bluuebunny/crossref_metadata_2025 huggingface dataset:
The Role of Nuclear Stiffness and Resilience in Mechanotransduction
Authors: Dahl Kris Noel , Booth-Gauthier Elizabeth A. , Ribeiro Alexandre J. S. , Zhong Zhixia
Published: July 2013

Mechanical force is found to be increasingly important during development and for proper homeostatic maintenance of cells and tissues. The nucleus occupies a large volume fraction of the cell and is interconnected with the cytoskeleton. Here, to determine the direct role of the nucleus itself in converting forces to changes in gene expression, also known as, mechanotransduction, we examine changes in nuclear mechanics and gene reorganization associated with cell fate and with extracellular force. We measure mechanics of nuclei in many model cell systems using micropipette aspiration to show changes in nuclear mechanics. In intact cells we characterize the rheological changes induced in the genome organization with live cell imaging and particle tracking, and we suggest how these changes relate to gene expression.
Effects of Aging and TGF-Beta 3 on Chondrocyte and Mesenchymal Stem Cell Matrix Formation
Authors: Erickson Isaac E. , van Veen Steven C. , Sengupta Swarnali , Kestle Sydney R. , Burdick Jason A. , Mauck Robert L.
Published: July 2013

Articular cartilage pathology is common in the aged population. Numerous studies have shown that aged chondrocytes (CHs) are inferior to juvenile CHs in their ability to proliferate and produce cartilage-specific extracellular matrix proteins, potentially limiting their use in tissue engineering applications for cartilage restoration [1,2]. Mesenchymal stem cells (MSCs) are an alternative cell type that can be expanded in vitro while maintaining their ability to differentiate into cell types comparable to articular chondrocytes. However, organismal aging also influences human MSC proliferation [3,4] and multi-potential differentiation [5], though for chondrogenesis these findings are mixed, with some suggesting that aged progenitor cells retain their chondrogenic capacity [6]. The objective of this study was to assess age related differences in donor-matched CH and MSC potential for chondrogenic repair. In addition, the effects of the chondrogenic growth factor TGF-β3 on CHs and MSCs were evaluated.
Biomechanics of Early Cardiac Development: A Nonlinear Explicit FE Model of C-Looping in the Embryonic Chick Heart
Authors: Young Jonathan M. , Taber Larry A. , Perucchio Renato
Published: July 2013

C-looping is the morphomechanical process through which the initially straight embryonic heart tube (HT) reconfigures into a doubly bent, twisted, swollen, c-shaped tube [1] between stages HH10− and HH12 [2]. According to the biomechanical hypotheses proposed by Taber [3], the ventral and rightward bending of the heart tube are intrinsic to the initially straight HT, and are caused by actin polymerization within myocardial cells. The torsion and rotation of the HT are due to a rightward oriented force generated by the elongation of the left omphalomesenteric vein (OV) and a dorsally oriented force due to tension in the splanchnopleure (SPL) [4]. In order to numerically test these biomechanical hypotheses, the standard stiffness-based nonlinear finite element formulation (standard FE) has been modified to include growth-based deformation to simulate c-looping [5]. However, due to numerical difficulties, such an approach can represent only the initial stages of c-looping and does not include SPL contact, or the merger (fusion) of the OV, which contributes to the elongation of the caudal heart tube [6]. To overcome these modeling difficulties, we propose the use of the explicit finite element formulation (explicit FE) as an alternative technique for modeling c-looping.
Viscoelastic Behavior of the Rat Uterine Cervix at Mid-Pregnancy
Authors: Barone William R. , Feola Andrew J. , Moalli Pam A. , Abramowitch Steven D.
Published: July 2013

Preterm labor is the leading cause of neonatal mortality and accounts for 70% of the total cost of neonatal health care. Premature softening of the cervix has been identified as one of the primary causes of preterm labor. As the biochemistry of the cervix is distinct between the proximal and distal portions, the objective of this study was to determine the viscoelastic properties of these portions in mid-pregnancy (Day 15–16) relative to virgin Long-Evans rats. This will serve to establish baseline data for future studies that will aim to induce preterm labor in this model. The cervix was divided into distal and proximal portions that were tested independently. Each portion was tested in unconfined compression to 20% strain and held for 4 minutes followed by a recovery period of 30 minutes. The stress-relaxation response was modeled using the quasi-linear viscoelastic (QLV) theory developed by Professor Fung (1972). The parameters governing the viscous response, C, τ1 and τ2, were found to be significantly different between virgin and pregnant tissues in distal portions; however τ2 was the only viscous parameter found to be significantly different for the proximal portion (p<0.05). These results show an increased magnitude of the viscous response with more rapid relaxation for the pregnant cervix. Future studies will evaluate the cervix both postpartum and upon induction of preterm labor. Additionally, contractile and biochemical assays will be used to correlate these changes in passive behavior to active properties and tissue constituents.
Direct Measurement of the Time Dependent Poisson’s Ratio in Rat Tail Tendon During Stress Relaxation
Authors: Reese Shawn P. , Weiss Jeffrey A.
Published: July 2013

The viscoelastic behavior of tendons and ligaments contributes to the normal function of these tissues. However, the underlying mechanisms for this behavior are still poorly understood. Although stress and strain in the loading direction have been well studied for uniaxial tensile creep and stress relaxation, data on the lateral contraction during these tests are unavailable. This information is necessary to obtain an understanding of the underlying mechanisms of viscoelasticity. The purpose of this study was to begin filling this gap by providing a direct measurement of the Poisson’s ratio as a function of time in rat tail tendon (RTT) samples during uniaxial stress relaxation testing. A further objective of this study was to determine if there exists a correlation between the Poisson’s ratio and the stress during stress relaxation testing.
Micromechanical Deformation of Chondrogenic Mesenchymal Stem Cells in 3D Hydrogels is Modulated by Time in Culture and Matrix Connectivity
Authors: Farrell Megan J. , Zachry Tiffany L. , Mauck Robert L.
Published: July 2013

Mesenchymal stem cells (MSCs) are a clinically attractive alternative to chondrocytes for the development of engineered cartilage tissue owing to their ease of isolation and chondrogenic potential [1]. However, the mechanical properties of MSC-based constructs have yet to match those of native cartilage or of chondrocyte-based constructs cultured similarly [1]. One route for improving these properties may be the application of mechanical stimulation, as normal cartilage development and homeostatic maintenance is dependent on force transduction. In a tissue engineering context, dynamic compression applied to chondrocyte-seeded hydrogels modulates both matrix production and mechanical properties [2, 3]. Similarly, when MSCs are embedded in 3D hydrogels, expression of chondrogenic markers and cartilaginous ECM synthesis are differentially regulated by dynamic compressive loading [4, 5]. Indeed, we have recently shown that long-term dynamic loading initiated after a pre-culture period of 21 days in pro-chondrogenic medium improves matrix distribution and the compressive properties of MSC-seeded constructs [5]. Interestingly, when loading was initiated after a single day of culture, mechanical properties failed to develop [6, 7], suggesting that elaboration of matrix was required prior to dynamic loading in order to positively direct construct maturation. When chondrocytes are embedded in agarose, the initial growth phase is characterized by the establishment of a dense pericellular matrix (PCM). At early times in culture, before these islands of PCM become connected into an interterritorial matrix, cells are protected from bulk deformation applied to the gel [8]. In a recent study, we showed that clonal heterogeneity in stem cell populations determines the rate at which this PCM forms, with some MSC clones rapidly establishing a dense PCM, while others fail to develop a robust PCM (and so continue to deform with gel deformation) through several weeks in culture [9]. To further this investigation, this study charted the culture time-dependent changes in ECM connectivity and MSC deformation under basal and chondrogenic conditions.
Differential Responses of Endothelial Cells to Positive and Negative Wall Shear Stress Gradients
Authors: Dolan Jennifer , Singh Sukhjinder , Meng Hui , Kolega John
Published: July 2013

Cerebral aneurysms tend to develop at bifurcation apices or the outer side of curved vessels where the blood vessel wall experiences complex hemodynamics. In vivo studies have recently revealed that the initiation of cerebral aneurysms is confined to a well-defined hemodynamic microenvironment. Specifically aneurysms form where the vessel wall experiences high fluid shear stress (wall shear stress, WSS) and flow is accelerating, so that the wall is exposed to a positive spatial gradient in the fluid shear stress (wall shear stress gradient, WSSG)[1,2]. Closer examination of such in vivo studies reveals that exposure of the vessel wall to equally high WSS in the presence of decelerating flow, that is, negative WSSG, does not result in aneurysm-like remodeling.
Design of a Novel Cavopulmonary Assist Device for Fontan Procedures: CFD, PIV, and Hydraulic Testing
Authors: Kennington Jeffrey R. , Frankel Steven , Chen Jun , Rodefeld Mark D. , Giridharan Guruprasad A.
Published: July 2013

Single ventricle heart disease is the leading cause of death for birth defects in children under one years of age [1]. The current surgical procedure requires the use of a shunt for the first stage of the surgery. The following surgeries remove the shunt but cannot be performed on a newborn due to higher lung resistance during the first weeks of life. The overall surgical process, known as the Fontan procedure, results in a reconstructed anatomy where the left and right pulmonary arteries are sutured to the superior and inferior vena cavae (SVC/IVC), hence bypassing the right heart. This anatomy is called a total cavopulmonary connection or TCPC.
Sliver-Free Fully Automated Robust Mesh Generation for Complex Embedded Organic Shapes From 3-D Volumetric Images
Authors: Doehring Todd C. , Stober Spencer
Published: July 2013

Robust, automated mesh generation remains a difficult challenge for complex organic shapes encountered in biomedical modeling, particularly for multilayered or embedded topologies. Often, these objects cannot be described using parametric surfaces that are used in most available commercial mesh generation software.
A Rat Model for Pressure Induced Deep Tissue Injury
Authors: Lin Fang , Modi Mauli , Reprogle Briana , Bajema Mike , Wang Ziyan , Kaskin Gordon , Makhsous Mohsen
Published: July 2013

Deep tissue injury (DTI), as a recently emphasized mechanism for PU formation [1], has received increased attention lately and several studies reported findings on newly developed DTI animal models [2]. The clinical view of DTI emphasizes the severity of clinically identified DTI as that a true DTI progresses rapidly even with the most aggressive treatment and its massive tissue necrosis is in a similar nature of a Stage-IV full-thickness wound [3]. Many animal PU models have been developed to test different hypotheses related to deep tissue injury (DTI) [3]. However, none of DTI studies reported that the experimentally induced DTI eventually progressed to be an open wound which affected superficial skin, and the reported histological or imaging data of the induced DTI did not suggest massive tissue necrosis. Although it might be that most studies did not keep their DTI animals long enough to observe the formation of an open wound from the DTI, the results from our own observation and Kwan, et al [4], in which no skin lesion was formed after 7 days of DTI, do not support this speculation. It may be that, in these DTI studies, the injured deep layer had healed. By examination of the existing PU rat models, especially those for DTI research, we came to our assumption that the missing bony prominence may possibly be a flaw that prevents those models from yielding more clinically relevant data. It has long been the understanding that PUs often occur at tissue pressure points around a bony prominence. We believe that, to more accurately simulate the clinical scenario of DTI formation, a bony prominence is necessary for a rat DTI model.
Influence of Wall Compliance on Epithelial Cell Structure and Injury During Airway Reopening
Authors: Higuita-Castro Natalia , Huang Yan , Mihai Cosmin , Hansford Derek J. , Ghadiali Samir N.
Published: July 2013

The present work describes the implementation of an in-vitro model for the evaluation of the injury mechanisms of lung epithelial cells during simulated airway reopening events. Collagen-coated polyacrylamide substrates with different rigidities served as cell culture substrates, and a parallel plate perfusion chamber was used for simulating the reopening of fluid-filled airways. Human alveolar epithelial cell (A549) monolayers were grown to confluence on the different substrates and the cellular response was evaluated in terms of cytoskeletal distribution, proliferation rate, and cell stiffness. One and five reopening events were simulated, and cell response was characterized via live/dead fluorescence imaging. Cells cultured on stiffer substrates showed higher proliferation rate, as well as a more spread and tightly packed morphology. Airway reopening simulations showed that cells cultured on softer substrates are less susceptible to cell injury.
Patient-Specific Hemodynamic Simulations in Coronary Artery Aneurysms Caused by Kawasaki Disease
Authors: Sengupta Dibyendu , Burns Jane C. , Kahn Andrew , Marsden Alison L.
Published: July 2013

Kawasaki disease (KD) is an acute pediatric illness and the leading cause of acquired heart disease in children, with over 4,000 cases diagnosed annually in the US. The incidence of KD in San Diego County is 25/100,000 for children less than 5 years of age. In absence of a diagnostic test for KD, many patients are not diagnosed in time to receive treatment with intravenous gamma globulin. Approximately 25% of untreated patients develop large aneurysms in their coronary arteries, which puts them at risk for myocardial infarction. In this project we performed patient specific computational simulations of blood flow in aneurysmal left and right coronary arteries of a 10-year-old KD patient. Several relevant hemodynamic parameters such as wall shear stress (WSS) and recirculation time were obtained, as a first step toward developing a risk assessment tool for thrombosis in KD patients.
Effects of Static Compression on Energy Metabolism of Porcine Intervertebral Disc
Authors: Yuan Tai-Yi , Fernando Hanan N. , Czamanski Jessica , Wang Chong , Gu Wei Yong , Huang Chun-Yuh
Published: July 2013

Degeneration of the intervertebral disc (IVD) has been associated with low back pain, which is one of the major socio-economic problems in the United States. Since IVD is the largest avascular cartilaginous structure in the human body, poor nutrient supply has been suggested as a potential mechanism for IVD degeneration. Biosynthesis of extracellular matrix is an energy demanding process which is required to maintain tissue integrity [1]. Cells consume glucose and oxygen to produce adenosine triphosphate (ATP), the main energy form in cells. Glycolysis, the primary metabolic pathway for production of ATP in IVD cells, is strongly regulated by local oxygen concentration and pH (which is governed by lactate concentration) [2]. Therefore, energy metabolism may play an important role in the malnutrition pathway leading to IVD degeneration. The objective of this study was to investigate the effect of mechanical loading on cellular energy metabolism in whole disc and in agarose gels.
Fading Memory Formulation for Active Stress Fibre Contractility
Authors: McGarry Patrick , McMeeking Robert M. , Deshpande Vikram S.
Published: July 2013

Cytoskeletal alignment and morphological changes in cells under conditions of cyclic stretching have been reported in several in-vitro studies. Of particular interest is the experimental work of Wille et al. [1] in which the contractile response of fibroblast stress fibres was isolated and quantified by testing both untreated cells and cells treated with Cytochalasin-D.
Generating Parameters of a Multi-Body Meniscus Model From Experimental Data
Authors: Paiva Gavin , Guess Trent , Kia Mohammad
Published: July 2013

The meniscus is a crucial anatomical structure in the mechanics of vertebrate hind legs [3]. Menisci function primarily by distributing the tibio-femoral contact forces, and thereby reducing the stress in the articular cartilage of the knee joint. As the meniscus is a flexible body that undergoes large strains, it is typically ignored in rigid-body biomechanical simulations. One documented method of including this factor in the multi-body framework is to represent the menisci as discrete bodies connected by linear 6-axis spring and damper elements [2]. The difficulty arises in determining the stiffnesses and viscosities that correspond to the material properties of the real meniscus. Material properties have previously been determined by a design of experiments approach to match the force displacement behavior of a multi-body model to a linear finite element model. This study explores a method of determining the said properties from experimental data collected in a semi-physiological loading, where the force orientation is principally circumferential tension and compression in the other directions.
Spinal Movement Centers of Rotation for Modeling and Development of Rehabilitation and Exoskelton Devices
Authors: Lura Derek , Dubey Rajiv
Published: July 2013

Recent years have seen the rapid development of various upper limb devices, especially in prosthetic [1] and exoskeleton devices [2–5]. Although the capabilities of these devices have been greatly increased, the effect of these devices in real world applications is still being tested. In exoskeletons and prostheses, the majority of development has been focused on lower and upper extremity devices, many times excluding the effects of torso movement. The torso contributes a significant amount of movement in the performance of tasks, and the spine is prone to injury if overexerted [6]. For continued development and expansion of these devices the movements of the torso must be considered. This paper presents work done in the development of functional joint centers of the spine to be used in upper body modeling for development and testing of prostheses and exoskeletons.
The Effects of Angiotensin II Infusion on the Mechanical Response and Microstructural Organization of Mouse Aorta
Authors: Haskett Darren , Fouts Marie , Utzinger Urs , Larson Doug , Azhar Mohamad , Vande Geest Jonathan
Published: July 2013

Vascular diseases such as aneurysm and aortic dissection account for almost 16,000 deaths in the United States annually. In both of these diseases vascular inflammation is a common pathogenic factor. Another common pathologic feature of vascular disease includes structural matrix remodeling. It is also increasingly believed that inflammation may play a key role in the formation and progression of atherosclerotic vascular disease. Angiotensin II (AngII), a potent vasopressor, is also a strong inducer of vascular inflammation and aortic remodeling in atherosclerosis-prone mice. Based on this knowledge studies have been conducted using subcutaneous AngII infusion in order to produce aortic remodeling and aneurysm formation, with acute thoracic and abdominal aortic dissections [1].
Pulsatile Efficiency and Pediatric Venous Assist Options in Failing Fontan Patients
Authors: Dur Onur , Kocyildirim Ergin , Degroff Curt G. , Soran Ozlem , Wearden Peter , Morell Victor , Pekkan Kerem
Published: July 2013

Single ventricle (SV) anomalies are the fifth most common heart defect (2000 patients per year) and the leading cause of death from all structural birth defects. Total cavopulmonary connection (TCPC) is the last stage of the palliative surgical reconstruction i.e. Fontan procedure for the infants with SV. A large number of children continue to benefit from the Fontan operation. However, despite many refinements of the surgical procedure in the past 20 years, a relatively high proportion of patients demonstrate a gradual decline in functional capacity and premature death. Most of these failing Fontan patients require heart transplantation [1]. However, donor shortage and the high-risk nature of transplantation for these complex and often very ill patients demand alternative therapeutic options.
Comparison of Imaging Modalities in the Quantification of Cerebral Aneurysm Geometry
Authors: Ramachandran Manasi , Retarekar Rohini , Hasan David , Policeni Bruno , Harbaugh Robert E. , Raghavan Madhavan L.
Published: July 2013

Longitudinal studies of a large cohort of cerebral aneurysm patients are essential for assessing the ability of geometric and biomechanical indices in predicting their growth or rupture risk [1,2]. Patients with these lesions are routinely subjected to volumetric scans, but these can be one of four modalities — 3D rotational angiography (3DRA), Computed Tomography Angiography (CTA), Magnetic Resonance Angiography (MRA) and MR Time-of-flight (MR-TOF) — the choice of which is often dictated by clinical considerations. One of the challenges in geometric analysis of cerebral aneurysms is the consistency in the process of 3D reconstruction of aneurysm geometry when data from multiple imaging modalities are used. It is reasonable to wonder if the same aneurysm were imaged using different imaging modalities, whether the quantified measures of the aneurysm’s shape and size will be different. The objective of this study is to assess the sensitivity of geometric indices of cerebral aneurysms to the modality from which the image volume is obtained. A patient-specific silicone model of the head and neck vasculature with an aneurysm was imaged using all four modalities, geometric measures were estimated and compared.
Appearance and Development of Secondary Ossification Center: A Mathematical Model Approach
Authors: Garzón-Alvarado D. A. , Peinado-Cortés L. M.
Published: July 2013

This paper introduces an “hypothesis about the growth pattern of the secondary ossification centre (SOC)”, whereby two phases are assumed. First, the formation of cartilage canals as an event essential for the development of the SOC. Second, hence the canals are merged in the central zone of the epiphysis, molecular factors are released (primarily Runx2 and MMP9) spreading and causing hypertrophy of adjacent cells. In order to test this hypothesis we solve a system of coupled partial differential equations using the finite element method and we have obtained spatio-temporal patterns of the growth process of the SOC. The model is in qualitatively agreement with experimental results previously reported by other authors.
Mixed Mode Delamination of Stent Coatings During Deployment
Authors: McGarry Patrick , Parry Guillaume
Published: July 2013

Recent advances in angioplasty have involved the application of polymer coatings to stent surfaces for purposes of drug delivery in order to prevent a reblockage of the artery due to smooth muscle cell proliferation. This advance has reduced instances of such restenosis from ∼40% for bare metal stents to ∼5% for drug eluting stents, and has yielded a milti-billion dollar per annum market. However, delamination of polymer coatings on commercial stents has recently been reported using SEM analysis [1, 2]. Such delamination results from interface failure due to high interface tractions developed in the region of the stent plastic hinge.
An Improved Dummy Neck Assembly for Dynamic Rollover Testing
Authors: Paver Jacqueline G. , Caplinger Justin , Mattos Garrett , Friedman Donald
Published: July 2013

In the U.S., more than 27,000 catastrophic and fatal injuries occur annually in rollover crashes. Due to the incidence and severity of injuries in rollover crashes, a strategy for injury mitigation is dynamic compliance testing with dummy-occupied vehicles and occupant protection requirements, similar to that required for frontal and side impacts. Presently, there are dynamic vehicle rollover test devices like the Controlled Rollover Impact System and the Jordan Rollover System that realistically recreate real-world rollover crash scenarios. However, the Hybrid III dummy, which is considered to be the best available human surrogate for dynamic rollover tests, has a very stiff neck with limited biofidelity in rollover crashes; the Hybrid III neck is much stiffer than the human neck. Catastrophic human head or neck injuries resulting from roof interaction and partial ejection in real-world rollover crashes are poorly replicated by dynamic rollover tests with the non-biofidelic Hybrid III dummy neck. Only with a more biofidelic dummy can effective testing result in injury mitigation in rollover crashes.

This study is part of an ongoing research project aimed at mitigating catastrophic human neck injuries in real-world rollover crashes. The goal was to develop a biofidelic neck assembly for the Hybrid III dummy in rollover crash environments. The design goals of this prototype neck included decreased stiffness and a mechanism that represents the unknowable human muscle tension in rollover crash environments.

This paper and its companion paper in this conference introduce the new neck design, present results of matched-pair tests that compare the responses of the new neck with the production Hybrid III neck, and propose preliminary rollover injury criteria for this neck. The neck demonstrates repeatability, improved biofidelity, which results in more realistic occupant kinematics, dynamics, injury prediction, and evaluation of various countermeasures.
Development of a 3D FSI Model of the Aortic Root Incorporating Coronary Structure
Authors: Nobari Soroush , Mongrain Rosaire , Leask Richard , Cartier Raymond
Published: July 2013

The aortic valve is a critical part of the cardiovascular system which carries an important role in hemodynamic of the region. As a consequence, numerous studies have been carried out during recent years to comprehend its complexities and provide more accurate information towards understanding the hemodynamic of the region pre and post operatively in view of applications to valve prosthetics.
Functionalized Collagen Scaffolds for Peripheral Nerve Regeneration
Authors: Masand Shirley , Chen Jian , Schachner Melitta , Shreiber David I.
Published: July 2013

Despite the robust regenerative potential of the peripheral nervous system, a permanent loss of function is often associated with injury. A multitude of causes have been implicated in this outcome, including the presence of a non-permissive microenvironment surrounding the injury and the regrowth of emerging neurites towards inappropriate targets. Preferential motor reinnervation is a naturally occurring phenomenon where motor axons have increased accuracy in reaching their appropriate end targets as the course of regeneration proceeds1. Several molecules have been implicated in encouraging this response, including two carbohydrates — Polysialic Acid (PSA) and Human Natural Killer Epitope-1 (HNK-1)2,3. Peptide mimics of these molecules have been identified4,5, which are more stable and economical than their glycan counterparts, and have independently been shown to enhance PMR in a soluble form, but only for transection distances substantially smaller than the 5-mm ‘critical gap’ size for mice6,7.
Increasing Storage Modulus, Contact Angle and Surface Tension of Airway Mucus Increases Clearance by Simulated Cough Through a Model Trachea
Authors: Ragavan Anpalaki J. , Evrensel Cahit A. , Krumpe Peter
Published: July 2013

Altered surface and viscoelastic material properties of mucus during respiratory diseases have a strong influence on its clearance by cilia and cough. Combined effects of the surface properties (contact angle and surface tension) and storage modulus with relatively unchanged viscosity on displacement of the simulated mucus aliquot during simulated cough through a model adult human trachea is investigated. For the mucus simulants used in this study contact angle and surface tension increase significantly as storage modulus increase while viscosity remains practically unchanged. Displacement of mucus simulant aliquots increased significantly with increasing storage modulus (and contact angle) at a given cough velocity in the range between 5 meters/second (m/s) and 30 m/s with duration 0.3 s. Results suggest that the interactive effects of elasticity and surface properties may help facilitate mucus displacement at low cough velocities.
Fatigue Behavior of Stainless Steel, Titanium, and Cobalt Chromium Molybdenum Spinal Rods
Authors: Paris Anthony , Bergeron Alex , Cullin Matthew , Munk Andres
Published: July 2013

The objective of this study was to measure and compare the fatigue behavior of 316L stainless steel, titanium (Ti-6Al-4V), and cobalt chromium molybdenum (CoCrMo) spinal rods in vitro. Spinal rods are used to immobilize the spine while fusion of the vertebrae occurs (spinal arthrodesis). Implanted spinal rods are subjected to cyclic loading and are therefore susceptible to fatigue failure if fusion does not occur sufficiently quickly. A significant number of spinal rod fatigue failures have been observed between six months to one year following surgical implantation. On average, the spine will experience about 3 million cycles per year. Stress overloads can result in permanent deformation or immediate failure of the rod, however these overloads are seldom the root cause of failure—rods typically fail by fatigue [1].
Biofilm Formation by the Fish Pathogen Flavobacterium columnare: Development and Parameters Affecting Surface Attachment
Authors: Cai Wenlong , De La Fuente Leonardo , Arias Covadonga R.
Published: July 2013

Flavobacterium columnare
is a bacterial fish pathogen that affects many freshwater species worldwide. The natural reservoir of this pathogen is unknown, but its resilience in closed aquaculture systems posits biofilm as the source of contagion for farmed fish. The objectives of this study were (i) to characterize the dynamics of biofilm formation and morphology under static and flow conditions and (ii) to evaluate the effects of temperature, pH, salinity, hardness, and carbohydrates on biofilm formation. Nineteen
F. columnare
strains, including representatives of all of the defined genetic groups (genomovars), were compared in this study. The structure of biofilm was characterized by light microscopy, confocal laser scanning microscopy, and scanning electron microscopy.
F. columnare
was able to attach to and colonize inert surfaces by producing biofilm. Surface colonization started within 6 h postinoculation, and microcolonies were observed within 24 h. Extracellular polysaccharide substances and water channels were observed in mature biofilms (24 to 48 h). A similar time course was observed when
F. columnare
formed biofilm in microfluidic chambers under flow conditions. The virulence potential of biofilm was confirmed by cutaneous inoculation of channel catfish fingerlings with mature biofilm. Several physicochemical parameters modulate attachment to surfaces, with the largest influence being exerted by hardness, salinity, and the presence of mannose. Maintenance of hardness and salinity values within certain ranges could prevent biofilm formation by
F. columnare
in aquaculture systems.
A Novel Bacillus thuringiensis Cry-Like Protein from a Rare Filamentous Strain Promotes Crystal Localization within the Exosporium
Authors: Ammons David R. , Reyna Antonio , Granados Jose C. , Ventura-Suárez Antonio , Rojas-Avelizapa Luz I. , Short John D. , Rampersad Joanne N.
Published: July 2013

Mutation of a novel
cry
-like gene (
cry256
) from
Bacillus thuringiensis
resulted in a protein crystal, normally located within the spore's exosporium, being found predominately outside the exosporium. The
cry256
gene codes for a 3-domain Cry-like protein that does not correspond to any of the known Cry protein holotypes.
Live-Cell Imaging Tool Optimization To Study Gene Expression Levels and Dynamics in Single Cells of Bacillus cereus
Authors: Eijlander Robyn T. , Kuipers Oscar P.
Published: July 2013

Single-cell methods are a powerful application in microbial research to study the molecular mechanism underlying phenotypic heterogeneity and cell-to-cell variability. Here, we describe the optimization and application of single-cell time-lapse fluorescence microscopy for the food spoilage bacterium
Bacillus cereus
specifically. This technique is useful to study cellular development and adaptation, gene expression, protein localization, protein mobility, and cell-to-cell communication over time at the single-cell level. By adjusting existing protocols, we have enabled the visualization of growth and development of single
B. cereus
cells within a microcolony over time. Additionally, several different fluorescent reporter proteins were tested in order to select the most suitable green fluorescent protein (GFP) and red fluorescent protein (RFP) candidates for visualization of growth stage- and cell compartment-specific gene expression in
B. cereus
. With a case study concerning
cotD
expression during sporulation, we demonstrate the applicability of time-lapse fluorescence microscopy. It enables the assessment of gene expression levels, dynamics, and heterogeneity at the single-cell level. We show that
cotD
is not heterogeneously expressed among cells of a subpopulation. Furthermore, we discourage using plasmid-based reporter fusions for such studies, due to an introduced heterogeneity through copy number differences. This stresses the importance of using single-copy integrated reporter fusions for single-cell studies.
LuxR- and LuxI-Type Quorum-Sensing Circuits Are Prevalent in Members of the Populus deltoides Microbiome
Authors: Schaefer Amy L. , Lappala Colin R. , Morlen Ryan P. , Pelletier Dale A. , Lu Tse-Yuan S. , Lankford Patricia K. , Harwood Caroline S. , Greenberg E. Peter
Published: July 2013

We are interested in the root microbiome of the fast-growing Eastern cottonwood tree,
Populus deltoides
. There is a large bank of bacterial isolates from
P. deltoides
, and there are 44 draft genomes of bacterial endophyte and rhizosphere isolates. As a first step in efforts to understand the roles of bacterial communication and plant-bacterial signaling in
P. deltoides
, we focused on the prevalence of acyl-homoserine lactone (AHL) quorum-sensing-signal production and reception in members of the
P. deltoides
microbiome. We screened 129 bacterial isolates for AHL production using a broad-spectrum bioassay that responds to many but not all AHLs, and we queried the available genome sequences of microbiome isolates for homologs of AHL synthase and receptor genes. AHL signal production was detected in 40% of 129 strains tested. Positive isolates included members of the
Alpha
-,
Beta
-, and
Gammaproteobacteria
. Members of the
luxI
family of AHL synthases were identified in 18 of 39 proteobacterial genomes, including genomes of some isolates that tested negative in the bioassay. Members of the
luxR
family of transcription factors, which includes AHL-responsive factors, were more abundant than
luxI
homologs. There were 72 in the 39 proteobacterial genomes. Some of the
luxR
homologs appear to be members of a subfamily of LuxRs that respond to as-yet-unknown plant signals rather than bacterial AHLs. Apparently, there is a substantial capacity for AHL cell-to-cell communication in proteobacteria of the
P. deltoides
microbiota, and there are also
Proteobacteria
with LuxR homologs of the type hypothesized to respond to plant signals or cues.
Core Fluxome and Metafluxome of Lactic Acid Bacteria under Simulated Cocoa Pulp Fermentation Conditions
Authors: Adler Philipp , Bolten Christoph Josef , Dohnt Katrin , Hansen Carl Erik , Wittmann Christoph
Published: July 2013

In the present work, simulated cocoa fermentation was investigated at the level of metabolic pathway fluxes (fluxome) of lactic acid bacteria (LAB), which are typically found in the microbial consortium known to convert nutrients from the cocoa pulp into organic acids. A comprehensive
13
C labeling approach allowed to quantify carbon fluxes during simulated cocoa fermentation by (i) parallel
13
C studies with [
13
C
6
]glucose, [1,2-
13
C
2
]glucose, and [
13
C
6
]fructose, respectively, (ii) gas chromatography-mass spectrometry (GC/MS) analysis of secreted acetate and lactate, (iii) stoichiometric profiling, and (iv) isotopomer modeling for flux calculation. The study of several strains of
L. fermentum
and
L. plantarum
revealed major differences in their fluxes. The
L. fermentum
strains channeled only a small amount (4 to 6%) of fructose into central metabolism, i.e., the phosphoketolase pathway, whereas only
L. fermentum
NCC 575 used fructose to form mannitol. In contrast,
L. plantarum
strains exhibited a high glycolytic flux. All strains differed in acetate flux, which originated from fractions of citrate (25 to 80%) and corresponding amounts of glucose and fructose. Subsequent, metafluxome studies with consortia of different
L. fermentum
and
L. plantarum
strains indicated a dominant (96%) contribution of
L. fermentum
NCC 575 to the overall flux in the microbial community, a scenario that was not observed for the other strains. This highlights the idea that individual LAB strains vary in their metabolic contribution to the overall fermentation process and opens up new routes toward streamlined starter cultures.
L. fermentum
NCC 575 might be one candidate due to its superior performance in flux activity.
Assimilation of Cellulose-Derived Carbon by Microeukaryotes in Oxic and Anoxic Slurries of an Aerated Soil
Authors: Chatzinotas Antonis , Schellenberger Stefanie , Glaser Karin , Kolb Steffen
Published: July 2013

Soil microeukaryotes may trophically benefit from plant biopolymers. However, carbon transfer from cellulose into soil microeukaryotes has not been demonstrated so far. Microeukaryotes assimilating cellulose-derived carbon in oxic and anoxic soil slurries were therefore examined by rRNA-based stable-isotope probing. Bacteriovorous flagellates and ciliates and, likely, mixotrophic algae and saprotrophic fungi incorporated carbon from supplemental [U-
13
C]cellulose under oxic conditions. A previous study using the same soil suggested that cellulolytic
Bacteria
assimilated
13
C of supplemental cellulose. Thus, it can be assumed that ciliates, cercozoa, and chrysophytes assimilated carbon by grazing upon and utilizing metabolic products of
Bacteria
that hydrolyzed cellulose in the soil slurries.
Differential Growth of and Nanoscale TiO
2
Accumulation in Tetrahymena thermophila by Direct Feeding versus Trophic Transfer from Pseudomonas aeruginosa
Authors: Mielke Randall E. , Priester John H. , Werlin Rebecca A. , Gelb Jeff , Horst Allison M. , Orias Eduardo , Holden Patricia A.
Published: July 2013

Nanoscale titanium dioxide (TiO
2
) is increasingly used in consumer goods and is entering waste streams, thereby exposing and potentially affecting environmental microbes. Protozoans could either take up TiO
2
directly from water and sediments or acquire TiO
2
during bactivory (ingestion of bacteria) of TiO
2
-encrusted bacteria. Here, the route of exposure of the ciliated protozoan
Tetrahymena thermophila
to TiO
2
was varied and the growth of, and uptake and accumulation of TiO
2
by,
T. thermophila
were measured. While TiO
2
did not affect
T. thermophila
swimming or cellular morphology, direct TiO
2
exposure in rich growth medium resulted in a lower population yield. When TiO
2
exposure was by bactivory of
Pseudomonas aeruginosa
, the
T. thermophila
population yield and growth rate were lower than those that occurred during the bactivory of non-TiO
2
-encrusted bacteria. Regardless of the feeding mode,
T. thermophila
cells internalized TiO
2
into their food vacuoles. Biomagnification of TiO
2
was not observed; this was attributed to the observation that TiO
2
appeared to be unable to cross the food vacuole membrane and enter the cytoplasm. Nevertheless, our findings imply that TiO
2
could be transferred into higher trophic levels within food webs and that the food web could be affected by the decreased growth rate and yield of organisms near the base of the web.
Impact of Manure Fertilization on the Abundance of Antibiotic-Resistant Bacteria and Frequency of Detection of Antibiotic Resistance Genes in Soil and on Vegetables at Harvest
Authors: Marti Romain , Scott Andrew , Tien Yuan-Ching , Murray Roger , Sabourin Lyne , Zhang Yun , Topp Edward
Published: July 2013

Consumption of vegetables represents a route of direct human exposure to bacteria found in soil. The present study evaluated the complement of bacteria resistant to various antibiotics on vegetables often eaten raw (tomato, cucumber, pepper, carrot, radish, lettuce) and how this might vary with growth in soil fertilized inorganically or with dairy or swine manure. Vegetables were sown into field plots immediately following fertilization and harvested when of marketable quality. Vegetable and soil samples were evaluated for viable antibiotic-resistant bacteria by plate count on Chromocult medium supplemented with antibiotics at clinical breakpoint concentrations. DNA was extracted from soil and vegetables and evaluated by PCR for the presence of 46 gene targets associated with plasmid incompatibility groups, integrons, or antibiotic resistance genes. Soil receiving manure was enriched in antibiotic-resistant bacteria and various antibiotic resistance determinants. There was no coherent corresponding increase in the abundance of antibiotic-resistant bacteria enumerated from any vegetable grown in manure-fertilized soil. Numerous antibiotic resistance determinants were detected in DNA extracted from vegetables grown in unmanured soil. A smaller number of determinants were additionally detected on vegetables grown only in manured and not in unmanured soil. Overall, consumption of raw vegetables represents a route of human exposure to antibiotic-resistant bacteria and resistance determinants naturally present in soil. However, the detection of some determinants on vegetables grown only in freshly manured soil reinforces the advisability of pretreating manure through composting or other stabilization processes or mandating offset times between manuring and harvesting vegetables for human consumption.
Interaction of Lactobacillus fermentum BGHI14 with Rat Colonic Mucosa: Implications for Colitis Induction
Authors: Lukic Jovanka , Strahinic Ivana , Milenkovic Marina , Golic Natasa , Kojic Milan , Topisirovic Ljubisa , Begovic Jelena
Published: July 2013

The present study was carried out to test the colonic mucosal response of rats to oral supplementation with
Lactobacillus fermentum
BGHI14 and to correlate the tissue reaction to trinitrobenzenesulfonate (TNBS)-induced colitis with mucosal barrier alterations caused by bacterial ingestion. An immune cell-mediated reaction of healthy colonic tissue was noticed after bacterial feeding. After prolonged bacterial treatment, the observed reaction had retreated to normality, but the mRNA levels of proinflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor alpha (TNF-α) remained elevated. These data point to the chronic low-grade inflammation that could be caused by long-term probiotic consumption. Although no detrimental effects of bacterial pretreatment were noticed in colitic rats, at least in the acute state of disease, the results obtained in our study point to the necessity of reassessment of existing data on the safety of probiotic preparations. Additionally, probiotic effects in experimental colitis models might depend on time coordination of disease induction with treatment duration.
Prevalence of Gastrointestinal Clostridium difficile Carriage in Australian Sheep and Lambs
Authors: Knight Daniel R. , Riley Thomas V.
Published: July 2013

Recently,
Clostridium difficile
has been isolated from a wide variety of animals, particularly production animals, mainly cattle and pigs. Concurrently, the incidence of
C. difficile
infection (CDI) in humans has increased in the community, with some suggestions that food-borne transmission of
C. difficile
is occurring. Interestingly, sheep and lambs appear not to have been investigated for carriage/colonization with
C. difficile
. The aim of this project was to determine the prevalence of carriage of
C. difficile
in sheep and lambs in Australia by culturing fecal samples. A total of 371 sheep and lamb fecal samples were received in seven batches from three different geographic areas in eastern Australia and two in Western Australia. The overall rate of detection in sheep and lambs was low (4.0%); however, carriage/colonization in lambs (6.5%) was statistically significantly higher than that in sheep (0.6%) (
P
= 0.005). Seven distinct PCR ribotype patterns were observed, three of which were known international ribotypes (UK 056 [
n
= 1], UK 101 [
n
= 6], and UK 137 [
n
= 2]), while the remainder were unable to be matched with our available reference library. This low rate of carriage/colonization in Australian ovines suggests they are unlikely to be a major source/reservoir of human infections.
CMF22 Is a Broadly Conserved Axonemal Protein and Is Required for Propulsive Motility in Trypanosoma brucei
Authors: Nguyen HoangKim T. , Sandhu Jaspreet , Langousis Gerasimos , Hill Kent L.
Published: July 2013

The eukaryotic flagellum (or cilium) is a broadly conserved organelle that provides motility for many pathogenic protozoa and is critical for normal development and physiology in humans. Therefore, defining core components of motile axonemes enhances understanding of eukaryotic biology and provides insight into mechanisms of inherited and infectious diseases in humans. In this study, we show that component of motile flagella 22 (CMF22) is tightly associated with the flagellar axoneme and is likely to have been present in the last eukaryotic common ancestor. The CMF22 amino acid sequence contains predicted IQ and
A
TPase
a
ssociated with a variety of cellular
a
ctivities (AAA) motifs that are conserved among CMF22 orthologues in diverse organisms, hinting at the importance of these domains in CMF22 function. Knockdown by RNA interference (RNAi) and rescue with an RNAi-immune mRNA demonstrated that CMF22 is required for propulsive cell motility in
Trypanosoma brucei
. Loss of propulsive motility in CMF22-knockdown cells was due to altered flagellar beating patterns, rather than flagellar paralysis, indicating that CMF22 is essential for motility regulation and likely functions as a fundamental regulatory component of motile axonemes. CMF22 association with the axoneme is weakened in mutants that disrupt the nexin-dynein regulatory complex, suggesting potential interaction with this complex. Our results provide insight into the core machinery required for motility of eukaryotic flagella.