bluuebunny/crossref_metadata_2025 huggingface dataset:
A Kinematics Based Testing Protocol for Studying Lumbar Disc Dynamics
Authors: Zufelt Nephi A. , Sander Elizabeth J. , Kelly Brian P. , DiAngelo Denis J.
Published: March 2014

The human lumbar intervertebral disc helps stabilize the vertebral bodies by absorbing and distributing loads acting on the spine while maintaining motion across the joint [1]. Current testing methodologies have been designed to study rigid mechanical devices (plates, rods, screws, mechanical joints), and are not suitable for assessing the overall ability of a compliant structure, like the intervertebral disc, to interact with the surrounding tissue structures and restore functionality to the joint [2]. The objective of this study was to develop a kinematics-based testing protocol that prescribes a known kinematics input to a lumbar spinal motion segment unit (MSU) and measures the capacity of the intact MSU to accommodate the motion in terms of compressive and shear loads and range of motion.
Effects of Extrinsic Muscle Integrity on Latissimus Dorsi Transfer for Irreparable Rotator Cuff Tears: A Simulation Study
Authors: Ling Hang-yin , Angeles Jovito G. , Horodyski MaryBeth
Published: March 2014

Massive rotator cuff tears are one of the most common shoulder problems among the elderly, leading to pain and disability of the upper extremity. Muscle transfer, which can compensate for some of the deficits, has been advocated as the primary treatment of irreparable massive rotator cuff tears or as a salvage procedure after failed repairs. Latissimus dorsi transfers offer a promising solution in the treatment of irreparable posterosuperior rotator cuff tears, resulting in pain relief and function improvement of patients with the tears. However, the clinical results are variable and the factors which determine outcome are poorly understood. Prior studies have revealed that the functional outcomes of latissimus dorsi transfers were adversely affected if there was a deficit in deltoid and teres minor muscles [1, 2]. For the patient with a deltoid injury, the transfer that follows a failed rotator cuff repair produces less functional improvement than if the transfer is performed as the primary treatment to repair the rotator cuff. It was revealed that the presence of a tear of the teres minor muscle might have some predictive value prior to surgery with regard to motion and function [1], whereas the degree of fatty infiltration also played a critical role after the transfer [2]. Outcomes of muscle transfers have been reported in the literature, but the effects of extrinsic muscle integrity on the functional outcomes in the latissumus dorsi transfer have not been addressed quantitatively. The purpose of this work was to study the effects of the extrinsic muscle integrity on the functional outcomes in the latissumus dorsi transfer using a three-dimensional integrated model of the upper extremity [3]. First, the effects of extrinsic muscle integrity on the preoperative functions of shoulders with massive rotator cuff tears were investigated. Second, these effects on the functional outcomes of muscle transfers were evaluated quantitatively.
Assessment of Possible Thermal Damage of Tissue due to Atherectomy by Means of a Mechanical Debulking Device
Authors: Lovik Ryang D. , Abraham John P. , Sparrow Eph M.
Published: March 2014

In vitro and cadaver experiments, coupled with numerical simulations, were performed to assess the possibility that orbital atherectomy might cause thermal damage of tissue. The experiments involved debulking operations on a surrogate artery and on the plaque-lined posterior tibial artery of a cadaver. Temperatures and coolant flow rates measured during these experiments enabled a numerical simulation of the debulking of a plaque-lined artery in a living human. The temperature variations from the numerical simulations were used to evaluate a thermal injury index. The resulting values of the index were found to be several orders of magnitude below the threshold value for thermal injury. It is concluded that it is extremely unlikely that the use of an orbital debulking device, the Diamondback 360°™ (Cardiovascular Systems, Inc.), can lead to thermal injury of the artery wall.
Biomechanics of the Human Anterior Lens Capsule
Authors: Pedrigi Ryan M. , Humphrey Jay D.
Published: March 2014

The primary function of the lens of the eye, termed accommodation, is to precisely focus light onto the retina by changing curvature and corresponding refractive power. Investigators have long sought to understand the mechanism of accommodation in terms of interactions of the constituent tissues, which recently has been aided by biomechanical modeling. Such models depend heavily on accurate measurements of tissue mechanical properties and seek to predict stresses and strains. A critical component of the accommodative apparatus is the lens capsule, a bag-like membrane that encapsulates the lens nucleus and cortex and mediates tractions imposed onto this structure by the ciliary body. In addition to this physiologic process during normalcy, the lens capsule also plays a fundamental role in cataract surgery; a procedure that involves three basic steps: a quarter of the anterior lens capsule is removed via the introduction of a continuous circular capsulorhexis (CCC), the lens is broken up and suctioned out, and an artificial intraocular lens (IOL) is placed within the remnant capsular bag. Although novel IOL designs have decreased post-surgical complications, they currently lack the important feature of accommodation. Therefore, mechanical analysis of the lens capsule will allow for an understanding of its interaction with an implant that may further assist in the design of future accommodating IOLs (AIOLs). Here, we report a novel experimental approach to study in situ the regional, multiaxial mechanical behavior of both normal and diabetic human anterior lens capsules. Furthermore, we use these data to calculate material parameters in a nonlinear stress-strain relation via a custom sub-domain inverse finite element method (FEM). These parameters are then used to predict capsular stresses in response to imposed loads using a forward FEM model.
Effect of Pathological and Physiological Loads on Interleukin-1α Protein Production in Porcine Menisci
Authors: Killian Megan L. , Haut Donahue Tammy L.
Published: March 2014

The meniscus performs several functions for the maintenance of knee joint health, such as load transmission and joint stability. Meniscal lesions have been suggested as a precursor to the onset of osteoarthritis (OA)[1]. Such lesions often lead to surgical removal of the torn portion of the meniscus, increasing cartilage to cartilage contact area. Partial meniscectomies have been shown using finite element analysis and histology to lead to altered and increased mechanical loading on the remaining meniscus and underlying articular cartilage[2,3]. Consequently, pathological compressive strains of more than 15% have been shown to increase proteoglycan breakdown and meniscal matrix degradation[4]. Preliminary investigations in our laboratory have demonstrated an increase in interleukin-1α (IL-1α) gene expression of meniscal explants subjected to pathological levels of dynamic compressive strain [6,7]. This inflammatory cytokine has been attributed to apoptosis and matrix degradation[5]. However, gene expression measurements merely suggest possible matrix remodeling mechanisms and do not necessarily result in protein syntheses from which matrix changes occur. Therefore, the purpose of this study was to quantify protein synthesis of IL-1α in porcine meniscal implants after compressive strain exercises. It was hypothesized that, similar to mRNA expression, protein synthesis for pathologically loaded (0 or 20% dynamic strain) samples would be greater than samples loaded to physiological levels (10% strain).
Skin Viscoelasticity Under Hypothermic Temperatures
Authors: Xu Feng , Lu Tianjian
Published: March 2014

Advances in electromagnetic technologies have led to recent developments in thermal treatments of diseased and injured skin tissue. These thermal treatment methods normally involve either a raising or lowering of temperature in targeted skin area to kill or thermally denaturize the necrotic cells but without affecting the surrounding, healthy tissue. It is proposed that a detailed understanding of the coupled biological-mechanical response under thermal loading will contribute to the design, characterization and optimization of strategies for delivering better treatments. Since it is technically very difficult to measure experimentally the bio-thermo-mechanical behaviour of skin tissue in physiological conditions, analytical and numerical simulations are used, where the quantification of the skin mechanical properties is an essential step towards building reliable computer simulations. So far, the mechanical properties of the skin tissue under normal physiological conditions have been studied experimentally a lot both in vivo and in vitro. However, little has been done on characterization of the mechanical properties of skin tissue under hypothermic conditions, which will be addressed in this study.
In Situ Tissue Engineering Using Angiogenic Nanoscaffold Enhances Diabetic Wound Healing in db/db Mouse Model
Authors: Balaji Swathi , Vaikunth Sachin S. , Parvadia Jignesh K. , Crombleholme Timothy M. , Narmoneva Daria A.
Published: March 2014

Tissue engineering offers an attractive alternative for treatment of chronic nonhealing diabetic ulcers, which account for more than 27% of the $10.9 billion total diabetic health care costs in the US annually [1]. The harsh environment of a diabetic ulcer is characterized by reduced expression of angiogenic factors, insufficient vascularization, excess protease activity, matrix degradation and hyperglycemia-induced cell apoptosis [2]. A major factor contributing to insufficient neovascularization in diabetic nonhealing wounds may be deficiency in the recruitment of endothelial cells (ECs) and endothelial precursor cells (EPCs) to the wound site [3]. Recent studies focusing on altering the wound’s cellular and molecular environment using bone-marrow-derived stem cells, growth factors (delivered either directly or using gene or cell therapy), bioengineered skin constructs, and biological matrices, such as collagen and hyaluronic acid gels had promising wound healing outcomes [4]. These studies suggest that strategies aimed at modifying the extracellular environment of the diabetic wound to enhance cell survival and angiogenesis are promising for development of new therapies for diabetic wound healing.
Anisotropic Wall Mechanics of Abdominal Aortic Aneurysms
Authors: Martufi Giampaolo , Rodriguez Jose F. , Finol Ender A.
Published: March 2014

The prevalence of AAA is growing along with population age and according to different studies AAA rupture is the 13th most common cause of death in the U.S., causing an estimated 15,000 deaths per year. In biomechanical terms, AAA rupture is a phenomenon that occurs when the developing mechanical stresses within the aneurysm inner wall, as a result of the exerted intraluminal pressure, exceed the failure strength of the aortic tissue. To obtain a reliable estimation of wall stress, it is necessary to perform an accurate three-dimensional reconstruction of the AAA geometry and model an appropriate constitutive law for the aneurysmal tissue material characterization. In this regard, a recent study on the biaxial mechanical behavior of human AAA tissue specimens [1] demonstrates that aneurysmal arterial tissue behaves mechanically anisotropic. The objectives of the present work are to determine the effect of material anisotropy of the aneurysmal abdominal aorta on wall stress distribution and to establish a comparison of wall mechanics between ruptured and unruptured aneurysms.
An Experimental Study of Blast Traumatic Brain Injury
Authors: Zhang Jiangyue , Yoganandan Narayan , Pintar Frank A. , Son Steven F. , Gennarelli Thomas A.
Published: March 2014

Traumatic brain injury from explosive devices has become the signature wound of the U.S. armed forces in Iraq and Afghanistan [1–4]. However, due to the complicated nature of this specific form of brain injury, little is known about the injury mechanisms. Physical head models have been used in blunt and penetrating head trauma studies to obtain biomechanical data and correlate to mechanisms of injury [5–8]. The current study is designed to investigate intracranial head/brain injury biomechanics under blast loading using a physical head model.
Effect of Tissue Dehydration on Smooth Muscle Cell Contractility, Collagen Matrix Structure and Overall Artery Biomechanics
Authors: Venkatasubramanian Ramji , Wolkers Wim , Soule Charles , Iaizzo Paul , Bischof John
Published: March 2014

Applications involving freeze-thaw in arteries such as cryoplasty and cryopreservation alter the arterial biomechanics significantly [1]. Tissue dehydration or bulk water loss is observed following freeze-thaw in native arteries as well as other artificial tissues [1, 2]. It is hypothesized that tissue dehydration observed during freeze-thaw is an important mechanism underlying the biomechanical changes in arteries. In order to test this hypothesis, dehydration was induced in arteries (without changing temperature or phase) by treating them with different concentrations of hyperosmotic mannitol solutions. Changes to smooth muscle cell (SMC) contractility, collagen matrix structure and overall artery biomechanics were studied following tissue dehydration. SMC contractility and relaxation were measured by studying the response of arteries to norepinephrine (NE) and acetylcholine (AC) respectively. Collagen matrix structure was assessed by studying the thermal denaturation of collagen due to heating using Fourier transform infrared (FTIR) spectroscopy and the overall artery biomechanics through uniaxial tensile tests.
Effects of Mechanical Strain on Syndecan-4, Focal Adhesion Complexes, and Site-Specific FAK Phosphorylation
Authors: Cheng Chao-Min , Steward Robert L. , Wang Danny L. , LeDuc Philip R.
Published: March 2014

Cellular mechanics involves the ability of cells to sense and respond to external forces. The type of deformations that cells undergo such as stretching, compression or shearing depends on physiological conditions such as how muscle deforms during movement. Using a custom fabricated stretching device, we focused on investigating how statically applied mechanical stretch affects syndecan-4, focal adhesion complexes and phosphorylated focal adhesion kinase (p-FAK). These results have potential implications in a variety of fields including biophysics, mechanotransduction, and cellular structure.
Image-Based Multiscale Modeling of Collagen Tissue-Equivalents: Comparison of Predicted Fiber Mechanics With Polarimetric Imaging
Authors: Sander Edward A. , Stylianopoulos Triantafyllos , Tranquillo Robert T. , Barocas Victor H.
Published: March 2014

The mechanical properties of tissue-equivalents and native tissues are derived from the composition and organization of their underlying components. In order to understand, predict, and engineer tissues, it is necessary that we understand how the underlying structure governs macroscopic behavior. Multiscale models provide a means to unravel these relationships, and are most effective when based on the structure of the tissue. In this work, we compared experimentally measured fiber kinematics and the macroscopic mechanical response of cell-compacted collagen cruciforms [1] with predictions from our multiscale model technique [2].
Post Thaw Processing of Red Blood Cells Using Microfluidics
Authors: Hubel Allison , Hanna Jacob , Mata Clara , Glass Katie , Longmire Ellen
Published: March 2014

Transfusion of red blood cells (RBCs) has been an integral part of medicine since the middle of the last century. In particular, RBCs have been the most transfused blood product in battlefield trauma care[1]. Cryopreservation of red blood cells has been used in particular by the military for a variety of reasons. The ability to preserve cells facilitates transportation of blood from one location to another. Combat can result in sharp increases in blood use for the treatment of civilian and military and frozen blood supplies can be used to meet variations in blood demand. In the civilian blood services, cryopreserved blood is typically used only for rare blood types[2] or for transfusion of neonates[3].
Method to Determine the Effect of the Frontal Plane Tibiofemoral Knee Angle on the Varus-Valgus Moment at the Knee During Stance and Gait
Authors: Canavan Paul K. , Yang Nicholas H. , Nayeb-Hashemi Hamid
Published: March 2014

Osteoarthritis (OA) is a degenerative disease of articular cartilage that affects millions of people [1]. Local biomechanical factors may severely affect initiation and progression of OA due to changes in loading conditions at the cartilage. The frontal plane tibiofemoral alignment effects the varus/valgus moment which could increase the overall loading at the knee. Biomechanical studies have reported that the varus moment is a key determinant in the load distribution at the knee [2, 3] and has been linked to OA progression [4, 5]. A normal knee will have a tibiofemoral angle approximately 7° valgus [6]. Deviation from this angle leads to a knee joint with a varus or valgus condition. In this investigation, a motion analysis procedure was developed to determine the affect of the frontal plane tibiofemoral angle on the force and moment reactions at the knee. The results of these methods could be utilized in a subject specific finite element model to determine the stress and strain at the knee cartilage and to suggest measures to prevent OA.
Bi-Articulate Approach to Addressing Shoulder Pain Issues in Manual Wheelchair Users
Authors: Dubowsky Sarah R. , Sisto Sue Ann , Langrana Noshir A.
Published: March 2014

Pain throughout wheelchair (WC) propulsion is a very real fact of life for individuals who use a manual WC as their primary means of locomotion. A number of studies have reported the prevalence of shoulder pain in manual wheelchair users (MWU’s) ranging between 30–73% [1, 2]. Questions exist as to what may cause the extent of such shoulder pain. It is possible that a lack of education on proper propulsion techniques leads to poor propulsion habits that can be detrimental to overall shoulder health. It is also possible that such acquired techniques translate into shoulder joint forces whose repetition and magnitude may be so high that they are injurious to the user.
Amniotic Fluid Derived Stem Cells for Cardiac Muscle Therapies
Authors: Soker Shay , Delo Dawn , Neshat Samira , Atala Anthony
Published: March 2014

Many forms of pediatric and adult heart disease are accompanied by high morbidity and mortality, as the heart muscle has limited regenerative potential. Cell therapy has been proposed as a means to promote the regeneration of injured heart muscle. We have established lines of broad spectrum multipotent stem cells derived from primitive fetal cells present in human amniotic fluid (hAFS) cells (1). AFS cells offer several advantages: They are easy to isolate and grow (no feeder layers needed), are highly expansive including clonal growth and they can differentiate into all germ layers. In the current study, we demonstrate that AFS cells can differentiate into cardiac muscle cells and be used for cardiac tissue regeneration.
Inhomogenous Stiffness of Articular Chondrocytes Measured by Atomic Force Microscopy
Authors: Chahine Nadeen O. , Sulchek Todd A.
Published: March 2014

Chondrocytes are responsible for the elaboration and maintenance of the extracellular matrix (ECM) in articular cartilage. Previous studies have demonstrated that mechanical loading modulates the biosynthetic response of chondrocytes in cartilage explants [1,2]. Therefore, the mechanical properties of chondrocytes play a pivotal role in regulating the interaction between the cell and ECM in situ [eg. 3–5]. The goal of this study is to investigate the indentation-dependent stiffness of chondrocytes using atomic force microscopy. Due to the composite nature of cellular organelles and the cytoskeleton, we hypothesize that chondrocytes exhibit a non-linear elastic modulus, requiring a non-Hertzian analysis of the contact and resulting stress-strain response [6,7]. The response of chondrocytes is investigated in a manner to probe the bulk stiffness of the cell (using 10 μm spherical probes), as well as the stiffness arising from composite subcellular structures (utilizing 3 μm spherical probes).
Non-Newtonian Study of Blood Flow in a Bifurcation With a Stabilized Finite Element Method
Authors: Marrero Victor L. , Tichy John A. , Jansen Kenneth E.
Published: March 2014

In recent years the methods of computational fluid dynamics (CFD) have been applied to the human cardiovascular system to better understand the relationship between arterial blood flow and the disease process. Obviously, the technical challenges associated with such modeling are formidable. Among the many problems to be addressed, in this paper we add yet another complication — the known non-Newtonian nature of blood. Due to the preliminary nature of the study, we limit ourselves to a generic and idealized geometry — a simple standard bifurcation of a tube with rigid walls. The pulsatile nature of the flow is considered. We use the Carreau-Yasuda model to describe the non-Newtonian viscosity variation. Preliminary results are presented for the Newtonian and non-Newtonian cases, at mean Reynolds number of 340, averaged over the cardiac cycle. The broad fundamental issue we wish to eventually resolve is whether or not non-Newtonian effects in blood flow are sufficiently strong that they must be addressed in meaningful simulations. Interesting differences during the flow cycle shed light on the problem, but further research is needed.
A Time Periodic Coupling for Fluid Structure Interaction in Distensible Vessels
Authors: Beulen Bart , Rutten Marcel , van de Vosse Frans
Published: March 2014

In clinical practice, ultrasound velocimetry is often used as a non-invasive method to determine flow through arteries. Generally, the flow is derived by assessment of the centerline velocity and assuming a certain velocity profile, e.g. a Poiseuille or Womersley profile. In order to apply these velocity profiles it is assumed that the measurement is performed on a relatively long, straight vessel. However, in-vivo vessels are slightly curved, which causes asymmetry in the velocity distribution and thus an inaccurate flow determination.
Three-Dimensional Segmental Coupling Responses of the Cervical Spine
Authors: Yoganandan Narayan , Stemper Brian D. , Pintar Frank A. , Paskoff Glenn , Shender Barry
Published: March 2014

The objective of the present study is to determine to the three-dimensional segment-specific coupling factors from healthy, normal, non-degenerated human cervical spinal columns under bending. Using pure moment loading protocols, cadaver subaxial columns were fixed at the two ends, off-axis forces and moments were recorded using a distal six-axis load cell, and primary and secondary rotations were obtained as a function of applied moments, up to 2.0 Nm. Segmental bone mineral densities were determined using quantitated computed tomography (QCT). Coupling factors were the smallest at the cervico-thoracic spinal segment. Cranial and caudal decreases of the coupling factors occurred from the mid-cervical segment at all applied moment levels, from 65 to 72% at the C4-C5 segment and 59 to 75% at the C5-C6 segment. On average, 55% of the primary rotation was coupled with the secondary rotation across the entire column. Peak coupling occurring in these segments may indicate a greater propensity for age-related changes to these vertebral levels, and offer support to the commonly observed lower cervical degeneration in clinical studies.
Platelet Damage Accumulation and Recovery due to Hemodynamic Shear Stresses: An In Vitro Study
Authors: Sheriff Jawaad , Jesty Jolyon , Bluestein Danny
Published: March 2014

It is well established that shear stress exposure activates platelets, and it has been shown that this flow-induced activation contributes significantly to thromboembolic complications in mechanical heart valves (MHVs) [1]. In addition, the platelet activation state (PAS) assay has been demonstrated to be an efficient technique to measure procoagulant activity [2]. However, there is a lack of reliable models to predict platelet damage accumulation. Such a tool allows thrombogenicity optimization of implanted prosthetic devices. Prior to developing this tool, certain aspects of platelet behavior in response to shear stress must be elucidated. Of special importance for developing accountable damage accumulation models is the recovery potential of platelets during repeated passages through devices, when not exposed to the elevated stresses characterizing blood flow in these devices. To accomplish this, PAS measurements were conducted in a Hemodynamic Shearing Device (HSD), where platelets were exposed to prescribed waveforms with alternating periods of high and low shear stresses.
Failure Properties and Material Characterization of Human Meniscal Attachments
Authors: Villegas Diego F. , Hauch Karen , Odegard Gregory M. , Haut Donahue Tammy L.
Published: March 2014

Menisci are C-shaped fibrocartilage structures that play an important role in supporting loads in the knee joint. The meniscal attachments anchor to the tibia by means of a ligamentous structure at the anterior and posterior horns. It has been shown that the meniscal attachments are important for restoring functionality to the knee [2].
Articular Surface-to-Tibial Baseplate Micromotion on the Natural-Knee® II and Natural-Knee® Flex Components
Authors: Mimnaugh Kimberly D. , Stoller Alex P.
Published: March 2014

The function of the locking mechanism between the ultra high molecular weight polyethylene (UHMWPE) articular surface and the tibial baseplate is to ensure that the two components remain connected and to minimize the relative motion that may occur between them. This relative motion that can occur between the two components has the potential to generate wear debris, which may eventually lead to bone osteolysis [1–2].
Modeling the Optical Performance of the Human Cornea Following Refractive Surgery
Authors: Pinsky Peter M. , van der Heide Dolf
Published: March 2014

Disturbances of the stromal microstructure occurring in refractive surgical procedures may create unexpected and undesired changes to the vision quality of the eye. Examples of common procedures which can profoundly alter the integrity of the stroma include laser ablation techniques such as Laser in situ keratomileusis (LASIK) for treating myopia, hyperopia and astigmatism, scleral incisions for lens extraction in cataract surgery and conducting keratoplasty (CK) for the treatment of hyperopia and presbyopia. The stroma is the primary load-carrying layer of the cornea and in the normal eye it is in a state of tension resulting from the intraocular pressure (IOP). When a surgical procedure disrupts the stromal tissue, the stresses in the tissue will be redistributed inducing what may be called the biomechanical response of the tissue to the surgical procedure. In the case of LASIK and CK, for example, surgeons wish to change the optical power of the cornea by reshaping the anterior surface. Biomechanically induced deformations may cause the achieved power to deviate from the planned correction and may also introduce aberrations in the resulting optical path. In contrast, in cataract surgery, surgeons may wish to preserve the original power of the cornea and in this case biomechanical deformations may defeat this objective.
Effects of Encapsulation Microenvironment on Embryonic Stem Cell Differentiation
Authors: Li Lulu , Schloss Rene , Langrana Noshir , Yarmush Martin
Published: March 2014

Pluripotent embryonic stem cells represent a promising renewable cell source to generate a variety of differentiated cell types. Although many investigators have described techniques to effectively differentiate stem cells into different mature cell lineages, their practicality is limited by the absence of large scale processing consideration and low yields of differentiated cells. Previously we have established a murine embryonic stem cell alginate-poly-l-lysine microencapsulation differentiation system. The three-dimensional alginate microenvironment maintains cell viability, is conducive to ES cell differentiation to hepatocyte lineage cells, and maintains differentiated cellular function. In the present work, we demonstrate that hepatocyte differentiation is mediated by cell-cell aggregation in the encapsulation microenvironment. Both cell aggregation and hepatocyte functions, such as urea and albumin secretion, as well as increased expression of cytokaratin 18 and cyp4507a, occur concomitantly with surface E-cadherin expression. Furthermore, by incorporating soluble inducers, such as retinoic acid, into the permeable microcapsule system, we demonstrate decreased cell aggregation and enhanced neuronal lineage differentiation with the expression of various neuronal specific markers, including neurofilament, A2B5, O1 and GFAP. Therefore, as a result of capsule parameter and microenvironment manipulation, we are capable of targeting cellular differentiation to both endodermal and ectodermal cell lineages.
Flow-Induced Wall Mechanics of Patient-Specific Aneurysmal Cerebral Arteries: Nonlinear Isotropic vs. Anisotropic Wall Stress
Authors: Cornejo S. L. , Rodriguez J. F. , Valencia A. A. , Guzman A. M. , Finol E. A.
Published: March 2014

There are several biomechanical factors involved in the formation, growth, remodeling, and eventual rupture of intracranial aneurysms. In particular, hemodynamic forces have a decisive role in the biomechanical environment of the aneurysmal cerebral vasculature. Most of the previous studies on vascular mechanics assessment of intracranial aneurysms are based on idealized geometries, where it has been suggested [1] that it is highly unlikely that saccular aneurysms expand due to a limit point instability. In addition, it has been reported [2] that some saccular aneurysms with non-spherical initial shape tend to become spherical when subjected to uniform pressure, because a spherical geometry is optimal to resist the pressure load, yielding a homogenous wall stress. In the present work, we present a comparison between anisotropic and isotropic constitutive models, which allows us to analyze the biomechanics of patient-specific cerebral aneurysmal arteries subjected to flow-induced pulsatile pressure. The results describe the effects of material anisotropy in the resulting wall mechanics of the intracranial vasculature geometries.
Parametric Finite Element Analysis of Physical Stimuli Resulting From Mechanical Stimulation of Tissue Engineered Cartilage
Authors: Babalola Omotunde M. , Bonassar Lawrence J.
Published: March 2014

The avascular nature of cartilage results in its limited inability to repair itself upon injury. As a result numerous approaches are being investigated as potential therapies for repair, including tissue engineering strategies. In addition, due to the low density of chondrocytes and the characteristic de-differentiation of the cells when expanded in monolayer [1], other cell types are being investigated as a source for cartilage repair as well. Mesenchymal stem cells (MSCs), which have been shown to differentiate into cells of several lineages including chondrocytes, osteoblasts and adipocytes [2], are being explored as a potential cell type for the regeneration of articular cartilage tissue [3,4].
The Dynamic Viscoelastic Properties of the Rat Lumbar Disc Are Decreased Following Nucleus Pulposus GAG Reduction
Authors: Orlansky Amy S. , Boxberger John I. , Elliott Dawn M.
Published: March 2014

The intervertebral disc has the important biomechanical function of dissipating energy during spinal loading. With degeneration, the disc experiences, among other changes, a loss of mechanical function and degradation of its composition. Using a rat model of early disc degeneration by injection of Chondroitinase ABC (ChABC), glycosaminoglycan (GAG) content in the nucleus pulposus (NP) was reduced which altered neutral zone mechanical properties. The contribution of decreased NP GAG content to the dynamic viscoelastic properties has yet to be determined. The advantage of dynamic viscoelastic testing is that it provides both viscous and elastic stiffness values as a function of loading frequency. These methods have been employed previously in a rabbit disc regeneration model, in ligament under three modes of loading, and in NP under oscillatory shear and compression. Therefore, the objective of this study was to determine the viscoelastic behavior of a rat lumbar disc at several equilibrium strains and to quantify the impact of GAG reduction on this behavior. Our hypotheses were: 1) elastic stiffness would be greater, and viscous stiffness and loss angle would be lower with increased frequency, and 2) both elastic and viscous stiffness would be lower in the reduced GAG discs at all frequencies.
Joint Distractions Sufficient to Produce Pain Increase Collagen Fiber Undulation in the Cervical Facet Capsular Ligament in the Rat
Authors: Quinn Kyle P. , Lee Kathryn E. , Winkelstein Beth A.
Published: March 2014

Whiplash and its associated disorders are significant societal and health problems with half of affected patients reporting neck pain at one year after injury [1]. The cervical facet joint and its capsule have been identified in both biomechanical and clinical studies as a common site of painful injury during whiplash [2]. Also, in vivo joint distractions, which mimic the facet capsule loading reported in human cadaveric whiplash simulations, can produce behavioral hypersensitivity suggestive of chronic pain symptoms in the rat [3]. Increased laxity and decreased stiffness in the capsule are also produced after both painful joint distractions in the rat [4] and whiplash loading of the neck using cadaveric spines [5]. Together, these findings suggest that subfailure loading of the joint and its capsule produces both mechanical changes and pain. Yet, identifying the mechanical response associated with pathophysiological conditions in the capsular ligament requires an understanding of if, and how, its load-bearing microstructure is altered following painful loading.
Biomechanical Analysis of Occupant Kinematics: Interpretation of Witness Marks
Authors: McGowan Joseph C. , Fisher Jacob L. , Lucas Scott R.
Published: March 2014

Understanding the occupant kinematics associated with an automotive accident is essential to evaluating injury causation and can lead to improved design of vehicles and restraint systems. Biomechanical analysis can be undertaken with knowledge of the accident reconstruction, that is, velocities and trajectories of the involved vehicle or vehicles, as well as the results of a detailed vehicle inspection and evaluation of other physical and photographic evidence. Evidence can be incomplete, seemingly contradictory, or compromised by the passage of time, and the biomechanical engineer must seek an explanation that is consistent with all that is known. Sometimes a physical examination of the accident vehicle provides a vivid understanding of injury causation. At other times the information obtained from the vehicle is understood only in the context of injuries sustained, witness statements, and/or information derived from other sources. We explain a methodology for conduct of a physical inspection of an accident vehicle to develop insight to be used in conjunction with information from other sources to elicit a clear and complete understanding of injury causation. We specify common and less common “witness marks” that are examined to develop constraints on possible occupant kinematics. Selected case studies highlight the importance of a careful inspection and suggest specific applications to accident scenarios.
Multiscale Simulations of the Healthy and Calcific Human Aortic Valve
Authors: Weinberg Eli J. , Mofrad Mohammad R. K.
Published: March 2014

In the heart’s aortic valve, maintenance of a healthy state and transition to disease states are modulated by the cells in the valve. The cells found within the valve leaflets are valvular interstitial cells (VICs) and those found on the fluid-facing surfaces are endothelial cells (ECs). Both types of cell are known to respond to their mechanical state; that is, the stresses and deformations imposed on a cell by its surrounding environment. Here we present a set of simulations to examine these mechanical states of the cells as the valve goes through its opening and closing cycle. We have created models at each of the cell, tissue, and organ length scales and introduced a system of reference configurations to link the scales. Each simulation and the set of multiscale simulation are verified against experimental data. This multiscale simulation approach allows us to accurately predict the dynamic, three-dimensional mechanical state of cells throughout the valve.
Geometric Control of Mechanical Forces and Stem Cell Differentiation
Authors: Wan Leo Q. , Kang Sylvia M. , Eng George , Lu X. Lux , Huo B. Bob , Gimble Jeffrey , Guo X. Edward , Mow Van C. , Vunjak-Novakovic Gordana
Published: March 2014

How can genetic information be translated to give specific and different spatial patterns of cellular differentiation? This is an important question in developmental biology. The spatial pattern of cellular behavior is generally considered solely dependent on the gradient of morphogens, which are usually soluble and diffusible chemicals. However, cellular function, e.g., proliferation, is found to be quite different even when cells are a few microns apart. Therefore, it has been proposed that tissue form arises as a result of feedback mechanism through mechanical forces, i.e., the tissue form will affect cellular function via mechanical force.
Comparative Freezing Response of Ejaculated and Epididymal Rhesus Monkey Sperm
Authors: Alapati Raghava , Goff Kelly , Kubisch Hans-Michael , Devireddy Ram V.
Published: March 2014

In the present study, we report the effects of cooling ejaculated and epididymal rhesus monkey (Macaca mulatta) sperm in the presence of extracellular. Water transport data during freezing of ejaculated and epididymal sperm cell suspensions were obtained at a cooling rate of 20 °C/min in the absence of any cryoprotective agents. Additional water transport data was obtained from ejaculated sperm at a cooling of 5 °C/min without CPAs and at 20 °C/min in the presence of 0.7M of glycerol, as well. Using previously published values, the bovine sperm cell was modeled as a cylinder of length 73.83 μm and a radius of 0.32 μm with an osmotically inactive cell volume, Vb, of 0.772Vo, where Vo is the isotonic cell volume. The subzero water transport response is analyzed to determine the variables governing the rate of water loss during cooling of bovine spermatozoa, i.e. the membrane permeability parameters (reference membrane permeability, Lpg and activation energy, ELp). The predicted best-fit permeability parameters ranged from, Lpg = 0.0023 to 0.0029 μm/min-atm and ELp = 10.6 to 45.5 kcal/mol. The subzero water transport response and consequently the subzero water transport parameters are not significantly different between the ejaculated and epididymal macaque spermatozoa under corresponding cooling conditions.
A Novel Scanning Method to Measure Shear Rate Around a Thrombus Using Micro Particle Image Velocimetry
Authors: Tolouei Elham , Nesbitt Warwick , Fouras Andreas , Carberry Josie , Jackson Shaun
Published: March 2014

The ability of platelets to adhere and aggregate to form a stable thrombus plays a key role in the normal haemostatic process at sites of vascular injury. However, thrombus formation plays a sinister role in arterial diseases leading to heart attacks or strokes.
Linear Viscoelastic Behavior of Adipose Tissue
Authors: Geerligs Marion , Peters Gerrit W. M. , Ackermans Paul A. J. , Oomens Cees W. J. , Baaijens Frank P. T.
Published: March 2014

Adipose tissue plays an important role in the load transfer between different tissue structures like skin and muscle. Though a plethora of papers can be found on properties of these surrounding tissue layers, only few papers addressed the properties of the adipose layer with its specific morphology. As a result, a thorough constitutive model describing the mechanical behavior of adipose tissue is lacking. This seems odd, because numerical models including the subcutaneous adipose tissue are needed in a wide field of applications such as skin device contact, needle insertion procedures, and understanding deep tissue injuries.
Numerical Study of Nanoparticle-Enhanced PCR
Authors: Zhang Aili , Chen Chao , Xu Lisa X.
Published: March 2014

The polymerase chain reaction (PCR) exponentially amplifies a DNA template and produces large numbers of specific DNA fragments. Because of its high sensitivity and efficiency, it becomes a common technique that is widely used in molecular biological. The addition of nano-gold particles into the template solution was found to greatly enhance the efficacy of PCR [1, 2]. Although the thermal effect has been suggested, the underlying mechanisms are still not clear, e.g. how the temperature field affects the replication of DNA at the molecular level. A typical PCR process consists of repeated cycling of three major steps: (1) fast heating to a temperature around 94°C for separating of the two strands DNA templates into single strand (Denaturation); (2) lowering the temperature to about 54°C for the primers to find the complementary part and anneal to the single stranded templates (Annealing); (3) increase of the temperature again to around 72°C for copying of the single templates with the action of the polymerase enzyme (Extension). The thermal history of the PCR determines the activity of the polymerase and rate of each reaction taken place during the process. And the motion of the primers, the DNA templates and the bases owing to both the Brownian effects and concentration gradients can also influence the specificity and reaction rates. The addition of nano-gold particles is expected to greatly alter both the heat and mass transfer efficiency. Thus, the micro-heat and mass transfer analysis of the nano-gold added PCR process has been performed. The temporal and spatial temperature distribution, and the reactants and products concentration have been numerically simulated. The influence of added nano-gold particles on the polymerase reaction rate, the efficiency and specificity of the PCR has evaluated. The possible thermal wave and resonance of the two-phase fluid at the micro-scale level has also been investigated, as well as the enhanced mass transfer of the templates and the reaction rate. The results show that both the thermal effects and physical properties of the nano-particles have contributed to the increase of the efficiency and specificity in the PCR process.
Impact of Outlet Valve Orientation on Fluid Dynamics of the 12 cc Penn State Pediatric Ventricular Assist Device
Authors: Valenti Isabella E. , Roszelle Breigh N. , Perone Michael V. , Deutsch Steven , Manning Keefe B.
Published: March 2014

Congenital cardiovascular defects are the leading cause of death among live births [1]. These defects involve the interior walls of the heart, valves, arteries, and veins and change the normal flow of blood through the heart and into the systemic system. Fortunately, several options exist for the more than 35,000 children born with congenital heart disease. Ventricular assist devices (VADs) currently hold the most promise for bridge-to-transplant treatment; however, a major problem for these devices is thrombus formation and deposition.
Comparison of LVAD Design Variants Using CFD Computed Thrombus Susceptibility Parameter
Authors: Medvitz Richard B. , Paterson Eric G.
Published: March 2014

The 70cc LionHeart was developed for use in patients weighing more than 70 kg, which prevents its use in many women, smaller men, and children. Scaled-down devices have been prone to thrombus formation during animal testing [1, 2]. It is suspected that the increased level of thrombosis is related to changes in the flow field when scaling from the 70cc to the 50cc device. Low fluid shear stresses and high residence times are traits that are believed to influence thrombus formation and deposition within artificial blood pumps [1].
Computational Analysis of Cerebrospinal Fluid Flow in the Normal and Obstructed Subarachnoid Space
Authors: Roldán Alejandro , Haughton Victor , Osswald Tim , Chesler Naomi
Published: March 2014

Patients with Chiari I malformations have increased cerebrospinal fluid (CSF) velocities compared to subjects without the malformation. Improved methods of analyzing the CSF fluid dynamics are needed to evaluate the impact of increased fluid velocities on pressure differentials in the upper cervical spinal canal and the potential impact of surgery on flow dynamics in patient-specific geometries. Here, a numerical technique based on the boundary elements method (BEM) for modeling the CSF flow within the spinal canal is presented. Results for velocity and pressure throughout the spinal canal were obtained at flow rates representative of different phases of the cardiac cycle for a healthy geometry and a Chiari model. In the healthy geometry, peak CSF velocities occurred anterolateral to the spinal cord at all flow rates. Partially obstructing the subarachnoid space increased peak systolic and diastolic velocities and shear stresses anteriorly. In addition, in the obstructed (Chiari) model, stagnation regions were evident posteriorly. The effects of surgical treatment on these CSF flow patterns warrant further study.
Viscoelastic Material Properties of the Hamburger-Hamilton Stage 12 Chick Heart
Authors: Yao Jiang , Varner Victor D. , Perucchio Renato , Taber Larry A.
Published: March 2014

Mechanical force is believed to play a significant role in regulating the morphogenetic process of cardiac looping. To better understand this process, it is crucial to determine the material properties of the early chick heart. It is well known that biological tissues are viscoelastic, however previous data on early stage embryonic heart tissue shows a hyperelastic behavior only [1] and currently, only late stage heart tissues have been quantified using viscoelastic properties [2]. The objective of this study is to use microindentation and nonlinear finite element method (FEM) to characterize the viscoelastic material properties of stage 12 chick heart during cardiac looping.
Affect of Abdominal Aortic Aneurysm Stent-Graft Design on Arterial Haemodynamics
Authors: Molony David S. , Callanan Anthony , Doyle Barry J. , Morris Liam G. , Walsh Michael T. , McGloughlin Tim M.
Published: March 2014

Abdominal Aortic Aneurysm is an irreversible dilation of the abdominal aorta. If left untreated the aneurysm may rupture possibly leading to death. There are currently two surgical treatments for AAA, the traditional open surgery and the minimally invasive repair also known as the endovascular aneurysm repair procedure (EVAR) [1–2]. The endovascular technique having been introduced in 1991 is still beset by problems [3]. These problems mainly consist of graft migration, endoleaks and occlusion. It has been suggested that redesigning current stent-graft devices is the best method of remedying these problems [4]. Conventional graft design has normally revolved around a constant proximal diameter which includes a sudden large diameter reduction at the iliac bifurcation. In the naturally occurring case the aorta tapers into the iliac arteries.