bluuebunny/crossref_metadata_2025 huggingface dataset:
Simplified Medium Scale FEM Numerical Models of Magnetic Nanoparticle Heating: Study of Thermal Boundary Condition Effects
Authors: Pearce John
Published: January 2014

Magnetic nanoparticles are currently under intense investigation as a heating strategy for hyperthermia cancer treatment because they are promising as a means to target the heating specifically to the tumor.[1–4] Currently, our ability to create practical and useful numerical models in dimensional spaces similar to ordinary small tumors is severely hampered by the multiple orders of magnitude of the relative scales: nm to mm. Consequently, the preponderance of literature on the topic describes experimental studies only. Detailed individual nanoparticle model spaces with moderate dimensions up to mm would be nearly intractably computationally intensive, requiring peta-scale computing resources. It would advance the state of the art to be able to apply practical computing machinery to analyze realistic medium scale in vivo systems. Such a tool could be reasonably applied in experimental analysis, and potentially in treatment planning and assessment.
A 3D Biphasic Finite Element Model of the Human Knee Joint for the Study of Tibiofemoral Contact and Fluid Pressurization
Authors: Guo Hongqiang , Maher Suzanne A. , Spilker Robert L.
Published: January 2014

Biphasic theory which considers soft tissue, such as articular cartilage and meniscus, as a combination of a solid and a fluid phase has been widely used to model their biomechanical behavior [1]. Though fluid flow plays an important role in the load-carrying ability of soft tissues, most finite element models of the knee joint consider cartilage and the meniscus as solid. This simplification is due to the fact that biphasic contact is complicated to model. Beside the continuity conditions for displacement and traction that a single-phase contact problem consists of, there are two additional continuity conditions in the biphasic contact problem for relative fluid flow and fluid pressure [2]. The problem becomes even more complex when a joint is being modeled. The knee joint, for example, has multiple contact pairs which make the biphasic finite element model of this joint far more complex. Several biphasic models of the knee have been developed [3–9], yet simplifications were included in these models: (1) the 3D geometry of the knee was represented by a 2D axisymmetric geometry [3, 5, 6, 9]; (2) no fluid flow was allowed between contact surfaces of the soft tissues [4, 8] which is inconsistent with the equation of mass conservation across the contact interface [10]; (3) zero fluid pressure boundary conditions were inaccurately applied around the contact area [7].
Aneurismal Arteries are Vulnerable to Mechanical Buckling
Authors: Han Hai-Chao , Lee Avione Y. , Shadfan Ramsey H. , Xiao Yangming
Published: January 2014

Rupture of aneurysms is a leading cause of death in the United States. Extensive biomechanical studies have shown that mechanical stress in aneurysm walls plays a critical role in the rupture of aneurysms. Highly elevated local stress and degraded aneurismal walls are believed to make aneurysms vulnerable to rupture [1–3]. Asymmetric aneurysms with irregular shape and wall thickness are vulnerable to rupture. Aneurismal arteries are often tortuous such as in the Loeys-Dietz syndrome [4], but the mechanism is unclear.
Evaluation of Menisci Following a Compressive Tibiofemoral Load
Authors: Fischenich Kristine M. , Button Keith D. , Fajardo Ryan S. , Haut Roger C. , Haut Donahue Tammy L.
Published: January 2014

Genetics, obesity, and mechanical loading conditions such as trauma can increase the risk of development of OA. Posttraumatic OA, or OA resulting from trauma, is thought to account for 12% of all patients exhibiting OA. 1 A number of injuries can lead to posttraumatic OA, but it is most commonly seen following sports injuries where anterior cruciate ligament (ACL) and meniscal injuries have occurred. 2
Demands on Posterior Fusion Hardware During Lordosis Restoration Procedures
Authors: Martin Audrey , Telles Connor , Leasure Jeremi , Tang Jessica , Ames Christopher , Kondrashov Dimitriy
Published: January 2014

Lower lumbar lordosis plays a critical role in sagittal alignment. It has been shown that restoration of lumbar lordosis in patients with preoperative sagittal imbalance is necessary to prevent postoperative sagittal decompensation [1]. Further, restoration of lower lumbar lordosis in patients with degenerative flatback syndrome has been shown clinically to result in additional correction of the thoracic curve and sacral slope [2]. Currently, there are three commonly used intraoperative techniques to restore lumbar lordosis: (1) cantilever bending, (2) in situ bending, and (3) compression and/or distraction of screws along posterior fusion rods. Although powerful, all three techniques require the surgeon to impart large forces to the accompanying posterior fusion hardware, often causing failure of hardware and inconsistency to achieve pre-operatively planned lordosis. To date, there has been no clinical or biomechanical study to address the comparative performance of these three techniques. In efforts to determine a standard of care for sagittal alignment via lumbar lordosis restoration, the goal of this study is to establish a relation between the three techniques, and the resulting demands on posterior fusion hardware. It is hypothesized that greater loads will be observed in the hardware during in situ bending, increasing the risk of pedicle screw pullout.
Testing Image Processing Algorithms for Melanoma Detection
Authors: Zhu Liang , Chamani Alireza
Published: January 2014

Treatment of skin cancer depends upon the timely detection of abnormal skin lesions.1 Unfortunately, in the early stages of skin cancer, patients lack awareness of symptoms that should motivate them to visit their primary physician or dermatologist. Once patients detect the symptoms of skin cancer, particularly melanoma, it may have metastasized, by which time treatment outcomes are poor and medical costs are high.
Cadherin-11 Regulates Calcific Nodule Formation by Aortic Valve Interstitial Cells
Authors: Chen Joseph , Hutcheson Joshua D. , Sewell-Loftin M. K. , Ryzhova Larisa M. , Fisher Charles I. , Merryman W. David
Published: January 2014

Calcific aortic valve disease (CAVD) is characterized by the stiffening and calcification of the aortic valve leaflets which result in impaired valve function and increased load on the myocardium. In vitro models of CAVD involve the formation the calcific nodules via aortic valve interstitial cells (AVICs). Transforming growth factor β1 (TGF-β1) induced myofibroblast differentiation of AVICs, which is evidenced by increased αSMA expression, has been shown to be a key mediator of dystrophic calcific nodule formation. Benton et al. demonstrated the critical role of αSMA in nodule formation in that when αSMA was suppressed, calcific nodules did not form [1]. Confoundingly, preventing phosphorylation of Erk1/2 with a MEK1/2 inhibitor leads to increased αSMA expression yet prevents calcific nodule formation [2], suggesting the requirement of another essential component of nodule formation that has yet to be revealed.
Platelet Retraction Forces Induced Under High Shear Gradient Activation
Authors: Ting Lucas H. , Feghhi Shirin , Sniadecki Nathan J.
Published: January 2014

Hemodynamics play an important role in the activity of platelets. High shear rate gradients can occur at locations where blood vessels bend, branch, or narrow and can arise at a vascular stent or artificial valve. These shear gradients have been observed to cause platelets to adhere to the vessel wall, leading to their activation and aggregation [1, 2]. High shear gradients can cause a self-sustaining process where platelet aggregation increases the local shear gradient, further causing platelets to adhere and aggregate. This process can become dangerous if the aggregate grows large enough to obstruct the vessel or if it detaches and clogs a vessel downstream.
Simulating Microgravity in a Large Animal Model
Authors: Gadomski B. C. , McGilvray K. C. , Easley J. T. , Palmer R. H. , Puttlitz C. M.
Published: January 2014

The microgravity environment encountered during spaceflight has numerous deleterious effects on the human body, with one of the most drastic being decreased bone mass due to mechanical unloading. These alterations in bone mass and skeletal strength are one of the foremost limitations of future space exploration. Due to the cost of long-duration space missions, it is critically important to develop ground-based models of the microgravity environment encountered during spaceflight to investigate possible countermeasures to maintain skeletal integrity.
Glutaraldehyde Fixation of Bovine Humeral Head Articular Cartilage Maintains Functional Frictional Response
Authors: Jones Brian K. , Ahmad Christopher S. , Hung Clark T. , Ateshian Gerard A.
Published: January 2014

Hemiarthroplasty is a surgical procedure that replaces the injured half of a diarthrodial joint (such as the hip or shoulder) with a smooth impermeable metal surface, leaving the apposing healthy cartilage layer intact. In 2006, more than 260,000 hip and shoulder hemiarthroplasties were performed in the United States alone [1]. Hemiarthroplasties are often revised to total arthroplasties, due in part to premature erosion of the intact, initially healthy cartilage [2]. Recent theoretical and experimental studies [3, 4] have shown that the low friction and wear of healthy diarthrodial joints depend critically upon sustained, elevated pressure of the interstitial water within the porous cartilage. Because this fluid pressure is continuous across the porous-permeable cartilage contact interface, the impermeable bearing surface implanted in hemiarthroplasty may substantially disrupt the natural lubrication of the apposing healthy cartilage [5]. Motivated by the established clinical success of implanting glutaraldehyde-treated porcine and bovine heart valves and pericardial grafts in humans, the objective of this study was to investigate whether a novel bioprosthetic hemiarthroplasty, utilizing a glutaraldehyde-treated cartilage xenograft, can reproduce the sustained low friction of a healthy natural diarthrodial joint. The specific aim of this study was to measure and compare the 24 h in-vitro frictional response of a bovine shoulder joint with that of a bioprosthetic hemiarthroplasty consisting of a glutaraldehyde-treated humeral head and an untreated, native cartilage glenoid.
Selective Densitometry of the Lumbar Spine
Authors: Chu Bryant , Leasure Jeremi , Kondrashov Dimitriy
Published: January 2014

Bone mineral density (BMD) has been identified as a major factor in spine construct strength, with failures resulting in pedicle screw loosening and pullout2. Computed tomography (CT) scans have been shown to effectively measure BMD1,4. Previous research has utilized this linear correlation of CT Hounsfield Units (HU) to BMD in order to determine BMD as a function of anatomic location within cervical vertebrae1; however, the lumbar spine has not yet been reported on. The goal of this study was to describe BMD of anatomical regions within lumbar vertebrae using the correlation between HU and BMD. It was hypothesized that posterior elements of the spine would exhibit significantly different BMD than the vertebral body. This was tested through means comparison of BMD for each anatomical region.
Validation of a Novel 3D-Printed Instrumented Spatial Linkage That Measures Changes in the Rotational Axes of the Tibiofemoral Joint
Authors: Bonny Daniel P. , Howell S. M. , Hull M. L.
Published: January 2014

The two kinematic axes of the tibiofemoral joint, the flexion-extension (F-E) and longitudinal rotation (LR) axes [1], are unrelated to the anatomic landmarks often used to align prostheses during total knee arthroplasty (TKA) [1, 2]. As a result, conventional TKA changes the position and orientation of the joint line, thus changing the position and orientation of the F-E and LR axes and consequently the kinematics of the knee. However, the extent to which TKA changes these axes is unknown. An instrument that can measure the locations of and any changes to these axes is an instrumented spatial linkage (ISL), a series of six instrumented revolute joints that can measure the six degrees of freedom of motion (DOF) between two rigid bodies without constraining motion. Previously, we computationally determined how best to design and use an ISL such that rotational and translational errors in locating the F-E and LR axes were minimized [3]. However, this ISL was not constructed and therefore its ability to measure changes in the axes has not been validated. Therefore the objective was to construct the ISL and quantify the errors in measuring changes in position and orientation of the F-E axis.
Image Based Flow Computations Without User Generated Meshes
Authors: Dillard Seth , Mousel John , Shrestha Liza , Raghavan Madhavan , Vigmostad Sarah
Published: January 2014

Medical image processing has emerged as a powerful way to simulate fluid flows through realistic models of complex patient-specific geometries without relying upon simplifying geometric approximations. However, image-based flow modeling processes traditionally involve several steps (e.g. image segmentation, surface mesh generation, volumetric flow mesh generation, and finally computational simulation) that must often be performed using separate pieces of software. This work presents an alternative methodology in which the entire image-based flow modeling process takes place on a Cartesian domain with the image embedded as an implicit surface, circumventing the need for complex surface meshes and body-fitted flow meshes. The complete framework is demonstrated with flow calculations performed in a computed tomography (CT) image reconstruction of an intracranial aneurysm (ICA). Flow calculations are compared against calculations performed following a standard multi-step route using the Vascular Modeling Toolkit (VMTK) [1, 2] and Fluent™ (Ansys, Inc., Lebanon, NH).
Biomedical Evaluation of Polymerized Biodegradable Cement vs. PMMA Cement in Kyphoplasty for Vertebral Compressive Fractures
Authors: Agarwal A. K. , Kodigudla M. , Desai D. , Jones A. D. , Lin B. , Goel V. K. , Schlossber B.
Published: January 2014

Kyphoplasty/vertebroplasty procedures traditionally use PMMA to treat the fractured vertebrae due to its mechanical properties. However, with time the bone erodes around the cement due to osteoporosis and inhibited bone remodeling due to the cyotoxicity of PMMA (1). The exothermic reaction of PMMA is also responsible for thermal necrosis and can cause complications in cases of extravasation (1; 2; 3). Lastly, PMMA is not bioactive and will not be reabsorbed (1; 2; 3). Thus, alternative cements with similar mechanical strengths are being explored. Calcium phosphate cements (CaP) have been explored due to their bioactive and non-thermal properties (3; 4). Despite these advantages, there are reservations of traditional CaP cements due to deficiencies in mechanical properties (1; 4). We evaluated new polymerized calcium phosphate (pCaP) cement which is not brittle like traditional CaP cements. Mechanical properties of vertebral bodies augmented with either PMMA or pCaP after fracture were determined.
A New Device for an Early Rehabilitation of the Ankle Joint and its Effects on Brain Activation: A NIRS and EEG Study
Authors: Pittaccio Simone , Garavaglia Lorenzo , Molteni Erika , Guanziroli Eleonora , Zappasodi Filippo , Beretta Elena , Strazzer Sandra , Molteni Franco , Villa Elena , Passaretti Francesca
Published: January 2014

The ankle joint is a fundamental element in the biomechanical system of locomotion. When its functions are impaired, due to neurological insult such as brain trauma or a stroke, severe disability and loss of personal independence may ensue. For this reason, great care is given to the physical rehabilitation of the lower limb. On the other hand, it is often the case that only a limited amount of time can be specifically devoted to the ankle joint manipulation during routine rehabilitation sessions. Furthermore, early initiation of active workout may be impossible for patients showing paresis; even passive exercise is often delivered to a minimal degree while the general conditions of the patients impose that they are kept bedridden. The delay in commencing rehabilitation may have negative consequences in terms of detrimental changes in tissue properties, deafferentation through lack of proprioceptive stimulation, learned non-use, and, ultimately, spastic paresis [1].
Surface Modified Nitinol Stents Release Metal Ions in Blood
Authors: Kapnisis Konstantinos , Eleftheriou Polyvios , Lapathitis George , Karaiskos Christos , Beck Preston , Lemons Jack , Connolly David , Pitsillides Costas , Anayiotos Andreas
Published: January 2014

Intravascular nitinol stents are used in the treatment of atherosclerosis and intracranial aneurysms. Despite the unique physical properties of shape memory and superelasticity, the chemical composition of NiTi has raised concerns due to the presence of nickel ions within the alloy which can have adverse effects on human health. Currently, stents are manufactured from corrosion resistant alloys which form protective titanium oxide films, insulating the bulk material from the corrosive physiologic fluid. However, nanometer thick regions of oxides are lost at locations of high strain due to significant bending, micromotion between overlapping stents or local calcification1‐2. Recent studies have revealed that some stents undergo corrosion in vivo, with significant release of metallic ions into surrounding tissues3–4. In this project, a range of techniques has been employed to modify the surface of miniature NiTi stents in order to mimic in vivo corrosion and correlate the amount of nickel ions released with the findings in explanted tissue.
Dynamic Splints, Functionally-Customized With Nitinol, Can Reduce Joint Rigidity in Pediatric Subjects With Spasticity
Authors: Garavaglia Lorenzo , Beretta Elena , Strazzer Sandra , Sala Felice , Delle Fave Morena , Brunati Fabio , Passaretti Francesca , Pittaccio Simone
Published: January 2014

Neuromuscular diseases as a consequence of brain damage are complex phenomena involving disuse, immobility, brain tissue remodeling and cortical function remapping. They may have various causes and strike any part of the population. The vicious circle leading to a worsening of the patients’ conditions proceeds through muscle shortening by contractures, disruption of the normal reflex behavior and sensory problems, development of spasticity [1]. Physical rehabilitation alone or in association with surgery or pharmacological treatments can be useful in limiting those degenerations. Besides manual rehabilitation, splints and braces are prescribed to control the limb posture and obtain stretching of the muscles. The role of those orthoses is to maintain the paretic limb in a set ‘physiological’ position and let it relax into that posture, in an attempt to reduce muscle rigidity and contractures. However applying a fixed constraint to the limb and waiting for relaxation to take place, may cause discomfort, pain, skin rash, and sundry different complications [2]. Also, any residual voluntary movement is prevented by a fixed-angle splinting. In addition, all these negative characteristics limit tolerability and daily application times. This work presents a different way to promote limb repositioning, based on the application of NiTi-alloy-based dynamic splints, which favor mobility and any residual use of the affected limb. Furthermore it suggests that application of mild contact forces prolonged in time has the advantage of feeling less painful and uncomfortable for the patients, improving overall treatment tolerability.
Development and Preliminary Testing of a Rehabilitation Game to Improve Listening in Background Noise
Authors: Ringleb S. I. , Watson G. S. , Schwartz K. S. , Sandberg H. M. , Raymer A. M.
Published: January 2014

A trivia game was developed to improve listening in background noise in a variety of impaired populations. Preliminary data were collected in 10 healthy asymptomatic volunteers (n = 7 treatment and n = 3 control) using Quick Speech in Noise Test (QSIN) (Etymotic Research, Elk Grove Village, IL) to assess each participant’s ability to process speech with varying levels of background noise. Playing trivia game led to improved listening in noise in the treatment group, when compared to the controls. Additional data were collected from one patient with aphasia as a result of left hemisphere stroke. This participant’s performance improved in QSIN and these improvements were retained after six months.
Analysis of Blood Flow Through Side Branches Jailed by Flow Diverters in Rabbit Models
Authors: Cebral Juan R. , Mut Fernando , Raschi Marcelo , Kadirvel Ramanathan , Kallmes David
Published: January 2014

Since treatment of cerebral aneurysms with flow diverters (FD) has gained much attention in recent years, it is important to understand what is the effect of these devices on the flow through arteries jailed or crossed by these devices [1].
The Strain Response of Lung Myofibroblasts Cultured on Electrospun Polycaprolactone Nanofibers
Authors: Fee Timothy J. , Zhou Yong , Marshall Lauren E. , Berry Joel L.
Published: January 2014

Idiopathic Pulmonary Fibrosis is a devastating condition characterized by excessive localized production of collagen in the lungs. Over 131,000 people are living with IPF in America (1, 2). There is currently no known treatment or cure for the disease. It has recently been shown that IPF myofibroblasts are sensitive to the stiffness of their substrate. Specifically, alpha Smooth Muscle Actin (alpha-SMA), a known indicator of IPF activity, was differentially produced on soft vs. stiff substrates (3). This suggests a mechanotransduction pathway within the IPF myofibroblasts.
Murine Osteochondral Stem Cells Express Collagen Type I More Strongly on PDMS Substrates Than on Tissue Culture Plastic
Authors: Van Dyke William S. , Akkus Ozan , Nauman Eric
Published: January 2014

The discovery of the multipotent lineage of mesenchymal stem cells has dawned a new age in tissue engineering, where an autologous cell-seeded scaffold can be implanted into different therapeutic sites. Mesenchymal stem cells have been reported to differentiate into numerous anchorage-dependent cell phenotypes, including neurons, adipocytes, myoblasts, chondrocytes, tenocytes, and osteoblasts. A seminal work detailing that mesenchymal stem cells can be directed towards differentiation of different cell types by substrate stiffness alone [1] has led to numerous studies attempting to understand how cells can sense the stiffness of their substrate [2–3] Substrate stiffness has been shown to be an inducer of stem cell differentiation. MSCs on extremely soft substrates (250 Pa), similar to the stiffness of bone marrow, became quiescent but still retained their multipotency [4]. Elastic substrates in the stiffness range of 34 kPa revealed MSCs with osteoblast morphology, and osteocalcin along with other osteoblast markers were expressed [1]. However, osteogenesis has been found to increase on much stiffer (20–80 kPa) [5–6] (400 kPa) [7] as well as much softer substrates (75 Pa) [8]. Overall, cells have increased projected cell area and proliferation on stiffer substrates, leading to higher stress fiber formation. This study seeks to understand if the stiffness of the substrate has any effect on the differentiation potential of osteochondral progenitor cells into bone cells, using an in vitro dual fluorescent mouse model.
A Computational Study for Motor Vehicle Crash Injuries of Obese Child Passengers
Authors: Kim Jong-Eun , Hsieh Min-Heng , Shum Phillip C. , Tubbs R. Shane , Allison David B.
Published: January 2014

According to current definitions [1], individuals ages 2 to 18 years are determined to be overweight (≥ 85th and < 95th percentile [of prior population distributions]) or obese (≥ 95th percentile) based on U.S. age- and sex-specific body mass index (BMI; kg/m 2) charts updated by the Centers for Disease Control and Prevention (CDC) in 2000 [2]. The prevalence of being obese among children has increased over the last several decades and is a major public health concern. A recent survey [3] indicated that 16.3% of children and adolescents aged 2 through 19 years were at or above the 95 th percentile of the BMI-for-age growth charts.
Instantaneous Axis of Rotation for Lumbar Spine Torsion Measured
In Vivo
Authors: Ma Xue Xiao , Espinoza Orías Alejandro A. , An Howard S. , Andersson Gunnar B. J. , Inoue Nozomu
Published: January 2014

Segmental spine instability — especially that of torsional nature — is difficult to diagnose in a degenerative lumbar spine in vivo. The motion of the lumbar segment is of a coupled nature and is described by a total of six degrees of freedom. Relative motion between two bodies in space is described by translations and rotations, and this includes the concept of the instantaneous axis of rotation (IAR). References 1–3 are representative reports of the many available in the literature about calculations of the IAR in cadaveric tissue, usually single motion segments [1–3]. In contrast, results of the IAR for lumbar motion measured in vivo (and by extension, for the whole lumbar spine) are actually scarce. Based on the preliminary report presented by group [4], in the present study we describe the characteristics of the IAR for lumbar spine torsion measured in vivo in a much larger cohort of normal subjects through the application of the method originally described by Kinzel et al. [5].
Characterization of Passive Elastic Properties of the Human Tibialis Anterior Muscle Using Supersonic Shear Wave Elastography
Authors: Koo Terry K. , Guo Jingyi , Cohen Jeffrey H. , Parker Kevin J.
Published: January 2014

In a companion ex vivo study of chicken muscles [1], we demonstrated that muscle elasticity measured by Supersonic shear wave elastography (SWE) increases linearly with passive tension, and hence, SWE could be an indirect measurement of passive muscle force. Objectives of the present study were: (1) Determine the test-retest reliability of SWE for in vivo measurements of passive muscle elasticity of the tibialis anterior (TA) muscle; (2) Assess the relationship between elasticity and ankle angle of the TA; and (3) Extract physiologically meaningful parameters from the elasticity-angle curves for better quantification of passive elastic properties.
Glycosaminoglycan and Collagen Remodeling During In Vitro Dynamic Compression of Articular Cartilage: Experiments and Finite Element Modeling
Authors: Yamauchi Kevin A. , Raub Christopher B. , Chen Albert C. , Sah Robert L. , Hazelwood Scott J. , Klisch Stephen M.
Published: January 2014

The biomechanical properties of articular cartilage (AC) can be altered by chemical and mechanical stimuli. Dynamic unconfined compression (UCC) has been shown to increase biosynthesis at moderate strain amplitudes (1–4%) and frequencies from 0.01Hz. to 0.1Hz [1]. Furthermore, interstitial fluid velocity and maximum principle strain have been proposed as candidates for controlling glycosaminoglycan (GAG) and collagen (COL) remodeling, respectively [2,3]. The goal of this study was to integrate in vitro growth data, including biochemical and microstructural properties, into a computational continuum mixture model to elucidate potential mechanical triggers for AC tissue remodeling.
Development of a Traumatic Anterior Cruciate Ligament and Meniscal Rupture Model to Study Osteoarthritis
Authors: Button Keith D. , Leikert Kevin M. , Fajardo Ryan S. , Haut Donahue Tammy L. , Haut Roger C.
Published: January 2014

Participation in sports, recreation, and exercise is progressively gaining more popularity in American culture and, along with it, the risk of acute and chronic injuries. People who injure a knee before the age of 22 have a greater than 3-fold risk of developing osteoarthritis (OA) in the injured joint by their mid 50s 5. Specifically, anterior cruciate ligament (ACL) and meniscal injuries are strongly associated with the development of OA 4, a common and widespread musculoskeletal disease 1.
Complex Matrix Remodeling and Durotaxis Can Emerge From Simple Rules for Cell-Matrix Interaction in Agent-Based Models
Authors: Reinhardt James W. , Krakauer Daniel A. , Gooch Keith J.
Published: January 2014

Using a top-down approach, an agent-based model was developed within Netlogo where cells and extracellular matrix (ECM) fibers were composed of multiple agents to create deformable structures capable of exerting, reacting to and transmitting mechanical forces. Simulated cells remodeled the fibrous matrix to change both the density and alignment of the fibers and migrated within the matrix in ways that are consistent with previous experimental work. Cells compacted the matrix in their pericellular regions much more than the average compaction experienced for the entire matrix. Between pairs of cells, the anisotropy index increased, fibers became more aligned in the direction parallel to a line connecting the two cells and the matrix density increased. To explore the potential contribution of matrix stiffness gradients in the observed migration (i.e., durotaxis), a single-cell on a regular lattice of fibers possessing a stiffness gradient was simulated. Cells migrated preferentially in the direction of increasing stiffness at a rate of ∼2 cell diameter per 10,000 AU. This work demonstrates that matrix remodeling and durotaxis, both complex phenomena, might be emergent behaviors based on just a few rules that control how a cell can interact with a fibrous ECM.
Macro- and Microscale Analysis of Bearing Surface Damage on Total Shoulder Replacements
Authors: Ansari Farzana , Koller Jeff , Swan Amelia , Kung Sunny , Gunther Stephen B. , Norris Tom R. , Reis Michael , Pruitt Lisa
Published: January 2014

Damage to bearing surfaces of total joint replacements (TJR) can have clinical consequences: wear debris generated from ultra-high molecular weight polyethylene (UHMWPE) surfaces can cause osteolysis and subsequent implant loosening [1]. Counterbearing metallic damage may significantly increase UHMWPE wear [2]. Documenting the morphology, frequency and location of bearing surface damage may provide insight into wear initiation and prevention. While scoring methodologies have been available and validated for total hip replacements (THR) and total knee replacements (TKR) [3–4], there is a paucity of validated scoring protocols for total shoulder replacements (TSR) [5]. Our previous work presented a damage scoring methodology to evaluate the severity and coverage of six damage modes on retrieved cobalt chrome (CoCr) humeral heads [6]. In this study, we adapt that protocol to include bearing surface damage on the counter-bearings (UHMWPE glenoid components). Additionally, we incorporate the results of 3D profilometry analysis of scratches in the Co-Cr humeral heads [6]. Ultimately, this macroscale and microscale analysis, combined with clinical data, for coupled TSR retrievals will provide insight on the origin, evolution and consequences of bearing damage in vivo.
Simulation of the Whole Human Spine Using Finite Elements: P & H Version Convergence
Authors: Lipscomb Kristen E. , Sarigul-Klijn Nesrin
Published: January 2014

Most computational simulations of the human spine focus on one region of interest, often examining the lumbar or cervical spine alone. This allows for simplification the complex nature of the spine and reduction of computational costs. As computational power is increasing, we can begin to examine more of the spine simultaneously without overusing resources. In addition, while current spine simulations provide valuable information regarding local effects of spinal problems, such as scoliosis or intervertebral disc (IVD) degeneration [1], they do not evaluate how these injuries affect the spine as a whole. Understanding the motion implications of spine pathologies on the whole spine can influence medical treatment practices in the future.
Development of a Patient-Specific Computer Model of Glenohumeral Capsular Plication and Shoulder Instability
Authors: Yongpravat Charlie , Urruela Adriana M. , Levine William N. , Bigliani Louis U. , Gardner Thomas R. , Ahmad Christopher S.
Published: January 2014

Shoulder dislocations occur when the humeral head translates over the edge of the glenoid socket of the scapula, permanently stretching the capsular ligaments. This injury of the capsular tissue results in pathological joint laxity which is a major contributor to recurrent dislocations and is a key feature of shoulder instability. The ideal surgical parameters to correct this pathology have yet to be established due to a lack of understanding of how shoulder kinematics and capsular mechanics are affected by different surgical procedures. To address this knowledge gap, we developed patient-specific computer models of the shoulder which include anatomically accurate models of the capsule. The purpose of this study was to simulate capsular plication of the glenohumeral ligaments and to evaluate the effect different degrees of plication had on glenohumeral joint laxity and rotation.
Cerebrovascular Dysfunction Following Sub-Failure Axial Stretch
Authors: Bell E. David , Monson Kenneth L.
Published: January 2014

Cerebral blood vessels are critical in maintaining the health and function of the brain, but their function can be disrupted by traumatic brain injury (TBI), which commonly includes damage to these vessels [1]. However, even in cases where there is not apparent mechanical damage to the cerebral vasculature, TBI can induce physiological disruptions that can lead to breakdown of the blood brain barrier or loss of cerebral autoregulation.
CFD and VH-IVUS Biomechanical Analysis of Coronary Artery Disease With One Year Follow-Up
Authors: Molony David S. , Timmins Lucas H. , Eshtehardi Parham , Samady Habib , Giddens Don P.
Published: January 2014

Coronary atherosclerotic plaques are frequently focal lesions that have variable rates of progression. Wall shear stresses (WSS) create a number of responses in endothelial cells that can lead to the localization and progression of these lesions, and in vivo coronary segments with low WSS have been found to develop greater plaque progression than segments of higher WSS.
Development of a Traumatic Brain Injury Bioreactor
Authors: Heller Zachery E. , Wyatt Joseph , Wolchok Jeffery C.
Published: January 2014

An in-vitro system was developed to mimic the impact deceleration and strain associated with concussive injuries. Similar in concept to a full scale crash test, the bench top concussive bioreactor can deliver decelerations from 0–250 g and biaxial strains from 5–25% to cells in culture. We are not aware of another system like this. From cellular testing, an injury threshold of 100g combined with 10% strain was identified. These values appear consistent with human brain injury data.
Constitutive Modeling of Biaxial Mechanical Response of Arteries Subjected to Gradual Elastin Degradation
Authors: Zeinali-Davarani Shahrokh , Chow Ming-Jay , Turcotte Raphaël , Zhang Katherine Yanhang
Published: January 2014

The passive mechanical response of arteries is believed to be mainly dominated by elastin and collagen fibers. Many arterial diseases are accompanied by significant changes in quantity and as well as the microstructure of these constituents due to the mechanical and biological adaptive processes. In this study we focus on the biaxial tensile test data of elastase-treated porcine aortic tissues [1]. We study the mechanical behavior of aortic tissues under gradual elastin degradation through constitutive modeling and associate the mechanical response with the microstructure of collagen observed in the microscopic images of fresh and digested tissues.
Rheological Study of Collagen Gel With Different Surface Conditions
Authors: Li Haiyue , Zhang Katherine Yanhang
Published: January 2014

Most biological soft tissues are known to be viscoelastic. Storage and loss moduli measured by rheological tests are commonly used to characterize the mechanical properties of viscoelastic material [1]. During rheological measurements, samples are sandwiched between two parallel plates with an appropriate compression. The top plate is oscillated and the torque transmitted through the sample is measured. Due to compression, the fluid inside the biological samples is likely to be squeezed out and can be regarded as a lubricant between the sample and plates, which may lead to slippage between sample and plates. As a result, the measured mechanical properties can significantly misestimate the actual properties of the sample [2].
Biomechanical Effects of Lumbar Pedicle Screw Insertion Depth on Screw Loosening and Fulcrum Location
Authors: Buckenmeyer Laura E. , Karami Kristophe J. , Kiapour Ata M. , Goel Vijay K. , Demetropoulos Constantine K. , Soo Teck M.
Published: January 2014

Osteoporosis is a critical challenge in orthopedic surgery. Osteoporotic patients have an increased risk of loosening and failure of implant constructs due to a weaker bone-implant interface than with healthy bone. Pullout strength of pedicle screws is enhanced by increased screw insertion depth. However, more knowledge is needed to define optimal pedicle screw insertion depth in relation to screw-bone interface biomechanics and the resulting loosening risk. This study evaluates the effects of screw length on loosening risk in the osteoporotic lumbar spine.
Accounting for Aggregation in Heating and Imaging of Magnetic Nanoparticles for Application in Thermal Therapies
Authors: Etheridge Michael L. , Zhang Jinjin , Garwood Michael , Bischof John C.
Published: January 2014

Magnetic nanoparticles (mNPs) are known to heat and produce contrast for magnetic resonance imaging (MRI) in response to varying magnetic fields. These phenomena are being clinically applied in the detection and treatment of diseases such as cancer. However, one important factor that has been largely overlooked in the field is the effect of aggregation on the mNPs’ performance once they are delivered into target cells and tissues. Specifically, nanoparticle aggregation caused by protein interactions and cellular uptake can lead to shifts in their behavior due to increases in the interparticle magnetic interactions and changes to Brownian motion. This will affect both the mNPs’ ability to heat and to be imaged by MRI.
Experimental Study of a Hybrid Renal Replacement System
Authors: Huang Zhongping , Ren Jie , Attaluri Anilchandra
Published: January 2014

Kidney failure is a major issue in the United States. The numbers of kidney failure patients are rapidly increasing with the simultaneous rise in diabetes, obesity and hypertension1. Kidney transplantation has shown excellent results, but insufficiency of donors has been a limiting factor. Most end-stage renal disease (ESRD) patients depend on hemodialysis (HD) for survival which is highly expensive. On an average ESRD patients receive 3 dialysis treatment a week and 4 hours per treatment, i.e., approximately 12 hours a week. Technology has not yet reached to a state where all the kidney functions can be mimicked. The only major kidney function being performed in HD is toxin removal. Even the toxins are not being continuously removed from the patients. To compensate the toxin and fluid removal of a whole week within 12 hours, high volumes of fluid are removed in HD treatments. Patients suffer due to the high fluid removal in a short period of time. Also the patients are restricted from taking fluids between the HD treatments. More frequent HD can improve both survival rate and life quality of patients with chronic kidney disease since normal people has his kidneys functioning continuously. It is a well known fact that daily dialysis offers many benefits over regular intermittent HD1. But providing daily dialysis is not affordable currently. Therefore, new modes of delivering continuous renal support are required.
A Continuous-Discrete Finite Element Model of Angiogenesis That Couples Vessel Growth With Matrix Deformation
Authors: Edgar Lowell T. , Maas Steve A. , Guilkey James E. , Weiss Jeffrey A.
Published: January 2014

Recent developments in tissue engineering have created demand for the ability to create microvascular networks with specific topologies in vitro. During angiogenesis, sprouting endothelial cells apply traction forces and migrate along components of the extracellular matrix (ECM), resulting in neovessel elongation [1]. The fibrillar structure of the ECM serves as the major pathway for mechanotransduction between contact-dependent cells. Using a three-dimensional (3D) organ culture model of microvessel fragments within a type-I collagen gel, we have shown that subjecting the culture to different boundary conditions during angiogenesis can lead to drastically different vascular topologies [2]. Fragments cultured in a rectangular gel that were free to contract grew into a randomly oriented network [3, 4]. When the long-axis of the gel was constrained as to prevent contraction, microvessels and collagen fibers were found aligned along the constrained axis (Fig. 1) [4].
A Study on the Mechanical Properties of Acellular Dermal Matrices and Their Interface Properties After Implantation in an Acute Abdominal Wall Defect in a Primate
Authors: De Deyne P. G. , Diab T. , Sandor M.
Published: January 2014

Within Regenerative Medicine, non-cell-based approaches such as biologically-derived materials have been commercially successful and represent an important proportion of medically-used biomaterials1. Several acellular matrices are commercially available, to be used as a reinforcement of soft tissue where weakness exists. The goal of this study was to determine whether out-of-package mechanical properties of an acellular tissue matrix was predictive of its in vivo interface strength and whether the in vivo interface strength was associated with a particular histological response. We chose to test three porcine dermis-derived acellular matrices and one bovine pericardium derived matrix.
Modular Steering and Braking System for Assistive Bicycling
Authors: Klixbull Matthew R. , Durst Matthew R. , Pfeiffer Michael G. , Buckley Jenni M.
Published: January 2014

There are a variety of commercially available cycling systems for users with physical disabilities. These include arm-driven recumbent bicycle and tricycle frames for individuals with limited leg function and tandem system for visually or mobility-impaired individuals. More complex adaptive cycling systems, such as the BerkelBike, have also been developed, which have integrated arm and leg driving mechanisms as well as on-board motor assistance and, in some cases, Functional Electrical Stimulation (FES). These units cost upwards of US$8,000 and are beyond the price range of many individuals and community centers. All current assistive cycling systems also require some degree of fine motor control, either in the torso or the arms, to control steering and braking mechanisms. That would make these systems inaccessible for individuals with severe motor control disabilities, such as Parkinsons or advanced MS.
Neonatal Resuscitation: A Global Perspective
Authors: Gu Brian , Hemani Malvi , Kim Barbara , Herrera Angelica , Kim Eun Yong , Jang Hyun Soo , Lamberti Megan , Pigula Anne
Published: January 2014

Approximately 904,000 newborns die of breathing complications, or birth asphyxia, each year[1]. It is estimated that 30% of these deaths could be prevented[2]; however, healthcare workers in developing nations often lack the training, skills, or equipment necessary to properly resuscitate these infants. For this reason, child mortality is disproportionally clustered in low-resource locations in which the current standard of care is ineffective. The bag-valve mask resuscitator (or BVM) is the recommended treatment for a newborn who is not breathing properly.
Quantification of Shockwave Transmission Through the Cranium Using an Experimental Model
Authors: Shah Alok S. , Stemper Brian D. , Yoganandan Narayan , Shender Barry S.
Published: January 2014

Studies have hypothesized mechanisms for brain injury resulting from exposure to blast waves. Theories include shockwaves increasing fluid pressure within brain tissue by transmitting through bones and blood vessels 1, indirect brain tissue damage due to ischemia from pulmonary blast injury 2, and formation of mechanical stresses that can result in tissue distortion 3. Mechanical damage to brain tissue can occur due to skull flexure resulting in loads typically seen in impact-induced injury 4 or axonal shearing/stretching, due to linear or rotational accelerations resulting in Diffuse Axonal Injury (DAI) 5. Despite several investigations it remains unclear whether direct propagation of the shockwave through the cranium can deform brain tissue and result in mechanically-induced injury 6. Finite element 7, 8 and animal 9, 10 models provide information on mechanisms and outcomes of blast-induced mTBI (mild traumatic brain injury). However, validations of FEM studies were limited due to the paucity of high rate material properties. Animal tests were designed to understand mechanisms of shockwave transmission but most did not report intracranial pressures. Understanding blast injury mechanisms requires a better delineation of shockwave energy transfer through the head and the influence of factors including region-specific differences, and mechanical properties of brain simulant. A Post Mortem Human Subjects (PMHS) model was used in this study to examine these factors and provide an understanding of shockwave transmission through the tissues of the human head.
Electrochemical Compaction of the Collagen: Effects on Matrix Mechanics and MSC Response
Authors: Kishore Vipuil , Younesi Mousa , Panit Stefi , Akkus Ozan
Published: January 2014

The molecules of the extracellular matrix in connective tissues are densely packed. Biofabrication methods to attain such molecular packing density are limited and electrochemical processing (EP) of monomeric collagen solutions is one of few means to attain molecular packing. During EP, the pH gradient between electrodes drives the electrophoretic mobility of collagen molecules toward the isoelectric point where molecules are compacted. Our earlier work used linear electrodes to fabricate highly aligned crosslinked collagen fibers for tendon tissue engineering [1–4]. Prior work compared electrocompacted-aligned matrices with uncompacted randomly oriented ones. Therefore, the effects of alignment and compaction were compounded in terms of assessing cell response. So as to take the matrix alignment variable out of the picture to investigate matrix compaction effects only, we employed disc shaped electrodes to obtain electrocompacted sheets which lack matrix alignment. The current study investigated: a) the degree of compaction, b) effect of compaction on the mechanical properties of the sheets, and, c) mesenchymal stem cell (MSC) proliferation and morphology on compacted sheets relative to uncompacted collagen gels.
An Automated Simulation Protocol for Exercise Physiology in Fontan Patients Using a Closed-Loop Lumped-Parameter Model
Authors: Kung Ethan , Giardini Alessandro , Migliavacca Francesco , Pennati Giancarlo , Hsia Tain-Yen , Marsden Alison
Published: January 2014

Single ventricle physiology is one of the most severe forms of congenital heart disease in which an infant is born with only one functional pumping chamber. These patients must go through a series of surgical procedures concluding with the Fontan procedure, which connects the superior and inferior vena cavae to the pulmonary arteries, bypassing the right side of the heart entirely. Reduced exercise capacity is a common morbidity in Fontan patients1, leading to decreased quality of life, and the etiology of lowered exercise performance remains unclear. Exercise conditions place high demands on the cardiovascular system; any good surgical design must consider the behavior of the system at stress. Invasive clinical measurements during exercise pose many challenges and are typically not standard of care. There is a need to better understand Fontan exercise physiology and to predict clinical outcomes using computational tools.