bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Characterization of Contact Lenses by Microindentation: Constant Velocity and Relaxation Testing
Authors: Lee Sung Jin , Bourne Gerald R. , Chen Xiaoming , Sawyer W. Gregory , Sarntinoranont Malisa
Published: March 2014

Mechanical and fluid transport properties of soft contact lenses may influence clinical performance, e.g., on-eye movement, fitting, and wettability, and may be related to the occurrence of complications, e.g. lesions [1, 2]. In the mechanical assessment of soft hydrated materials, indentation is increasingly being used because of its nondestructive methods for testing these material properties allow for multiple tests to be performed on the same sample, which will speed up the design and testing process for hydrogel contact lenses. [3]. Contact lens hydrogels may be described as a biphasic material. The material properties governing biphasic behavior are the Young’s modulus of the solid phase, Poisson ratio’s, and hydraulic permeability which is measure of fluid conductance in porous media. Previous studies of indentation of biphasic media have been completed by Mow and coworkers [4]. Also, computational finite element (FE) models have also been developed [5].
Theoretical and Experimental Investigation on Cross-Shear Dependency of Polyethylene Wear in Artificial Knee Implants
Authors: Schwenke Thorsten , Wimmer Markus A.
Published: March 2014

It has been shown that the contact motion path in artificial knee bearings is implant design dependent [1]. It is also known that multidirectional motion of artificial joints leads to higher wear rates compared to the application of unidirectional motion [2,3]. This phenomenon has been linked to “strain-hardening” of ultra-high molecular weight polyethylene (PE): the molecular chains in the surface layer align along the direction of shear. Since more energy is required to rupture the fibrils in their longitudinal direction than perpendicularly, less wear is generated if the direction of movement follows the molecular chain orientation [3]. Computer models could potentially become an important tool in wear prediction if this relationship could be quantified. A variable, defined as ‘cross-shear’ A/(A+B), with A being the fraction of motion along the molecular orientation and B being the fraction of motion perpendicular to the molecular orientation, takes this into account (Fig.1); however, pin-on-disc studies trying to validate this model found agreement for small cross-shear values only [4].
Modeling Heat Transfer in Human Arm and Forearm: Effect of Countercurrent Heat Exchange and Superficial Veins
Authors: Ferreira Maurício S. , Yanagihara Jurandir I.
Published: March 2014

In 1948, Pennes [1] presented a mathematical model of heat transfer in human tissue. The effect of blood flow on heat transfer was modeled as heat sink or source whose magnitude is proportional to the volumetric perfusion rate and difference between arterial and venous temperature [2]. Pennes assumed that thermal equilibrium occurs in the capillary beds, although Chen [3] showed that it occurs in bigger vessels before the blood enters the beds. Weinbaum et al. [2] and Zhu et al. [4] studied the thermal effect of vessels in the range of 50 to 1,000 μm on muscle tissue, and recognized the importance of countercurrent heat exchange. Hirata et al. [5] showed that the heat loss in the forearm is enhanced by the venous blood returning through the superficial veins and that arterious-venous anastomoses (AVAs) presented in the hands are important to thermoregulation.
Dynamic In-Vivo Scapular Motion in Abduction and Adduction
Authors: Massimini Daniel F. , Warner Jon J. P. , Li Guoan
Published: March 2014

Preserving scapular function following total shoulder arthroplasty (TSA) is essential for maintaining the normal range of dynamic motion of the shoulder joint complex. However, the ability to accurately measure in-vivo glenohumeral and scapular motion remains a challenge in the field of bioengineering. Single plane radiography was used to explore scapular rotation, but is limited to motion parallel to the imaging plane [1]. Bi-plane x-ray systems have been developed to overcome this limitation; however, these systems can suffer from relatively high radiation dosages [2, 3]. To minimize these effects, 6DOF electromagnetic tracking devices have been attached to the shoulder joint complex to measure scapulothoracic kinematics; except at large humeral abduction angles they can suffer skin motion artifacts [4, 5]. The purpose of this study was to investigate the feasibility and repeatability of using dual orthogonal cine fluoroscopy to quantify the dynamic scapular motions of living subjects after anatomic TSA, simulating an arm raise/lower cycle of drinking from a coffee mug.
Application of Acoustoelasticity: Identifying Tendon Damage
Authors: Frisch Catherine E. , Kobayashi Hirohito , Vanderby Ray
Published: March 2014

Damage to connective tissue such as tendons can occur via stretch injuries. During stretch injury, a tendon experiences permanent subfailure damage. Provenzano et al. showed that irreversible damage to the cellular structure of tendon or ligament occurs before noticeable changes can be measured in the mechanical behavior of the tissue [1]. The same paper also showed that during loading a portion of the curve can be classified as a sub-damage region where repeated loading in that range will have no effect on mechanical properties. There is also a damage region where plastic deformation and fiber tearing occurs. In this region, the severity of damage increases as the amount of strain increases. For the same level of functional loading after damage, tissue stiffness decreases while tissue strain increases. In-vivo measurements of damage indicators, such as strain and stiffness of a tendon, prove difficult using current techniques, since many of those methods are invasive (implanted strain gages) or large and non-portable (MRI)[2]. Recent studies have shown that ultrasound can be employed to assess ligaments and tendons by measuring ultrasound wave velocity and echo reflection [3,4].
Laboratory Modules for Reinforcement of Concepts Taught in Undergraduate Tissue Mechanics Course
Authors: Akkus Ozan , Sieving Allison
Published: March 2014

Tissue mechanics is one of the key courses of the Biomechanics subtrack of the undergraduate curriculum. The aims of the course include: 1) To understand the concepts of stress, strain, viscoelasticity and how these concepts apply to musculoskeletal tissues. 2) The ability to infer the state of stress and strain at a given point in a biological structure under torsional, axial, bending and other types of loads. 3) To understand the anatomy of musculoskeletal tissues. Accomplishment of these aims requires a holistic understanding of statics, strength of materials and microanatomy of connective tissues. Conveying this wide range of topics in one class is a major challenge and most textbooks on this subject lack depth either in engineering or in physiology. The purpose of this abstract is to describe the benefits of the integration of theory with experimental practice for bridging the difficult topics of statics, strength of materials and tissue anatomy within the framework of undergraduate biomedical engineering curriculum.
Carotid Plaque and its Effect on Ultrasound Carotid Distension Measurements: An In Vitro Study
Authors: Kips Jan G. , De Schryver Thomas , Swillens Abigail , Van Bortel Luc M. , Segers Patrick
Published: March 2014

Atherosclerosis can lead to formation of plaques in the arterial wall. Plaque rupture is a frequent and life-threatening event, resulting from complex degradative processes, especially when occurring in the coronary or carotid arteries where it can lead to myocardial infarction or stroke. The relation with plaque morphology and its mechanical characteristics has been elaborated extensively. However, from a mechanical point of view, most clinical research — especially in the carotid arteries — has been focused on noninvasive ultrasonic assessment of wall kinematics (distension) and, to a lesser extent, to strain and stresses in the radial direction.
A Comprehensive Flow Study of the 12 cc Penn State Pulsatile Pediatric Ventricular Assist Device
Authors: Roszelle Breigh N. , Deutsch Steven , Manning Keefe B.
Published: March 2014

While medical options for children born with congenital heart defects include transplantation, the amount of available organs remains limited. This lack of donors led to the development of the National Institute of Health’s National Heart, Lung and Blood Institute Pediatric Circulatory Support Program. Contracts have been awarded to five teams with the task of creating novel support systems for children, ranging from 2 to 25 kg [1]. As part of this program, Penn State has developed a 12 cc pulsatile pediatric ventricular assist device (PVAD), based on the successful 70 cc Pierce-Donachy adult assist device. During the process of reducing the volume of the device for pediatric use, changes were made to the design including altering the angles of the inlet and outlet ports. Previous two-dimensional flow visualization in the PVAD by Manning et al. had shown that these changes led to an increased three-dimensionality of the flow, the influence of which required further investigation [2]. It is important to characterize the fluid dynamics of the flow field inside assist devices such as the PVAD because certain characteristics including high blood residence time, stagnant flow and wall shear rates below 500 s−1 can lead to an increased propensity of thrombus deposition [3,4].
Numerical Study of Blood Flow at the End-to-Side Anastomosis of a Left Ventricular Assist Device for Adult Patients
Authors: Yang Ning , Deutsch Steven , Paterson Eric G. , Manning Keefe B.
Published: March 2014

Ventricular assist devices (VADs) have been used for years in adult patients with end-stage heart failure, during bridge-to-transplant, and they have recently shown promise in aiding in myocardial recovery [1]. While the fluid mechanics within VADs has been studied extensively [2], an area which must be more adequately addressed is the outflow cannula attached as an end-to-side anastomosis to the aorta. This attachment may lead to unnaturally high and low shear stresses, turbulence, flow separation, and stagnant flows. As a result, platelet activation and thrombus formation may occur. May-Newman et al. [3] developed a laminar, continuous, computational fluid dynamics (CFD) model to study how different outflow cannula anastomoses affect flow patterns in an adult aortic model. Turbulent flows, however, were not considered. The effects of the anastomosis on the flows in the secondary vessels were neglected as well. There is a lack of detailed description of the flow field across the cannulated adult aorta based on different VAD outflow cannula configurations and operating conditions. As a result, we have developed a comprehensive model to simulate turbulent blood flow in three-dimensional models of the cannulated adult aorta under continuous flow conditions and to study the impact of the secondary vessels on the aortic arch.
A Combined Theoretical-Experimental Paradigm for Studying Mechanical Conditioning of Tissue Engineered Arteries
Authors: Raykin Julia , Rachev Alexander , Zaucha Michael , Gleason Rudolph L.
Published: March 2014

There is a great unmet clinical need to develop small diameter tissue engineered blood vessels (TEBV) with low thrombogenicity and immune response, suitable mechanical properties, and a capacity to remodel to their environment [2, 3]. Development of a clinically useful small diameter TEBV will surely rely on techniques from a wide variety of disciplines, ranging from molecular and cell biology and biochemistry to material science and biomechanics. With regard to the latter, biomechanical stimuli, such as cyclic strain, have been shown to stimulate remodeling of collagen gel-derived TEBVs to greatly improve their mechanical behavior [5]. In native blood vessels, remodeling mechanisms appear to be aimed towards maintaining the local, 3-D mechanical environment (i.e., the local stresses or strains). It is becoming increasingly obvious that tissue engineered constructs also adapt to altered mechanical loading, and specific combinations of multidirectional loads appear to have a synergistic effect on the remodeling. Tissue engineered heart valve constructs exposed to cyclic flexure and shear stress, for example, exhibit a five-fold increase in production of extracellular matrix (ECM) constituents compared to constructs exposed to cyclic flexure or shear stress alone [1]. A critical gap remains, however, in understanding the role of both unidirectional and multidirectional loading on TEBV remodeling. Towards this end, we have developed theoretical and experimental frameworks to study remodeling of collagen and fibrin gel-derived TEBVs.
New Metric for Quantifying Stiffness of Intact Human Vertebrae
Authors: Buckley Jenni M. , Parmeshwar Rina , Lotz Jeffrey C.
Published: March 2014

Accurately quantifying the compressive stiffness of whole human vertebrae is important in the development of new treatment regimes for osteoporotic fracture repair and vertebral height restoration. Historically, whole bone stiffness has been measured from in vitro load-deformation behavior of isolated vertebrae using two different methods: 1) maximum slope of the load-deflection curve over a 0.2% strain window (“Method #1) [1, 2], and 2) slope of the best-fit line to the load-deflection curve over a specified loading range (most commonly 100–250 lbs, “Method #2”) [3, 4]. Because the whole bone load-displacement response is non-linear, these two measurement systems may yield different stiffness values for the same set of experimental data. Furthermore, both measurement systems are arbitrary, and there has been no investigation of the sensitivity of the whole bone stiffness metric to its method of measurement. The goal of this study is to develop and validate a standard method for calculating whole bone stiffness based on basic principles. In developing this method, we will also evaluate the robustness of existing stiffness calculation methods.
Adaptation of the Cardiac Myofiber Orientations Through Deformation: Computational Analysis of the Myocardial Structure
Authors: Kroon Wilco , Delhaas Tammo , Bovendeerd Peter , Arts Theo
Published: March 2014

The distribution of mechanical load throughout the wall is very sensitive to the myofiber orientation [1]. Yet, heterogeneity myofiber shortening, metabolism as well as oxygen consumption is limited, indicating heterogeneity in mechanical load is limited [2,4]. This suggests that mechanical loading is able to control the myofiber direction. However, the relation between mechanical loading and the myocardial structure remains unclear. Understanding this relation may be useful to gain additional knowledge about the role of mechanical factors in (patho-)physiology of the myocardial structure.
Analysis of Side Branch Access During Bifurcation Stenting
Authors: Mortier Peter , De Beule Matthieu , Van Loo Denis , Verhegghe Benedict , Verdonck Pascal
Published: March 2014

A common technique to improve the local blood flow through stenotic arteries involves the implantation of a metallic scaffold known as a stent. These devices have shown excellent results in unbranched vessels. However, the treatment of coronary bifurcation lesions remains an enormous challenge and is generally associated with an increased complication rate. Many different techniques have been proposed in clinical literature, but all the suggested methodologies have specific limitations [1]. In many cases, a stent is deployed in the main branch (MB) and logically, this compromises the side branch (SB) patency. This is a frequently encountered situation that can be improved by balloon dilatation through the side of the MB stent (fig. 1). However, such balloon inflation may result in unwanted distortions of the stent [2].
Multiscale Structural Analysis of Porcine Aortic Heart Valves Using a Collagen Fiber Network (CFN) Micromodel
Authors: Kim Hee Sun , Yap Choon Hwai , Dasi Lakshmi Prasad , Yoganathan Ajit P. , Haj-Ali Rami
Published: March 2014

Current Aortic Valve (AV) computational structural models do not explicitly account for the layered leaflet microstructure, i.e. collagen fibers and elastin matrix. Homogenized anisotropic hyperelastic material models are commonly used for the effective mechanical behavior of the leaflets. The later are difficult to calibrate and often unstable in structural simulations. In this study, we introduce a new heterogeneous material micromodeling approach for the porcine leaflet tissue that explicitly recognizes the collagen fiber network (CFN) distribution and integrate it with the elastin matrix into the global structural analysis of the AV system. The proposed multiscale (heterogeneous) material and structural (MMS) models are verified in their ability to predict the overall AV structural response from in-vitro pulsatile and static loops. Sophisticated imagery measurements are used to examine the kinematics and deformations of the leaflets. The proposed MMS framework is computationally effective in predicting the overall mechanical behavior of the AV structure.
Detection of Lumen, Thrombus and Outer Wall Boundaries of an Abdominal Aortic Aneurysm From 2D Medical Images Using Level Set Methods
Authors: Kossioris Georgios , Papaharilaou Yannis , Zohios Christos
Published: March 2014

Abdominal aortic aneurysm (AAA) is a localized dilatation of the aortic wall. Accurate geometric characterization is critical for a reliable patient specific estimate of AAA rupture risk. However, current imaging modalities do not provide sufficient contrast between thrombus, arterial wall and surrounding tissue thus making the task of segmenting these structures very challenging.
Asymmetry of Structural Characteristics of Lipid Bilayers Induced by Dimethylsulfoxide: An Atomistic Simulation Study
Authors: Alapati Raghava , Moldovan Dorel , Devireddy Ram V.
Published: March 2014

In a typical cryopreservation protocol, the system to be preserved is first equilibrated with chemicals known as cryoprotective agents (CPAs). CPAs have been shown to alleviate cell damage from either the solute effects or the formation of intracellular ice during the subsequent freezing process. Thus, an extensive body of literature reporting the effects of CPAs on cellular systems has been accumulated over the last 50 years; detailing largely experimental interactions between cell systems and chemicals. Recent advances in computational methodology now offer an additional dimension in our ability to understand the molecular interactions between cell membranes, idealized as lipid bilayers and CPAs at atomistic scales. Computer simulations provide unique capabilities for analyzing biomembrane properties from atomistic perspective with a degree of detail that is hard to reach by other techniques. The excellent agreement with the experiment obtained in various molecular dynamics (MD) studies [1] on simple model membranes has raised the confidence in applying the molecular dynamics simulations to even more complex systems. Dimethylsulfoxide (DMSO) is one of the most widely used solvents in cell biology and cryopreservation. During a typical cryopreservation protocol the DMSO composition of aqueous buffers inside and outside of the cell is known to differ considerably. To model and understand the structural changes in cell membranes in such a situation we performed MD simulations of an idealized lipid bilayer membrane which separates two aqueous reservoirs with and without DMSO. Zwitterionic dimyritoylphosphatidylcholine (DMPC) lipid bilayers was chosen as the model membrane.
Effect of Vascular Stiffness on Pulmonary Flow in Normotensive and Hypertensive States: Numerical Study With Fluid Structure Interaction
Authors: Su Zhenbi , Hunter Kendall , Shandas Robin
Published: March 2014

Invasive measurement of pulmonary vascular flow and pressure provides the hemodynamic status of the pulmonary circulation for children with pulmonary arterial hypertension (PAH). Clinicians are primarily interested in pulmonary vascular resistance, which is the mean pressure of the circuit divided by the mean flow through it [1], in that it is believed to well-quantify the right ventricular (RV) afterload, the primary determinant of mortality. However, previous and current investigations on the pulmonary vascular stiffness (PVS), input impedance and RV power [2–4] have found PVS to be an important contributor to power, and thus, afterload. These previous and current investigations focus on the analysis of clinical data, which is limited by the clinical equipment and techniques.
Biotransport in Optical Diagnostics, Imaging, and Therapy
Authors: Venugopalan Vasan
Published: March 2014

Non-invasive characterization and manipulation of tissue structure and function across spatial scales is one of the most challenging problems facing the use of optical techniques in biomedicine. A broad technical goal for the use of optical methods is the non-invasive measurement and/or manipulation of tissue structure and function on the microscopic scale while preserving the ability to interrogate the largest possible tissue volume. This overall goal has resulted in a plethora of optical diagnostic, imaging, and therapeutic methodologies that utilize specific light-tissue interactions and exploit various endogenous and/or exogenous optical contrast elements.
Strain Dependent Oxygen Diffusivity in Bovine Annulus Fibrosus
Authors: Yuan Tai-Yi , Jackson Alicia R. , Huang Chun-Yuh , Gu Weiyong
Published: March 2014

Intervertebral disc (IVD) is the largest avascular structure in the human body and nutrition supply into IVD is mainly through diffusion from the peripheral blood vessels. Poor nutrition supply to the disc is believed to be one of the causes for disc degeneration. While many studies have aimed at studying and analyzing the effect of mechanical loading on water content, chemical composition, and nutritional levels in IVD [1–3], no study has been reported to investigate the effect of mechanical compression on oxygen diffusion in the IVD tissue. The objective of this study was to determine oxygen diffusivity in annulus fibrosus (AF) samples under different levels of compression.
Reconstruction and Biomechanical Analysis of Low Speed Automobile Crashes
Authors: Lucas Scott R. , Fisher Jacob L. , McGowan Joseph C.
Published: March 2014

Biomechanical engineers are often asked to determine if and how the forces and motions in automobile accidents may be injurious to the vehicle occupants. In low-speed automobile crashes, where there is little or no vehicle damage and few if any distinct acute injuries, the materials available to analyze the crash may be sparse. The vehicles involved in low-speed crashes may not be available for inspection, or are only available after damage has been repaired or subsequent damage has been incurred. Repairs may be made “off the books” with no formal estimate or written record and no photographs. Medical records may be limited to an attorney’s recollection of an occupant’s complaints. In minor cases, police accident reports may be cursory and incomplete, summaries may be brief, and one or more vehicles may leave the scene prior to the police arriving.
Fluid Shear Stress Modulates S1P-Induced Endothelial Cell Invasion Into Three-Dimensional Matrices
Authors: Kang Hojin , Bayless Kayla J. , Kaunas Roland
Published: March 2014

Endothelial cells are subjected to biochemical and mechanical stimuli which regulate their angiogenic potential. We determined the synergistic effects of sphingosine-1-phosphate (S1P) and fluid shear wall stress (WSS) on the invasion of human umbilical vein endothelial cells (HUVECs) into three-dimensional collagen matrices. A collagen gel was incorporated into a parallel-plate flow chamber to apply controlled WSS to the surface of HUVEC monolayers over a period of 24hr. Cell invasion into the gels required the presence of S1P, with the effects of S1P being enhanced by WSS to an extent comparable to growth factor (VEGF + FGF-2) stimulation. The number of invading cells depended on the magnitude of WSS, with a maximal induction at a WSS of ∼5 dyne/cm2. The enhancement of invasion by WSS coincided with the phosphorylation of Akt and MMP-2 activation. These results provide evidence that WSS is a positive modulator of S1P-induced EC invasion into collagen gels and may contribute to the localization of sprouting angiogenesis at regions of low WSS such as post-capillary venules.
Quantification Using Fluoroscopic RSA of Distal Tibiofibular Syndesmotic Motion in the Intact State and Following Simulation of High Ankle Sprain
Authors: Kedgley Angela E. , Jenkyn Thomas R.
Published: March 2014

The distal tibiofibular syndesmosis is the articulation that lies between the tibia and the fibula at the ankle. Four ligaments — the anterior, posterior, and transverse tibiofibular ligaments and the interosseous ligament — are responsible for maintaining the stability of this articulation. Injuries of the syndesmosis are relatively rare but are frequently misdiagnosed [1]. Anterior-posterior and mortise radiography are often used to assist with diagnosis; however, they are not always accurate in identifying syndesmotic injuries, with success rates of 48% for anterior-posterior views and 64% for mortise views [2].
Determination of Natural Frequencies of Spherical Cells
Authors: Molavi Marjan , Bonakdar Ali , Stiharu Ion
Published: March 2014

In this paper, a finite element (FE) and scaled-up experimental modal analysis are employed to estimate the natural frequencies of the baker’s yeast cells. It is apparent the mechanical properties of the living cells and particularly the natural frequencies are highly related to the health condition of cells, and therefore a comprehensive analysis is carried out to determine the natural frequencies of individual cells.
Shear Fatigue Testing of All-Polyethylene Patellar Components
Authors: Stoller Alex P. , Mimnaugh Kimberly D.
Published: March 2014

Many total knee arthroplasty patellar implants are designed as all-polyethylene components with either 1 or 3 pegs for cement fixation. Failure of patellar components due to peg fracture is rare, but has been reported [1–4]. Excessive shear forces due to high patient weight and/or activity level have been implicated as potential causes of these rare failures. In order to assist with the design of all-polyethylene patellar components, a test method was developed to replicate the peg shear failure mode observed clinically. Peak patellofemoral forces have been predicted during mid-flexion activities such as stair climbing or sitting [5], therefore testing utilized patellofemoral contact load magnitudes consistent with these activities. The Natural-Knee® II System (N-K II) all poly patellar components manufactured from Durasul™ Highly Crosslinked Polyethylene were chosen for testing as a representative patella component design.
Effects of Endovascular Graft Morphology on the Migration Force
Authors: Hyun Sinjae , Hyun Young-Eun , Klyachkin Michael
Published: March 2014

Abdominal aortic aneurysm (AAA) is a result of the enlargement of the infra-renal aorta, expanding to a diameter of greater than 29 mm, or 1.5 times the diameter of the normal aorta. AAAs affect about 0.4% of people older than 50 years old; annually approximately 15,000 people die of aneurysm rupture [1,2]. For aneurysms less than 50 mm in diameter, the risk of rupture ranged from 0–2.3% per year, and for AAAs greater than 50 mm in diameter, the risk is 5–9% per year. However, 55 mm is the critical diameter for elective repair [3].
In Vivo Evaluation of Composite Polymeric Materials for Potential Application in a Trileaflet Heart Valve
Authors: Wang Qiang , Gallocher Siobhain L. , Datye Amit , Pinchuk Leonard , Schoephoerster Richard T.
Published: March 2014

The novel trileaflet heart valve that is presently undergoing investigation is a composite design of a proprietary polymer (SIBS), with an embedded fabric. SIBS had been shown to be a biocompatible, oxidatively stable polymer, and by adopting the natural valve leaflet design (reinforcement fabric), the SIBS trileaflet valve has the potential to have outstanding hemodynamic performance, durability, and biocompatibility [1,2].
An Anisotropic Hyperelastic Model Applied to Nondegenerate and Degenerate Annulus Fibrosus
Authors: O’Connell Grace D. , Guerin Heather L. , Elliott Dawn M.
Published: March 2014

The intervertebral disc is comprised of complex components that provide the disc with nonlinear, viscoelastic and anisotropic mechanical properties. The annulus fibrosus (AF) is a highly organized structure composed of concentric layers of collagen fibers embedded in a proteoglycan matrix. The AF has a high tensile stiffness and supports the large loads encountered by the disc. Mathematical models are needed to interpret and elucidate the meaning of experimental measurements made in mechanical tests. Based upon the classic work of Spencer [1], the AF has been modeled as a fiber-induced anisotropic hyperelastic material [e.g.,2–6], using the principle invariants of the Green deformation tensor and structural tensors representing the collagen fiber populations. Contributions of other AF components to mechanical behaviors are less understood than the fibers or matrix and may include connections between collagens and proteoglycans that can be incorporated into models through fiber-matrix interactions [2–4]. The previous models, however, have not been applied to experimental data from both nondegenerate and degenerate tissue. Constitutive modeling applied to nondegenerate and degenerate AF may elucidate microstructural changes with degeneration, will be useful for finite element models [5], and provide targets for disc treatments, such as tissue engineered constructs [7].
Test Methods for Accurate and Robust Material Property Measurements of Rodent Cortical Bone
Authors: Adams Douglas J. , Lublinsky Svetlana , Barrero Mauricio
Published: March 2014

Direct measurements of cortical bone material properties are difficult to achieve in rodent long bones due to the inherently small dimensions and difficulties in machining standard test specimen geometries [1]. Bone tissue properties in nearly all rodent studies are thus limited to estimates from flexural tests of long bone diaphyses. In addition to the inaccuracies imposed by the bending stress state itself, these material property estimates are further confounded by the non-uniform geometry of long bones along the diaphyseal length. The goal of this work was to develop a series of techniques to improve the accuracy and precision of material property measurements in rodent long bones, with explicit mathematical correction for geometrical complexity and multiple measurements from individual bones. In combination, these techniques provide a pragmatic serial test routine for collecting multiple direct measurements of cortical tissue elastic modulus and strength, with a potential for improving sensitivity and statistical power in skeletal studies using rodents.
Multi Layered Polycaprolactone-Elastin-Collagen Small Diameter Conduits for Vascular Tissue Engineering
Authors: McClure Michael J. , Sell Scott A. , Bowlin Gary L.
Published: March 2014

The architecture of the vascular wall is highly intricate and requires unique biomechanical properties in order to function properly. Native artery is composed of a mix of collagens, elastin, endothelial cells (ECs), smooth muscle cells (SMC), fibroblasts, and proteoglycans arranged into three distinct layers: the intima, media, and adventitia. Throughout artery, collagen and elastin play an important role, providing a mechanical backbone, preventing vessel rupture, and promoting recovery while undergoing pulsatile deformations [1]. The low-strain mechanical response of artery to blood flow is dominated by the elastic behavior, of elastin, which prevents pulsatile energy from being dissipated as heat [2]. A higher amount of energy loss indicates a decrease in recoverability, which could lead to eventual disruption of blood flow. An effective way to quantify recoverability is through hysteresis and compliance measurement. The hypothesis of this study was that the fabrication of a multi-layered electrospun tissue engineering scaffold composed of polycaprolactone (PCL), elastin, and collagen would demonstrate dynamic mechanical properties indicative of a highly elastic material, similar to the three distinct layers of native arterial tissue, while remaining conducive to tissue regeneration. PCL was chosen, in this case, to provide mechanical integrity and elasticity, while elastin and collagen would provide further elasticity and bioactivity [3,4].
Solute Transport in the Bone Lacunar-Canalicular System is Size and Shape Dependent
Authors: Li Wen , Pan Jun , Wang Liyun
Published: March 2014

Solute transport through the bone lacunar-canalicular system is believed to be essential for osteocyte survival and function. We have developed an approach that permits direct measurement of real-time solute movement in intact bones by using fluorescence recovery after phtobleaching (FRAP) technology [1]. The movement of vitally injected fluorescence dye (sodium fluorescein) among individual osteocytic lacunae was visualized in situ and the transport was analyzed by using a two-compartment mathematical model of solute diffusion. Our previous studies [1] suggested that the matrix surrounding osteocytes is similar to the glycocalyx of endothelial cells as first proposed by Weinbaum et al. (1994) [2]. In the present study, we investigated diffusive transport of five fluorescent tracers of different molecular weights and shapes in the bone lacunar-canalicular system (LCS). Our hypothesis is that the solute transport in lacunar-canalicular system is size and shape dependent, due to the molecular sieving of the pericellular matrix.
Hemodynamic Energy Dissipation in the Cardiovascular System: Generalized Theoretical Analysis on Disease States
Authors: Dasi Lakshmi P. , Pekkan Kerem , Sundareswaran Kartik S. , de Zelicourt Diane , Krishnankutty Resmi , del Nido Pedro J. , Yoganathan Ajit P.
Published: March 2014

Independent of the disease type, high hemodynamic energy dissipation in the circulation always impacts the pumping ventricle that, often always resulting in chronic heart failure as a secondary disease. For aortic stenosis, which is an arterial disease, an index based on total pressure (static plus dynamic) loss, which is a pseudo indicator of energy dissipation based on Bernoulli’s Equation, is widely used, while raw energy loss has been proposed to assess the severity of the Fontan connections clinically. Both diseases have separate frameworks for hemodynamic assessment of the respective dissipative lesions.
Ligament Property Optimization Within a Virtual Biomechanical Knee
Authors: Bischoff Jeffrey E. , Siggelkow Eik , Sieber Daniel , Kersh Mariana , Ploeg Heidi , Münchinger Marc
Published: March 2014

Specimen-specific modeling of the knee can be an effective tool for understanding knee mechanics [1–2]. It can also serve as a design tool for orthopaedic implant design through enhancing understanding of mechanics in the reconstructed knee [3], particularly when used in conjunction with instrumented components that record in vivo joint forces [4]. Techniques for developing specimen-specific computational geometric models of hard tissue and soft tissue are fairly commonplace, using imaging tools such as computed tomography (CT) and magnetic resonance (MR) in conjunction with software tools for image processing. Determination of specimen-specific material properties relies on measuring kinematics of the tissue associated with a defined load, either in vivo or in vitro, selecting an appropriate material model, and estimating values of the parameters of the model that closely match the experimental data. The goal of this work was to utilize inverse finite element (FE) analysis to determine material parameters of ligaments in a specimen-specific model of the knee, using both local and global optimization algorithms.
Development of a Novel In-Vitro Simulator for Elbow Motion
Authors: Ferreira L. M. , Pollock J. W. , King G. J. , Johnson J. A.
Published: March 2014

In-vitro simulation of active joint motion is useful to compare various rehabilitation protocols and surgical procedures. However to date, simulated active elbow flexion has only been achieved in the vertical orientation, in which the gravity load direction is constant. This makes vertical flexion analogous to lifting a weight. Flexion in the varus, valgus and horizontal orientations (of the humerus) are more challenging because gravity load resistance reverses direction part way through flexion, thus requiring more refined muscle control. Furthermore, horizontal flexion generates exceptionally high muscle and joint forces, while varus and valgus flexion challenge the stability of elbow joint articulation.
Biomechanical Comparison of the Load Sharing Properties of Unidirectional and Bidirectional Multilevel Anterior Cervical Plates
Authors: DiAngelo Denis J. , Roberson Jason , Kelly Brian P. , Karahalios Dean G.
Published: March 2014

Anterior cervical discectomy and graft fusion with spinal instrumentation is an accepted surgical method for the treatment of cervical spondylosis or other spinal disc diseases. Our previous biomechanical experiences with multi-level strut-graft mechanics have shown that constrained anterior instrumentation reverses the loading mechanics of a multi-level cervical strut-graft tested under physiologic flexion and extension conditions, which may promote graft pistoning [1]. The design of a constrained or static anterior cervical plate (ACP) may contribute to this phenomenon. Concurrently graft subsidence has also been noted with anterior cervical plate fusion surgery [2]. As the graft subsides, a gap can occur at the interface between the graft and vertebral end plates which can lead to pseudoarthrosis.
Correlation of Impact Force and Left Ventricular Pressure for Chest Impacts in an Animal Model for Evaluation of Commotio Cordis Protection
Authors: Dau Nathan , Link Mark S. , Madias Christopher , Bir Cynthia
Published: March 2014

Commotio cordis (CC) is defined as sudden cardiac death from a chest impact without any observable physical damage. This phenomenon is most prevalent in the youth population, especially during sporting events. Over 85% of those affected do not survive [1].
Biomechanics of Temporo-Parietal Skull Fracture From Blunt Ballistic Impact
Authors: Raymond David E. , Crawford Greg S. , Van Ee Chris A. , Bir Cynthia A.
Published: March 2014

The majority of engineering studies that quantify the biomechanical tolerance of the human skull to blunt impacts have been focused primarily on replicating automotive-related trauma [1]. Relatively little biomechanical data exists on skull fracture tolerance due to impacts with small surface area objects moving at high velocity, previously defined as blunt, ballistic impacts [2]. These impacts can occur with the deployment of less-lethal kinetic energy munitions that are now available to police and military personnel. The goal of less-lethal munitions is to impart sufficient force to a subject to deter uncivil, or hazardous, behavior with minimal risk for serious or fatal injury. A basic understanding of human biomechanical response and tolerance to blunt ballistic impact is needed for all areas of the human body in order to guide the design of such munitions. Law enforcement are trained to direct such munitions away from the head and at body regions such as the legs, however impacts to the head have occurred [3]. Previous research efforts have investigated facial impact tolerance to blunt ballistic impacts [4] however data regarding the temporo-parietal region are lacking. The goal of this research project is to provide basic bone strain data on temporo-parietal skull fracture for the purpose of developing finite element models of the human skull and fracture criterion for future study of blunt ballistic head impact.
Biomechanical Testing of a Novel Four-Rod Technique for Lumbo-Pelvic Reconstruction
Authors: Kelly Brian P. , Shen Francis H. , Schwab John , Arlet Vincent , DiAngelo Denis J.
Published: March 2014

Lumbo-pelvic fixation in cases involving total resection of the sacral vertebrae is difficult to achieve. Total sacrectomy results in enormous osseous and soft tissue defects as well as mechanical instabilities. Restoration of continuity and stability to the pelvic ring and spinal column is necessary for ambulation, and to enable patients to resume daily living activities sooner during rehabilitation.
Full-Field Viscoelastic Inflation Response of Bovine Cornea
Authors: Boyce B. L. , Nguyen T. D. , Jones R. E.
Published: March 2014

Most previous experimental studies and mechanical cornea models have ignored time-dependence of the cornea’s modulus, with only a few notable exceptions [1–3]. The purpose of the present work was to evaluate the time-dependent properties of cornea tissue independent of scleral contributions in a condition that is as physiologically-relevant as possible without resorting to costly and difficult in vivo characterization. A non-contact 3-dimensional displacement mapping tool was employed to image the entire deformation field across the entire cornea in real-time during pressurization. Unlike prior inflation-based studies, the present study’s unique approach permits dynamic real-time full-field mapping of deformation during inflation for the examination of viscoelasticity, isotropy, and homogeneity.
Reduction of Flow-Induced Blood Damage in Bileaflet Mechanical Heart Valves Through Passive Flow Control
Authors: Murphy David W. , Dasi Lakshmi P. , Glezer Ari , Yoganathan Ajit P.
Published: March 2014

Bileaflet mechanical heart valves (BMHVs), though a life-saving device in treating heart valve disease, are often associated with several complications including a high risk of hemolysis, platelet activation, and thromboembolism. To address this risk, patients must undergo prophylactic anticoagulation therapy. One likely cause of this hyper-coagulative state is the nonphysiologic levels of stress experienced by the erythrocytes and platelets flowing through the BMHVs. Research has shown that the combination of shear stress magnitude and exposure time found in the highly transient leakage jet emanating from the b-datum gap during valve closure is sufficient to cause hemolysis and platelet activation [1–3]. Reducing the shear stresses experienced by the blood flowing through the b-datum gap during valve closure may therefore reduce the prevalence of valve-related blood damage. Such shear stress reduction could be achieved by passive flow control, in particular vortex generators, incorporated onto the BMHV leaflet surface. Vortex generators have been used to control shear flows in various aerodynamic applications, and it is thus thought that their application to mechanical heart valve leaflet surfaces may reduce shear stresses by creating streamwise vortices that will serve to dissipate the regurgitant jet originating from the b-datum gap at the time of valve closure.
Validation of a Second-Generation Echo PIV System in Patient-Specific Carotid Artery Models: In Vitro Studies Using Pulsatile Flow
Authors: Zhang Fuxing , Lanning Craig , Mazzaro Luciano , Rech Bryan , Chen S. James , Shandas Robin
Published: March 2014

Echo Particle Image Velocimetry (Echo PIV), a novel opaque flow velocimetry technique developed in our laboratory, has been shown to be an effective 2-D flow measurement velocimetry method in prior studies for both steady and pulsatile flow conditions [1,2]. However, certain limitations remained in the first-generation system. These include inconsistent spatial resolution caused by the phased array transducer, and the relatively low frame rate (i.e., lower temporal resolution) [2]. To overcome these limitations, we developed a second-generation Echo PIV system with a custom-designed linear array transducer (5–14MHz, center frequency 10MHz) and customized post-processing of backscatter data. In vascular applications, the new system can provide frame rates up to 1428 fps (temporal resolution of 0.7 ms). The transducer has a consistent axial resolution of 150um, which brings a maximal velocity field resolution around 500um in axial direction. An ECG module was also integrated to enable the capture of ensemble data over the cardiac cycle.
Biocompatible Ionic Liquids: A New Approach for Stabilizing Proteins in Liquid Formulation
Authors: Kemp Regina , Fraser Kevin , Fujita Kyoko , MacFarlane Douglas , Elliott Gloria
Published: March 2014

The stabilization of proteins is a priority for several important fields, most notably the pharmaceutical industry. Protein-based therapeutic drugs have demonstrated significant efficacy in controlling and curing disease. Unlike traditional small molecule-based drug therapies, a major hurdle in the development of protein drugs is the challenge of maintaining the protein in the folded state throughout processing and also during storage at the end point-of-use. When a protein is taken from its native environment, it is often unstable and unfolds. Because the protein’s 3-dimensional structure is responsible for its functional activity, much work has been dedicated to finding excipients that will stabilize proteins outside of their native environment.
Treatment Planning Model for Nanotube-Mediated Laser Cancer Therapy
Authors: Sarkar Saugata , Rylander Marissa Nichole
Published: March 2014

The goal of the project is to develop an effective treatment planning computational tool for nanotube-mediated laser therapy that maximizes tumor destruction and minimizes tumor recurrence. Laser therapies can provide a minimally invasive treatment alternative to surgical resection of tumors. However, the effectiveness of these therapies is limited due to nonspecific heating of target tissue and diffusion limited thermal deposition which often leads to healthy tissue injury and extended treatment durations. These therapies can be further compromised due to induction of molecular chaperones called heat shock protein (HSP) in tumor regions where non-lethal temperature elevation occurs causing enhanced tumor cell viability and imparting resistance to chemotherapy and radiation treatments which are generally employed in conjunction with hyperthermia.
A Novel Break Point Parameter as a Diagnostic Tool for Left Ventricular Diastolic Dysfunction
Authors: Stewart Kelley C. , Kumar Rahul , Charonko John J. , Vlachos Pavlos P. , Little William C.
Published: March 2014

Cardiovascular disease is one of the leading causes of death worldwide and claims one out of every three deaths in the United States [1]. There is a greater need than ever for more accurate and robust diagnostic tools with the increasing number of deaths caused by this disease. Color M-mode echocardiography is a technique that is commonly used in the diagnosis of Left Ventricular Diastolic Dysfunction (LVDD).
Effects of Simulated Injury on Tissue Deformation and Mechanical Properties of the Anteroinferior Glenohumeral Capsule
Authors: Voycheck Carrie A. , Brown Andrew J. , McMahon Patrick J. , Debski Richard E.
Published: March 2014

The glenohumeral joint is the most dislocated major joint in the body with most dislocations occurring anteriorly. [1] The anterior band of the inferior glenohumeral ligament (AB-IGHL) is the primary passive restraint to dislocation and experiences the highest strains during these events. [2,3] It has been found that injuries to the capsule following dislocation include permanent deformation, which increases joint mobility and contributes to recurrent instability. [4] Many current surgical repair techniques focus on plicating redundant tissue following injury. However, these techniques are inadequate as 12–25% of patients experience pain and instability afterwards and thus may not fully address all capsular tissue pathologies resulting from dislocation. [5] Therefore, the objective of this study was to determine the effect of permanent deformation on the mechanical properties of the AB-IGHL during a tensile elongation. Improved understanding of the capsular tissue pathologies resulting from dislocation may lead to new repair techniques that better restore joint stability and improve patient outcome by placating the capsule in specific locations.