bluuebunny/crossref_metadata_2025 huggingface dataset:
Biomechanical Effects of Laminoplasty and Laminectomy on the Stability of Cervical Spine
Authors: Kode Swathi , Kallemeyn Nicole A. , Smucker Joseph D. , Fredericks Douglas C. , Grosland Nicole M.
Published: July 2013

Cervical spondylotic myelopathy is the most common spinal cord disorder in persons more than 55 years of age in North America and perhaps in the world [7]. It is a chronic degenerative condition of the cervical spine that results in the reduction of spinal canal diameter and thereby compresses the spinal cord and the associated nerve roots [1].
In Situ Observation of Nuclear Behavior During Laser Nano-Dissection of Actin Stress Fibers: Mechanical Interaction Between Actin Stress Fibers and Nucleus
Authors: Nagayama Kazuaki , Yahiro Yuki , Matsumoto Takeo
Published: July 2013

In order to elucidate the mechanotransduction mechanism of adherent cells, it is crucial to clarify how forces applied to cells are transmitted through intracellular components. Actin stress fibers (SFs) play important roles in various cellular events including cell proliferation [1], differentiation [2] and gene expression [3]. SFs generate internal forces and contribute to physical interactions between cells and extracellular matrices [4]. It has recently been suggested that cytoskeletons have the potential to interact with nuclei via certain nuclear membrane proteins [5, 6]. However, it remains unclear at this stage whether SFs are involved in a mechanical interaction with the cell nucleus and their internal forces are transmitted directly to the nucleus.
Experimentally and Theoretically Narrowing Carpal Arch Width to Increase the Area Formed by the Transverse Carpal Ligament
Authors: Yu Suk H. , Mondello Tracy A. , Li Zong-Ming
Published: July 2013

Carpal tunnel syndrome is conventionally treated by open and endoscopic release surgeries in which transecting the transverse carpal ligament (TCL) relieves mechanical insults around the median nerve. The TCL release surgeries yield an increase in the tunnel cross-sectional area particularly within the volar aspect of the tunnel, the arch area, where the median nerve is located. As a result of increased arch area, post-operative follow-up studies using MRI confirmed a significant volar migration of the median nerve [1]. However, transecting the TCL compromises critical biomechanical roles of the carpal tunnel [2], and therefore, it is imperative to investigate an alternative method for treating carpal tunnel syndrome patients while preserving the TCL. Li et al. suggested that increasing the TCL length and narrowing the carpal arch width (CAW) as potential alternatives for increasing the arch area [3]. However, the data from their application of palmarly directed forces to the TCL from inside of the tunnel showed that the TCL length remained relatively constant while the carpal bones were mobilized to increase the arch area [3]. The purpose of this study was to investigate the relationship between CAW narrowing and the TCL-formed arch area by experimental and geometrical modeling.
Kinematics and Kinetics of Flagellar Locomotion in Chlamydomonas Reinhardtii
Authors: Bayly P. V. , Lewis B. L. , Ranz E. C. , Okamoto R. J. , Pless R. B. , Dutcher S. K.
Published: July 2013

The forces exerted on the flagellum of the swimming alga Chlamydomonas reinhardtii by surrounding fluid are estimated from video data. “Wild-type” cells, as well as cells lacking inner dynein arms (ida3) and cells lacking outer dynein arms (oda2) were imaged (350 fps; 125 nm). Digital image registration and sorting algorithms provide high-resolution descriptions of the kinematics of the cell body and flagellum. The swimming cell is then modeled as an ellipsoid in Stokes flow, propelled by viscous forces that depend linearly on the velocity of the flagellum. The coefficients (CN and CT) that related normal and tangent forces on the flagellum to corresponding velocity components are estimated from equilibrium requirements. Their values are consistent among all three genotypes and similar to theoretical predictions.
Comprehensive Simulations of the Microcirculation in Rat Spinotrapezius Muscle Fascia
Authors: Jacobitz Frank G. , Jones Adam M.
Published: July 2013

The microcirculation in rat spinotrapezius muscle fascia is studied using a comprehensive computational approach. The simulations use a realistic network structure obtained from microscope images and consider both blood rheology and vessel elasticity. An apparent viscosity model for blood considers vessel diameter, blood hematocrit, and the local shear rate. The vessel elasticity model includes passive dilatation of vessels as well as active constriction in arterials. Many diseases first manifest themselves in the microcirculation and an improved understanding may help with early detection and treatment [6].
The Roles of HS and Its Glypican-1 Core Protein in Flow-Induced Endothelial NOS Activation and Cell Remodeling
Authors: Ebong E. E. , Spray D. C. , Tarbell J. M.
Published: July 2013

Endothelial cell (EC) glycocalyx (GCX) is an endovascular protective coat that is degraded in disease. GCX heparan sulfate (HS) proteoglycan is essential for flow-induced nitric oxide (NO) release and cell remodeling, but the HS core proteins involved in these mechanotransduction events are unknown. We hypothesize that the glypican-1 (GPC1) HS core protein mediates flow-induced EC NO synthase (eNOS) activation and is less important for flow-induced cell remodeling, because GPC1 is located in the caveolae where eNOS resides but, to our knowledge, GPC1 has no direct association with the cytoskeleton. We tested our hypotheses by exposing monolayers of bovine aortic EC (BAEC) with intact GCX, heparinase III (HepIII) enzymatically degraded HS, and RNA-silenced GPC1 to 12–15 dyne/cm2 average shear stress for 3 and 24 hours. HS removal by HepIII and GPC1 inhibition by shRNA equally blocked shear-induced eNOS activation that occurs in shear-conditioned BAEC with fully intact GCX. EC remodeling in response to flow was attenuated by HS degradation, but preserved with GPC1 knockdown. These results suggest that while HS is involved in both centralized and decentralized GCX-mediated mechanotransduction mechanisms, GPC1 plays a role in only centralized GCX-mediated mechanotransduction.
Direct Numerical Simulation of Transitional Flow in a Patient-Specific MCA Aneurysm
Authors: Valen-Sendstad Kristian , Mardal Kent-Andre , Mortensen Mikael , Reif Bjørn A. P. , Langtangen Hans Petter
Published: July 2013

Stroke is a leading cause of death in the Western world (1). One reason for stroke is the rupture of aneurysms usually found in or near the Circle of Willis, an arterial network located at the base of the brain. It is estimated that 1–6% of the population harbor aneurysms during their lifetime (2), and that the average risk of rupture is 1–2% annually. The initiation, growth, and rupture of intracranial aneurysms are complex and multi-factorial processes. The precise mechanism however, is still not known. If the wall shear stress (WSS) exceeds a limit of 40 Pa, the endothelial cells are believed to be damaged, and an aneurysm might form (3) (4).
Mechanical Stimulation of Scaffold-Free, Cell-Based Single Fibers for Tissue Engineered Tendon
Authors: Schiele Nathan R. , Koppes Ryan A. , Corr David T.
Published: July 2013

The clinical demand for tendon replacements following injury, surgical excision, or disease drives current tissue engineering endeavors. Great strides have been made in producing functional tissues, but none have gained clinical acceptance. Scaffold-free and cell-based engineered tissue constructs allow the use of autologous cells and avoid potential scaffold-based complications such as immune rejection and breakdown byproducts. However, scaffold-free approaches have yet to replicate the mechanical properties of tendon [1,2]. In an effort to mimic some key aspects of in vivo embryonic tendon development, such as high cellularity and subsequent cell-to-cell contact, we have utilized a cell-based and scaffold-free method to direct fibroblast cell growth through geometric constraint to form single fibers [3,4]. Early application of mechanical cues (within hours of cell attachment) is essential for cell and collagen fiber alignment, as well as tissue maturation through matrix protein synthesis, and perhaps most importantly, these structural changes will result in altered mechanical properties. We recently established a method to apply mechanical stimulation to developing scaffold-free, cell-based fibers with the goal of replicating tenogenic development cues [5]. As an important step towards scaffold-free tendon replacements, the objective of this study was to demonstrate the influence of dynamic mechanical cues on growing fibers, which can ultimately be optimized to achieve tendon-like structure and mechanical properties.
Design of an External Fixator and Motion Application System for Use in an In Vivo Fracture Study
Authors: Currey Jennifer A. , Nash Marc
Published: July 2013

In the United States, there are approximately 1 million fractures annually [1]. These fractures can be treated successfully with the use of casts or internal fixation (i.e. screws, bone plates, or intramedullary rods). However, for approximately 1 out of 20 people with a fracture, these treatments are not successful and result in either a malunion or a non-union. A malunion or a non-union reduces the ability of the bone to withstand the loads it is intended to take. This can cause pain and suffering for the patient. Clinically, non-unions can be treated using mechanical stimulation via an external fixator. Current treatments and the literature suggest that the mechanical environment of a healing fracture callus can influence tissue differentiation, perhaps even stimulate healing [2,3,4,5,6,7]. This leads to the overarching question, what is the precise relationship between the local mechanical environment of a fracture and patterns of bone repair? In order to answer this question, one must be able to control and measure the amount of motion or force applied to the fracture so as to properly relate the healing patterns with a particular stimulus.
Spatial Variations in the Mechanical Properties of the Porcine Thoracic Aorta
Authors: Kim Jungsil , Baek Seungik
Published: July 2013

Characterization of the mechanical properties of a blood vessel is essential in understanding the progression of a vascular disease and for computational studies of vascular adaptation. For example, stiffness of vascular tissue is one of the major indicators to diagnose the vascular disease and make a clinical decision. Although previous studies reported the heterogeneity of the mechanical properties of arterial wall along the arterial tree [2], little was taken account for its circumferential variations. With the lack of experimental studies for investigating the circumferential variation, the aortic wall is typically assumed to have uniform deformation. Our previous study, however, has observed that there are circumferential variations in aortic wall stress and stiffness [1]. In addition to our previous study, we investigate further regional variations of the porcine thoracic aorta in both circumferential and longitudinal directions during the inflation test. Hence, we additionally test the distal thoracic aorta at each anterior and posterior side, respectively, and compare with the proximal thoracic aorta.
Analysis of Heat Transfer in Bone Drilling
Authors: Lee JuEun , Ozdoganlar O. Burak , Rabin Yoed
Published: July 2013

Bone drilling is widely used to mount screws for anchoring plates and attaching exoskeleton devices to assist healing of bone fractures. The heat generated during drilling can cause significant thermal damage to the bone tissue. Hence, prediction of the developing temperature field as a function of the drilling parameters is of an important clinical value.
In Vivo Mechanical Characterization of Micro-Specimens Using a Novel Micro-Electro-Mechanical System
Authors: Ladani Leila , Preston Daniel
Published: July 2013

Mechanical probing, stimulation and characterization of tissues are of the most challenging areas of engineering due to limitations of working with bio specimens. Understanding the bio-mechanics of tissues could potentially help to understand mechanical degradation of biological tissues due to disease or change in physiological condition of the body. Biomechanical processes at the microscopic level have become increasingly recognized as an important factor in different biological conditions. In many of these conditions analyzing biomechanics of tissues at microscale in vivo or in vitro will provide invaluable information on microenvironment and physiological parameters that affect the microenvironment and mechanical properties. To address the issue of measuring mechanical properties at microscale, an electroactive-based micro-electromechanical machine is designed. The device is comprised of two electroactive (piezoelectric) micro-elements mounted on a rigid frame. Electrical activation of one of the elements causes it to expand and induce a stress in the intervening micro-specimen. The response of the microspecimen to the stress is measured by the deformation and thereby voltage/resistance induced in the second electro-active element. Figure 1 shows the device design and architecture. Analytical analysis and multiphysics finite element analysis (FEA) are used to prove the concept. A summary of the results are shown in the next sections.
Specimen Dynamics and Subsequent Implications in Heart Valve Tissue Engineering Studies
Authors: Salinas M. , Lange R. , Ramaswamy S.
Published: July 2013

In heart valve tissue engineering, appropriate mechanical preconditioning may provide the necessary stimuli to promote proper tissue formation [1–3]. Previous efforts have focused on a mechanistic heart valve (MHV) bioreactor that can mimic the innate mechanical stress states of flexure, flow and stretch in any combination thereof [1]. A fundamental component pertaining to heart valves is its dynamic behavior. Specific fluid-induced shears stress patterns may play a critical role in up-regulating ECM secretion by progenitor cell sources such as bone marrow derived stem cells [2] and increasing the possibility of cell differentiation towards a heart valve phenotype. Here, we take a computational predictive modeling approach to identify the specific fluid induced shear stress distributions that are altered as a result of valve-like movement and its resulting implications for tissue growth. Previous results have demonstrated the analogous deformation characteristics of heart valves in a rectangular geometry [2]. We conducted computational fluid dynamic (CFD) simulations of a bioreactor that houses these rectangular-shaped specimens (Fig.1).
Resident’s Ridge Formation Can Be Explained by ACL Force-Induced Bone Remodeling
Authors: Fujie Hiromichi , Matsuda Yohei , Shino Konsei
Published: July 2013

The reconstruction technique of the human anterior cruciate ligament (ACL) has been improved in the last decade. Current ACL reconstruction surgery aims to make femoral bone tunnels for graft fixation as close to the anatomical position of the ACL insertion site; the posterior-superior border of the lateral wall of the intercondylar notch of the femur1,2). Such a surgical technique is called “anatomical ACL reconstruction”. Biomechanical studies indicated that joint stability is highly restored in the anatomical ACL reconstruction as compared with the conventional ACL reconstruction3). In addition, the cortical bone beneath the ACL attachment site is thicker4), therefore it is beneficial to use the area for graft fixation. In order to succeed the anatomical ACL reconstruction, it is the most crucial to microscopically identify the anatomical site of the ACL insertion site. Previous studies indicated that the Resident’s ridge is located just anterior to the ACL femoral attachment4–6), therefore, can be used as a reference landmark for the anatomical ACL reconstruction. Although the Resident’s ridge seems to win endorsements of the role in the ACL reconstruction, no explanation was proposed so far as regard with the reason for ridge formation. The author believes that the formation of the Resident’s ridge can be biomechanically explained. Therefore, the objective of the present study was to propose a biomechanical hypothesis as regard with the Resident’s ridge formation, and to validate the hypothesis through a finite element method (FEM) analysis of ACL force-induced bone remodeling.
Influence of Permeability on the Compressive Property of Articular Cartilage: A Scaffold-Free, Stem Cell-Based Therapy for Cartilage Repair
Authors: Susa Tomoya , Nansai Ryosuke , Nakamura Norimasa , Fujie Hiromichi
Published: July 2013

Since the healing capacity of articular cartilage is limited, it is important to develop cell-based therapies for the repair of cartilage. Although synthetic or animal-derived scaffolds are frequently used for effective cell delivery long-term safety and efficiency of such scaffolds still remain unclear. We have been studying on a scaffold-free tissue engineered construct (TEC) bio-synthesized from synovium-derived mesenchymal stem cells (MSCs) [1]. As the TEC specimen is composed of cells with their native extracellular matrix, we believe that it is free from concern regarding long term immunological effects. our previous studies indicated that a porcine partial thickness chondral defect was successfully repaired with TEC but that the compressive property of the TEC-treated cartilage-like repaired tissue was different from normal cartilage in both immature and mature animals. Imura et al. found that the permeability of the immature porcine cartilage-like tissues repaired with TEC recovered to normal level for 6 months except the superficial layer [2]. Therefore, the present study was performed to determine the depth-dependent permeability of mature porcine cartilage-like tissue repaired with TEC. Moreover, we investigated the effect of difference of permeability on the compressive property of articular cartilage using a finite element analysis (FEM).
A 1D Wave Propagation Model of Coronary Flow in a Beating Heart
Authors: van der Horst Arjen , Boogaard Frits L. , Rutten Marcel C. M. , van de Vosse Frans N.
Published: July 2013

Due to recent developments in miniaturized sensors on guide-wires, assessment of coronary artery disease with intracoronary pressure and flow measurements has become available. However, direct quantification is still limited to the large epicardial vessels, which means that microvascular disease can only be determined from upstream measurements using an appropriate model of the vessels and their interaction with the cardiac muscle [1].
The Parametrized Diastolic Filling Formalism: Application in the Asklepios Population
Authors: Claessens Tom , Raja Muhammad Waheed , Pironet Antoine , Chirinos Julio , Desaive Thomas , Rietzschel Ernst , De Buyzere Marc , Van Ransbeeck Peter , Verdonck Pascal , Gillebert Thierry , Segers Patrick
Published: July 2013

The parametrized diastolic filling formalism is a kinematic model for early left ventricular diastolic function, and is believed to provide quantitative information on relaxation and stiffness. Application of this model in the Asklepios population provided normal values of the model parameters x0 (initial spring displacement), k (spring stiffness) and c (damping constant). In addition, a potentially important difference in c of about 20% between men and women was observed. The underlying mechanism is not clear and additional analyses are needed to verify whether or not this suggests intrinsic relaxation differences between men and women.
Impact of Material Anisotropy on Deformation of Myocardial Tissue due to Pacemaker Electrodes
Authors: Forsell Caroline , Gasser T. Christian
Published: July 2013

A Pacemaker electrode can penetrate the heart wall, and to design a penetration-resistent lead tip sound knowledge regarding failure of ventricular tissue is required. Numerical simulations can be particular helpful in that respect, but depend on a reliable constitutive description for ventricular tissue. In this study an anisotropic hyperelastic model for the myocardium has been implemented and compared to predictions from an isotropic description. Specifically, the response due to pushing a rigid punch into the myocardium was studied. Results between anisotropic and isotropic descriptions of the myocardium differed significantly, which justified the implementation of an anisotropic model for the myocardium.
Co-Registration of MRI and Motion Analysis Marker Sets: Proof of Concept
Authors: Mihcin S. , White D. , Holbrey R. , Hodgson R. J. , Redmond A. C. , Wilcox R. K.
Published: July 2013

When studying human kinematics, the intention is usually to isolate and model the movements of bony segments. With motion capture based on skin mounted marker systems, there is confounding of the extent to which the surface represents the movements of the underlying bony structures1 . Soft tissue artifact (STA) is an important confounder, caused by the relative movement between the skin mounted markers and the underlying bones. STA is a commonly encountered problem in biomechanics2 . Furthermore, for applications such as motion analysis of composite joints in the spine, wrist and ankle, the inability to associate surface markers closely with underlying bony segments has inhibited the construction of meaningful mechanical models3. The research question underpinning this program of work is whether it may be possible to use data from cross sectional imaging modalities in combination with surface mounted marker sets, to solve for the error associated with surface markers and so produce refined functional models of activities in real world settings.
The Effect of Continuous Positive Airway Pressure on Total Cerebral Blood Flow in 23 Healthy Awake Volunteers
Authors: Yiallourou Theresia I. , Odier Céline , Martin Bryn A. , Haba-Rubio José , Heinzer Raphael , Hirt Lorenz , Stergiopulos Nikolaos
Published: July 2013

Continuous Positive Airway Pressure (CPAP) is used as the gold standard treatment for sleep disordered breathing, acting as a pneumatic splint to prevent collapse of the pharyngeal airway. However, the influence that CPAP has on Cerebral Blood Flow (CBF) dynamics is not well understood. This preliminary study investigates the influence of CPAP on total CBF in 23 healthy awake subjects by measuring flow velocity and lumen diameter of the left and right proximal Internal Carotid Arteries (ICA), Vertebral Arteries (VA), and Middle Cerebral Arteries (MCA) using Duplex Color Doppler Ultrasound (US) with and without CPAP at a level of 15 cm H2O. Transcutaneous Carbon Dioxide (PtcCO2) level, heart rate, Blood Pressure (BP), and oxygen saturation (SaO2) were monitored before and after each test. The preliminary measurements indicate that CPAP results in a decrease of CBF by 17% (p-value < 0.05). The theoretically predicted decrease in CBF from PtcCO2 variation was 6%. The study should be further explored in patients with sleep apnea and various types of cerebrovascular and craniospinal disorders.
Numerical Modelling of Stenting Procedures in Coronary Bifurcations: A Structural and Fluid Dynamic Combined Approach
Authors: Morlacchi Stefano , Chiastra Claudio , Dubini Gabriele , Migliavacca Francesco
Published: July 2013

Stenting procedures give the opportunity to treat cardiovascular diseases with a time saving, cost effective and minimally invasive procedure if compared to coronary artery by-pass, ensuring at the same time better clinical results than balloon angioplasty. Despite their success, stenting procedures are still associated to some clinical problems like sub-acute thrombosis (ST) and in-stent restenosis (ISR) whose main outcome is the re-narrowing of the coronary vessels and the necessity of a new treatment to restore blood flow and perfusion to downstream tissues. Their mechanisms and causes are still not fully understood but clinical and biological studies agree the idea that these are caused by a combination of both structural and hemodynamic factors [1,2].
Simulating Diffuse Axonal Injury During Traumatic Brain Injury Events
Authors: Dolle Jean-Pierre , Schloss Rene , Yarmush Martin L.
Published: July 2013

Traumatic Brain Injuries (TBI) affect up to 1.5 million people annually within the United States with as many as 250,000 being hospitalized and 50,000 dying [1]. TBI events occur when the brain experiences a sudden trauma such as a rapid acc/deceleration. These events produce high inertial forces that result in a shearing or elongation of axons (commonly known as Diffuse Axonal Injury [2].
Extracellular Matrix Bioscaffolds to Enhance ACL Healing: Impact on the Contribution of the MCL to Joint Stability
Authors: Fisher Matthew B. , Jung Ho-Joong , Kim Kwang E. , McMahon Patrick J. , Woo Savio L-Y.
Published: July 2013

A torn anterior cruciate ligament (ACL) of the knee has poor healing potential, and thus, surgical reconstruction using soft tissue autografts is needed to restore knee stability. Unfortunately, these procedures have a high incidence of donor site morbidity and the progression to osteoarthritis in the long-term 1. In recent years, biological stimulation by means of growth factors and bioscaffolds has demonstrated successful early clinical results 2. Our research center has used extracellular matrix (ECM) bioscaffolds as a biological agent to improve ACL healing in a goat model 7, 8. Indeed, there was sufficient formation of neo-ACL tissue that led to up to a 30% reduction in the instability of the stifle joint by 12 weeks. Its biomechanical properties also increased by two-fold in comparison to those with suture repair alone 7, 8.
Dynamically-Loaded 3-D Model to Study the ECM Organization of Aortic Smooth Muscle Cells in Aneurysmal Patients With Bicuspid Aortic Valve
Authors: He Wei , Phillippi Julie , Miller Christopher E. , Vorp David A. , Gleason Thomas G.
Published: July 2013

Rupture of aortic aneurysms and dissections are the fifteenth leading cause of a death in the United States [1]. Over 40% of patients undergoing elective surgery for ascending aortic replacement due to thoracic aortic aneurysm (TAA) have a congenital defect in the aortic valve know as bicuspid aortic valve (BAV) [2]. BAV patients have uniformly larger diameter aortic roots and ascending aortas compared to age- and sex-matched controls [3] and abnormal elasticity even in the absence of valvular stenosis or aneurysm [4] and this greatly increases the risk of aortic dissection and sudden death [5]. The cause of TAA is uncertain, but recent studies suggest that oxidative stress may play a role in the pathogenesis of TAAs by degrading the extracellular matrix (ECM). We identified that BAV smooth muscle cells (SMCs) lack sufficient resistance to reactive oxygen species to maintain ECM homeostasis [6, 7].
Model-Based Investigation of Ankle Stiffness Control Versus Active Feedback Control During Quiet Standing
Authors: Mahboobin Arash , Cenciarini Massimo , Redfern Mark S. , Loughlin Patrick J.
Published: July 2013

The mechanisms involved in generating corrective torques to maintain balance during human upright stance have been attributed to passive control (i.e. intrinsic properties of muscles and tendons, such as the intrinsic stiffness and viscoelasticity of muscles) and active control (i.e. neurally-mediated sensory-based feedback control) [1–3]. While there continues to be some debate over the roles of active versus passive mechanisms in maintaining balance, especially during quiet (unperturbed) standing [4–6], the general consensus is that both mechanisms contribute to postural control [3]. However, active mechanisms have been shown to play a more dominant role in maintaining upright stance, particularly during perturbed conditions [7, 8].
Dynamic Culture Improves Mechanical Functionality of MSC-Laden Tissue Engineered Constructs in a Depth-Dependent Manner
Authors: Farrell Megan J. , Comeau Eric S. , Mauck Robert L.
Published: July 2013

Limitations associated with the use of autologous chondrocytes (CH) for cartilage tissue engineering beget the need for alternative cell sources. Mesenchymal stem cells (MSC) are clinically attractive due to their ability to undergo chondrogenesis in three-dimensional culture [1,2]; however, when compared to CH, MSC fail to develop functional equivalence [2,3]. We have previously shown a marked depth-dependence in local equilibrium modulus of MSC-laden gels, with the superficial zones (where maximal media exchange occurs) considerably stiffer than regions removed from nutrient supply (center and bottom of construct); less dramatic depth-dependence was observed in CH-laden gels [4]. Similarly, other studies have shown depth-dependent properties in CH-laden gels with the construct edge generally stiffer than the center [5]. Given this apparent influence of nutrient supply, the objective of the current study was to assess the impact of dynamic culture (via orbital shaking) on the development of depth-dependent mechanical properties in both MSC and CH-laden hydrogels. Furthermore, we assessed cell viability and matrix content throughout the construct depth to determine the mechanism by which this depth-dependency arises. We hypothesized that improved nutrient transport would reduce construct inhomogeneity (particularly for MSC-laden constructs) and improve bulk mechanical properties.
Voxelized 3D Computational Transport Model of Infusions Into the Ventral Hippocampus: Comparison With Experimental Studies
Authors: Kim Jung Hwan , Astary Garrett , Kantorovich Svetlana , Mareci Thomas H. , Carney Paul R. , Sarntinoranont Malisa
Published: July 2013

Convection enhanced delivery (CED) is a promising local delivery technique for overcoming the blood brain barrier (BBB) and treating diseases of the central nervous system (CNS). For CED, infusate is infused directly into brain tissue and the drug agent is spread through the extracellular space, which is considered highly tortuous porous media. Previous studies have indicated that the infusion of therapeutic agents into the hippocampus is a potential treatment method for epilepsy [1]. In this study, a 3D interstitial transport modeling approach is presented in which tissue properties and anatomical boundaries are assigned on a voxel-by-voxel basis using tissue alignment data from magnetic resonance (MR) diffusion tensor imaging (DTI). The developed model was used to predict CED transport in the ventral hippocampus and predicted tracer distributions were compared with experimental studies. In rat CED experiments, T1-weighted contrast-enhanced MR images were acquired to measure Gd-DTPA albumin tracer distributions after infusion into the ventral hippocampus. Similar infusate distribution patterns were obtained demonstrating the reliability and repeatability of this modeling scheme. Qualitative comparisons between predicted and measured distribution patterns, volumes and shapes were also conducted to determine the model’s proficiency.
Ibuprofen Release From Electrospun Nanofibers
Authors: Maiti Siddhartha , Jimenez-Rios Jorge L. , Bhowmick Sankha
Published: July 2013

Controlled and gradual drug delivery is important in order to improve therapeutic efficiency and to reduce potential toxic effects due to overdose of the particular drug. Electrospun nanofibres have gained much attention for controlled drug delivery as the electrospinning process produces scaffolds with very high surface to volume ratio, while being a very simple and cost-effective process. A wide variety of drugs can be effectively incorporated into the fibers, and the structure and function of the fibers and the drug has been found to be maintained (1, 2).
Mechanical Buckling of Artery Under Pulsatile Flow
Authors: Liu Qin , Han Hai-Chao
Published: July 2013

Tortuous or twisted arteries, often seen in carotid and many other arteries, can lead to transient ischemic attacks to distal organs including stroke [1]. The mechanisms for the development of tortuous arteries remain unclear. Our recent studies [1, 2] suggested that artery bent buckling could be a possible mechanism for vessel tortuosity. However, these studies were performed under static pressure but arteries in vivo are usually under pulsatile flow where both the mean pressure and pulse pressure may change at physiological or pathological conditions. The aim of this study was to investigate the biomechanical buckling of arteries under pulsatile flow to determine the effect of pulsatile flow on the critical buckling pressure.
Effects of Edemagenic Stress on Lymph Transport in the Rat Mesentery
Authors: Rahbar Elaheh , Akl Tony , Zawieja David C. , Cote Gerard L. , Moore James E.
Published: July 2013

The lymphatic system transports fluid from the interstitium into the vascular network of lymphatic vessels through a series of valves, nodes and post-nodal ducts that converge into the subclavian veins. The lymphatics are intimately involved in fluid circulation, macromolecular homeostasis, lipid absorption, and immune function. All of these functions rely on the generation and regulation of lymph flow along the collecting lymphatic vessels. An imbalance between the lymphatic load and the ability to transport lymph can lead to lymphedema. Lymphedema occurs with a pathological increased in load, impaired vasculature (either anatomically or functionally deranged), or in situations where there is a relative distortion of both factors [1]. Edema has become a growing concern amongst breast cancer patients; surveys have reported up to 90% of women develop lymphedema in their arms within 3 years of nodal dissection surgery [2]. Despite these statistics, our knowledge of edema remains very basic and thus there is a lack of effective treatment.
Piconewton Level Loading and Sub-Cellular Deformation of Bone Cells Using a Novel Stokesian Fluid Stimulus Probe (SFSP)
Authors: Wu Danielle , Ganatos Peter , Weinbaum Sheldon , Spray David C.
Published: July 2013

A new quantifiable in vitro force probe, the Stokesian Fluid Stimulus Probe (SFSP), is developed to hydrodynamically stimulate local regions of the osteocyte whereby neither antibody decoration nor probe membrane perturbation is necessary. Osteocytes are imbedded in hard mineralized matrix where single-cell, in vivo experimentation is extremely challenging. Whole bone tissue loading induces cyclic fluid flow throughout the bone porosity to hydrodynamically load osteocytic networks within the lacunar-canalicular-system (LCS). A theoretical model has been developed to describe the fluid flow through the dynamic and structurally complex microenvironment surrounding the osteocytic network within the LCS. The model predicts tensile forces of 1–10pN to occur at discrete attachment sites connecting the osteocyte cell process to canalicular wall projections during physiological loading1. Our new force probe’s design and implementation has successfully 1) reproduced in vivo level forces at subcellular precision to assess cellular polarity in vitro and 2) demonstrated that cellular signaling is initiated at integrin attachment sites along the cell process.
Progressive Subchondral Sclerosis During OA Explained by Depth-Dependent Bone Demineralization
Authors: Cox L. G. E. , van Rietbergen B. , van Donkelaar C. C. , Ito K.
Published: July 2013

For many years, pharmaceutical therapies for osteoarthritis (OA) have been focused on the degenerating cartilage. However, there is increasing evidence that bone plays an important role in OA as well. The structural and material properties of the subchondral bone are modified, and bone cysts and osteophytes may develop. The mechanisms behind these bone changes are subject of debate, and a better understanding may help in the development of bone-targeting OA therapies.
Effect of Aortic Distensibility on Coronary Flow: A 3D FSI Model of Aortic Valve With the Inclusion of Coronary Arteries
Authors: Nobari Soroush , Mongrain Rosaire , Leask Richard , Cartier Raymond
Published: July 2013

Aortic stiffening and CAS are thought to affect coronary blood flow [1,2]. Pathological conditions such as aortic aneurysm, aortic wall stiffening and calcific aortic stenosis (CAS) will affect the distensibility of the aortic root and therefore the hemodynamics of the region. Reduced aortic distensibility (i.e. increased aortic stiffness) via presence of pathologies such as severe CAS results in a decrease of diastolic backflow. This reduction will cause less flow to enter the coronaries [2,3,4] and therefore reduce the amount of oxygen delivered to myocardium. This reduction of coronary flow can be explained by the concomitance of reduced myocardial supply as a result of decreased coronary perfusion pressure, and increased myocardial metabolic demand.
Human Tibiofemoral Joint Displacements Determined by Displacement-Encoded MRI
Authors: Chan D. D. , Neu C. P.
Published: July 2013

Articular cartilage and surrounding soft tissues in the knee are important to normal joint function. Osteoarthritis (OA) is highly prevalent in the United States [1] and features precocious degeneration of articular cartilage. Effective OA treatments require the ability to detect early degeneration, including mechanical and biochemical changes. Magnetic resonance imaging has shown promise for the detection of early degenerative changes, including various quantitative MRI techniques [2]. Displacement-encoded MRI has the ability to detect changes in mechanical behavior, and such techniques have previously been used in cartilage explants [3] and intact juvenile animal joints [4]. However, the authors are aware of no studies with displacement-encoded MRI of human articular cartilage. Tissue-level displacement patterns could be key to revealing early degeneration in articular cartilage. This study demonstrates for the first time displacement encoding with stimulated echoes (DENSE) in an adult human tibiofemoral joint.
Steady Versus Pulsatile Flow Modeling for Hemodynamics Based Stratification of a Population of Intracranial Aneurysms
Authors: Retarekar Rohini , Berkowitz Benjamin , Raghavan Madhavan L.
Published: July 2013

Hemodynamics is thought to play a role in the initiation and subsequent growth of intracranial aneurysms. Hemodynamics of an aneurysm is strongly related to its underlying morphology, specifically, the size and shape of the aneurysm sac and its contiguous vasculature [1]. Although the Computational Fluid Dynamic (CFD) simulations of transient blood flow seemingly provide in depth information of intra-aneurysmal hemodynamics, the simulations are often computationally expensive and demand additional measurements or assumptions such as the temporal variations in boundary conditions. When a population of aneurysms, with distinct sizes and shapes, are being studied in order to stratify them according to hemodynamics, it is conceivable that steady flow simulations are as effective as pulsatile flow simulations, especially when anatomical information is the only patient-specific information available. The objective of this study is to compare steady versus pulsatile flow simulations for a controlled hypothetical population of aneurysms with realistic variation in sac morphology and contiguous vasculature.
Experimental Validation of Computer-Simulated Glenoid Preparation for Total Shoulder Arthroplasty
Authors: Yongpravat Charlie , Lester Jonathan D. , Trubelja Alen , Greiwe R. Michael , Saifi Comron , Levine William N. , Bigliani Louis U. , Ahmad Christopher S. , Gardner Thomas R.
Published: July 2013

The use of three-dimensional (3D) computer simulations for pre-operative planning of total shoulder arthroplasty (TSA) has greatly increased in the past decade [1,2]. These studies have primarily focused on optimizing glenoid resurfacing to elucidate the factors involved in glenoid loosening, the most common cause of TSA failure [3,4]. While finite element analyses have investigated the effects of glenoid resurfacing parameters such as implant placement and depth of reaming on the stresses associated with the glenoid/cement/implant construct, none have determined if their method for simulating glenoid surface preparation is physically representative or accurate. In TSA, the first step in glenoid resurfacing is reaming the glenoid surface in preparation for the placement of the glenoid implant. The purpose of this study was to validate the volume removed as determined by computer simulated reaming against the volume removed by ream of cadaveric scapulae.
Injury to the Glenohumeral Capsule During Anterior Dislocation Leads to Higher Joint Contact Forces During Simulated Clinical Exams
Authors: Voycheck Carrie A. , Browe Daniel P. , McMahon Patrick J. , Debski Richard E.
Published: July 2013

Glenohumeral joint stability is maintained by a combination of active and passive soft tissue structures and osteoarticular contact. Anatomical structures that contribute to each of these categories include the rotator cuff muscles, the glenohumeral capsule, and the contact between the articular surfaces of the humeral head and glenoid of the scapula, respectively. Dislocation may result in injury to one or more of these stabilizing components requiring the other structures to account for the deficit. For example, previous research has shown that a torn supraspinatus tendon results in increased bony contact forces during glenohumeral abduction. [1] Another common injury resulting from dislocation is permanent deformation of the glenohumeral capsule as the capsule is the primary static restraint to anterior translation in positions of external rotation. [2] Increased joint translations and rotations usually occur following permanent deformation [3] indicating a loss in joint stability provided by the capsule. These changes in joint kinematics following dislocation imply that differences in the contact forces between the humerus and scapula may exist as well. Irregular contact between two articular surfaces can lead to abnormal wear and an increased risk of osteoarthritis when left untreated. Therefore, the objective of this work was to assess the affect of anterior dislocation on glenohumeral joint stability by determining the in situ force in the glenohumeral capsule and the bony contact forces between the humerus and scapula during a simulated clinical exam at three joint positions in the intact and injured joint.
A Novel 3D Model System to Study Deformation-Induced Cytoskeletal Remodeling
Authors: Foolen Jasper , Baaijens Frank
Published: July 2013

Native fibrous tissues contain complex anisotropic matrices. This results in essential direction-dependent mechanical properties, primarily originating from the fibrillar collagen. When engineering fibrous tissues in vitro, matrix anisotropy is crucial for in vivo functionality and durability. However, it is not fully understood how to guide, maintain and control matrix anisotropy. Cell traction and associated cell orientation may contribute significantly to collagen orientation. Therefore, the ability to manipulate cell orientation may be essential to develop a preferred matrix anisotropy for tissue engineering applications.
Controlled Release and Intracellular Delivery of Small Molecules Using Thermally Responsive Pluronic F127-Chitosan Nanocapsules
Authors: Zhang Wujie , Gilstrap Kyle , Wu Laying , Moss Melissa A. , Wang Qian , Lu Xiongbin , He Xiaoming
Published: July 2013

Nanoscale particulate systems have been studied as the delivery vehicle of various drugs and therapeutic agents for decades with promising outcomes. Recently, nano-particulate systems that are responsive to one or more environmental stimuli (such as temperature, pH, and electromagnetic field) are attracting increasing attention because they allow drug delivery and release to be done in a more controllable fashion [1]. The thermally (temperature) responsive nanoparticles are of particular interest to many researchers because the temperature controlled release of the encapsulated drug can be conveniently done with either thermo (using supraphysiologic temperatures) or cryo (using sub-zero temperature) therapies, minimally invasive energy-based surgical techniques that have been widely studied as potential alternatives to radical surgical intervention for the treatment of cancer and other diseases. Moreover, a significantly improved outcome of cancer treatment has been reported by combining thermotherapy (using supraphysiologic temperatures) and anticancer drug encapsulated in thermally responsive nanoparticles [2]. Here, we report thermally responsive nanocapsules that can be combined with cryotherapy for cancer treatment.
Intact Knee and ACL Forces for the Human and Ovine Model During Simulated In Vivo Human and In Vivo Ovine Motions
Authors: Herfat Safa T. , Boguszewski Daniel V. , Shearn Jason T.
Published: July 2013

Patients frequently experience knee injuries, with the ACL being one of the most commonly injured structures requiring surgery [1]. ACL tears typically lead to osteoarthritis in the long term, even after surgical treatment [2]. This chronic joint degeneration has been attributed to the failure of current ACL reconstructions to restore the native biomechanics of the knee joint [3]. To design more effective treatments, investigators must first understand normal knee function for multiple activities of daily living (ADLs). The 3D in vivo forces and moments of the normal intact knee, as well as those for just the ACL have not yet been determined for any ADL. These in vivo forces and moments can potentially be measured for multiple ADLs in an animal model. A biomechanical surrogate allows for 1) sensors or marker systems to be rigidly fixed to the knee joint to accurately measure the 6 degree of freedom (DOF) kinematics, and for 2) the kinematics to be simulated and applied to the harvested limb to measure the corresponding joint forces and moments.
Hemodynamic Comparisons Between Different Anastomotic Configurations in Dialysis Access Fistulae
Authors: McGah Patrick M. , Aliseda Alberto , Riley James J. , Leotta Daniel F. , Beach Kirk W.
Published: July 2013

Arteriovenous fistulae are created surgically to provide an adequate access for dialysis in patients with End-Stage Renal Disease. Producing an autogenous shunt linking an artery and a vein in the peripheral circulation bypasses the high resistance capillary bed in order to provide the necessary flow rates at sites easily accessible for dialysis. In successful fistulae, venous flow rates can easily exceed 1000 mL/min. It has long been recognized that the hemodynamics constitute the primary external influence on the remodeling process [1, 2]; The high flow rate, together with the exposure of the venous tissue to the high arterial pressure, leads to a rapid process of wall remodeling that may end in a mature access or in stenosis and failure. Given the high failure rate of dialysis access (up to 50% require surgical revision within one year [3]), understanding the dynamics of blood flow within the fistula is a necessary step in understanding the remodeling, and ultimately, in improving clinical outcomes.