modeling and Computational Simulation
Authors: Zheng Chun hua , Doll Joseph , Gu Emily , Hager-Barnard Elizabeth , Huang Zubin , Kia AmirAli , Ortiz Monica , Petzold Bryan , Usui Takane , Kwon Ronald , Jacobs Christopher , Kuhl Ellen
Published: March 2014

The term tensegrity was first coined by Buckminster Fuller to describe a structure in which continuous tension in its members forms the basis for structural integrity. Fuller most famously demonstrated the concept of tensegrity in architecture through the design of geodesic domes while his student, artist Kenneth Snelson, applied the concept of tensegrity to create sculptures that appear to defy gravity (Figure 1). Snelson’s tensegrity sculptures have minimal components and achieve their stability through dynamic distribution of tensile and compressive forces amongst their members to create internal balance [1]. It was upon viewing Snelson’s sculptures that Donald Ingber became inspired by their structural efficiency and dynamic force balance to adopt tensegrity as a paradigm upon which to analyze cell structure and mechanics. It has been 30 years since the premier appearance of the cellular tensegrity model and although the model is still much under debate, empirical evidence suggests that the model may explain a wide variety of phenomena ranging from tumor growth to cell motility [1–4].
Capillary Driven Fluid Flow in Medical Devices
Authors: O’Leary Fiachra A. , Griffin Philip C.
Published: March 2014

Microscale fluid dynamics has played a significant role in the development of many applications in the medical diagnostic sector and in recent years many devices have implemented advances in this field. Capillary driven assays are commonly used in diagnostic areas, such as, cardiac risk, fertility, drug abuse and infectious diseases1. Typically a platform is used where bodily fluids or samples are taken, filtered and by means of small microchannels, transported and mixed with a variety of antibodies2. In order to perform correctly, these antibodies need to bind to the proteins in the fluid. It is therefore essential that the exposure of the proteins to the antibodies is maximized. To achieve this, capillary dimensions can be altered to obtain the required flow rates and exposure times3. This paper focuses on controlling these parameters.

In this paper, a study was conducted in which the flows in four straight rectangular microchannels of varying cross sectional areas were assessed. The four microchannels were fabricated from an epoxy material. The microchannel widths varied from 100μm to 1000μm with each channel having a dept of 200μm. The four microchannels had aspect ratios of 0.5, 1, 2 and 10. The microchannels were sealed using a heat sealing hydrophilic tape. Fluid velocity rates were measured experimentally using an X-Stream XS-4 high speed camera at 500 frames per second. Preliminary contact angle results between water and the epoxy material gave a contact angle of 81.5 degrees +/− 6 degrees. Computational models of the four microchannels were performed using a Volume Of Fluid (VOF) model in Fluent 6.2.16, a commercially available CFD code. The computational models had four boundary types: pressure inlet, pressure outlet, epoxy wall and hydrophilic tape wall. The inlet boundary has an initial pressure applied to it, capillary pressure between the water and air interface in the microchannel. It was found that as the dimensions of the microchannels increased, the governing equations were less accurate in predicting the experimental fluid velocity in the microchannels.
Microscopic Mechanical Analysis of Aortic Wall: Estimation of Stress in the Intramural Elastic Laminas and Smooth Muscle Cells in a Physiological State
Authors: Matsumoto Takeo , Fukunaga Akihisa , Narita Kengo , Nagayama Kazuaki
Published: March 2014

It is well known that the artery walls change their dimensions and mechanical properties adaptively in response to the mechanical environment they are exposed to [1]. Because mechanical adaptation of the artery wall is driven by the smooth muscle cells (SMCs) in its media, it is crucial to know the mechanical environment of SMCs in the wall to reveal the details of the adaptation mechanism. Mechanical stress applied to the SMCs in the media should be different from that applied to the wall, because at a microscopic level, the media has a highly heterogeneous structure composed of various materials with different elastic modulus. For example, aortic media has a layered structure of a lamellar unit, a pair of elastic lamina (EL) mainly composed of elastin and a smooth muscle-rich layer mainly composed of SMCs and collagen [2], and Young’s modulus of elastin, SMCs, and collagen is about 0.6MPa, 10kPa, and 1GPa, respectively [3]. Such heterogeneity should cause complex distribution of stress and strain depending on the histological structure both in the unloaded state and in the physiological state [4].
Desiccation of Geobacter Sulfurreducens: Membrane Response to Osmotic Stress
Authors: Ragoonanan Vishard , Malsam Jason , Bond Daniel R. , Aksan Alptekin
Published: March 2014

Geobacter sulfurreducens is a δ-proteobacterium capable of electron transfer to extracellular compounds and surfaces [1] that has possible technological applications in microbial-based sensors, bioremediation of contaminated environments and harvesting electricity from waste organic matter [2]. Further development of many of these applications requires stabilization and preservation of bacteria as thin films on surfaces. One method of encapsulating bacteria in thin films is through the use of porous latex coatings [2]. However, during the formation of these films, the bacteria are exposed to osmotic stresses.
Progressive Energy Dissipations of Human Cortical Bone in Compression
Authors: Leng Huijie , Dong Xuanliang , Wang Xiaodu
Published: March 2014

Bone fracture has imposed a significant burden on the health of society. The “bone quality” is used to refer to factors affecting bone fracture risk [1]. Energy dissipation till fracture, known as toughness, is a major measure of bone quality [2]. However, underlying mechanisms of energy dissipation in bone is still not clear. It has been well documented that the post-yield behavior of bone determines the major part of the toughness of bone [3, 4]. Therefore, it is important to study post-yield behaviors of human bone, especially the different pathways for energy dissipation, in order to better understand how age-related change affects bone quality. Bone behaves differently under different loading modes [5]. Different from loading in tension, after reaching the maximum stress, cortical bone in compression can continue to bear load till large deformation without brittle failure and dramatic reduction in elastic modulus [5, 6]. However, few studies of progression of post-yield behaviors of cortical bone in compression were reported in the literature.
Boundary Stiffness Regulates Fibroblast Behavior in Collagen Gels
Authors: John Jeffrey , Billiar Kristen L.
Published: March 2014

Recent studies utilizing compliant culture substrates clearly demonstrate that many cell behaviors such as migration and contraction are strongly influenced by the stiffness of the local environment. The goal of this work was to develop a method for studying stiffness-dependent biology within 3D cell-populated gels without altering the biochemical environment of the gel. A device was developed utilizing compliant anchors to tune the boundary stiffness of suspended collagen gels. Human fibroblasts compacted the gels to a greater extent as the stiffness of the anchors was decreased. Further, the force generated by the cells increased with increased boundary stiffness, and the response of the cells to TGF-β1 was accentuated as the stiffness increased. This new method represents a promising tool for the controlled study of stiffness-dependent biology within tissuelike 3D environments.
Permeability and Porosity of Embolic Protection Filters: An Experimental Study
Authors: Siewiorek Gail M. , Finol Ender A.
Published: March 2014

Endovascular therapies are an evolving form of treatment for stenosed atherosclerotic blood vessels. In particular, stenting and angioplasty of the carotid artery has recently gained more attention. Due to risk of periprocedural distal embolization, cerebral protection devices such as embolic protection filters (EPFs), which maintain distal perfusion during the intervention, have been developed to capture embolized plaque particles. This investigation studied in vitro the effects of a deployed EPF on flow rate in the internal carotid artery. The pseudopermeability of each device was calculated by maintaining a constant pressure gradient during its deployed state and after injection of emboli by adjusting the flow rate. High resolution images were used to calculate the porosity of each device. Experimentally-determined permeability and porosity can be used in computational fluid dynamics simulations as a design optimization approach to determine the optimal pore size for each EPF.
Primary Cilia Mediate Intracellular cAMP Responses in Bone Cells Exposed to Dynamic Fluid Flow
Authors: Kwon Ronald Y. , Temiyasathit Sara , Tummala Padmaja , Quah Clarence , Jacobs Christopher R.
Published: March 2014

It is well accepted that fluid flow is an important mechanical signal in regulating bone structure and function. Primary cilia, which are non-motile, microtubule based organelles that extend from the centrosome and project into extracellular space in many cell types, have recently been shown to mediate fluid flow-induced osteogenic responses in MLO-Y4 osteocyte-like cells [1]. However, primary cilia did not mediate increases in intracellular Ca2+ concentration, and the second messenger system(s) involved in primary cilia-mediated mechanosensing has yet to be elucidated. In this study, our goals were to (1) determine whether exposing bone cells to oscillatory fluid flow modulates intracellular levels of cyclic adenosine monophosphate (cAMP), another ubiquitous second messenger molecule, and (2) investigate whether this modulation may be mediated by primary cilia.
Inverse Mechanical Characterization of Tissue Engineered Heart Valves
Authors: Cox Martijn A. J. , Kortsmit Jeroen , Driessen Niels J. B. , Bouten Carlijn V. C. , Baaijens Frank P. T.
Published: March 2014

Over the last few years, research interest in tissue engineering as an alternative for current treatment and replacement strategies for cardiovascular and heart valve diseases has significantly increased. In vitro mechanical conditioning is an essential tool for engineering strong implantable tissues [1]. Detailed knowledge of the mechanical properties of the native tissue as well as the properties of the developing engineered constructs is vital for a better understanding and control of the mechanical conditioning process. The nonlinear and anisotropic behavior of soft tissues puts high demands on their mechanical characterization. Current standards in mechanical testing of soft tissues include (multiaxial) tensile testing and indentation tests. Uniaxial tensile tests do not provide sufficient information for characterizing the full anisotropic material behavior, while biaxial tensile tests are difficult to perform, and boundary effects limit the test region to a small central portion of the tissue. In addition, characterization of the local tissue properties from a tensile test is non-trivial. Indentation tests may be used to overcome some of these limitations. Indentation tests are easy to perform and when indenter size is small relative to the tissue dimensions, local characterization is possible. We have demonstrated that by recording deformation gradients and indentation force during a spherical indentation test the anisotropic mechanical behavior of engineered cardiovascular constructs can be characterized [2]. In the current study this combined numerical-experimental approach is used on Tissue Engineered Heart Valves (TEHV).
Towards a Multi-Flagella Architecture for E.coli Inspired Swimming Microrobot Propulsion
Authors: Taheri Arash , Mohammadi-Amin Meysam
Published: March 2014

One of the primary goals of medical micro and nano robots is to reach currently inaccessible areas of the human body and carry out a host of complex operations, such as minimally invasive surgery (MIS), highly localized drug delivery, and screening for diseases at their very early stages. One of the innovative approaches to design microrobot propulsion is based on the flagellar motion of bacteria [1]. Certain bacteria, such as Escherichia coli (E.coli) use multiple flagella often concentrated at one end of their bodies to induce locomotion. Each flagellum is formed in a left-handed helix and has a motor at the base that rotates the flagellum in a corkscrew motion. As pointed out by Purcell in his Lecture “Life at low Reynolds numbers” [2], microorganisms experience an environment quite different from our own. In particular, because of their small size (of the order of microns), inertia is, to them, essentially irrelevant. The fact that inertia is irrelevant for micro-organisms makes it difficult for them to move. The propulsive mechanisms based on flow inertia will not work on a mesoscopic scale. To overcome this problem, organisms living in low Reynolds number regimes have developed moving organelles which have a handedness to them. For instance, E. Coli’s flagella rotate with a helical motion, much like a corkscrew. This configuration produces patterns of motion that do not repeat the first half of the cycle in reverse for the second half, allowing the organisms to achieve movement in their environment.
Heating in a Stenosed Coronary Artery With Pulsating Flow and Non-Newtonian Viscosity
Authors: Lantz Jonas , Gårdhagen Roland , Wren Joakim , Karlsson Matts
Published: March 2014

Cardiovascular disease is the most prevalent cause of death in the developed countries and most deaths are due to coronary atherosclerosis [1]. During the development of atherosclerosis, several stages can be distinguished including vulnerable plaque. This group of plaque has an inclination for erosion and rupture and is therefore of particular interest. Due to the inflammatory response of vulnerable plaque including an increased metabolism and thereby a locally increased temperature, it is possible to detect such warm cores by intracoronally temperature measurement under some prerequisitions. Temperature differences up to 2.2 K on the surface of carotid plaques have been measured [2], but the relation between plaque vulnerability, inflammatory response, temperature increase and possibility to detection by means of temperature measurement is far from fully perceived.
Use of Polyelectrolyte Films in Vascular Tissue Engineering
Authors: Kerdjoudj H. , Moby V. , Berthelemy N. , Voegel J. C. , Menu P. , Stoltz J. F.
Published: March 2014

Vascular diseases with their high morbidity and mortality are a major challenge for medical science, engaging the best minds in modern medicine. The development of antithrombogenic surfaces still remains a huge challenge in the vascular tissue engineering field. Various researchers have expanded surface coating procedures allowing endothelial cells (EC) adhesion and retention on vascular substitutes or by incorporating some of the mechanisms employed by vascular endothelial cells i.e. heparin. The short in vivo patency of these grafts is related. Our group study evaluates a new surface modification based on polyelectrolyte building. The layer by layer self assembly and the result in polyelectrolyte multilayer films (PEM) became also in a recent past a challenging, simple and versatile way to engineer surfaces with highly specific properties. Previous studies indicated that the poly(sodium-4 styrene sulfonate)/poly (allylamine hydrochloride) PSS/PAH multilayered films when ended by PAH induce strong adhesion and retention of mature EC which spread and keep their phenotype as well on glass [1,2], on expanded polytetrafluoroethylene ePTFE [3] and on cryopreserved arteries [4,5]. The mechanical properties (compliance), leading to early intimal hyperplasia and graft failure, were lost after artery cryopreservation. We have demonstrated the compliance restoration of PEM treated cryopreserved close to native arteries [5]. The use of an autologous EC source avoids the immunological rejections of the grafts. With an autologous origin, high proliferation capacity and potentialities to proliferate and differentiate into matures EC, the endothelial progenitor cells (EPC) have raised huge interest and offer new opportunities in vascular engineering. Currents protocols for isolation and differentiation of EPC from peripheral blood requires at least 1 month to observe an endothelium-like morphology and about 2 months for confluent EC monolayer. The EPC cultivated on PEM treated glasses showed a monolayer development after only 14 days of culture. The morphological appearance and mature phenotype markers expression and repartition of the monolayer cells are close to mature EC [6]. These main results have led to French patent deposit in June 2007[7].
Systemic Mesenchymal Stem Cell Delivery and Axial Mechanical Stimulation Accelerate Fracture Healing
Authors: Weaver Aaron S. , Su Yu-Ping , Begun Dana L. , Zade Ralph T. , Alford Andrea I. , Hankenson Kurt D. , Kreider Jaclynn M. , Ablowitz Stephanie A. , Kilbourn Michael R. , Goldstein Steven A.
Published: March 2014

Fracture healing is a complex process involving numerous cell types, whose actions are regulated by many factors in their local environment. Mechanical factors are known to exert a strong influence on the actions of these cells and the progression of the repair process. While prior studies have investigated the effect of physical forces on cell differentiation, biofactor expression, and mechanical competence of repair, the mechanosensory and response mechanisms are poorly understood. This study was designed to explore the influence of a controlled mechanical environment on temporal aspects of the bone repair process. Specifically, this study examines how the timing of an applied strain influences local cell behavior during fracture repair, and how this load affects the migration of systemically introduced mesenchymal stem cells (MSCs) to the fracture site.
Arterial Remodeling in Response to Increased Blood Flow Using a Constituent-Based Model
Authors: Tsamis Alkiviadis , Stergiopulos Nikos
Published: March 2014

Changes in medial elastin are critical to arterial remodeling following a sustained increase in blood flow, wherein the lumen enlarges in two phases tending to restore the intimal shear stress to control: 1st, via rapid smooth muscle relaxation and, 2nd, via chronic reconstruction of the media [1]. At the same time, wall thickening takes place aiming at restoring the baseline levels of wall stress [2].
Design of Experiments for Exposure of Astrocytes to Elevated Hydrostatic Pressure and Hypoxia
Authors: Rajabi Shadi , Simmons Craig A. , Ethier C. Ross
Published: March 2014

Glaucoma, a chronic optic neuropathy, is the second most common cause of blindness, affecting 67 million people worldwide. The damage in glaucoma occurs at the optic nerve head (ONH), where the axons of the retinal ganglion cells leave the eye posteriorly. Glaucoma is frequently associated with elevated intraocular pressure (IOP), and visual field loss can be prevented by significant lowering of IOP. Hence, the role of pressure in glaucoma is important. Unfortunately, the mechanism by which pressure leads to vision loss in glaucoma is very poorly understood.
Change in Knee Passive Envelope of Motion With Total Knee Replacement Design
Authors: Mane Amit M. , Clary Chadd W. , Reeve Amber N. , Maletsky Lorin P. , Dodd Kevin A.
Published: March 2014

Many researchers have studied the tibial passive motion, the boundaries of which are defined by various knee ligamentious and bony constraints [1, 2, 3]. The technique has been used in clinical practices and experimental research to assess injury and predict likely surgical outcomes [1, 2]. After total knee replacement surgery (TKR), the implants’ design features and altered ligamentious tension provide the joint constraint and stability. Therefore, the change in passive envelope of motion from the natural condition could be used to observe the altered constraints and stability achieved in TKR knees. The objective of this study was to assess the change in passive envelope of motion after TKR with two implant designs: cruciate retaining and posterior stabilized.
A Dynamic Boundary Condition for the Pulmonary Vasculature
Authors: Clipp Rachel B. , Steele Brooke N.
Published: March 2014

Computational models can be used to predict the blood pressure and blood flow in a region of interest within the vascular system. To provide an accurate model, it is important to consider the organ-specific properties of the region of interest and apply those properties to the model. The pulmonary vasculature has several organ-specific properties, including the vessel compliance, specific geometry and respiratory process [1,2].
Polarized Light Microscopy for Analyzing Tissue Mechanics During In Vitro Acupuncture
Authors: Edgar Lowell Taylor , Julias Margaret , Shreiber David I. , Buettner Helen M.
Published: March 2014

Acupuncture is a traditional therapy originating in China almost 2000 years ago. Acupuncture has slowly been growing in popularity in the West, and clinical evidence has shown the potential for acupuncture as a low-cost ‘alternative’ therapy for an assortment of ailments [1]. The practice of acupuncture involves inserting fine needles into the skin followed by needle manipulation, usually by rotation. Recent studies by Langevin et al demonstrate that this rotation causes the subcutaneous connective tissue to couple to and wind around the needle [2–4], which suggests that mechanotransduction in the connective tissue might play a role in the therapeutic mechanisms that underlay acupuncture [2, 3]. To begin to decompose and quantify this complex mechanism at the tissue level in a controlled setting, we have simulated acupuncture in type I collagen gels in vitro, and have developed algorithms to quantify the tissue response following imaging with polarized light microscopy (PLM).
Effect of Anterior Translation on Anterior Knee Force in a Porcine Model
Authors: Boguszewski Daniel V. , Shearn Jason T. , Wagner Christopher T. , Butler David L.
Published: March 2014

The knee is a complex load-bearing joint that is subjected to compound loading patterns that often lead to injury. The most common traumatic injury occurs in the anterior cruciate ligament; with approximately 80,000 ACL injuries annually in the United States and 50,000 of these requiring reconstructions [1]. The role of the ACL is critical in knee joint stability. It prevents excess movement accounting for over 80% of the total restraining force for anterior tibial translation [2]. ACL reconstruction has been found to have a 10–25% failure rate [3]. These failures could be attributed to our limited understanding of the forces in the ACL during daily activities [3]. ACL measurements have been taken with invasive methods using strain gauges and other types of transducers surgically implanted within the ACL [4]. Noninvasive methods have used ultrasound and MRI to measure strains, or ground reaction forces, motion tracking systems, and biomechanical models to interpolate the in vivo forces [1,4,5]. Recently the use of robotic technology has offered the possibility of simulating in vivo motion paths to determine the force and moments in the knee [3,6,7]. This method has the ability to accurately and precisely control motions and allows for testing one specimen under different experimental conditions (e.g. ACL-intact versus ACL-deficient) [7]. It is important to use this robotics technology with an appropriate animal model taking into consideration joint size and anatomical structure to ensure the results are relevant [8]. The objectives of this study were to examine how anterior translation affected anterior knee force, to determine if right-left differences exist, and to determine if the porcine knee is ACL dependent.
In Vivo Tibiofemoral Contact Kinematics and Contact Forces During Dynamic Weight-Bearing Activities Following Total Knee Arthroplasty
Authors: Varadarajan Kartik M. , Moynihan Angela , D’Lima Darryl , Colwell Clifford W. , Rubash Harry E. , Li Guoan
Published: March 2014

Accurate knowledge of in vivo articular contact kinematics and contact forces is required to quantitatively understand factors limiting life of total knee arthroplasty (TKA) implants, such as polyethylene component wear and implant loosening [1]. Determination of in vivo tibiofemoral contact forces has been a challenging issue in biomechanics. Historically, instrumented tibial implants have been used to measure tibiofemoral forces in vitro [2] and computational models involving inverse dynamic optimization have been used to estimate joint forces in vivo [3]. Recently, D’Lima et al. reported the first in vivo measurement of 6DOF tibiofemoral forces via an instrumented implant in a TKA patient [4]. However this technique does not provide a direct estimation of tibiofemoral contact forces in the medial and lateral compartments. Recently, a dual fluoroscopic imaging system has been used to accurately determine tibiofemoral contact locations on the medial and lateral tibial polyethylene surfaces [5]. The objective of this study was to combine the dual fluoroscope technique and the instrumented TKAs to determine the dynamic 3D articular contact kinematics and contact forces on the medial and lateral tibial polyethylene surfaces during functional activities.
Verification of a Dynamic Knee Simulator Computational Model
Authors: Reeve Amber N. , Strickland Mike A. , Maletsky Lorin P. , Taylor Mark
Published: March 2014

Dynamic knee simulators aim to reproduce prescribed physiological loading and motions of the knee. The natural knee achieves stability through a complex interaction of the neuro-musculoskeletal system; thus, a knee simulator also requires a sophisticated control system to replicate human motion. Guess and Maletsky [1] developed a computational model to predict the required simulator inputs to produce the desired knee loading for dynamic activities on the Kansas Knee Simulator (KKS). The model built demonstrated conceptually that multi-body dynamics models could be used to simulate the KKS. However, as desired loading profiles became more complex, key limitations were discovered in the model; such as the model controller limited to a single axis under feedback control, no out-of-plane loading, not accounting for dynamic joint friction or damping of the actuators, and an inability of the model to flex pass 80° degrees of knee flexion. Thus, there was a need for a new computational model to overcome the limitations and to provide a more robust and complete comparison to the KKS. The new computational model will allow better utilization of the KKS capabilities for future cadaveric and prosthetic testing. This work outlines the sagittal-plane validation of the new computational model.
Vascular Remodeling During Atherosclerotic Plaque Build Up Is Controlled by the Plaque Free Part of the Vessel Wall
Authors: Wentzel Jolanda J. , Groen Harald C. , van der Giessen Rose , Rodriguez-Granillo Gaston , Gijsen Frank J. H. , van der Giessen Alina G. , Schuurbiers Johan C. H. , de Feyter Pim J.
Published: March 2014

Glagov et al. observed that positive, compensatory vascular remodeling during plaque build up prevents lumen narrowing until plaque burden, this is the relative plaque area to media bounded area, exceeds a threshold of 40% [1]. Until now it is not clear what mechanism controls the compensatory vascular remodeling during the atherosclerotic plaque build up and what determines absence or limits compensatory vascular remodeling. Plaque burden does not seem to reflect a parameter, which could serve as a limiting step in the known control process in the vascular system. For instance, healthy arteries control vascular remodeling by fluid flow induced shear stress via a number of endothelium dependent pathways [2]. The endothelium at the atherosclerotic plaque side is considered to be dysfunctional [2] and might thereby limit the remodeling process. Since plaques are mostly eccentric, we hypothesize that the healthy part of the artery (or plaque free wall) will respond to changes in shear stress and will determine the capacity of the arteries to remodel up till the moment of complete circumferential involvement of the disease. We investigated whether the size of the plaque free wall contributes to vascular remodeling over a 3 year period using serial intravascular ultrasound measurements by determining 1) the frequency of positive remodeling in segments with varying size of plaque free vessel wall 2) the degree of vascular remodeling for segments with varying size of plaque free vessel wall.
Morphological and Mechanical Property Correlations in Rabbit Tibial Plateau Cartilage Using a Fibril-Reinforced Biphasic Model
Authors: Golenberg Nurit , Kepich Eugene , Haut Roger C.
Published: March 2014

The rabbit model is often used for the study of the mechanical properties of articular cartilage. In numerous cases the authors are investigating the initiation and progression of osteoarthritis. The studies have shown that the mechanical properties of articular cartilage vary across the medial and lateral compartments of the tibial plateau. A review of these data indicates numerous inconsistencies in the location dependent mechanical properties and correlations with the macroscopic and microscopic characteristics of the tissue. For example, Hoch et al. [1] and Rasanen et al. [2] document a higher equilibrium tissue modulus in the medial than the lateral compartments of the tibial plateau, using a linear elastic model of the cartilage due to Hayes et al. [3]. In contrast, a recent study by Roemhildt el al. [4] documents a lower aggregate modulus in the medial versus the lateral compartments of the plateau, based on a linear biphasic model analysis. The study also documents a lower Poisson’s ratio in the medial than lateral facets, while more surface fissuring is noted in the medial compartment. While this surface morphology explains a higher permeability of the tissue in the medial than lateral compartments, the data are inconsistent with a notion set forth by Kiviranta et al. [5]. Using a fibril reinforced biphasic model analysis, this study would suggest a less structurally intact collagen network in the cartilage would yield a higher Poisson’s ratio in the medial than lateral compartments. These various inconsistencies in mechanical properties across the tibial plateau may be, in part, due to limitations of each computational model. The hypothesis of the current study is that a more structurally-based fibril-reinforced, biphasic model analysis of the rabbit cartilage will correlate better with the macroscopic and microscopic aspects of the tissue across the tibial plateau.
Concurrent Simulation of Neuromuscular Control and Tissue Deformation Is Possible by Adaptive Surrogate Modeling
Authors: Halloran Jason P. , Erdemir Ahmet , van den Bogert Antonie J.
Published: March 2014

Computational biomechanics has largely consisted of two distinct modeling domains, finite element (FE) analysis [1] and multi-body dynamics. Due to computational efficiency, muscle driven musculoskeletal models (or multi-body forward dynamic models) have been the primary method used in prediction of movement patterns [2]. FE methods, while computationally expensive, have the ability to yield important soft-tissue information such as stress [3] and coupling the two domains would yield more complete and useful simulations. Dynamic FE models have been successfully used for passive movement predictions but computational cost makes them unfeasible for movement optimization, where thousands of simulations may be required to find an optimal solution. Surrogate modeling is one possible approach to utilize a database of previous FE results to overcome the relatively high computational cost of FE simulations with different inputs. In general, surrogate modeling methods can be classified as global or local. Global methods fit a regression model to the complete set of input/output pairs whereas local methods include regression within a neighborhood of data points.
CT Imaging of Abdominal Aortic Aneurysms: Semi-Automatic Vessel Wall Detection and Quantification of Wall Thickness
Authors: Shum Judy , Goldhammer Adam , DiMartino Elena , Finol Ender
Published: March 2014

Quantitative measurements of wall thickness in human abdominal aortic aneurysms (AAAs) may provide useful information to predict rupture risk. Our procedure for estimating wall thickness in AAAs includes medical image segmentation and wall thickness detection. Image segmentation requires identifying and segmenting the luminal and outer wall boundaries of the blood vessels and wall thickness can be calculated by using intensity histograms and neural networks. The goal of this study is to develop an image-based, semi-automated method to trace the contours of the vessel wall and measure the wall thickness of the abdominal aorta from in-vivo, contrast-enhanced, CT images. An algorithm for the lumen and inner wall segmentations, and wall thickness detection was developed and tested on 10 ruptured and 10 unruptured AAAs. Reproducibility and repeatability of the algorithm were determined by comparing manual tracings made by two observers to contours made automatically by the algorithm itself. There was a high correspondence between automatic and manual area measurements for the lumen (r = 0.96) and between users (r = 0.98). Based on statistical analyses, the algorithm tends to underestimate the lumen area when compared to both observers.
An Innovative Method to Construct Silicone Cerebrovascular Replicas
Authors: Chueh Juyu , Wakhloo Ajay K. , Gounis Matthew J.
Published: March 2014

Our objective is to create cerebrovascular replicas that offer detailed geometry from clinical imaging data and have versatile applications such as testing new endovascular devices. To facilitate optical observation, simulate physiological environment and obtain reliable data, the replica is designed to be transparent and elastic with uniform thickness and good compatibility with imaging modalities such as computed tomography (CT), magnetic resonance imaging (MRI) and three-dimensional rotational angiography (3DRA). Several different manufacturing processes have been demonstrated in previous studies [1,2]. The physical 3D vasculature models were first obtained either by injecting methylmethacrylate into the human specimens to get vascular lumen casts of the part of interest or sending data derived from images generated from the imaging facilities to 3D printer for rapid prototyping. Different methods including repeated painting, dip-spin processing, and lost-wax technique were then applied to the casts to form the elastomeric replicas.
Spatiotemporal Temperature Measurement Using Quantum Dot Thermometry During Nanoshell Mediated Thermal Therapy
Authors: Han Bumsoo , Hanson Willard L. , Bensalah Karim , Tuncel Altug , Stern Joshua , Cadeddu Jeffrey A.
Published: March 2014

Due to advances and routine use of various diagnostic technologies, tumors are increasingly detected at very early stages. Thus, there is growing interest in employing minimally invasive surgical techniques for the management of tumors. Many of these procedures are thermal therapies, in which localized thermal lesions, either hyperthermic or cryogenic, are created to destroy malignant tissue in situ. However, the major drawback to the widespread dissemination and acceptance of thermal therapy is the lack of a reliable real-time intraoperative monitoring technique of the thermal lesion.
Universal Attachment for the Wheeling Striker
Authors: Hill Daniel C. , Todd Beth A.
Published: March 2014

Seeking to improve the quality of life for a disabled child, Stephen Horne of Birmingham, AL, designed and built a device to allow a person in a wheelchair to bowl. Although wheelchair bowling is not a new concept, Stephen’s Wheeling Striker was anything but common. Unlike similar devices, the Wheeling Striker provides the bowler a more independent bowling experience. The simple u-shaped device allows more control over the ball, yielding a more fulfilling and independent method of participating in the sports arena. The Wheeling Striker, however, was originally designed for one style wheelchair. This presented a need to make the device applicable for all wheelchairs. Because wheelchairs vary in size and configuration, designing a device that is capable of attaching to most wheelchairs is complex. The design of the universal attachment could not compromise the capability of the Wheeling Striker, the function of the wheelchair, or the safe operation of the wheelchair. The result was a universal attachment engineered to adapt to any wheelchair configuration and allow the Wheeling Striker to be a safe and effective bowling aid for the disabled.
High Shear Stress Induces Production of Matrix Metalloproteinase in Endothelial Cells
Authors: Sakamoto Naoya , Ohashi Toshiro , Sato Masaaki
Published: March 2014

One of the major physiological functions of vascular endothelial cells (ECs) includes remodeling of vessel walls. ECs secrete matrix metalloproteinases (MMPs) to degrade extracellular matrix (ECM), such as elastin and collagen. At least 23 different MMPs have been identified and have the capacity to degrade components of ECM. For example, MMP-9, known as a gelatinase, can degrade elastic fibers. The balance between MMPs and their specific inhibitors, tissue inhibitor of metalloproteinases (TIMPs), tightly governs vascular remodeling and is belived to play a central role in the pathogenesis of arterial aneurysms [1].
First Attempts Towards the Computational Simulation of Novel Stem-Cell Based Post Infarct Therapies
Authors: Ulerich Joseph P. , Goktepe Serdar , Kuhl Ellen
Published: March 2014

Cardiac disease is the most common cause of death in developed nations and affects more than 80 million American adults every year. Among cardiac diseases, myocardial infarction is one of the leading causes of congestive heart failure. Due to an infarct, the loads within the heart alter and within hours a remodeling process begins as the heart attempts to optimize function given its diminished capacity. This remodeling process itself can cause inconsistent thinning and dilation leading to potential problems such as volume overloaded hypertrophy and often causes further functional deterioration.
Lipid Phase Behavior: Databases, Rational Design and Membrane Protein Crystallization
Authors: Caffrey Martin
Published: March 2014

The relationship that exists between structure and function is a unifying theme in my varied biomembrane-based research activities. It applies equally well to the lipid as to the protein component of membranes. With a view to exploiting information that has been and that is currently being generated in my laboratory, as well as that which exists in the literature, a number of web-accessible, relational databases have been established over the years. These include databases dealing with lipids, detergents and membrane proteins. Those catering to lipids include i) LIPIDAT, a database of thermodynamic information on lipid phases and phase transitions, ii) LIPIDAG, a database of phase diagrams concerning lipid miscibility, and iii) LMSD, a lipid molecular structures database. CMCD is the detergent-based database. It houses critical micelle concentration information on a wide assortment of surfactants under different conditions. The membrane protein data bank (MPDB) was established to provide convenient access to the 3-D structure and related properties of membrane proteins and peptides. The utility and current status of these assorted databases will be described and recommendations will be made for extending their range and usefulness.
Fluid-Structure Interaction Study on Human Arterial Plaque With Patient Specific Geometry and Boundary Conditions
Authors: Gao Hao , Long Quan , Graves Martin , Li Zhi-Yong , Gillard Jonathan H.
Published: March 2014

Atherosclerotic plaque rupture has been extensively considered as the leading cause of death in western countries. It is believed that high stresses within plaque can be an important factor on triggering the rupture of the plaque. Stress analysis in the coronary and carotid arteries with plaque have been developed by many researchers from 2D to 3-D models, from structure analysis only to the Fluid-Structure Interaction (FSI) models[1].
Using Animal Models to Study Pediatric Cardiovascular Devices: The Impact on Fluid Dynamics
Authors: Long Tobias C. , Perone Michael V. , Deutsch Steven , Manning Keefe B.
Published: March 2014

Due to a high mortality rate for pediatric patients on the heart transplant list, smaller versions of ventricular assist devices (VADs) are being developed for these patients [1]. Ventricular assist devicess used in adult patients with end-stage heart failure have already become a viable option during the bridge-to-transplant period [2] and have also shown potential for aiding in myocardial recovery. A challenge to the development of pediatric VADs is the use of the aortic cannulae attached to them. During the development of the 12cc Pennsylvania State pediatric pulsatile VAD, particle image velocimetry (PIV) illustrated that hematocrit levels affected the fluid dynamics. The objective of this study is to compare the fluid dynamics of a pediatric blood analog and a goat blood analog within PVAD aortic cannulae.
Effect of Glenoid Shape on Stress in Glenoid Implants Undergoing Superior Subluxation
Authors: Li Jihui , Gardner Thomas R. , Levine William N. , Bigliani Louis U. , Ahmad Christopher S.
Published: March 2014

Today nonconforming glenohumeral implants are a common choice for total shoulder arthroplasty (TSA). Use of the conforming implant has decreased because of the “rocking-horse” effect [1], which leads to high stress and moments at the glenoid rim when the humeral head subluxes during range of motion. Retrieval studies have provided evidence that the rocking-horse effect is the major cause of implant loosening and fracture, delamination and deformation of the glenoid rim. Nonconforming glenoid implants, owing to a larger radius of the glenoid articular surface, can reduce the rocking-horse effect by improving the rim-head contact during subluxation. However, the nonconforming shape increases the contact stress and instability when the humeral head is in the central region, where motion frequently occurs [2].
Multiscale Modeling of Platelet Dynamics in Blood Flow With Application to Thrombus Formation
Authors: Mousel J. A. , Udaykumar H. S. , Chandran K. B.
Published: March 2014

From an averaged point of view, blood can often be treated computationally as a single-phase fluid of non-Newtonian character. Such a model may be appropriate if information regarding the bulk motion of the blood is all that is required. If, however, one seeks to describe the mechanisms leading to diseases such as thrombosis in the presence of foreign surfaces such as prosthesis, accurate predictions of platelet behavior in the dynamic environment of the blood are required. There are several effects that necessitate a careful treatment of platelet dynamics. For example, it is well known that the presence of red blood cells has a significant impact on radial distribution of platelets as well as the shear stress experienced by the platelets [1]. Therefore, the paths of and forces experienced by individual platelets are to be determined in order to predict the location and predilection for thrombus formation. However, since the length scales of the platelets are much smaller than the typical dimensions of the flow regions through which blood flows, it is not possible to capture platelet dynamics in a single-scale computation. Therefore, a multiscale technique for incorporating the dynamics of platelets and platelet-RBC interactions into large-scale flow simulations is required. We therefore examine a suspension of ellipsoidal and circular rigid particles that are representative of red blood cells and platelets carried in a Newtonian fluid to study the interaction or red blood cells and platelets.
Moving Living Cells and Fluids on Microchips for Diagnostics
Authors: Toner Mehmet
Published: March 2014

Biomedical applications of microfabricated devices is no longer limited to non-living systems as genes-on-a-chip or lab-on-a-chip, recent advances in the understanding of cellular behavior in microenvironments have started to pave the way toward living micro-devices. These emerging devices are expected to become key technologies in the 21st century of medicine with a broad range of applications varying from diagnostic, tissue engineered products, cell-based drug screening tools, and basic molecular biology tools. They will also include multiple cell types and/or genetically engineered cells to investigate complex interactions between cells from different tissues. These sophisticated devices will contain micro-engineered tissue units coupled to each other by complex microfluidic handling network. Microfluidic mixing systems will also precisely regulate the composition and concentration of drugs to be tested. This presentation will briefly review the early historical literature on the use of microtechnologies in cellular systems and then focus on various applications in cancer biology, HIV/AIDS and global health, inflammation, and systems biology. The presentation will primarily focus on interesting transport phenomena at the microscale and how such information can be used for the development of microfluidic systems for diagnostics and other applications.