bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative Assessment of Abdominal Aortic Aneurysm Geometry and Rupture Potential
Authors: Shum Judy , Martufi Giampaolo , DiMartino Elena S. , Finol Ender A.
Published: July 2013

Recent biomechanics studies have shown that the maximum transverse diameter of an abdominal aortic aneurysm (AAA) and its expansion rate are not reliable indicators of rupture potential. We hypothesize that geometrical shape and size, as well as wall thickness may be related to rupture risk and can therefore be deciding factors in the clinical management of the disease. A non-invasive, image-based evaluation of AAA size and geometry was implemented on a retrospective study of twenty subjects. The contrast enhanced, computed tomography (CT) scans of 10 patients who suffered AAA rupture within 1 month of the scan were compared to those of 10 patients who received elective repair. The images were segmented and three-dimensional models were generated. Twenty-eight geometry-based indices were calculated to characterize the size and shape of each AAA and regional variations in wall thickness were estimated. A multivariate analysis of variance was performed for all indices comparing the ruptured and non-ruptured data sets to determine which indices are statistically significant. Receiving Operating Characteristic (ROC) curves were generated to determine the indices’ potential as predictors of rupture risk. In addition to maximum diameter, five other geometry-based indices were found to be statistically significant, with the minimum wall thickness being the best discriminator between ruptures and non-ruptured AAAs.
Influences of Aging and Footedness on Stepping Over Obstacles
Authors: Chen Shih Shan , Chang Hsuan Sung , Chen Chia Ling , Chen Hsieh Ching , Chern Jen Suh , Chang Susan
Published: July 2013

Stepping over obstacles is an essential ability to walk safely in daily living. There are internal and external factors interacting to keep us stay in balance during negotiating obstacles. As we get older, the walking patterns and avoidance strategies may change due to the age-related degradation of our body. Since many studies show that tripping over obstacles is one of the most frequent causes of falls in the elderly [1], it is important for us to understand the control strategies of older adults during obstacle avoidance. The observation could let to an increased awareness of obstacle avoidance tasks and help diminishing falls risks in older adults [2].
Ultrasound Flow Assessment in Curved Vessels: An In-Vitro Study
Authors: Beulen Bart , Verkaik Anna Catharina , Rutten Marcel , van de Vosse Frans
Published: July 2013

In clinical practice, ultrasound is frequently used as a non-invasive method to assess blood velocity and vessel wall position. For the velocity assessment, often Doppler ultrasound is applied. To perform Doppler velocity measurements, the ultrasound probe needs to be positioned at a certain insonification angle (non perpendicular) with respect to the blood velocity vector (figure 1). For volume flow estimation, both an accurate assessment of vessel wall position and axial velocity distribution is necessary. However, in order to achieve an accurate wall position assessment, a perpendicular insonification is necessary. As a result, a simultaneous assessment of velocity by Doppler ultrasound and wall position is impossible, which hampers an accurate flow assessment.
A Mixed Experimental-Numerical Estimation Strategy to Characterize Arterial Wall Properties Including Residual Strains
Authors: van der Horst Arjen , van den Broek Chantal N. , Rutten Marcel C. M. , van de Vosse Frans N.
Published: July 2013

To model materials mechanically, it is necessary to determine the parameters of the constitutive model which determine its mechanical behavior. To be able to do this correctly it is important to know the zero-stress state of the material.
Morphology and Blood Flow Analysis of Pulmonary Arteries Under Respiratory Disorders
Authors: Christophe Jean-Joseph , Ishikawa Takuji , Imai Yohsuke , Matsuki Noriaki , Takase Kei , Yamaguchi Takami
Published: July 2013

Numerical methods are used to provide quantitative and qualitative information about effects of pulmonary disorders on blood flow. From patient’s CT images, arterial geometries are extracted and compared for healthy and unhealthy conditions. We show that pulmonary artery shape is strongly affected by the pulmonary disorders, e.g., the inlet is elongated and the branches are bent. In order to clarify the effect of geometrical change on the blood flow, we performed computational simulation of blood flow in the extracted geometries.
Effects of Reduced Compliance on Endothelial Functionality With Regards to Inflammation
Authors: Thacher Tyler N. , Gambillara Veronica , da Silva Rafaela , Silacci Paolo , Stergiopulos Nikos
Published: July 2013

The aging process is associated with a stiffening of the arteries. In this study we focused on how reduced wall compliance induces pulse pressure-mediated changes in endothelial function with regards to inflammation and adhesion.
Using Mathematica to Automatically Generate Abaqus User Material Subroutines
Authors: Young Jonathan , Yao Jiang , Perucchio Renato , Taber Larry A.
Published: July 2013

It is often difficult for commercial finite element (FE) analysis developers to implement highly specialized materials. Therefore, it is advantageous to allow users to code subroutines for specialized constitutive equations. The disadvantage is that the user must learn and understand the developer’s implementation of the nonlinear FE formulation. It is therefore beneficial to develop a process which can reduce the complexity of writing specialized material subroutines by generating the code automatically.
Characterization of Isolated Urethral Smooth Muscle Cells and Their Incorporation Into a Tissue Engineered Urethral Wrap
Authors: Patel Sanket N. , Haworth Donna J. , Xavier Anton E. , Chew Douglas W. , Vorp David A.
Published: July 2013

Millions of people worldwide suffer from an involuntary leakage of urine, a condition known as urinary incontinence. In the US alone, the estimated cost of managing this is more than $16 billion [1]. Stress urinary incontinence (SUI), the most common form, is characterized by involuntary leakage of urine from effort or exertion during actions such as laughing, coughing, or sneezing. SUI largely occurs as a result of weak or damaged pelvic muscles that support the bladder and urethra, which makes the urethra unable to maintain its seal and allows urine to leak. Current SUI treatments such as pelvic floor muscle training, vaginal inserts, pharmacologic therapeutics, and surgical procedures are limited by ineffectiveness and/or subsequent complications [2, 3].
Finite Element Modeling of Entangled Collagen Fiber Gels With Randomly Oriented Fibers
Authors: Ma Xiaoyue , Green J. Edward , Gooch Keith J. , Jansen Rebecca M. , Hart Richard T.
Published: July 2013

Collagen is an important structural protein in the human body, and its molecules form structural aggregates at multiple length scales (i.e., microfibrils, fibrils, fibers, and bundles of different sizes) in biological tissues and organs [1]. The mechanical properties of most tissues are dependent on the underlying network of collagen fibers, proteoglycans, and other extracellular matrix components [2]. Similarly, the properties of in vitro tissue analogs, often created from collagen or fibrin gels, are also dependent on the organization of the biopolymers [3]. The overall mechanical response is intrinsically multi-scale and dynamic in both materials. As a result, a satisfactory description of the microstructure is important for exploring the essential physics of the tissue.
Mechanical Characterization of Fresh Human Carotid Atherosclerotic Plaque
Authors: Maher Eoghan , Creane Arthur , Sultan Sherif , Hynes Niamh , Lally Caitríona , Kelly Daniel J.
Published: July 2013

Quantifying the properties of atherosclerotic plaques is critical to improving our understanding of the pathogenesis of the disease. Furthermore realistic tissue properties are vital in order to obtain legitimate results from finite element models of surgical interventions used to treat cardiovascular disease. The aim of this study is to determine the mechanical properties of fresh human carotid plaques immediately following removal during endarterectomy. A number of studies have reported atherosclerotic plaque properties previously [1–3], however all of these tested cadaveric tissue. This study will further investigate in-patient and inter-patient variability, the relationship between plaque properties and their clinical classification (calcified, mixed or echolucent) and the location of the sample (common, internal, external carotid).
Analysis of Post-Operative Abdominal Aortic Aneurysm Repair: A Multi Patient-Specific Study
Authors: Molony David , Walsh Michael , McGloughlin Tim
Published: July 2013

Abdominal aortic aneurysm is an irreversible dilation of the infrarenal aorta, which if left untreated may rupture. Surgical intervention is usually necessary to prevent this outcome. The decision to operate is based on the maximum diameter of the aneurysm. Two types of treatment exist; these are open repair and endovascular repair (EVAR). Of concern here is EVAR, which is the minimally invasive technique of inserting a stent-graft into the site of the aneurysm in order to shield the aneurysm wall from the stresses of blood pressure.
Secondary Flow Structure Induced by Physiologically Relevant Waveform in a Curved Tube
Authors: Prince Chekema N. , Peterson Sean D. , Plesniak Michael W.
Published: July 2013

The complex geometry of the vascular system can induce the development of complex primary and secondary flow regimes within blood vessels. Recent literature has focused on the impact of these complex flow regimes on endothelial cells (EC), which line blood vessels, and their role on the progression of vascular disease. One such disease, atherosclerosis has been linked to the reaction of ECs to flow conditions. Atherosclerosis is often treated by stent implantation to return the vessel lumen to its native diameter. It is hypothesized that stent struts may alter the development of secondary flow within the vessel and cause re-stenosis and/or thrombosis distal to the stent.
Finite Element Analysis of Buckling of Arteries With Aneurysms
Authors: Northcutt Avione , Han Hai-Chao
Published: July 2013

Tortuosity of arteries occurs when a normally straight artery starts to take on a twisted path. This is often referred to as tortuosity and kinking of arteries. This phenomenon occurs in arteries throughout the body including the aorta and cerebral [1, 2]. Arterial tortuosity is a potentially dangerous condition that can lead to cerebrovascular symptoms, ischemia, and stroke [3].
Development of 3D Finite Element Model of Human Elbow to Study Elbow Dislocation and Instability
Authors: Al Kork Samer Khodor , Amirouche Farid , Abraham Edward , Gonzalez Mark
Published: July 2013

The mechanics of elbow dislocation and its stages of dislocation are complex and not well understood. Reconstructing a fall where someone lands on their hand is one of the most challenging problem in biomechanics. Current models which attempt to reconstruct falls usually focus on experimental kinematical conditions that cause the fall coupled with inverse dynamics to determine the joint and muscles forces [1,2] to provide on insight into the joint instability. Our hypothesis based on our experimental investigation is that the mechanism of posterior elbow dislocation is initiated at radial head where the ulna and coronoid fracture followed by anterior tearing of the joint capsule, lateral collateral ligament will then rupture followed by posterior medial collateral ligament rupture and then the medial collateral ligament peeling off the ulna. In this study we developed a quasi-static three-dimensional finite element of human elbow joint, and conducted several cadaveric studies to study elbow dislocation. The FE model is used to investigate how the ligaments, cartilages behave under different flexion, extension of the elbow. Dislocation is investigated as function of different loads and moments applied to the radius-ulna with arm being flexed and configured into a supination or pronation.
An Analytical Solution for Flexible Substrates Undergoing Small Equibiaxial Strains
Authors: Chiang Martin Y. M. , Dunkers Joy
Published: July 2013

Cells can distinguish between different types of mechanical signals, such as stretch (tension), pressure (compression), and shear, to guide mechanosensitive cellular activities. Cell culture systems with controlled delivery of a mechanical input such as substrate strain, hydrostatic pressure, or fluid shear stress are used for the in vitro application of these forces. The work reported here uses a system that imparts equibiaxial loading on a flexible substrate to study cell response to stretch, similar to the Bioflex in the Flexcell [1] family of products. The objective of this study is to introduce an analytical (closed-form) solution of the relationship between the substrate strain and pressure under small strains, less than 2%. The solution is derived from the superposition of two elastic responses induced in the equibiaxial strain culture system after applying pressure.
Three-Dimensional In-Vivo Cervical Spine Kinematics: Preliminary Comparison of Fusion Patients and Normal Control Subjects
Authors: McDonald Colin P. , Bilkhu Sukhinder K. , Chang Victor , Bachison Casey , Bartol Stephen W. , Bey Michael J.
Published: July 2013

Degenerative disc disease (DDD) of the cervical spine is a common condition that causes significant pain and disability. Treatment for DDD in 2000 exceeded 110,000 patients in the United States alone [1]. A common treatment option for patients involves removal of the degenerated disc and fusion of the adjacent vertebral bodies. However, previous research has shown that as many as 25–92% of patients treated with fusion have disc degeneration at the adjacent levels within 10 years after surgery [2,3]. It has been hypothesized that this is the result of a change in adjacent vertebral segment motion [4]. However, it is unknown if spinal fusion alters motion at these segments. Thus, the objective of this study was to compare the dynamic, three-dimensional (3D) motion of the cervical spine in normal control subjects and spinal fusion patients.
Anisotropic Mechanical Properties of Soft Tissues by Magnetic Resonance Elastography
Authors: Namani Ravi , Wood Matthew , Sakiyama-Elbert Shelly E. , Bayly Philip V.
Published: July 2013

Structure-function relationships incorporate anisotropy of soft tissues, to account for their direction-dependent loading response [1]. Empirical measures: fiber alignment and distribution have been used to describe soft tissue response due to cell-matrix interactions and applied loads [2, 3]. To complement these measures, noninvasive estimation of anisotropic mechanical properties is essential. Magnetic resonance elastography (MRE) is a noninvasive technique to obtain elastic properties form propagating shear waves [4]. Wave propagation patterns in MRE were found to vary with direction of tissue excitation and fiber orientation [5]. Accurate estimates of anisotropic elastic properties of soft tissues have yet to be obtained by MRE.
The Effect of Dynamic Alterations in Stiffness of the Substrate on Cell Growth
Authors: Jiang Frank X. , Chippada Uday , Li Lulu , Yurke Bernard , Schloss Rene S. , Firestein Bonnie L. , Langrana Noshir A.
Published: July 2013

Cells reside in a dynamic environment composed of extracellular matrix (ECM) and other cells, and take a variety of cues, of which mechanical stresses and strains are an important subset. ECM undergoes constant synthesis and degradation, and its mechanical stiffness can also be altered, with ageing, upon external assault or via pathological processes. Particularly in load barring tissues, the mechanical properties of the ECM can vary, by exposure to changing load conditions through, for example, collagen realignment. Tissue-implant interfaces also present medically important dynamic mechanical environment. Furthermore, recent studies revealed that the ranges of mechanical stiffness of ECM or substrates can alter specific cellular properties in distinct ways. From an engineering viewpoint, it is thus beneficial to be able to modify the physical properties of the biomaterials for the implants, providing optimal conditions for a specific desired outcome at different points during time progression. All of these reasons make it desirable to have a dynamic culture system with controlled property changes.
Virtual Axis Finder: A New Method to Identify the Two Kinematic Axes of Rotation for the Tibio-Femoral Joint
Authors: Roland Michelle , Hull Maury L. , Howell Stephen M.
Published: July 2013

Kinematic modeling of the knee requires an accurate method to identify the rotational axes [1]. The tibio-femoral joint has two fixed rotational axes: the flexion-extension axis in the femur (FE) and the longitudinal rotational axis in the tibia (LR) [2–4]. Because the knee naturally produces coupled rotation about the LR axis during flexion, attempting to identify the axes from natural flexion alone creates an underdetermined system. A previous study using a mechanical axis finder identified the FE and LR axes by initially identifying the LR axis from pure internal-external (I/E) rotations [4]. Because the major source of error in this method was the visually-based alignment of the axis finder, it should become more repeatable and reliable by utilizing a mathematical optimization to situate the axis finder. Therefore, the two objectives were to develop and validate a new axis finding method, which is based on a mathematical optimization, for identifying the two fixed rotational axes of the tibio-femoral joint.
Finite Element Modelling of Cell Adhesion Mediated by Receptor-Ligand Binding
Authors: Li Jianrong , Cheng Tianle , Chiang Martin Y. M.
Published: July 2013

The process of cell adhesion and spreading on the extracellular matrix (ECM) protein layer is mediated by the interaction of cell receptors and ECM ligands [1]. Receptors diffuse along the cell membrane surface and interact with ligands in ECM to form bonds. Cells spread and the adhesion zone grows as bond formation at the adhesion front increases to a critical level. This process involves coupling of reaction-diffusion and mechanical contact between cells and ECM. In this study, a novel numerical algorithm is developed to implement this coupling into the finite element method for modeling the process of cell adhesion and spreading. By taking the mass diffusion and the user-defined gap conductance features provided in a commercial FEM code, Abaqus [2], the process has been solved in an integrated and fully coupled manner. Preliminary results have been obtained from the simulation of cell spreading on a rigid substrate. The influence of glycocalyx layer (present at cell surface) on the adhesion development has also been incorporated into the modeling.
Mapping the Elastic and Osmotic Properties of Cartilage Extracellular Matrix
Authors: Lin David C. , Horkay Ferenc
Published: July 2013

The inhomogeneous distribution of crosslinks in polymer networks results in nonuniform swelling. Concomitant with this behavior is local variability in the elastic properties of synthetic and biopolymer gels. Articular cartilage exemplifies the compositional and structural complexities found in soft tissues. At the most basic level, cartilage extracellular matrix (ECM) is a relatively stiff network of collagen type II fibers with entangled hyaluronic acid chains and enmeshed aggrecan molecules. Despite significant differences in composition, synthetic and biological gels exhibit qualitatively similar responses (e.g., viscoelasticity and nonlinear stress-strain behavior at large deformation). Scaling theory [1] and experiments [2–3] have verified that the shear modulus (Ge) of chemically identical, fully swollen gels differing only in the degree of crosslinking is proportional to the polymer concentration (ce): (1)Ge=Acen where A and n are constants. In a good solvent, n = 2.25 [1]. Recent studies have shown that the power law applies to collagen gels, with n ≈ 2.68 [4]. In the general case, (2)G=Acen-mcm where G and c are the general shear modulus and polymer concentration, respectively, and m = 1/3 [5].
Roughness Evolution of Metallic Implant Surfaces Under Contact Loading and Nanoscale Chemical Etching: Influence of Surface Roughness and Contact Loading
Authors: Ryu Jae-Joong , Shrotriya Pranav
Published: July 2013

Metallic materials are chosen for orthopedic implants because of their high load-bearing capacity, low cost and low wear rates. However, repeated contact loading at taper-locked or clamped of metallic implant interfaces results in formation of soluble and particulate debris due to the simultaneous action of mechanical loading and electrochemical reactions in the corrosive physiological environment [1–3]. Previous work on understanding metallic implant surface damage due to mechanical load assisted dissolution has run the gamut from examination of retrieved implants [4, 5, 6 ] to in-vitro implant scale experiments (see for instance [7] and references in review articles [2, 5]). Results of these studies indicate that there is a synergistic interaction of mechanical loading and electrochemical oxidation i.e. material degradation is accelerated by the combined effects of contact loading and corrosion.
Validation of a Simple, Laser-Guided System for Prescribing Acetabular Cup Inclination Angle in Total Hip Arthroplasty
Authors: Peter Jennifer , Currey Jovauna M. , Marmor Meir , Buckley Jenni M. , McGann William
Published: July 2013

In total hip arthroplasty (THR) cases, it can be technically challenging to achieve the correct inclination angle for the acetabular component. Commercial intra-operative navigation systems have been successfully used to precisely guide acetabular orientation [1]; however, these systems are costly, time consuming, and have a steep learning curve for new users [2]. In an effort to simplify the procedure, McGann et al. have developed a laser-guided system to address the inclination angle [3]. In preliminary clinical trials, this system has been used successfully, but its accuracy and repeatability have never been quantified.
Quantification of In Vivo Knee Joint Laxity
Authors: Westover Lindsey M. , Küpper Jessica C. , Ronsky Janet L.
Published: July 2013

In biomechanical terms, passive joint laxity is a measure of joint movement within the constraints of ligaments, capsule, and cartilage [1] when an external force is applied to the joint during a state of muscular relaxation. Excessive knee joint laxity (reduced stiffness) can result from soft tissue injury, such as a ligament tear, or from genetic factors such as benign joint hypermobility syndrome, and can predispose the joint to instability including recurrent dislocations, and low-grade inflammatory arthritis [2]. The link between laxity and instability may be better understood if laxity can be reliably and accurately quantified. To more fully understand the underlying joint mechanics, it is necessary to quantify both gross knee joint stiffness as well as the stiffness characteristics of individual joint structures, such as the anterior cruciate ligament (ACL).
Computational Analysis of the Tether Pulling Experiment to Probe Cellular Membranes
Authors: Schumacher Kristopher , Popel Aleksander , Anvari Bahman , Brownell William , Spector Alexander
Published: July 2013

Membrane tethers can form naturally such as during leukocyte rolling (pre-adhesion) stage. Tethers can also be experimentally pulled from cellular membranes to estimate membrane mechanical and electromechanical properties, including bending modulus, adhesion energy of the membrane-cytoskeleton interaction, tension, and electromechanical forces produced by membranes. This technique has been effectively applied to a variety of cells such as red blood cells [1], neutrophils [2], and cochlear outer hair cells [3,4]. Fig. 1 presents the experiment where tethers are pulled from cellular membranes using optically trapped beads.
Development of a Bridge-Microcantilever by CMOS Process for Surface Stress Measurement
Authors: Yang Shih-Ming , Chang Chun , Yin Tsung-I
Published: July 2013

Microcantilever based biosensor have been the recent research interests for its versatility in data acquisition and interpretation. A microcantilever can measure the surface stress generated on any specific functional layer coating on a biochemical sensor. Berger et al. [1] showed the surface stress change by the alkanethiols on a probe. Fritz et al. [2] measured the DNA hybridization and receptor-ligand binding by a microcantilever. The surface stress measurement in the above works is mainly by measuring the microcantilever deflection based on the optical lever technique in scanning probe microscopy; however, alignment and calibration of the optical element for different testing species are by no means trivial. The technique may be futile when operating in non-transparent liquid.
Patient-Specific Modelling of Aortic Arch Wall Shear Stress Patterns in Patients With Marfan Syndrome
Authors: Trachet Bram , Devos Daniel , De Backer Julie , De Paepe Anne , Loeys Bart L. , Segers Patrick
Published: July 2013

Marfan syndrome (MFS) is a genetic connective tissue disorder with a high prevalence of aortic aneurysm formation (a pathological dilatation of the aorta), typically at the aortic root. The disorder is caused by mutations in the gene encoding fibrillin-1 [1]. Recently, it has been shown in mouse models that selected manifestations of MFS, such as aortic aneurysm formation, can be explained by excessive signaling by the transforming growth factor–beta (TGF-beta) family of cytokines [2]. Although the footprint of the disease is clearly genetic, there is still a role for (computational) biomechanics and hemodynamics to elucidate why aneurysms develop preferentially at the level of the aortic root, since the genetic defect affects the entire (arterial) system. One of the most obvious parameters to study is the arterial wall shear stress (WSS). WSS plays an important role in the regulation of the vascular system and is considered a significant factor in the development and progression of cardiovascular disease in humans. Low and/or oscillating values of WSS have been associated with the formation of atherosclerotic lesions [3] and with the growth of aneurysms [4]. It is, however, hard to show a link between low WSS and aneurysm initiation, since in most cases the geometrical and physiological data are lacking during the first and most important stages of the aneurysm development. Furthermore follow-up studies in human patients are difficult, since aneurysms grow very slowly (only 0.9 mm/year in MFS patients treated with beta-blockers) and it will take several years before significant changes will have taken place. Therefore, in this study, we have computed the aortic flow field and WSS patterns for 5 different MFS patients with ages varying from 14 to 54 years old, in order to get an idea about the effect of age on the development of the disease.
Injury Driven Biological Model of Restenotic Lesion Development Predicts the Effects of Stent Geometry on Restenosis
Authors: Boyle Colin J. , Lally Caitríona , Prendergast Patrick J.
Published: July 2013

One of the most significant limitations of percutaneous coronary intervention using stents is the growth of tissue within the stent, leading to re-occlusion of the target vessel. There is a wide range of stents available, and stent designs differ in their efficacy [1]. Stent parameters such as stent length, strut configuration, diameter and expansion method have been shown to influence the amount of restenosis provoked [2]. Despite many generations of coronary stents — and the advent of drug elution — up to 10% of percutaneous coronary interventions require revision, climbing to 50% in some high risk lesions [3].
Inter-Rater Reliability of 3D Polygonal Reconstructions From CT Scans
Authors: Buford W. L. , Ivey F. M. , Fogarty J. P. , McMorries R. G.
Published: July 2013

Computed tomography (CT) scans have long been used as a diagnostic tool in many areas of medicine. With advances in computer image analysis methods, it is now possible to generate 3-D polygonal reconstructions from CT scans, which provide an accurate representation of the muscles and skeleton of the patient. The Mimics program (Materialise, Leuven, Belgium) is one of several available software packages that through user dependent interactive techniques can create these 3-D reconstructions of body parts from CT scans.
Automated Building Block Assignments for Finite Element Mesh Development of Patient-Specific Orthopaedic Models
Authors: Ramme Austin J. , Magnotta Vincent A. , Grosland Nicole M.
Published: July 2013

Medical imaging technologies have allowed for in vivo exploration and evaluation of the human musculoskeletal system. The utility of these technologies has grown exponentially as the time required for data collection has decreased and the image resolution has increased. Medical imaging obviously has diagnostic value, but the vast amount of information contained within each image set is useful in other important applications including the modeling and analysis of anatomic structures. With advances in both the resolution of the acquired images and computing power, patient-specific orthopaedic model development is becoming a reality.
Electrospinning of Recombinant Protein Polymer Nanofibers
Authors: Qiu Weiguo , Stokes Arjun , Cappello Joseph , Wu Xiaoyi
Published: July 2013

Structural proteins often in the form of micro and nanofibers, constituting most of intra- and extracellular matrix (ECM), are the fundamental building blocks of life [1]. Recent efforts to replace diseased or damaged tissues and organs have resulted in the molecular design and genetic engineering of recombinant proteins, and the advent of new technology for fabricating structural proteins into micro-/nanofibrous scaffolds, hoping to resemble some or all the characteristics of ECM structure and function. The fabrication of such an ECM mimic may be an important step in engineering a functional tissue. To this end, we have produced a series of silk-elastin-like proteins (SELPs) [2]. Revealed by our subsequent studies, SELPs in the form of hydrogels, thin films, and microfibers, have displayed a set of outstanding biological and physical properties. In this study, electrospinning will be pursued as a mechanism for the formation of SELP nanofibers.
Effect of Continuous and Intermittent Mechanical Loading on the Development of Skeletal Muscle Damage - A Combined Experimental/Numerical Approach
Authors: Loerakker Sandra , Stekelenburg Anke , Strijkers Gustav J. , Nicolay Klaas , Bader Dan L. , Baaijens Frank P. T. , Oomens Cees W. J.
Published: July 2013

Prolonged mechanical loading of soft tissues, as present when individuals are bedridden or wheelchair-bound, can lead to degeneration of skeletal muscle tissue. This can result in a condition termed pressure-related deep tissue injury (DTI), a severe kind of pressure ulcer that initiates in deep tissue layers, e.g. skeletal muscle, near bony prominences and progresses towards the skin. Complications associated with DTI include sepsis, renal failure, and myocardial infarction. Damage pathways leading to DTI involve ischemia, ischemia-reperfusion injury, impaired lymphatic drainage, and sustained tissue deformation. Recently, the role of tissue deformation in the onset of skeletal muscle damage was established by combining animal experiments with finite element (FE) modeling [1]. After 2 hours of continuous loading, a clear correlation between maximum shear strain and damage was found.
The Expression of A-Type Lamins as a Regulator of Mechanics of the Nucleus and Cell Mechanotransduction
Authors: Ribeiro Alexandre S. , Wren Nicholas S. , Jarvik Jonathan W. , Dahl Kris N.
Published: July 2013

Mechanotransduction of extracellular stimuli into the chromatin located in the cell nucleus and overall cell mechanics may require the physical support of structures of A-type lamins. Several cellular pathologic phenotypes and phases of stem cell differentiation involve regulation and reorganization of A-type lamins. Here is presented a study of changes in cell mechanics associated to the reorganization of nuclear structures consequent to knockdown of A-type lamins. Transient dysmophism of the cell nucleus is observed during knockdown of A-type lamins, which seems to be driven by inner cellular forces resultant of cytoskeletal and chromatin structural reorganization.
Comparison of Cortical and Cancellous Screws for Sternal Fixation
Authors: Christakis Alexander , Dieselman John , Ahn Jonathan , Sandefer Andrew , Psoinos Charles , Ignotz Ronald , Lalikos Janice , Dunn Raymond , Billiar Kristen
Published: July 2013

The goal of this study is to compare the performance of currently available screw types and configurations for rigid sternal fixation. Bone fixation plates were attached to osteoporotic human sternum with cortical or cancellous screws in either a unicortical or bicortical manner. The plates were cyclically loaded transversely (0–50N at 2Hz) for 15,000 cycles; the resulting lateral screw displacement was measured continuously. Bicortical attachment allowed significantly lower initial displacement than unicortical (p = 0.015), whereas cortical screws allowed significantly lower displacement than cancellous screws after long term cycling (p = 0.039). These initial findings indicate that both screw type and cortical purchase are important parameters in the design of a rigid plating system for sternal closure. Cortical screws appear to be more applicable to the osteoporotic sternum, as the cortical shell regions support more screw purchase than the degenerated cancellous part, and bicortical screw purchase appears to decrease screw loosening.
Strain Rate Dependence in the Structure Property Relationship of Porcine Brain
Authors: Begonia Mark G. T. , Liao Jun , Horstemeyer Mark F. , Williams Lakiesha N.
Published: July 2013

The brain is the control center for the central nervous system (CNS), and it is composed of specialized divisions that are attributed to a vast assortment of structural, homeostatic, and cognitive functions. These distinct regions are surrounded by supportive tissue and comprised of a complex arrangement of neurons that can be further categorized as either gray or white matter. The cerebrum constitutes the larger surrounding portion of the forebrain and includes sinuous ridges called gyri that are separated by grooves or fissures called sulci. The intermediate layer of the cerebrum primarily consists of white matter tracts that are responsible for integrating various regions throughout the cerebrum. The innermost and outermost layers of tissue mainly contain gray matter and are collectively known as the subcortical nuclei and cerebral cortex, respectively, which are crucial integrating components of the CNS [1]. An investigation into the mechanical properties of this vital organ coupled with microstructural characterization of its constituents under varying deformation levels is therefore crucial for implementing more accurate prediction and prevention of traumatic brain injury (TBI).
Comparison of Experimental and Real-Time Data in Amateur Boxers
Authors: Stojsih Sarah E. , Bir Cynthia A.
Published: July 2013

The sport of boxing dates back to the time of the ancient Greeks and Romans. While boxing has come a long way from its origin in fist fighting, head injury is of great concern in the sport of boxing. A study found that over 70% of acute injuries occur in the head region, with almost half of the injuries to this region being concussions [1]. Various techniques have been implemented to discern the risk of head injury in boxing. Although some surrogate data have been collected to assess the mechanism that causes the injuries [2], real-time head acceleration data from the ring has yet to be obtained.
K12 Outreach: Using Biomechanical Engineering Design Projects to Teach Difficult STEM Concepts to Middle School Students
Authors: Billiar Kristen L. , Belisle Robin , Cezar Tanea , Fusco Mary , Gray Cecelia , Oliva Thomas , Tate Veronica L. , Hubelbank Jeanne , Camesano Terri A.
Published: July 2013

Science, technology, engineering and math (STEM) concepts become more difficult and less interesting for many students in middle school, thus discouraging many from pursuing science and engineering. To aid in student learning and motivation, we collaborated with middle school teachers to develop engineering design projects to teach difficult STEM concepts. Biomechanics projects appear to motivate student learning and reinvigorate the teaching of engineering topics.
Apoptotic Response and Differentiation Ability of Adipose Derived Stem Cells (ASCs) Frozen/Thawed in the Presence of Polyvinylpyrrolidone (PVP)
Authors: Thirumala Sreedhar , Gimble Jeffrey M. , Devireddy Ram V.
Published: July 2013

Effective techniques for the cryopreservation of human Adipose Stem Cells (ASCs) could increase the usefulness of these cells in tissue engineering and regenerative medicine. The traditional method of using fetal calf serum (FCS) and a chemical cryoprotectant like dimethylsulfoxide (DMSO) during freezing storage restricts the direct use of ASCs in regenerative medicine and reconstruction surgery. The objective of this study was to investigate the apoptotic, necrotic and viability response of ASCs frozen/thawed in the presence of a high molecular weight polymer, Polyvinylpyrrolidone (PVP) and in the absence of FCS. Post-freeze/thaw studies were also conducted to evaluate the effect of PVP on the in vitro osteogenic and adipogenic differentiation of ASCs. The results were compared with those obtained using the most commonly used cryopreservation media of 10%DMSO + 10% Dulbecco’s Modified Eagle Media (DMEM) + 80%FCS.
Kinematic Differences Between the Flat, Kick, and Slice Serves Measured Using a Markerless Motion Capture Method
Authors: Sheets Alison L. , Corazza Stefano , Abrams Geoff , Safran Marc , Andriacchi Thomas
Published: July 2013

Tennis, is a globally popular sport enjoyed by approximately 25 million people worldwide. While recreational and professional tennis offer numerous health benefits, innovations in racquet technology and improved training methods have recently placed a greater emphasis on increased power and ball velocity. Following this change, the number injuries has risen to an estimated 10 per 1,000 hours played [1].
Micromechanical Models of Helical Fiber Organization in Crimped Tendon and Ligament Fibers Predict Large Poisson’s Ratios
Authors: Reese S. P. , Maas S. A. , Weiss J. A.
Published: July 2013

The Poisson’s ratio is a measure of how much lateral contraction occurs in response to a uniaxial tensile strain, therefore making it a metric of the volumetric behavior of a material. A Poisson’s ratio greater than 0.5 for an isotropic material subjected to uniaxial tension is indicative of volume loss, which in the scheme of biphasic theory is believed to be manifested as fluid exudation. Experimentally obtained values for the Poisson’s ratio range from 0.8 in rat tail tendon, 1.3 in capsular ligament to 3.0 in flexor tendon [1,2,3]. In spite of the important implications of this volumetric response the micromechanical origins of these large Poisson’s ratios have been largely uninvestigated.
Screening of a Biodegradable Polymer Library for Optimal Scaffolding for Mineralized Tissue Engineering
Authors: Brey Darren M. , Margulies Bryan S. , Hankenson Kurt D. , Burdick Jason A.
Published: July 2013

Combinatorial libraries have been developed recently for identifying large numbers of potentially bioactive compounds or materials for a range of medical applications[1]. While drug companies have been using methods for screening libraries of compounds for therapeutic benefit for years, only recently have libraries been exploited for the generation of scaffolds for regenerative medicine[2–4]. Our lab has developed a library of photocrosslinkable and biodegradable poly(β-amino ester)s (PBAEs)[5] that can be easily tuned for stiffness and degradation for a variety of applications [6]. Here, we screened these materials for their degradation behavior, mechanical properties, and cellular interactions sequentially using specified criteria to identify potential candidates for scaffolding in bone tissue engineering. One candidate material was further investigated for scaffold processing, biocompatibility, and the ability to form mineralized tissue in a rodent cranial defect model with the addition of osteoinductive factors.
Efficient Synchronization and Reconstruction of 4D Non-Gated Cardiac Images of Chick Embryos Obtained From Optical Coherence Tomography
Authors: Liu Aiping , Wang Ruikang , Thornburg Kent L. , Rugonyi Sandra
Published: July 2013

Four-dimensional (4D) imaging with optical coherence tomography (OCT) — a high-resolution, noninvasive tomographic imaging technique — applied to cardiac development can be used to study the interaction of cardiac morphology and function in vivo. However, to image the fast beating embryonic heart, the biggest challenge confronted by current OCT systems is the slow rate of 3D volume image data acquisition.
A 3D Shoulder Scan Compatible Humeral Coordinate System for Glenohumeral Joint Kinematics
Authors: Amadi Hippolite O.
Published: July 2013

Advanced surgical planning techniques often require modeling the functional characteristics of the affected body region. Most patient-specific modeling in vivo relies on medical image scans that are expensive and may also allow patient’s exposure to ionizing radiation. This poses a challenge for the modeling of the kinematics of the glenohumeral joint (GHJ) based on the tissue geometries of the affected patients. The humeral morphology uniquely presents its canal (HC) and epicondyle (EC) axes as the two longest axes that are nearly orthogonal. This gives them the mathematical advantages as best axes for the definition of humeral coordinate system (HCS), especially from 2D radiographic images. This is however limited in 3D in vivo kinematics as minimization of radiation exposure may not allow medical imaging of the whole volume of interest all the way down to the distal epicondyles. It is therefore necessary that landmarks for use are captured within the field of view (FOV) of standard shoulder scans. This would avoid extra radiation exposure to patients and imaging cost as the scan might have been used earlier for traditional diagnosis. The aims of this study were to (1) confirm that HC-axis quantified from a ‘stack of discs (SOD)’ technique was the most reliable and consistent (2) identify the most closely oriented or most inter-subject related axis to the EC-axis for its replacement or prediction respectively from 3D proximal humeral scan and (3) use these to propose a HCS definition procedure that can be applied to a standard shoulder scan.
Biopolymer Polyelectrolyte Complex Nanocomposites for Bone Tissue Engineering
Authors: Verma Devendra , Katti Kalpana , Katti Dinesh
Published: July 2013

Recent studies have shown that its necessary for synthetic matrix to provide similar mechanical response as cell’s host environment in the body for desired tissue growth [1,2]. Osteoblast cells reside in the rigid matrix made of collagen fibers and hydroxyapatite crystals. Therefore for the growth of proper functional bone tissue, its utmost necessary that scaffolds provide mechanical response similar to bone matrix. Bone also serves as a mechanical support to the body. Thus scaffolds used for bone tissue engineering should also provide adequate mechanical support to prevent collapse of the neonatal tissue. The mechanical response of scaffolds decreases significantly as porosity increases. The porosity of scaffold around 90% has been considered optimal for tissue engineering. At such high porosity, the mechanical strength and elastic modulus decreases significantly. Various polymers both of synthetic and biological origin have been investigated as a material for scaffold [3]. Synthetic polymers are biodegradable, biocompatible, and can be easily formed into different shapes and sizes. However, hydrophobicity, lack of functional groups and release of acidic products on degradation are causes of concern. Biopolymers such as collagen, chitin, chitosan etc. promote cell adhesion, proliferation and differentiation, and evoke minimal foreign body reaction on implantation [4]. But, they have inadequate mechanical properties for bone regeneration and tend to loose structural integrity under wet and body fluid conditions. The quest for scaffold materials which, not only promote cell adhesion, proliferation and differentiation but also have adequate mechanical strength to support bone tissue growth is still on. In the current work, we discuss the synthesis and characterizations of nanocomposites based on biopolymers and hydroxyapatite. The biopolymers used are chitosan and polygalacturonic acid. These two biopolymers are biocompatible, biodegradable and electrostatically complementary to each other. We have also investigated the molecular mechanics involved in their mechanical behavior. Their in vitro response have been investigated by seeding human Osteoblast cells and studying their adhesion, proliferation and differentiation. Synthesis and characterizations of nanostructured fibers based on chitosan and polygalacturonic acid will also be discussed here.
Intracranial Aneurysm Morphology and Flow Dynamics to Assess Rupture Risk
Authors: Xiang Jianping , Tremmel Markus , Ma Ding , Mocco J. , Siddiqui Adnan , Meng Hui
Published: July 2013

The effectiveness of Intracranial Aneurysm (IA) size as a predictor for rupture has been debated. The confusing trends observed *unicefwhile stratifying IA rupture risk according to IA size may have arisen from overlooking its morphology and size relative to its parent vessel.
High Wall Shear Stress and Positive Wall Shear Stress Gradient Trigger the Initiation of Intracranial Aneurysms
Authors: Metaxa Eleni , Tremmel Markus , Xiang Jianping , Kolega John , Mandelbaum Max , Siddiqui Adnan , Mocco J. , Meng Hui
Published: July 2013

While the pathogenesis of an intracranial aneurysm (IA) is poorly understood, it has been generally postulated to be related to hemodynamic insult. IAs are predominantly located at apices of arterial bifurcations or outer curves on or near the Circle of Willis, suggesting a potential role of the specific hemodynamics at such locations characterized by high wall shear stress (WSS). Clinically, new IA formation has been observed following local flow increase.
Coupled and Multi-Scale Building Blocks for a Comprehensive Computational Lung Model
Authors: Wall Wolfgang A. , Comerford Andrew , Wiechert Lena , Rausch Sophie
Published: July 2013

Mechanical ventilation is a vital supportive therapy for critical care patients suffering from Acute Respiratory Distress syndrome (ARDS) or Acute Lung Injury (ALI) in view of oxygen supply. However, a number of associated complications often occur, which are collectively termed ventilator induced lung injuries (VILI) [1]. Biologically, these diseases manifest themselves at the alveolar level and are characterized by inflammation of the lung parenchyma following local overdistension or high shear stresses induced by frequent alveolar recruitment and derecruitment. Despite the more recent adoption of protective ventilation strategies based on the application of lower tidal volumes and a positive end-expiratory pressure (PEEP), patient mortality rates are with approximately 40% still very high. Understanding the reason why the lungs still become damaged or inflamed during mechanical ventilation is a key question sought by the medical community. In this contribution, an overview on recently developed building blocks of a comprehensive lung model will be given, with a main focus on lower airways.