bluuebunny/crossref_metadata_2025 huggingface dataset:
CFD Challenge: Solutions Using the Mesher, Harpoon, and the Finite Volume Solver, Fluent
Authors: Bressloff Neil W. , Hameed Ahsan T.
Published: July 2013

The Bressloff group has focused on cardiovascular disease and its treatment for the last ten years. Possessing close ties with Southampton General Hospital, much of the work has sought understanding and/or solutions to clinically relevant problems, including the design of vascular stents. For the CFD Challenge, preliminary verification studies were performed by Masters student Ahsan Hameed using a fast hex-dominant mesher, Harpoon (Sharc Ltd) and V12.1.4 of the ANSYS Fluent solver (ANSYS, Inc.).
Contribution of Mineral Crystals to the Bulk Behavior of Human Cortical Bone in Compression
Authors: Wang Xiaodu , Giri Bijay , Almer Jonathan
Published: July 2013

In this study, human cortical bone was tested in compression to determine the in situ behavior of mineral crystals using a synergistic approach combining a progressive loading scheme and synchrotron X-ray scattering techniques. By quantifying the orientation distribution of mineral crystals, the average strain tensor of each subset of mineral crystals in the same orientation was determined based on its lattice deformation in three distinct crystallographic directions. The stress tensor of the crystals was determined based on the Hooke’s law using the stiffness tensor well derived in the literature (1). By examining the concurrent changes in the in situ and bulk behaviors, the contribution of mineral crystals to the bulk behavior of bone was discussed.
Finite Element Simulation of Pelvic Fractures in Side Impact
Authors: Kim Young-Ho , Kim Jong-Eun , Eberhardt Alan W.
Published: July 2013

Motor vehicle crashes (MVCs) are the most common cause of serious injury (Healthy People, 2010). Moffat et al. (1990) estimated that, in 1985 alone, 15,300 pelvic fractures occurred during MVCs in the United States. Since the early 1990’s, the incidence of pelvic fractures has significantly increased (Inaba et al., 2004), which is alarming since more patients die from pelvic fracture than from any other skeletal injury (Cryer, 1996).
Gurney Mattress Redesign
Authors: Brakefield Timothy , Burkhardt Thomas , Meehan Andrew , Nemunaitis Gregory , Hefzy Mohamed Samir , Pourazady Mehdi
Published: July 2013

One of the most devastating yet survivable injuries today is trauma to the spinal cord. Often times this injury results in the inability of the patient to move and feel below the neck. When transporting these individuals on a gurney to perform routine tests, they are prone to excessive pressures over long periods of time that may result in the breakdown of skin, muscle and other tissues over pressure sensitive areas resulting in the formation of pressure ulcers [1]. The financial burden to treat pressure ulcers is high. The cost to heal a single complex full-thickness pressure ulcer has been estimated to be $70,000 [2] and the total economic burden of treating all pressure ulcers was estimated to be as high as $1.335 billion per year [3]. These costs not only load society with an enormous financial burden, but the patient must undergo a series of treatments that may last for months which will remove them from productive activities.
Cumulative Effect of Repeated Impacts on Lumbar Intervertebral Disc Mechanics: A Diurnal Cycle Study
Authors: Jamison David , Massey Chris J. , Pierce Eric C. , Martin Shawn K. , Marcolongo Michele A.
Published: July 2013

In the U.S. Navy, high speed boat (HSB) crewman frequently suffer from lower back pain and accelerated intervertebral disc (IVD) degeneration. It is believed that this stems primarily from the large vertical accelerations and forces experienced while navigating on the open seas as the boats pitch and crash into the water. In a study of self-reported injuries for HSB operators, 33.6% of these subjects had suffered a lower back injury while on duty3. This is high when compared with the 15 to 20% of adults in the general population who experience low back pain.
Adhesive Signature-Based, Label-Free Isolation of Human Pluripotent Stem Cells
Authors: Singh Ankur , Suri Shalu , Lee Ted T. , Chilton Jamie M. , Stice Steve L. , Lu Hang , McDevitt Todd C. , Garcia Andrés J.
Published: July 2013

Generation of human induced pluripotent stem cells (hiPSCs) from fibroblasts and other somatic cells represents a highly promising strategy to produce auto- and allo-genic cell sources for therapeutic approaches as well as novel models of human development and disease1. Reprogramming protocols involve transduction of the Yamanaka factors Oct3/4, Sox2, Klf4, and c-Myc into the parental somatic cells, followed by culturing the transduced cells on mouse embryonic fibroblast (MEF) or human fibroblast feeder layers, and subsequent mechanical dissociation of pluripotent cell-like colonies for propagation on feeder layers1, 2. The presence of residual parental and feeder-layer cells introduces experimental variability, pathogenic contamination, and promotes immunogenicity3. Similar to human embryonic stem cells (hESCs), reprogrammed hiPSCs suffer from the unavoidable problem of spontaneous differentiation due to sub-optimal feeder cultures4, growth factors5, and the feeder-free substrate6. Spontaneously differentiated (SD)-hiPSCs display reduced pluripotency and often contaminate hiPSC cultures, resulting in overgrowth of cultures and compromising the quality of residual pluripotent stem cells5. Therefore, the ability to rapidly and efficiently isolate undifferentiated hiPSCs from the parental somatic cells, feeder-layer cells, and spontaneously differentiated cells is a crucial step that remains a bottleneck in all human pluripotent stem cell research.
Flow in the Vascular System Post Stent Implantation: Examining the Near-Stent Flow Physics
Authors: Prince Chekema , Gu Mingyao , Peterson Sean D.
Published: July 2013

As a simplified stent model, fully-developed flow of an incompressible, Newtonian fluid through a curved tube with axially aligned wall protuberances is investigated to define the impact of stent implantation on hemodynamic behavior in curved vessels. According to previous research local hemodynamics tends to trigger biochemical pathways that result in the inception and progression of in-stent restenosis (ISR) and ultimately lead to stent failure. In this manuscript, we focus on hemodynamic changes due to stent strut protrusion into the vessel lumen as a facilitator of ISR. We investigate a range of physiologically relevant stent strut heights and flow parameters using computational fluid dynamics (CFD).
Dynamic Compressive Loading and Crosslinking Density Influence the Chondrogenic and Hypertrophic Differentiation of Human Mesenchymal Stem Cells Seeded in Hyaluronic Acid Hydrogels
Authors: Bian Liming , Mauck Robert L. , Burdick Jason A.
Published: July 2013

While hyaluronic acid (HA) hydrogels provide a stable 3D environment that is conducive to the chondrogenesis of mesenchymal stem cells (MSCs) in the presence of growth factors [1], the neocartilage that is formed remains inferior to native tissue, even after long culture durations. Additionally, MSCs eventually transit into a hypertrophic phenotype after chondrogenic induction, resulting in the calcification of the ECM after ectopic transplantation [2]. From a material design perspective, variation in the HA hydrogel scaffold crosslinking density via changes in the HA macromer concentration can influence chondrogenesis of MSCs and neocartilage formation [3]. Recent studies have also demonstrated that dynamic compression enhances the expression of chondrogenic markers and cartilage matrix synthesis by MSCs encapsulated in various hydrogels, including agarose [4], alginate [5] and fibrin [6]. Furthermore, mechanical signals also regulate growth plate and articular cartilage chondrocyte hypertrophy via the IHH-PTHrP (India hedgehog, Parathyroid hormone-related protein) pathway [7]. In contrast to biologically inert scaffold materials, HA is capable of interacting with cells (including MSCs) via cell surface receptors (CD44, CD54, and CD168) [8; 9]. Therefore the objectives of this study were to (i) evaluate the effects of both hydrogel crosslinking and dynamic compressive loading on (i) chondrogenesis and cartilage matrix production/distribution of human MSCs encapsulated in HA gels and (ii) hypertrophic differentiation of human MSCs using an in vitro MSC hypertrophy model [10].
A Nonlinear Viscoelastic Model for the Relaxation Behavior of Tendon
Authors: Davis Frances M. , De Vita Raffaella
Published: July 2013

Tendons are viscoelastic materials which undergo stress relaxation when held at a constant strain. The most successful model used to describe the viscoelastic behavior of tendons is the quasi-linear viscoelastic (QLV) model [1]. In the QLV model, the relaxation function is assumed to be a separable function of time and strain. Recently, this assumption has been shown to be invalid for tendons [2] thus suggesting the need for new nonlinear viscoelastic models.
Migration of Human Mesenchymal Stem Cells is Stimulated by Low Shear Stress via MAPK Signaling
Authors: Yuan Lin , Sakamoto Naoya , Song Guanbin , Sato Masaaki
Published: July 2013

Mesenchymal stem cells (MSCs) represent as multipotent stem cells which hold the abilities of self-renewal and give rise to cells of diverse lineages [1]. With their remarkable combination of multipotent differentiation potential and low immunogenicity, MSCs are considered to be an attractive candidate for cell-based tissue repair and regenerative tissue engineering [2, 3]. Increasing number of studies has demonstrated that mobilization and migration of injected MSCs to the damaged tissues is a key step for these cells to participate in disease treatment and tissue regeneration [4, 5].
Effect of Arterial Distensibility and Stenoses on Pressure Drop in Pulsatile Flow
Authors: Rotman Oren , Zaretsky Uri , Shitzer Avraham , Einav Shmuel
Published: July 2013

The most accepted standard tool of cardiologists for assessing stenoses severity in the coronary tree is coronary angiography. Information from coronary angiography is limited to geometrical data on the coronary lumen, and provides limited functional data on the severity of stenoses. In addition, histopathological studies have demonstrated that angiographic evidence of stenosis is usually detected when the cross-sectional area of a plaque approaches 40% to 50% of the total cross-sectional area of the vessel [1]. Hence, managing the intermediate coronary lesions (40% to 70% diameter stenosis) are a true challenge for cardiologists. These geometrical limitations have led to the development of several hemodynamic parameters, which functionally assess stenoses severity and the cardiovascular tree, among which the most pronounced is Fractional Flow Reserve (FFR), which is defined as the ratio of hyperemic flow in the stenosis artery to the flow in the same artery in the theoretic absence of the stenosis [2]. FFR is lesion specific and provides functional assessment of the stenosis severity by means of pressure measurement as a surrogate for flow. Under hyperemic flow conditions, FFR can be calculated as the ratio of pressures distal and proximal to a lesion. FFR values of 0.75–0.80 have been established as threshold values that distinguish normal from abnormal levels for a given measurement. Stenoses with an FFR < 0.75 are considered as a cause of myocardial ischemia, whereas stenoses with an FFR > 0.80 are considered to be ischemic ‘safe’ [2]. One of the limitations of FFR is its absolute dependency in pharmacologically-induced maximal hyperemia. The current clinical standard for coronary hyperemia is the intracoronary administration of ademosine, however in 10% to 15% of patients, intracoronary adenosine induces submaximal hyperemia only, and therefore FFR may be overestimated by up to 0.10 [3, 4].
A Finite Element Model of the Occupant Lower Extremity for Automotive Impact Applications
Authors: Untaroiu Costin D. , Yue Neng , Shin Jaeho
Published: July 2013

Although not life-threatening, lower limb injuries are the most frequent injury of moderate severity (AIS 2), sustained in a vehicle crash (Pattimore et al., 1991). To better understand the injury mechanisms, several lower extremity (LEX) finite element (FE) models were developed to investigate traffic accidents involving occupants in vehicles (Yang et al., 2006). The main limitations of existing lower limb FE models are due to their geometries, the modeling approaches used to represent their components, and limited test data used for the model validation.
Combinations of Biomechanical Metrics Involving Single and Multi Level Lumbar Posterior Dynamic Spinal Treatments
Authors: Cheng Boyle C. , Cook Daniel J. , Yeager Matt , Lu Bin , Whiting Donald M.
Published: July 2013

The subtle effects of motion preservation devices are comparatively more difficult to detect based wholly on the range of motion (RoM) parameter, despite the historical success in characterizing fixation devices. Additional approaches such as descriptive facet techniques, i.e., facet translations analysis, and newly defined metrics, i.e., interpedicular displacement (ID) must first be established, verified and standardized. Ideally, more complete biomechanical parameters would facilitate clinical understanding of specific new devices. The recent focus in our lab has been to measure the RoM in conjunction with other parameters, including ID, to more completely characterize a lumbar spine treated with a posterior dynamic systems (PDS). Furthermore, understanding the construct and which components dominate overall tissue response is important for PDS systems.
Dynamic Mechanical Properties Control Adult Stem Cell Fate
Authors: Guvendiren Murat , Burdick Jason A.
Published: July 2013

Stem cells respond to many microenvironmental cues towards their decisions to spread, migrate, and differentiate and these cues can be incorporated into materials for regenerative medicine.1 In the last decade, matrix stiffness alone has been implicated in regulating cellular functions such as migration, proliferation and differentiation. With this in mind, a variety of natural and synthetic polymer systems were used in vitro to mimic the elasticity of native tissues. Despite helping to develop this important field and gather valuable information, these substrates are primarily static and lack the dynamic nature that is observed during many cellular processes such as development, fibrosis and cancer. Thus, it is of great interest to temporally manipulate matrix elasticity in vitro to better understand and develop strategies to control these biological processes. In this work, we utilize a sequential crosslinking approach (initial gelation via addition reaction, secondary crosslinking through light-mediated radical polymerization) to fabricate hydrogel substrates that stiffen (e.g., ∼3 to 30 kPa) either immediately or at later times and in the presence of cells. We demonstrate the utility of this technique by investigating the short-term (several minutes to hours) and long-term (several days to weeks) stem cell response to dynamic stiffening
A Rheological Technique for Extracting Dynamic Moduli From Creep Testing of Pediatric Porcine Vitreous
Authors: Moran Patrick , Coats Brittany
Published: July 2013

An advanced rheological technique was used to estimate the dynamic material properties of pediatric porcine vitreous. Validation of the technique was performed with two simulant materials. Interconversion of time-dependent data to frequency-dependent data resulted in good approximation of storage and loss modulus for a primarily viscous material, but resulted in an erroneous loss modulus for a primarily elastic material. This can likely be overcome by utilizing free oscillations resulting from creep testing. Porcine storage modulus was significantly lower in older animals, but additional testing is necessary to completely characterize the material properties of pediatric vitreous over a wide range of frequencies.
In-Vivo Loads on the Lumbar Intervertebral Discs During Weight Lifting
Authors: Wang S. , Park W. M. , Miao J. , Wood K. , Kim Y. H. , Li G.
Published: July 2013

The most common reason for occupational low back pain is the overload on the spine [1]. Determination of the load on the spine is critical for preventing low back pain, understanding injury mechanism and developing treatment techniques and surgical implants. However, due to the limitations in technology, only few in-vivo measurements were performed using pressure transducer [1] and telemeterized implants [2]. Because of the risks involved, neither of these techniques was suitable for a large healthy population. In this study, we proposed a new non-invasive technique and estimated the forces and moments on the lumbar intervertebral discs (IVDs) of three healthy subjects during a dynamic weight lifting activity.
Rheological Properties of Anisotropic Tissues at Large Amplitude Oscillatory Shear
Authors: Tan Kristy , Cheng Shaokoon , Bilston Lynne E.
Published: July 2013

The mechanical properties of soft biological tissues have been widely investigated over the past five decades [1–5]. Reported measurements of soft biological tissues such as the brain, spinal cord, liver and muscle vary by orders of magnitude, depending on the sample preparation, anisotropy and loading regime. Knowing the accurate mechanical properties of biological tissues is important for many applications, for example car crash testing and simulations require accurate information on how different parts of the body deform due to a combination of loads. Deformation of tissues around prosthetics and artificial limbs are critical in understanding load transfer at interfaces with the body. The recent use of Magnetic Resonance Elastography (MRE) in diagnostic imaging has resulted in a surge of interest in accurate measurements of mechanical properties of tissues [6].
A Predictable and Repeatable Method to Rapidly Manufacture Function-Customized Passive-Dynamic Ankle Foot Orthoses
Authors: Schrank Elisa S. , Razzook Alexander , Takahashi Kota , Tierney John , Gillespie John W. , Hitch Lester , Wallace Kevin , Moore Rick , Higginson Jill S. , Stanhope Steven J.
Published: July 2013

Passive-dynamic ankle-foot orthoses (PD-AFOs) are a type of ankle brace that rely on design and material properties to establish functional characteristics. Stiffness (resistance to bending) is an important functional characteristic that influences a brace’s level of assistance. While many agree that customizing a PD-AFO’s stiffness to meet an individual’s needs is essential to achieving enhanced function1, currently prescribed PD-AFOs are manually crafted, making it difficult to predictably or repeatedly customize orthoses. We have introduced a novel PD-AFO customization and manufacturing framework that uses freeform fabrication to rapidly fabricate PD-AFOs with objectively-customized characteristics including stiffness. Thus, the purpose of this study was to assess the predictability and repeatability of the stiffness values of PD-AFOs fabricated with our novel framework.
Enhancement of Bronchodilation Using Length Oscillations
Authors: Al-Jumaily A. M. , Mathur M. , Jo-Avila M. J.
Published: July 2013

In asthma treatment β-agonists such as isoproterenol are used for their ability to relax airway smooth muscle (ASM) through stimulation of cAMP production. In vitro experiments conducted on ASM tissues suggest that length oscillations applied to contracted muscle result in a reduction in the contractile ability of the tissue. Conducting experiments on tissues from two different species leads to a fact that length oscillation enhances ASM relaxation induced by β-agonists agent independent of the species.
Reduction of Alveoli Surface Tension Using Pressure Oscillation
Authors: Al-Jumaily A. M. , Reddy P. I.
Published: July 2013

This research investigates the effect of pressure oscillation (PO) on the alveoli surface tension. Experimental and modeling simulations are used to show that introducing superimposed oscillations on the tidal volume excursion between 0–70Hz in a surfactant bubble lowers interfacial surface tension below values observed using tidal volume excursion alone. Evidently this makes it easier for an infant with RDS to maintain the required level of functional residual capacity without collapse.
Regional Biomechanical and Microstructural Alterations of the Ovine Main Pulmonary Artery During Postnatal Growth
Authors: Fata Bahar , Carruthers Christopher A. , Gibson Gregory A. , Watkins Simon C. , Gottlieb Danielle , Mayer John E. , Sacks Michael S.
Published: July 2013

It has been estimated that worldwide 600,000 babies are born annually with significant congenital heart disease (1). Congenital heart and related vascular defects cause increased flow and pulmonary pressure leading to unfavorable vascular remodeling that results in pulmonary arterial hypertension (1). Developing tissue engineered replacements that mimic the growth and remodeling behavior of native tissue is the optimal approach in treatment of congenital arterial anomalies. The understanding of the underlying mechanisms leading to pulmonary arterial hypertension as well as replicating native pulmonary artery functionality in engineered replacements requires knowledge of native tissue mechanics and growth behavior. In the present study, we report novel information on the changes in the structure-mechanics behavior of the growing pulmonary artery.
The Effects of Arterial Tissue Reorganization on the Geometrical Outputs of Pressure- and Flow-Induced Remodeling: A Theoretical Study
Authors: Shazly Tarek , Rachev Alexander
Published: July 2013

Arterial remodeling in response to sustained alterations in blood pressure and/or flow induces changes in vessel geometry, structure, and composition. In conditions of hypertension and elevated blood flow, remodeling results in increased vessel mass that is distributed in a manner to maintain the local mechanical environment of the vascular cells at a baseline state. A majority of theoretical studies on remodeling have assumed that new mass is formed via a proportional production of load-bearing constituents, namely elastin, collagen, and smooth muscle. Therefore, when the vascular tissue is considered as a constrained mixture of these structural components, their mass fractions do not change as a result of remodeling. However, increased arterial mass is primarily attributed to smooth muscle cell hypertrophy and upregulated collagen production, implying a change in the mass fractions of all constituents and therefore the tissue mechanical properties [1]. Moreover, few papers account for remodeling-induced changes in the configuration and/or orientation of collagen fibers, both of which may also alter tissue mechanical properties. The objective of this study is to build a mathematical model that enables evaluation of the effects of mass redistribution among structural components and changes in collagen fiber configuration on the geometrical outputs of arterial remodeling.
Calculated Axial Forces at the Knee in Total Knee Replacement Patients During Chair and Stair Activities
Authors: Lundberg Hannah J. , Knowlton Christopher B. , Orozco Diego , Wimmer Markus A.
Published: July 2013

Knowledge of in vivo knee contact forces is essential for evaluating total knee replacement (TKR) designs. This is particularly true for activities other than walking, because there is still a limited understanding of its impact on wear. It has been shown that wear scars from retrieved implants have obvious differences compared with simulator tested components in both size of worn area and in damage mode. The divergence could be related to the omission of other activities than walking when testing components in the simulator. The purpose of this study was to use a parametric numerical model for predicting joint contact forces during stair ascent/descent and chair sitting/rising and compare those to measured forces from a database. We hypothesized that the contact force output of the numeric model would be similar to the measured forces.
Application of Manual Traction Forces on the Cervical Discs With Degenerative Annular Fibers: A Finite Element Model Analysis
Authors: Hussain Mozammil
Published: July 2013

Degeneration in intervertebral discs is a complex multifactorial process. Studies have speculated the biomechanical and biochemical reasons factoring the degenerative disc pathology. Disc degeneration begins in inner nucleus pulposus (NP) that has high fluid content. As degeneration advances over time, the load is shifted from inner NP to outer annulus fibrosus (AF) that is more fibrous in nature. In addition to morphological changes in the discs that occur with degeneration in the form of tears and delamination, tissue compositional variations are also noted. These degenerative changes have not only been seen in the disc tissue matrix, but they are also quite apparent in the fibers of AF in the form of incompleteness and laxity [1]. These tensile fibers in AF have a critical functionality in maintaining the mechanical strength of the disc segments, and any form of degenerative impairment in these fibers may lead to abnormal physiology, both in the AF and NP. Despite past research have reported the annular and nucleus stresses in degenerative discs, area that still unclear is the relative contributions of degenerative properties in annular fibers — incompleteness and slackness — to the overall degenerative disc response. Typically, degeneration related neck pain that involve abnormal disc pressures has been shown to be temporarily relieved by the therapeutical application of manual traction forces. The objective of the present study is to understand the pattern of stresses in the AF and NP due to degenerative AF fibers when the manual traction forces are applied on the degenerated discs.
Calculation of the Outcomes of Adaptive and Maladaptive Remodeling of Arteries Subjected to Sustained Hypertension Using a 3D Two-Layered Model
Authors: Rachev Alexander , Taylor W. Robert , Vito Raymond P.
Published: July 2013

Arteries respond to long-term alterations in arterial pressure and blood flow by changing geometry, structure, and composition. This response is termed as remodeling and plays an important role in normal arterial physiology and in the genesis and progression of certain vascular disorders. In healthy mature arteries, remodeling represents an adaptive process that tends to restore the local mechanical environment of vascular cells to baseline levels and thereby to preserve the optimal performance of the arterial function. The objective of this study is twofold — to develop a general method for calculation the remodeling outputs of an artery considered as a two-layered tube; and to provide results for adaptive and maladaptive remodeling of a coronary artery.
Engaging Students in Bioengineering: A Basic Structure for Collaborative Learning Journal Clubs
Authors: Kuxhaus Laurel , Corbiere Nicole C.
Published: July 2013

Biomechanics courses often attract students from diverse academic backgrounds including a mix of engineers and scientists. A Journal Club, in which students read and discuss articles from scientific literature, is a collaborative learning activity that is accessible to students from these diverse scientific backgrounds. Journal Clubs originated as way to cost-share periodicals [1] and have evolved as educational tools. Journal Clubs in medical education [2–4] are cited for both increasing medical knowledge in 88% of medical residents [2] and bridging the gap between research and clinical practice. [1] In an extensive literature review, 80% of 101 studies reported that Journal Club discussions improved knowledge and critical appraisal skills. [5] Journal Club format is flexible and no strong preference in method has emerged in the literature. [2] The present work describes a structured Journal Club that has been implemented in a biomechanics course for three years and presents results from student surveys.
Evaluating Pelvis Dynamics in Patients With Acetabular Labral Tears
Authors: Tanaka Martin L. , Long Benjamin L. , Stubbs Allston J. , Holst David C.
Published: July 2013

Common forms of hip disease include labral tears, synovitis, chondromalacia, or femoroacetabular impingement [1, 2]. Most patients with one of these medical conditions seek treatment to alleviate the pain. However, in addition to the pain, dynamic control of hip joint movement may also be impaired. This impairment may result from damage to proprioceptive organs or alterations in sensory capability caused by inflammation. Reduced biofeedback can lead to a loss of joint control that may result in additional injuries due to excessive tissue strain or falling due to a loss of balance. Our hypothesis is that acetabular labral tears alter normal pelvic movement and reduce subject balance control placing the patient at increased risk for additional injuries.
Electrospinning of Chitin Whisker-Reinforced Nanocomposite Fibrous Scaffolds
Authors: Ji Yali , Rodriguez Isaac , Bowlin Gary L.
Published: July 2013

Chitin is the second most abundant biopolymer next to cellulose and possesses many favorable properties such as non-toxicity, high crystallinity, biocompatibility and biodegradability. Acid-treatment of chitin can dissolve regions of low lateral order, resulting in elongated rod-like nanocrystals, termed “whiskers”. Chitin whiskers (CWs) are an emerging and novel nanofiller that have been shown to bring about reinforcing effects on both synthetic and natural polymeric structures. The biocompatibility and biodegradability also make it one of the most promising fillers.1 However; it was thought that CWs can only well disperse in aqueous solution, and poorly disperse in organic solvents, which to some extent restricts the development of CW-based nanocomposites. In a previous study, we found that the CW can be well dispersed in 1,1,1-trifluoroethanol (TFE) solvent which is a good solvent for commonly used biodegradable polymers such as polycaprolactone (PCL), polylactide (PLA) and polydioxanone (PDO). Thus, it is possible to blend CWs with these biopolymers to prepare nanocomposite scaffolds. Electrospinning is a rather simple and promising technique to fabricate scaffolds, since the resulting microstructures are similar to the extracellular matrix (ECM) with potential facilitate the design of surgical implants and promote tissue regeneration. Thus, the focus of this work was to develop CW-reinforced nanocomposite fiber scaffolds via electrospinning and investigate their mechanical and biological properties, expecting them to be potential candidates for bone tissue engineering applications.
Tibiofemoral Joint Contact During the Loading Response Phase of Gait in Individuals With Concurrent Knee Osteoarthritis and Complaints of Joint Instability
Authors: Rainis Carrie A. , Farrokhi Shawn , Tashman Scott , Fitzgerald G. Kelley
Published: July 2013

Knee osteoarthritis (OA) is one of the most prevalent chronic conditions affecting older adults and commonly leads to pain and functional limitations. Many individuals with knee OA also report episodes of knee instability, which has been shown to adversely affect their ability to perform weight-bearing functional tasks. [1] Recently it was reported that individuals with knee OA and reports of joint instability demonstrate significant reductions in their sagittal and transverse plane rotational knee joint motion. [2] It is conceivable that the decreased rotational joint motion may represent a compensatory attempt to avoid pain and/or to stabilize an unstable knee joint. However, this movement strategy may be problematic in the long term as it could lead to increased compressive loading and a reduction of shock absorption capabilities. Since abnormal rotation is associated with altered joint contact position [3], and the internal/external rotation axis in the normal knee is located on the medial side [4,5], this patient population may exhibit a decreased contact path length in the lateral compartment during the loading response phase of gait. The combination of a reduced contact path length and cartilage loss could in turn lead to a decreased dynamic joint space [6] and concentration of joint stresses responsible for disease progression. Therefore, the objectives of this work were to 1) compare the tibiofemoral joint contact path length and dynamic joint space in the medial and lateral compartments during the loading response phase of gait in individuals with knee OA and complaints of joint instability to a healthy control group and 2) investigate the relationship between these parameters.
Mechanical Consequences of Needle Puncture Injury in the Mouse Caudal Spine
Authors: Martin John T. , Beattie Elizabeth E. , Gorth Deborah J. , Smith Lachlan J. , Elliott Dawn M.
Published: July 2013

Models of acute annulus fibrosus (AF) injury consistently produce a mechanical or biological response similar to that of human disc degeneration1–5. These methods are easily implemented, provide repeatable results and have controlled specificity in comparison to global knockout and spontaneous development models. AF injury studies have been conducted in many species including the sheep, rabbit, and rat1–4. The mouse caudal disc is a proposed model, as it degenerates as a result of needle puncture injury, displaying changes consistent with those in humans5. Limited mechanical data for puncture-initiated degeneration is available, however. The primary function of the disc is mechanical — transferring loads, dissipating energy and facilitating joint mobility. Evaluating disc mechanical properties is therefore important for understanding how functional changes can be targeted by potential therapeutics. The objective of this study was to quantify the acute and long term effects of needle puncture injury on mouse caudal disc mechanical function, disc height and nucleus pulposus (NP) glycosaminoglycan (GAG) content.
Modeling Cell-Cell Adhesion With a Cadherin Based Model
Authors: Dallon John
Published: July 2013

Cell-cell adhesion is critical in morphogenesis, tissue formation, cancer, and wound healing. A better understanding of cell-cell adhesion mediated by cadherins will allow all these processes to be mimicked and manipulated to achieve desired objectives. This paper investigates the role of the actin structure associated with cadherin adhesion sites.
Influence of Specimen-Specific Trabecular Anisotropy on QCT-Based Finite Element Analyses of Lumbar Vertebra
Authors: Unnikrishnan Ginu U. , Barest Glenn D. , Berry David B. , Hussein Amira I. , Morgan Elise F.
Published: July 2013

Quantitative computed tomography (QCT)-based finite element (FE) models provide better predictions of vertebral strength compared to traditional methods currently used in clinical diagnosis [1]. In QCT-based FE models, the intra- and inter-specimen variations in trabecular anisotropy are often ignored, despite evidence that the biomechanical behavior of the vertebra depends on the architecture of the vertebral trabecular bone [2]. A realistic representation of the specimen-specific, trabecular anisotropy in the FE models of vertebrae would potentially improve predictions of vertebral failure. The overall goal of this study was to evaluate the importance of incorporating specimen-specific, trabecular anisotropy for QCT-based FE predictions of vertebral stiffness and deformation patterns. The major aims of this study were (a) to compare the QCT-based FE results obtained with a constant, anisotropic, material model (the “generic-anisotropic” model) for trabecular bone to those obtained with a specimen-specific, anisotropic, material model and (b) to study the influence of degree of anisotropy (DA) on the FE predictions of vertebral stiffness.
Influence of Freezing (Thermal) Profiles on the Morphology and Mechanical Properties of Poly (L-Lactic Acid) Scaffolds
Authors: Chinnasami Harish , Breeden Frank , Hayes Daniel , Devireddy Ram
Published: July 2013

Bio-degradable Poly (l-lactic acid) (PLLA) scaffolds were prepared by using thermal liquid-liquid phase separation method. A solution of PLLA-Dioxane was prepared by dissolving PLLA in dehydrated 1,4-Dioxane. This PLLA-Dioxane solution was then directionally frozen in vials of similar dimensions but made of different materials (borosilicate glass, aluminum and copper). The frozen solution was then placed in a freeze-dryer to allow for the frozen dioxane to sublimate or lyophilized. The porosities of the resulting PLLA scaffolds were calculated and their porous structures were studied and compared between the three different vials (and the corresponding cooling rates).
Kinematic Implications of Altering the Design of the Wrist: A Cadaveric Study Examining Midcarpal Fusion and Scaphoid Excision
Authors: Nichols Jennifer A. , Bednar Michael S. , Havey Robert M. , Murray Wendy M.
Published: July 2013

During surgical salvage procedures, surgeons permanently alter the kinematic design of the wrist by removing and fusing carpal bones. Although salvage procedures successfully relieve arthritic pain, they have the unintended consequence of long-term functional impairments [1]. One common surgical salvage procedure is scaphoid-excision, four-corner fusion (SE4CF). During SE4CF, the scaphoid is removed, and the lunate, triquetrum, capitate, and hamate are fused together. Surgical preference dictates the amount of scaphoid removed and the position in which the bones are fused. Importantly, fusion eliminates motion between the carpal rows, creating a wrist joint in which motion occurs between the radius and a single, rigid block of carpal bones.
Bicuspid Aortic Valves Are Associated With Increased Turbulence Compared to Pure Aortic Stenosis: An In Vitro Study
Authors: Saikrishnan Neelakantan , Milligan Nicole C. , Yoganathan Ajit P.
Published: July 2013

In about 1–2% of all live births, the human aortic valve only consists of two anomalous leaflets and is known as the bicuspid aortic valve (BAV). BAVs are the most common congenital cardiac anomaly, and are associated with significant valvular dysfunction, including calcific aortic stenosis (AS) and aortic regurgitation (AR), as well as aortic wall abnormalities including coarctation of the aorta, ascending aortic dilatation and aneurysms [1]. Many studies have proposed a common underlying genetic defect in progression of complications with BAVs [2]. However, other recent studies have also suggested that the altered hemodynamic environment associated with BAVs could also be responsible for accelerated disease progression in these patients [3, 4]. A recent in vitro study showed elevated levels of turbulence associated with BAVs, and indicated that fluid flow patterns in the aortic sinuses are also affected due to the altered valve morphology [5]. The present work seeks to compare the levels of turbulence in BAVs to pure trileaflet aortic stenosis models.
Altered Mechanical Properties and Fiber Re-Alignment in Diabetic Mouse Supraspinatus and Achilles Tendons
Authors: Connizzo Brianne K. , Liechty Kenneth W. , Soslowsky Louis J.
Published: July 2013

Tendons function to transfer load, maintain alignment and permit motion in joints. To perform these functions, tendons have complex mechanical behavior which is modulated by the tissue’s structure and composition, such as the collagen fibers and surrounding extracellular matrix. When these matrix proteins are altered, the mechanical properties are also altered, which could potentially lead to reduced loading and healing capacity. Diabetes is a metabolic disease which, among other co-morbidities, has been associated with Achilles tendon disorganization and tendinopathy, as well as increased overall joint stiffness in humans [1]. We have recently reported that the skin from the Db/Db diabetic mouse, a model of Type II Diabetes, as well as the skin from human diabetics, have impaired biomechanical properties compared to non-diabetic skin as the result of altered extracellular matrix composition. [2]. However, the mechanical properties of tendons from these animals have never been studied and could serve as a unique model of altered collagen structure as well as provide further understanding to the cause of tendinous injuries in the diabetic population. Therefore, the objective of this study is to measure the tensile mechanical properties and collagen fiber re-alignment in the db/db mouse model compared to non-diabetic controls. We hypothesize that tendon stiffness and modulus will be increased in the db/db group in the insertion site and midsubstance, and that db/db tendons will re-align earlier and faster during the testing protocol.
A Study on the Impact of Helmet Padding Materials on the Brain Pressure Under Shock Loads
Authors: Salimi Jazi Mehdi , Rezaei Asghar , Karami Ghodrat , Azarmi Fardad , Ziejewski Mariusz
Published: July 2013

A traumatic brain injury (TBI) can occur from a sharp strain, or acceleration, to the human head. Based on the level of injury, TBIs are classified as mild, moderate, or severe, with the most common causes being motor vehicle crashes; violence related injuries; collisions in sports; and falls are the most common causes of TBIs for the general public. Many soldiers experience a TBI in combat zones when they are exposed to the shock waves from blasts, or to ballistic impacts.
Rate-Dependent Failure Characteristics of Thoraco-Lumbar Vertebrae: Application to the Military Environment
Authors: Stemper Brian D. , Yoganandan Narayan , Baisden Jamie L. , Pintar Frank A. , Shender Barry S.
Published: July 2013

Quantification of lumbar spine vertebral body tolerance to axial compressive loads is important to understand the biomechanics of injury and for the development of safety enhancements. While fracture tolerance for isolated lumbar vertebral bodies has been outlined in multiple experimental studies, compressive rates were generally in the quasi-static range (e.g., 5 mm/min) [1–4]. However, vertebral body fractures most commonly occur under dynamic mechanisms such as falls from height. In the military environment, lumbar fractures were demonstrated following aviator ejection, helicopter crashes, and underbody blast events involving improvised explosive devices. Vertebral body compression during those events is likely to be orders of magnitude greater than quasi-static rates used previously [5]. Due to the loading rate dependence demonstrated for other tissues, including thoracic vertebrae [6], arteries [7], ligaments [8], and isolated spines [9], tolerance limits obtained from quasi-static testing are not likely applicable for the dynamic loading environment. Therefore, this study was conducted to quantify dynamic fracture biomechanics of lumbar vertebrae.
Performing Clinical Exams at Specific Joint Positions May Help Identify Injured Regions of the Glenohumeral Capsule Following Anterior Dislocation
Authors: Rainis Carrie A. , Browe Daniel P. , McMahon Patrick J. , Debski Richard E.
Published: July 2013

The anteroinferior glenohumeral capsule (anterior band of the inferior glenohumeral ligament (AB-IGHL), axillary pouch) limits anterior translation, particularly in positions of external rotation. [1, 2] Permanent tissue deformation that occurs as a result of dislocation contributes to anterior instability, but, the extent and effects of this injury are difficult to evaluate as the deformation cannot be seen using diagnostic imaging. Clinical exams are used to identify the appropriate location of tissue damage and current arthroscopic procedures allow for selective tightening of localized capsule regions; however, identifying the specific location for optimal treatment of each patient is challenging. Although the reliability of clinical exams has been shown to change with joint position [3] a standardized procedure has yet to be established. This lack of standardization is particularly problematic since capsule function is highly dependent upon joint position [4–7], and could be responsible for failed repairs attributed to plication of the wrong capsular region [8]. Understanding the relationship between the location of tissue damage and changes in capsule function following anterior dislocation could aid clinicians in diagnosing and treating anterior instability. Therefore, the objective of this work was to compare strain distributions in the anteroinferior capsule before and after anterior dislocation in order to identify joint positions at which clinical exams would be capable of detecting damage (nonrecoverable strain) in specific locations.
Stereoscopic Particle Image Velocimetry of Native Ovine Mitral Valves in a Pulsatile Left Heart Simulator
Authors: Rabbah Jean-Pierre , Saikrishnan Neelakantan , Yoganathan Ajit P.
Published: July 2013

Patient specific mitral valve computational models are being actively developed to facilitate surgical planning. These numerical models increasingly employ more realistic geometries, kinematics, and mechanical properties, which in turn requires rigorous experimental validation [1]. However, to date, native mitral flow dynamics have not been accurately and comprehensively characterized. In this study, we used Stereoscopic Particle Image Velocimetry (SPIV) to characterize the ventricular flow field proximal to a native mitral valve in a pulsatile experimental flow loop.
Implementation of Finite Deformation Triphasic Modeling in the Finite Element Code FEBio
Authors: Ateshian Gerard A. , Maas Steve , Weiss Jeffrey A.
Published: July 2013

Many biological soft tissues exhibit a charged solid matrix, most often due to the presence of proteoglycans enmeshed within the matrix. The predominant solute content of the interstitial fluid of these tissues consists of the monovalent counter-ions Na+ and Cl−. The electrical interactions between the mobile ion species and fixed charge density of the solid matrix produces an array of mechano-electrochemical effects, including Donnan osmotic swelling, and streaming and diffusion potentials and currents. These phenomena have been successfully modeled by the triphasic theory of Lai et al. [1], which is based on the framework of mixture theory [2]. Other similar frameworks have also been proposed [3, 4]. The equations of triphasic theory are nonlinear, even in the range of infinitesimal strains. Therefore, numerical schemes are generally needed to solve all but the simplest problems using this framework.
CFD Challenge: Solutions Using the Commercial Solver Fluent and the Open-Source Solver OpenFOAM
Authors: Berg P. , Janiga G. , Thévenin D.
Published: July 2013

During the last decade, the research group in Magdeburg investigated the hemodynamics in cerebral aneurysms in close collaboration with experts from the fields of visualization and neuroradiology. Thanks to this, a considerable experience has been collected concerning unsteady blood flow simulation and analyses, involving a steadily increasing number of patient-specific aneurysms. Intermediate results have been presented at several VISC challenges. The simulations regarding this CFD Challenge as well as the post-processing have been carried out by the doctoral student Philipp Berg.
Predicting the Functional Impact of Residual Aortic Coarctation Lesions Using Fluid-Structure Interaction Simulations
Authors: Taelman L. , Bols J. , Degroote J. , Muthurangu V. , Panzer J. , Swillens A. , Vierendeels J. , Segers P.
Published: July 2013

Aortic coarctation is a congenital disease, characterized by a narrowing of the upper descending aorta, obstructing the blood flow from the heart towards the lower part of the body. The treatment can be minimally invasive using a stent and/or a balloon catheter to dilate the coarctation zone, or the narrow section can be removed surgically. Even after a successful treatment, a high risk of cardiovascular morbidity and mortality remains. Two aspects contribute to this increased risk: (1) a residual narrowing, leading to an additional resistance in the arterial system and (2) a local stiffening after treatment, disturbing the buffer function of the aorta. Moreover, these residual narrowing and stiffening lead to an impedance mismatch and are a source of wave reflections that reach the heart fast, given the short distance to the heart.