bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of In Vivo Lumbar Range of Motion During Flexion in Healthy Subjects
Authors: Claeson Amy A. , Nuckley David J. , Barocas Victor H.
Published: January 2014

The lumbar facet joint (FJ) is a unique structure located on the posterior spine. The joint is composed of two articular facets from adjacent vertebrae, which are connected by a flexible and strong facet capsular ligament (FCL) (Figure 1). Two FJs (one on each side of the spinous process) are located at every spine level and along with the IVD, create a motion segment. During spinal flexion and extension, the FCL undergoes a complex motion, with extension and shear dominating the deformation (Figure 2). The collagenous FCL guides and restricts the relative motion of adjacent vertebra in flexion.
Speeding Up Fluid-Structure Interaction Simulation of the Blood Flow in a Flexible Artery Using Sub-Cycling: Stability and Accuracy
Authors: Taelman L. , Degroote J. , Vierendeels J. , Segers P.
Published: January 2014

In the cardiovascular system, the distensibility of the blood vessels is the driving mechanism of wave propagation. As the blood flow interacts mechanically with the flexible vessel walls, this phenomenon gives rise to complex fluid-structure interaction (FSI) problems. Several studies comparing rigid wall with FSI simulations in settings with large deformations demonstrate the importance of including the flexible wall modeling, in particular with respect to the simulation of wall shear stress. As both the equations governing the flow and the arterial deformation (and their interaction) need to be solved, FSI simulations are characterized by a high computational cost. To make them applicable to a broader range of cardiovascular problems, efforts to reduce the calculation time (such as the use of so-called ‘sub-cycling’) should be made.
Spline Based Microstructural Mapping for Soft Biological Tissues: Application to Aortic Valves
Authors: Aggarwal A. , Aguilar V. S. , Lee C. H. , Ferrari G. , Gorman J. H. , Gorman R. C. , Sacks M. S.
Published: January 2014

Splines are the standard tools in computer aided design for geometric representations and have been recently integrated into the finite element analysis of structures and fluids [1]. As the biomedical engineering is making progress, there is a need for an integrated tool for expanding the geometrical representation to include the microstructural details specific to soft tissue, e.g. fiber alignment, orientation, crimp and stiffness. In this work, a spline-based method is presented for aortic valves which facilitates mapping of the fiber structure from any aortic valve specimen to any other aortic valve geometry through a common parameter space. This techniques also has the ability to calculate mean tissue microstructure of representative population. Also strain and pre-strain from in-vivo state to the in-vitro state, where all the mechanical tests are done, are calculated for forward and inverse modeling of aortic valves.
Relationship Between Supersonic Shear Wave Elastography Measurement and Passive Muscle Force: An Ex-Vivo Chicken Study
Authors: Koo Terry K. , Guo Jingyi , Cohen Jeffrey H. , Parker Kevin J.
Published: January 2014

As a skeletal muscle is being stretched, it reacts with increasing passive resistance. This passive force component is important for normal muscle function [1]. Unfortunately, direct measurement of muscle force is still beyond the current state-of-the-art. In the present study, we investigate the feasibility of using Supersonic shear wave elastography (SWE) to indirectly measure passive muscle force using an ex-vivo chicken model.
Development of a Laboratory Model of Aortic Valve Calcification
Authors: Biddle Stephen , Seaman Clara , Sucosky Philippe
Published: January 2014

Calcific aortic valve disease (CAVD) is the most prevalent heart valve disease in the U.S. and is characterized by the formation of calcific lesions within the valve leaflets [1]. The emerging hemodynamic theory of CAVD pathogenesis assumes a link between gradual hemodynamic alterations caused by the growing lesions and further disease progression [2–5]. In order to test this hypothesis, it is necessary to quantify the hemodynamic changes experienced downstream of a calcifying valve.
Variable Modulus Muscular Thin Films for Measuring the Effect of Mechanical Environment on Vascular Contractility
Authors: Steucke Kerianne E. , Voigt Paige A. , Hald Eric S. , Alford Patrick W.
Published: January 2014

Recent results have demonstrated that cell function is affected by local mechanical environment [1]. In vascular smooth muscle cells (VSMCs), for example, substrate stiffness can control phenotype expression and migration rate [2]. Pathologies, such as atherosclerosis, and therapeutic interventions, such as stents, can alter VSMCs’ mechanical environment. The primary function of VSMCs is vascular tone modulation via contraction and relaxation and loss of VSMCs’ contractile function may play a role in the pathogenesis of atherosclerotic plaques and restenosis of stents. To date, it is not known whether perturbation of the mechanical environment directly affects contractile function in these diseased vessels.
Hemodynamic Forces Regulate Collagen Deposition in the Embryonic Chicken Outflow Tract
Authors: Rennie Monique Y. , Danilchik Michael , Thornburg Kent L. , Rugonyi Sandra
Published: January 2014

Alterations in blood flow at early embryonic stages can lead to detrimental remodeling and heart defects, but these structural adaptations are not well understood. We hypothesize that deposition of collagens will be increased as shear stress is increased — leading to a stiffer wall. To test this hypothesis a suture (OTB) was tightened around the outflow tract (OFT) of stage HH18 chick embryos for 24 hours to reduce cross sectional area of the lumen. Sham and OTB embryos were immunostained for collagen I, III, VI and XIV, imaged with confocal microscopy, and staining was quantified by grayscale analysis. Changes in fibril collagens I and III were not observed, however deposition of collagens VI and XIV increased in a degree-of-constriction dependent manner. The observed increase in collagen VI and XIV deposition suggests they play a key role in structural adaptation to increased hemodynamic pressure.
3D Computed-Tomography Models for
In Vivo Analysis of the Neural Foramen Geometry After Anterior Cervical Decompression and Fusion
Authors: Ohara Yukoh , Hara Takeshi , Inoue Nozomu , Hirano Yoshitaka , Espinoza Orías Alejandro A. , Mizuno Junichi
Published: January 2014

Cervical radiculopathy is a dysfunction of a nerve root in the cervical spine, which is often a result of narrowing neural foramen of the cervical spine. The cervical foramen boundaries consist of the superior and inferior pedicles, the posteroinferior margin of the superior vertebral body, the posterosuperior margin of the inferior vertebral body, and the superior and inferior articular facets (Fig 1). Because the neural foramen’s boundaries consist of two movable joints, dynamic changes occur to the neural foramen dimensions. These dynamic changes and the presence of the dorsal root ganglia present the possibility of the neural foramen contributing to the complex etiology of radiculopathy. Current surgical practice recommends an Anterior Cervical Decompression and Fusion (ACDF) procedure to treat radiculopathy. For the reasons stated above, pre- and post-surgical neural foramen geometry assessment is important to evaluate effects of the treatment. To the best of the authors’ knowledge, an accurate in vivo and computerized tomography (CT) three-dimensional (3D) model has not been demonstrated in the literature.
Temperature Control During Fibrillogenesis Allows for Improved Magnetic Alignment of Collagen
Authors: Shannon Garrett , Novak Tyler , Voytik-Harbin Sherry L. , Neu Corey P.
Published: January 2014

Osteoarthritis (OA), commonly known as ‘wear and tear’ in human joints, affects over 27 million people in the United States [1]. There is currently no encompassing solution for the regeneration of damaged articular cartilage. One potential solution involves the close emulation of the native structure of articular cartilage, with special consideration given to maintaining the distinct organized zonal ultrastructure, characterized by both random and highly aligned zones of collagen fibrils, in order to preserve mechanical and cell signaling properties of the extracellular matrix [2]. Techniques such as electrospinning achieve high degrees of alignment, but do so at the cost of denaturing the collagen molecule [3] that may lead to inferior cell recognition and mechanical strength.
Continuum Description of the Time- and Strain-Dependent Poisson’s Ratio of Ligament Under Finite Deformation
Authors: Swedberg Aaron M. , Reese Shawn P. , Maas Steve A. , Ellis Benjamin J. , Weiss Jeffrey A.
Published: January 2014

Ligament volumetric behavior controls fluid and thus nutrient movement as well as the mechanical response of the tissue to applied loads. The reported Poisson’s ratios for tendon and ligament subjected to tensile deformation loading along the fiber direction are large, ranging from 0.8 ± 0.3 in rat tail tendon fascicles [1] to 2.98 ± 2.59 in bovine flexor tendon [2]. These Poisson’s ratios are indicative of volume loss and thus fluid exudation [3,4]. We have developed micromechanical finite element models that can reproduce both the characteristic nonlinear stress-strain behavior and large, strain-dependent Poisson’s ratios seen in tendons and ligaments [5], but these models are computationally expensive and unfeasible for large scale, whole joint models. The objectives of this research were to develop an anisotropic, continuum based constitutive model for ligaments and tendons that can describe strain-dependent Poisson’s ratios much larger than the isotropic limit of 0.5. Further, we sought to demonstrate the ability of the model to describe experimental data, and to show that the model can be combined with biphasic theory to describe the rate- and time-dependent behavior of ligament and tendon.
Detailed Cadaveric Simulation of Landing Reveals Timing Sequence of Multi-Planar Knee Kinematics: Implications for ACL Injury
Authors: Kiapour A. M. , Quatman C. E. , Goel V. K. , Wordeman S. C. , Hewett T. E. , Demetropoulos C. K.
Published: January 2014

Over 120,000 anterior cruciate ligament (ACL) injuries occur annually in the United States, mainly affecting the young athletic population. Non-contact injuries are reported to be the predominant mechanism of ACL injury (>70% of ACL injuries), which often occur during landing with high ground reaction forces, muscle forces and segmental inertia. An improved understanding of the mechanisms underlying non-contact ACL injury and inciting events can be used to improve current prevention strategies and decrease the risk of early-onset osteoarthritis. Previous biomechanical and video analysis studies have demonstrated that anterior tibial translation (ATT), knee valgus and internal tibial rotation (ITR) are associated with non-contact ACL injuries [1–3]. While the effects of these factors on ACL injury risk have been extensively studied, there is still controversy and debate about the timing in which these motions occur and reach maximum values during a jump landing task. The current study aimed to investigate interactions between tibio-femoral joint kinematics and ACL strain through a detailed cadaveric simulation of the knee biomechanical response during landing from a jump. For this purpose, instrumented cadaveric limbs were used to simulate bi-pedal landing following a jump utilizing a novel testing apparatus.
Theoretical Simulation of Temperature Elevations in Tumors Using Monte Carlo Method and Comparison to Experimental Measurements During Laser Photothermal Therapy
Authors: Manuchehrabadi Navid , Chen Yonghui , LeBrun Alexander , Ma Ronghui , Zhu Liang
Published: January 2014

Nanotechnology using gold nanoshells or nanorods is a newly developed hyperthermia approach and has been tested in the past several years in cancer treatment.1–2 Gold nanorods have a diameter of ∼10 nm and an aspect ratio of approximately four. By varying the geometric ratio, the nanostructures can be tuned to have strong absorption and scattering to a specific laser wavelength. Designing an optimal treatment protocol of laser photothermal therapy requires understanding of gold nanorod deposition inside the tumor after injection, its resulted specific absorption rate (SAR) distribution, and the ultimate temperature field in the tumor during the treatment. Recent microCT studies by our group have suggested that the gold nanorod solution injected into PC3 prostatic tumors results in an almost uniform distribution of the gold nanorods in the tumors.3 The Monte Carlo method has been used in the past to determine the heating pattern (SAR) of laser-tissue thermal interaction.4 However, the accuracy of the theoretical simulation of the temperature fields in tumors relies on precise measurements of the optical properties of the tumors with nanorods presence.
The Experimental Investigation of Flow Separation Downstream of an Axisymmetric Stenosis in Newtonian and Non-Newtonian Flow Environments
Authors: Walker Andrew M. , Johnston Clifton R. , Rival David E.
Published: January 2014

The assumption of Newtonian behavior to characterize circulating blood is applicable to large, healthy, arteries of the vasculature. However, at low shear strain rates, blood displays marked non-Newtonian behavior resulting from red blood cell adhesion. Consequently, the consideration of non-linear viscous behavior may be of critical importance to accurately quantify critical hemodynamic parameters in separated flow regimes associated with low shear strain rates (1). Walker et al. (1) measured noteworthy reductions in the propagation of negative axial velocities and oscillatory shear patterns downstream of a stent wire using a non-Newtonian blood analog while Choi and Barakat (2) used CFD to predict non-Newtonian reductions in recirculation length downstream of a backward facing step.
Statistical Shape and Alignment Modeling of the Lumbar Spine
Authors: Hollenbeck Justin F. M. , Rullkoetter Paul J. , Cain Christopher , Fitzpatrick Clare K. , Laz Peter J.
Published: January 2014

The mechanics of the lumbar spine are dependent on the morphology of the vertebral bodies and their alignment. As intersubject anatomic variability is significant, this paper developed a method to characterize shape and alignment variability in the lumbar spine using statistical shape modeling techniques. The primary modes of variation between subjects were sagittal plane curvature of the spine and height of the discs. Quantifying the biomechanical variation of the lumbar spine across the population facilitates designers and clinicians in making informed decisions regarding implant sizing and component placement.
Novel Hyaluronic Acid Nanocomposite Hydrogel for Cartilage Tissue Engineering: Utilizing Yield Stress for Ease of Implantation
Authors: Beck Emily , Berkland Cory , Gehrke Stevin , Detamore Michael
Published: January 2014

Arthritis is the leading cause of disability among U.S. adults, and yet surprisingly, current therapies fail to effectively treat cartilage damage [1]. Instead, treatment primarily involves reducing symptoms, or in the case of osteoarthritis, a costly joint replacement. Thus, tissue engineering is aspiring to regenerate cartilage by providing a biocompatible and biodegradable construct that provides the structural integrity of the native cartilage and facilitates cartilage cell growth and tissue integration. Promising materials for these constructs are hydrogels, which are commonly comprised of materials such as collagen, agarose, poly(ethylene glycol), and hyaluronic acid (HA) [2].
Improved Assessment of Coronary Flow Impairment Using N-13 Ammonia Positron Emission Tomography
Authors: Peelukhana Srikara Viswanath , Kolli Kranthi K. , Kerr Hanan , Effat Mohamed , Arif Imran , Fernandez-Ulloa Mariano , Banerjee Rupak K.
Published: January 2014

Non-invasive diagnosis of coronary artery disease (CAD) is achieved using rest and stress myocardial perfusion imaging (MPI) techniques. Currently, the MPI technique that is a standard of care is the Single Photon Emission Computed Tomography (SPECT). However, comparatively accurate and reliable MPI diagnostic test known as Positron Emission Tomography (PET) is also available and gaining increasing popularity. In this study, a comparison is made between the impairments and left ventricular (LV) ejection fraction (EF) reported by SPECT and PET. In addition, using PET data, flow defects were quantified using coronary flow reserve (CFR: ratio of flow at stress to the rest) in four coronary territories, left ventricle (LV), left circumflex (LCX), right coronary artery (RCA) and left anterior descending (LAD). Three patients with previous SPECT and suspected CAD were consented and further assessed with a PET cardiac N-13 ammonia scan according to the study protocol. The comparisons of the two imaging modalities showed discordance for patients 1 and 2 while they concurred for the patient 3. More importantly, quantification of the extent of defect showed an abnormal CFR value (< 2) of 1.67 (LCX) and 1.57 (RCA) for the patient 1 and 1.67 (LAD) and 1.75 (RCA) for patient 2. For the third patient, CFR value was abnormal at 0.85 for the RCA. Therefore, in contrast to SPECT, quantification of flow impairment using PET MPI in individual coronary territories will aid in better diagnosis of CAD.
Structure and Mechanical Properties of PCL/PG Devices Prepared by Selective Laser Sintering for Drug Delivery Applications
Authors: Salmoria Gean V. , Klauss Priscila , Roesler Carlos R. M. , Kanis Luiz Alberto
Published: January 2014

Selective laser sintering (SLS) is a rapid prototype process that creates objects, layer by layer, using infrared laser beams to process powder materials [1–8]. In recent years, the SLS process has shown great prominence in the medical field, and several researchers have conducted studies showing a wide diversity of materials and applications, such as the manufacture of porous drug delivery devices (DDDs) [9–12].
Computational Fluid Dynamics Simulation of Airflow Alteration in the Trachea Before and After Vascular Ring Surgery
Authors: Shih Tzu-Ching , Horng Tzyy-Leng , Chen Fong-Lin
Published: January 2014

Vascular rings, congenital intracardic anomalies of the aortic arch and the vessels emerging from the heart, completely encircle the trachea and esophagus [1]. The vascular ring results in narrowing and obstruction of the trachea and the esophagus. Due to the existence of a complete or partial vascular ring compressing either the trachea or esophagus, symptoms of a vascular ring in children include cough, stridor, chronic cough, dysphagia, persistent wheeze, and noisy breathing [2]. Some studies reported that the vascular ring surgery provides an excellent chance to improve the patient respiration conditions, especially for relief of symptoms [1–3]. Al-Bassam et al. reported that the thoracoscopic division of vascular rings in infants and children is a safe and effective surgery rather than an open thoracotomy[4]. Even after the treatment of a surgical division of the vascular ring, however, the fixed obstruction is relieved but the patient continues to have dynamic collapse because the compressed trachea segment is always malacic. Airway resistance to flow in the airway, thus, is a key factor for not only clinical diagnosis severity assessment but also therapeutic decision in tracheal stenosis. Furthermore, Malvè et al. (2011) utilized the finite element-based commercial software code (ADINA R&D Inc.) to model the fluid structure interaction of a human trachea under different ventilation conditions [5]. They also found that the positive pressure in the trachea does not result in the airway collapse during the time period of mechanical breathing. Therefore, the purpose of this study is to use the computational fluid dynamics (CFD) technique to calculate the local pressure drops in the tracheal segment for different inspiratory and expiratory flow rates due to preoperative and preoperative vascular ring surgery.
Application of Residence Time Distribution Analysis in Microchannel Hemodialysis Devices
Authors: Coblyn Matthew , Truszkowska Agnieszka , Jovanovic Goran
Published: January 2014

Current hemodialysis techniques rely on hollow-fiber tubes in a tube-and-shell operating approach. The method works satisfactorily; but, technological advantages of this method are already exhausted for a long time. Additional improvements are needed which could provide a way towards improving patient health and quality of life. Patients with renal failure undergo intense filtration sessions approximately three times a week leaving them fatigued. Large oscillations in concentration of various solutes within blood cause detrimental consequences on the overall health of patients.
In Vitro Phase-Contrast Magnetic Resonance Investigation on Development of Human Carotid Sinus in Young Age
Authors: Seong Jaehoon , Jeong Woowon , Smith Nataliya , Towner Rheal A.
Published: January 2014

The morphology of adult carotid sinus and atherosclerosis are major risk factors for ischemic stroke. It has been reported that the function of carotid sinus is pressure sensing and the regulation of heart rate. Seong and colleagues reported the lifelong development of carotid sinus morphology from infancy to maturity using post-image processed digital subtraction angiograms from 36 patients, ages from newborn to 36 years old [1]. The study unveiled the substantial growth of the internal carotid artery (ICA) with aging and the development of a carotid sinus at the root of the ICA during late adolescence. However, the development of the carotid sinus with associated hemodynamics is not clearly understood yet.
Residual Deformations of Ocular Tissues
Authors: Wang Roy , Ethier C. Ross
Published: January 2014

Biomechanics and mechanobiology play a potentially significant role in several ocular pathologies. Glaucoma is perhaps the best studied of these, but other ocular conditions where mechanics are important include retinal detachment and macular degeneration (1, 2). Knowledge of the mechanical properties of the relevant ocular tissues, including their constitutive relationships, is required to understand the biomechanical basis of pathology and also for developing biomechanically mediated therapies. Towards this end, it is necessary to understand the residual strain state of relevant ocular tissues prior to formulating accurate and predictive mechanical models (3).
Device to Assist Individuals in Dressing Themselves
Authors: Li Xiaotong , Kirgesner Aaron , Stephens Adam , Cramer Mitchell , Hefzy Mohamed Safir , Pourazady Mehdi
Published: January 2014

As many elderly citizens have diminished strength and balance, they must use their hands while standing to support and stabilize themselves. This prevents them from using their hands to pull up and buckle their pants. As a result, these individuals must ask for assistance from others or spend an unnecessary amount of time doing this task independently while risking a fall. This problem becomes worsened when coupled with ailments such as arthritis, torn rotator cuffs, or multiple sclerosis (MS). The purpose of this senior design project was to develop an automated device to assist individuals in dressing themselves. Specifically, this device is to be designed to help individuals with weakened physical conditions pull their pants and briefs up while standing and supporting themselves.
Contribution of Hemodynamic Shear Stress Magnitude and Frequency Abnormalities to Calcific Aortic Valve Disease Pathogenesis
Authors: Sun Ling , Sucosky Philippe
Published: January 2014

Calcific aortic valve disease (CAVD) is an active process presumably triggered by interplays between atherogenic risk factors, molecular signaling networks and hemodynamic cues. While our earlier work demonstrated that progressive alterations in fluid shear stress (FSS) on the fibrosa could trigger valvular inflammation [1], the mechanisms of CAVD pathogenesis secondary to side-specific FSS abnormalities are poorly understood. Supported by our previous studies, we hypothesize that valve leaflets are sensitive to both WSS magnitude and pulsatility and that abnormalities in either promote CAVD development. This study aims at elucidating ex vivo the contribution of isolated and combined alterations in FSS magnitude and pulsatility to valvular calcification.
Fibroblast-Mediated Fiber Realignment in Fibrin Gels
Authors: De Jesus Aribet M. , Aghvami Maziar , Sander Edward A.
Published: January 2014

When fibroblasts are added to a fibrin gel, the cells rapidly compact the gel and produce a fiber alignment pattern that depends in part on the cell traction forces, gel geometry, and gel mechanical constraints [1]. Over time the fibrin is digested and replaced with cell synthesized collagen and other extracellular matrix (ECM) proteins that follow the initial alignment pattern of the gel [2]. This remodeling process proceeds in a complex and integrated manner that is influenced by the mechanical environment [3]. In order to better understand fibroblast-fibrin interactions and the remodeling process, we obtained time-lapse images of the development of fiber alignment between clusters of dermal fibroblasts (i.e., explants) in a fibrin gel. The experimental results were then compared to a model that incorporated the effects of traction forces on ECM reorganization.
Treatment of the Aortic Coarctation: Prediction of the Hemodynamic Impact
Authors: Goubergrits L. , Mevert R. , Yevtushenko P. , Schaller J. , Meyer S. , Riesenkampff E. , Kuehne T.
Published: January 2014

Aortic coarctation (CoA) accounts for approximately 10% of congenital heart diseases 1. CoA causing high pressure gradient can be successfully treated surgical or catheter-based. Long-term results, however, revealed decreased life expectancy associated with abnormal hemodynamics 1. To develop a next-generation personalized diagnostic-prognostic tools allowing treatment optimization and thus to improve life expectance, the innovative combination of imaging science, biofluid mechanics, and computer modeling is necessary. Patient-specific computational fluid dynamics (CFD) models of the CoA based on MRI data were created to analyze pre- and post-treatment hemodynamics with a focus on pressure gradient.
Theoretical Predictions of Body Tissue and Blood Temperature During Cold Water Immersion Using a Whole Body Model
Authors: Paul Anup K. , Zachariah Swarup A. , Zhu Liang , Banerjee Rupak K.
Published: January 2014

Understanding the thermal response of the human body under various environmental and thermal stress conditions is of growing importance. Calculation of the core body temperature and the survivability of the body during immersion in cold water require detailed modeling of both the body tissue and the time-dependent blood temperature. Predicting body temperature changes under cold stress conditions is considered challenging since factors like thickness of the skin and blood perfusion within the skin layer become influential. Hence, the aim of this research was to demonstrate the capability of a recently developed whole body heat transfer model that simulates the tissue-blood interaction to predict the cooling of the body during immersion in cold water. It was shown that computed drop in core temperature agrees within 0.57 °C of the results calculated using a detailed network model. The predicted survival time in 0 °C water was less than an hour whereas in 18.5 °C water, the body attained a relatively stable core temperature of 34 °C in 2.5 hours.
Hemodynamics and Natural History Outcome in Unruptured Intracranial Aneurysms: A Prospective Longitudinal Cohort Study
Authors: Retarekar R. , Ramachandran M. , Dickerhoff B. , Harbaugh R. , Hasan D. , Ogilvy C. , Rosenwasser R. , Raghavan M. L.
Published: January 2014

There is increasing interest in assessing the role of hemodynamics in aneurysm growth and rupture mechanism. The ability to accurately predict the rupture risk of an aneurysm can help in providing immediate intervention to patients with aneurysms at high rupture risk Also, the small but significant risk associated with the treatment options can be avoided for patients with stable harmless aneurysms. Retrospective studies have been performed in the past to identify indices that differentiate ruptured aneurysms from unruptured aneurysms [1–3]. However, these differences may not necessarily translate to differences between aneurysms that present unruptured but over a period of time (months to years), fork towards growth/rupture and unruptured aneurysms that remain stable. In the present study, the hypothesis that hemodynamic indices of unruptured aneurysms when they first presented are predictive of their longitudinal outcome was tested.
Do Infarcts Really Expand or Compact? Relationship Between Changing Material Properties and Apparent Infarct Remodeling
Authors: Richardson William J. , Holmes Jeffrey W.
Published: January 2014

Myocardial infarction (MI) is a leading cause of mortality and morbidity with over 600,000 new Americans suffering an MI each year [1]. Following infarction, damaged muscle is gradually replaced by collagenous scar tissue, while undamaged (remote) myocytes remodel due to altered load. Remodeling of both the infarcted and remote myocardium are important determinants of cardiac function and the risk of progression to heart failure.
Non-Invasive Assessment of Lymphatic Pumping Pressure in a Rat Tail Model Utilizing Near-Infrared Imaging
Authors: Dixon J. Brandon , Akin Ryan , Weiler Mike , Kassis Timothy
Published: January 2014

The lymphatic vasculature consists of a network of vessels that promote unidirectional transport of fluid, proteins, and cells from the interstitium back into the blood, providing functions essential for maintaining fluid balance, immune cell trafficking, and lipid absorption from the intestine. The lymphatics generate flow through both extrinsic pumping mechanisms, such as contraction of surrounding skeletal muscle, and through the intrinsic contractility of each lymphatic vessel unit known as a lymphangion. Specialized lymphatic muscle, working in coordination with uni-directional valves separating each lymphangion, serves to contract up to 80% of the vessel diameter and drive flow from the interstitium back to the venous circulation.
Probabilistic Computational Analysis of Transcatheter Aortic Valve Leaflet Design
Authors: Li Kewei , Sun Wei
Published: January 2014

Aortic stenosis (AS) is abnormal narrowing of the aortic valve which partially obstructs outflow of blood from the left ventricle to aorta. Symptomatic AS is associated with a high mortality rate, approximately 50% in the first 2 years, if left untreated [1, 2]. Transcatheter aortic valve (TAV) implantation has been recently developed as an effective endovascular treatment for high-risk AS patients, in which a stented bioprosthetic valve is deployed through a catheter within the diseased aortic valve. Since the first procedure in 2002 [3], there has been an explosive growth in TAV implantation. By the end of 2011, there were 10 TAV companies that had first-in-man implantation data [4]. More than 50,000 TAV implantations have been performed worldwide since 2007. Short-term and medium-term outcomes after TAV implantation are encouraging with significant reduction in rates of death. However, adverse events associated with TAV implantation were reported [5, 6]. Furthermore, long-term durability and safety of these devices are largely unknown and needed to be evaluated and studied carefully [7, 8]. It is widely accepted that valve designs that reduce leaflet stresses are likely to give improved performance in long-term applications. The objective of this study was to quantify the effect of 2D TAV leaflet geometry design on 3D valve stress distribution using probabilistic computational simulation.
Biomechanical Versus Clinical Considerations in the Development of a Novel Polycarbonate-Urethane Meniscus Implant
Authors: Elsner J. J. , Condello V. , Zorzi C. , Arbel R. , Hershman E. , Guilak F. , Linder-Ganz E.
Published: January 2014

The menisci are semi-lunar wedge-shaped structures that play critical roles in load distribution, shock absorption, and joint congruity in the knee. Meniscal tears are common knee injuries that subsequently lead to degenerative arthritis, attributed primarily to the changes in stress distribution in the knee. In such cases there is a need to protect the articular cartilage by either repairing or replacing the menisci. While traditionally, meniscal replacement involves implantation of allografts, problems related to availability, size matching, cost and risk of disease transmission limit their use. Another potential treatment option is that of biodegradable scaffolds, which are based principally on tissue engineering concepts. The variability in body response to biodegradable implants and the quality of the tissue formed still pose a problem in this respect, particularly in light of the intense loading conditions in the knee. Moreover, the aforementioned repair and regenerative approaches are generally limited to younger patients. Therefore, the goal of this study was, to develop a synthetic meniscal implant which can replace the injured meniscus, restore its function, and relieve pain.
Active Stress in the Porcine Renal Artery
Authors: Zhou Boran , Rachev Alexander , Shazly Tarek
Published: January 2014

As a typical muscular conduit artery, the renal artery manifests an active response when the vascular smooth muscle is stimulated to contract. To present there are few experimental data [1] and no constitutive formulation of the renal arterial tissue that accounts for the active stress developed when the smooth muscle cells (SMCs) are stimulated to contract. Most studies identify the circumferential and axial active stresses by processing the in-vitro experimentally recorded change in diameter and axial force in a tubular arterial specimen inflated by an internal pressure, kept at constant axial stretch ratio, and with the SMCs stimulated to relax or contract. It is assumed that the stress borne by the extracellular matrix, termed as passive stress, and the active stress generated by the stimulated SMCs are additive. The directions of the active stresses and functional dependence on the strain measures are often postulated on the basis of histology, biophysics of SMC contraction, and an a priori guess, rather than on recordable mechanical information. The only exception is a recently proposed approach that allows decoupling of the passive and active response and identifying the arguments and the analytical form of the active stress directly from experimental data [2]. In this study, we follow this approach and determine the active stress in the porcine renal artery.
Estimation of Patient-Specific 3D In Vivo Abdominal Aortic Aneurysm Strain
Authors: Raut Samarth S. , Jana Anirban , Muluk Satish C. , Doyle Mark , Biederman Robert W. , Finol Ender A.
Published: January 2014

Abdominal Aortic Aneurysm (AAA) is a localized permanent dilatation occurring in abdominal region of the aorta. Nearly 8% of the population above 65 years old is diagnosed with this disease [1], which has been shown to be associated with smoking history, heredity, and male gender. As it is asymptomatic, vascular surgeons may opt for surgical intervention or follow a wait-and-watch strategy if their assessment of the risk of rupture is low. During surgical intervention grafts are placed inside the aorta. Design of such intravascular devices as well as monitoring the progression of the disease by means of scientific approach may benefit from information on the strains that occur in the aneurysmatic region at different instances due to cyclic internal pressurization during cardiac cycle.
Transition From the Fetal to Neonatal Circulation: Modeling the Effect of Umbilical Cord Clamping
Authors: Kowalski William J. , Yigit Berk M. , Hutchon David J. R. , Pekkan Kerem
Published: January 2014

The transition from fetal to neonatal circulation requires a concert of events to transfer gas exchange function from the placenta to the lungs and separate the pulmonary and systemic pathways. Pulmonary vascular resistance (PVR) rapidly decreases within the first minutes of extrauterine life and continues to gradually decrease during the first week, increasing pulmonary blood flow and reducing pulmonary pressure [1, 2]. Umbilical vessels constrict, removing the placental circulation and leading to closure of the ductus venosus (DV) [2]. The increased left atrial filling and reduced right atrial filling results in permanent closure of the flap of the foramen ovale, removing the R→L interatrial shunt. Closure of the ductus arteriosus (DA) completes the separation of the pulmonary and systemic circulations by 48 hours in 82% of term newborns and by 96 hours in 100% [3]. Removal of the placental circulation is routinely achieved by umbilical cord clamping (UCC) immediately after birth. This practice, however, has been called into question by many studies, which suggest that continued umbilical flow in the early neonate is beneficial, and immediate UCC can lead to infant anemia [4, 5]. Due to routine UCC, the effects of this practice on transitional flow patterns are largely unknown [1, 6]. We therefore developed a lumped parameter model (LPM) to study the role of UCC in the fetal to neonatal transition. Our model includes time-varying resistance functions that allow us to simulate the opening of the PVR and closure of the DA and umbilical vessels. This model demonstrates that UCC can lead to an earlier onset of DA flow reversal and slightly reduced cardiac output (CO).
Pressure Gradients in the Trabecular Pore Space of Femurs During Physiologic Loading
Authors: Metzger Thomas A. , Schwaner Stephen A. , Niebur Glen L.
Published: January 2014

Bone marrow is an important niche for mesenchymal stromal cells (MSCs), which are progenitors for connective tissue cells. MSCs respond to mechanical stimuli (1). For example, steady and oscillatory fluid flow both affect MSC differentiation to the osteogenic lineages (2), while hydrostatic pressure increases MSC osteogenic protein expression (3). Both pressure and fluid flow are induced in bone marrow during loading due to the poroelastic nature of trabecular bone, and these may affect the differentiation or proliferation of the resident stromal cells.
A Dynamic Response Model of Human Spine Under Superior-Inferior G Loads Using Voigt Viscoelastic Representation
Authors: Sarigul-Klijn Yasemin Maria , Sarigul-Klijn Nesrin
Published: January 2014

Transportation systems subject the human body to varying levels of vibrations, which causes lower back pain. Some studies presents that exposure to vibrations of 1.3 m/s 2 for ten minutes a day can be harmful even for healthy people. With transportation systems being part of our daily lives it is useful to better predict the effects of vehicle induced oscillations on human via mathematical models. Anthropometry of a person is highly important when it comes to fitting the occupant to the seat with the restraint system together with their mass. Spaceflight travel further complicate matters since 4–6 cm increase in body height can occur during space flight and space vehicles must be designed to accommodate these changes.
Continuous Flow Cell Separation From Human Peripheral Blood Using Dielectrophoresis and Numerical Analysis
Authors: Kim Sungho , Jung Youngdo , Frazier Bruno , Giddens Don
Published: January 2014

Cell manipulation using dielectrophoresis (DEP) has a great potential for biological applications in diagnostic devices because it has a capability to separate specific cells from mixed heterogeneous solutions, e.g., whole blood, selectively based on intrinsic dielectrophoretic characteristics. Thus, it does not require additional chemical tagging, which can lead to undesirable cell responses (1). Previous DEP cell separation has been run in a discontinuous mode, which may result in more complicated procedures, so that developing continuous flow DEP separation devices in practical sizes for larger throughput clinical applications is an unmet need. In this research, we model numerically a continuous flow dielectrophoresis (CF-DEP) device that was developed with novel angled-electrode design in a MEMs platform, and a pulsing mode was introduced between neighboring electrodes to obtain efficient cell separation. This allows examination of characteristic features of the electrode design and the coupling effect of dielectric and hydraulic forces to particle movement.
Modeling Collagen Synthesis and Degradation in Engineered Tissues Based on Fibrous Scaffolds
Authors: Argento G. , Oomens C. W. J. , Baaijens F. P. T.
Published: January 2014

In the tissue engineered approach, cells seeded onto a scaffold produce with time a load bearing extra cellular matrix. At the same time the original scaffold degrades and the matrix takes over the mechanical function. The development of a collagen network in tissue engineered constructs strongly depends on the mechanical and chemical stimuli that are applied to the growing tissue [1]. The morphology of the neo-formed tissue engineered collagenous networks is of fundamental importance for performance [2].
Elastin-Sprayed Tubular Scaffolds With Microstructures and Nanotextures for Vascular Tissue Engineering
Authors: Jang Jinah , Ko Junghyuk , Cho Dong-Woo , Jun Martin B. G. , Kim Deok-Ho
Published: January 2014

Development of a small-diameter vascular graft (<6 mm) have been challenging due to thrombosis and intimal hyperplasia [1]. To overcome this problem, cardiovascular tissue engineers have attempted to construct a highly porous and biocompatible fibrous scaffold providing a sufficient mechanical strength for the regeneration of a functional tissue [2–5]. Herein, we present a 3D tubular-shaped micro/nanofibrous composite-layered scaffold for vascular tissue engineering. The surface of scaffold has high surface roughness by introducing nanofibrous layer and the biophysical properties have been fulfilled by using microfibrous layer. Moreover, the atomized spraying technique is applied to spray elastin proteins, which is well known as an antithrombogenic material, on the surface of micro/nanofibrous composite-layered scaffold to introduce an appropriate antithrombogenic surface.
A Hemi Fontan Operation Performed by an Engineer: Considerations on Virtual Surgery
Authors: Biglino Giovanni , Kung Ethan , Dorfman Adam , Taylor Andrew M. , Bove Edward , Marsden Alison , Hsia Tain-Yen , Schievano Silvia
Published: January 2014

Single ventricle circulation, characterized at birth by a rudimentary or absent left or right ventricle, presents a challenging and life-threatening physiological scenario. Surgical palliation aims to restore the balance between systemic and pulmonary blood flow and is staged, each of the three stages presenting the surgeon with different options:

- Stage 1 (Norwood procedure) involves different types of shunting to source pulmonary blood flow, or recently a hybrid approach [1];

- Stage 2 can involve a superior cavopulmonary connection (Glenn operation) or patching between the right atrium and the pulmonary arteries (Hemi Fontan operation [2]);

- Stage 3 involves a total cavopulmonary connection with extracardiac conduit or lateral tunnel, or with novel alternatives such as the Y-graft [3].
Imaging-Based Wave Intensity Analysis: Applications in Congenital Heart Disease
Authors: Biglino Giovanni , Ntsinjana Hopewell N. , Parker Kim H. , Schievano Silvia , Taylor Andrew M.
Published: January 2014

Wave intensity analysis is a hemodynamic index evaluating the working condition of the heart in relation to the rest of the vasculature [1]. As such it carries valuable mechanistic information on ventriculo-arterial (VA) coupling. Its applications have ranged from studies of cardiac assist devices to fetal studies. Our group has proposed a way to derive wave intensity from phase-contrast magnetic resonance (PCMR) data [2]. We now suggest that this technique has a duple potential: (a) comparing patients against healthy subjects to investigate VA coupling and mechanistic changes related to surgery or devices, and (b) providing measures and indices to assess hemodynamic scenarios adding valuable mechanistic considerations. We aim to show both applications in the complex field of congenital heart disease. In the first instance, we will use this methodology to assess changes in wave speed and VA coupling in patients with transposition of the great arteries (TGA) repaired with arterial switch operation and palliated with atrial switch. In the second case, we will assess the potential of wave intensity-derived parameters for detecting diastolic dysfunction, and we selected a small population of patients with congenital aortic stenosis as a first suitable study cohort.
Computational Fluid Dynamics Analysis of Early Embryonic Aortic Arch-Ligation
Authors: Menon Prahlad G. , Kowalski William , Pekkan Kerem
Published: January 2014

Congenital heart disease occurs in 8 out of every 1000 live births in the US and more than half of this population is associated with great artery lesions. Selective remodeling of the paired, bilaterally symmetric embryonic aortic arches (AA) is a crucial stage in vascular morphogenesis and has known association with biomechanical forces [1]. Fetal cardiac interventions are currently explored clinically as an alternative repair technique for congenital anomalies, in-utero [2]. Several computational fluid dynamics (CFD) studies have been performed focusing on subject specific embryonic cardiovascular anatomies [3–5]. These developments could benefit fetal interventions that are planned in-silico before execution. To demonstrate this possibility, we computed the hemodynamic variation and wall shear stress (WSS) patterns resulting from systematic in-silico AA ligation intervention performed on normal chick AA models viz. Hamburger Hamilton (HH) stage 18 and 24 (3 and 4 days, respectively). A unique methodology employing CFD-computed WSS for modeling short-term biological growth response on AA morphogenesis is also presented.
Analysis of Collagen Fiber Organization in Mouse Achilles Tendon Using High-Frequency Ultrasound Imaging
Authors: Riggin Corinne N. , Sarver Joseph J. , Freedman Benjamin R. , Thomas Stephen J. , Soslowsky Louis J.
Published: January 2014

Achilles tendon ruptures are traumatic injuries that frequently occur in active individuals and result in significant medical expense. Common techniques for assessing outcomes of surgical repair and rehabilitation rely heavily on patient-based measures of pain and function. While these measures can provide evidence for recovery of functional performance, they do not directly assess tendon healing which, if insufficient, can lead to re-rupture. The clinical evaluation of collagen organization following Achilles tendon injury may provide a more accurate measure of healing than traditional, functional performance tests. It has been shown that changes in collagen organization precede and correlate with changes in mechanical properties in tendons [1–3] and that load and injury effect collagen organization [4–6]. Ultimately, if collagen organization could be quantified in vivo, it would represent a powerful, diagnostic tool to measure the progression of tendon healing, as well as to monitor damage accumulation due to injury.
Reduction in Mechanical Wall Strain Precedes Intimal Hyperplasia Formation in a Murine Model of Arterial Occlusive Disease
Authors: Favreau John T. , Liu Chengwei , Yu Peng , Mauro Christine , Tao Ming , Ozaki C. Keith , Gaudette Glenn R.
Published: January 2014

Coronary artery disease and peripheral artery disease remain a significant source of mortality and vascular morbidity in the United States; both affecting over 14 million Americans.[1] Although a number of both open and endovascular procedures are available for treating occlusive lesions, post-procedure intimal hyperplasia (IH) and pathological wall adaptation in treated arteries cause further need for treatment. As on average 50% of patients receiving these treatments must receive further vascular intervention to prevent the continued expansion of IH into the vessel lumen, there is a need to improve our understanding of the underlying causes of IH formation.[2]