bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamics of a Spherical Capsule in a Near-Wall Shear Flow
Authors: Nix Stephanie , Imai Yohsuke , Matsunaga Daiki , Ishikawa Takuji , Yamaguchi Takami
Published: July 2013

Lateral migration of cells in the bloodstream is affected by the material properties of the constituent cells. In blood vessels, red blood cells migrate to the center of the vessel, leading to the formation of a cell-free layer near the vessel wall; on the other hand, less deformable cells such as white blood cells and platelets are more likely to be found near the blood vessel wall. [1]
Role of Cells in Freezing-Induced Cell-Fluid Matrix Interactions Within Engineered Tissues
Authors: Seawright Angela , Ozcelikkale Altug , Dutton J. Craig , Han Bumsoo
Published: July 2013

Cryopreservation can provide long-term storage of various biological tissues, which has significant impact on tissue engineering and regenerative medicine. For successful cryopreservation of tissues, tissue functionality must be maintained including physical properties such as mechanical, optical, and transport properties, as well as cellular viability. Such properties are associated with the extracellular matrix (ECM) microstructure. Thus, the preservation of the ECM microstructure may lead to successful cryopreservation [1,2]. Yet, there is still very little known about changes in the ECM microstructure during freezing/thawing.
Novel Measuring System of ATP-Induced Transmembrane Potential Change of Nucleus Pulposus Cells
Authors: Gonzales Silvia D. , Wang Chong , Genemaras Amaris A. , Huang C.-Y. Charles
Published: July 2013

Low back pain is a serious concern in industrialized societies that affects millions of people around the world [1]. It can be attributed to several spine disorders; intervertebral disc (IVD) degeneration being one of the most common causes [2]. IVDs are the largest avascular tissue in the body and are composed of two differentiated anatomical structures: the nucleus pulposus (NP) and the annulus fibrosus (AF). The ability to withstand compressive loads due to weight and bending is provided by the swelling of the NP structure, while the ability to resist tensile forces during bending and twisting is provided by the AF fibers [3]. The biomechanical functions of NP and AF rely on their extracellular matrix (ECM) structure and composition. Previous studies have demonstrated that static and dynamic compressive loading alters ATP production, which may have an effect on ECM synthesis [2]. In addition, dynamic loading has shown an increase in ATP release from NP cells, which may contribute to endplate calcification and therefore to IVD degeneration [2, 4]. When tissue is damaged, ATP, which is found in millimolar concentrations in all cells, leaks or is released into the extracellular milieu [5, 6]. Extracellular ATP is a powerful signaling molecule that can regulate cell metabolism, survival, and growth [7]. However, IVD cell response to ATP has not been investigated. The receptors involved in transducing responses to ATP are found in many tissues throughout the body and are responsible for different kinds of intercellular communication. ATP receptor subtypes are ligand-gated ion channels (P2X) and G-protein coupled receptors (P2Y). P2X receptors show calcium permeability while P2Y receptors mediate calcium release from intracellular stores in response to ATP [6]. Direct ATP application to the cell has been reported to cause a change in membrane conductance in a variety of tissues [8]. The voltage sensitive dye di-8-ANEPPS allows for a noninvasive method of measuring fluorescence changes of the cell membrane, which are proportional to variations of the transmembrane potential [8]. Therefore, the objectives of this study were (1) to develop a novel transmembrane potential measuring system using di-8-ANEPPS dye and (2) to investigate the response of NP cells to ATP by measuring the change in transmembrane potential.
Poro-Visco-Elastic Modeling of Mechanical Wave Motion in the Lungs
Authors: Peng Ying , Dai Zoujun , Mansy Hansen A. , Royston Thomas J.
Published: July 2013

Noninvasive measurement of mechanical wave motion (sound and vibration) in the lungs may be of diagnostic value, as it can provide information about the mechanical properties of the lungs, which in turn are affected by disease and injury. In this study, two theoretical models of the vibro-acoustic behavior of the lung parenchyma are compared: (1) a Biot theory of poroviscoelasticity and (2) a simplified “bubble swarm” model for compression wave behavior. A “slow” compression wave speed predicted by the Biot theory formulation agrees well with the bubbly swarm theory in both analytical calculations and computational simulation. Biot theory also predicts a fast compression wave and a shear wave. The relative contributions of all three wave types are assessed. The effect of the air volume fraction is also investigated. Preliminary experimental measurements of the slow compression wave speed in the lung parenchyma are carried out and agree with theoretical predictions.
A Planar Micromixer Based on Sequential Logarithmic Spirals
Authors: Scherr Thomas F. , Quitadamo Christian , Tesvich Preston , Park Daniel Sang-Won , Tiersch Terrence , Hayes Daniel , Choi Jin-Woo , Nandakumar Krishnaswamy , Monroe W. Todd
Published: July 2013

Despite the advances made in recent years, mixing on the micro-scale remains a challenge. In typical microchannel flows, the lack of turbulence, evidenced by very low Reynolds numbers, constrains mixing to the natural time scale of diffusion. Peclet numbers, defined as the ratio of convective to diffusive transport, are typically very large in microfluidic applications, where transport is dominated by convection. As a result, a dedicated micromixing element is an integral part of most BioMEMS devices [1].
Functional and Anatomical Diagnosis of Coronary Artery Stenoses: A Retrospective Study in Humans
Authors: Kolli Kranthi K. , Effat Mohamed , Arif Imran , Helmy Tarek , Leesar Massoud , Back Lloyd H. , Peelukhana Srikara V. , Banerjee Rupak K.
Published: July 2013

Fractional flow reserve (FFR: ratio of distal to proximal pressure of a stenotic section) is used to evaluate hemodynamic significance of epicardial stenosis. However, FFR and coronary flow reserve (CFR: ratio of hyperemic blood velocity to that of resting condition) are used in conjunction to evaluate combination of both epicardial and microvascular disease. It has been proposed that optimization of cutoff values for diagnostic parameters in determining stenosis severity depends on coupling functional (pressure and velocity) and anatomical data (% area stenosis). We hypothesize that, pressure drop coefficient (CDP: the ratio of trans-stenotic pressure drop to distal dynamic pressure) which has the functional information of pressure and velocity in its formulation correlates significantly with FFR and CFR, and lesion flow coefficient (LFC: ratio of % area stenoses to CDP at throat region) which combines both functional and anatomical (% area stenoses) information in its formulation correlates significantly with FFR, CFR and % area stenosis. We retrospectively analyzed the hemodynamic information from Meuwissen et al [3] to test this hypothesis. It was observed that, CDP, a functional index based on pressure drop and velocity, correlated linearly and significantly with FFR and CFR. And, LFC (combined functional and anatomic parameter) also correlated significantly with FFR, CFR (both hemodynamic endpoints) and % area stenosis (anatomic endpoint).
Thermal Analysis Measurement of Gold Nanoparticle Interactions With Cell and Biomaterial
Authors: Qin Zhenpeng , Shah Neha , Akkin Taner , Chan Warren C. W. , Bischof John C.
Published: July 2013

The rapidly evolving field of nanomedicine focuses on the design and application of multi-functional nanoparticles for diagnosis and treatment of diseases especially cancer1. Many of these nanomaterials are designed to serve as drug delivery or image contrast agents, or even to generate heat for hyperthermia (i.e. treatment), of cancer. Heating examples include gold nanoparticles (GNPs) for photothermal therapy3, and superparamagnetic nanoparticles for magnetic fluid hyperthermia4.
Cerebral Aneurysm Sac Growth as the Etiology of Recurrence After Successful Coil Embolization
Authors: Hoppe Anna L. , Hasan David M. , Nadareyshvili Alexander I. , Mahaney Kelly B. , Kung David K. , Raghavan Madhavan L.
Published: July 2013

Cerebral aneurysm recurrence is characterized by the recanalization of an aneurysm lumen after treatment with embolization coils, necessitating additional interventional measures. Recurrence rates of ≤ 34% have been reported (with major recurrence rates of ≤ 21% cited).1 The etiology of cerebral aneurysm recurrence remains unclear; however, compaction of embolization coils within a treated aneurysm lumen has been referenced in the literature as the primary mechanism of recurrence.2–4 Nevertheless, it should be noted that the evidence presented has been observational in nature and thus qualitative.2–4 While coil compaction is a conceivable mechanism of cerebral aneurysm recanalization (allowing for increased luminal volume), it is hypothesized by the authors that growth of the sac itself is the primary recurrence mechanism. Previous studies concerning aneurysm sac growth have been limited to qualitative observations of 2D angiographic data.5–6 In these studies the ability to accurately measure aneurysm sac and coil mass size was vital; however, changes in scan magnification and patient orientation between initial and follow-up angiographic scans makes the reliable discernment of aneurysm sac and coil mass size over time difficult, and therefore limits the ability to rigorously assess the temporal evolution of both the coil mass and the aneurysm sac. The objective of this study was to utilize 3D image processing methods to quantify both aneurysm sac growth and coil mass volume in order to assess the association of each mechanism with recurrence. A study population of patients presenting with recurrent cerebral aneurysms post treatment with embolization coils at The University of Iowa Hospitals and Clinics (UIHC) were examined.
On Non-Newtonian Effects in Cerebral Aneurysms: A Computational Study on 12 Patient Specific Aneurysms
Authors: Evju Øyvind , Mardal Kent-Andre , Valen-Sendstad Kristian
Published: July 2013

The rupture of a cerebral aneurysm may cause subarachnoid hemorrhage (SAH), a type of stroke associated with a high risk of morbidity, and a mortality rate as high as 50% within 30 days. Cerebral aneurysms are relatively common. Roughly 6% of the population develop such during a life-time ([1]) and the average age of SAH is 51 years.
Fabrication of Organized Nanofibrous Scaffolds to Mimic the Macroscopic Curvature of the Meniscus: Structure and Mechanics
Authors: Fisher Matthew B. , Henning Elizabeth A. , Esterhai John L. , Mauck Robert L.
Published: July 2013

The menisci are crescent-shaped fibrocartilaginous tissues which function to transmit and distribute loads between the femur and tibia of the knee joint. As such, the meniscus experiences complex loads, including tension, compression, and shear. Meniscus function in tension arises from an organized microstructure — bundles of highly aligned collagen circumnavigate the tissue between insertion sites on the tibial plateau (1). These aligned collagen bundles endow the tissue with mechanical properties that are highly anisotropic, and highest in the primary collagen orientation (2). Commercial products to replace the meniscus lack this unique structure and organization (3,4). To address engineering the knee meniscus, we have developed aligned nanofibrous scaffolds that can recapitulate this mechanical anisotropy (5,6). However promising, fibers within these scaffolds are unidirectional, while the fibers within the native tissue have a pronounced c-shaped macroscopic organization. To mimic this macroscopic orientation, we developed a new electrospinning method to collect organized fibers on a planar spinning disc (7). The objective of this study was to quantify the structure and mechanics of nanofibrous scaffolds collected using this novel technique and compare the data to aligned scaffolds obtained from a traditional electrospinning approach. We hypothesized that these circumferentially aligned (CircAl) scaffolds would behave similarly to linearly aligned (LinAl) scaffolds on short length scales, but exhibit marked differences in mechanics as the length scale increased.
Experimental and Computational Studies of a Formed Thrombus Within a Backward-Facing Step Geometry
Authors: Taylor Joshua O. , Witmer Kory P. , Neuberger Thomas , Craven Brent A. , Meyer Richard S. , Deutsch Steven , Manning Keefe B.
Published: July 2013

Heart disease is one of the leading causes of death in the United States. This condition affects roughly 5.7 million Americans, with approximately 670,000 new cases and 300,000 deaths each year [1]. Heart failure, resulting from heart disease, is primarily treated with the implantation of a ventricular assist device (VAD) [2]. Along with VADs, arterial stents (primarily for treatment of atherosclerosis) and prosthetic heart valves (for defects in or other failures of the native heart valves) are other devices that are regularly used by clinicians to treat conditions within the circulatory system. While complications relating to cardiovascular devices have seen a decrease over the years, thrombosis and thromboembolization still remain obstacles. These phenomena are dependent upon the blood/material interface, surface topography, and fluid mechanics within the device [3].
Experimental Investigation of Blood Cells Flowing Through Microscale Geometries Using MicroPIV
Authors: Somashekar Vishwanath , Olsen Michael G. , Chandran K. B. , Udaykumar H. S.
Published: July 2013

The advances made in the field of cardiovascular prostheses have proved invaluable in saving human lives. However, implanting such a device may cause unwanted results like thrombosis, the formation of blood clots inside blood vessels. This formation of thrombi can affect the flow of blood, which if left untreated may result in strokes. As the blood moves through various arteries and veins, the platelets move toward the periphery and the red blood cells (RBC) are more concentrated near the center. This process is called margination and has been shown by Aarts et al.[1]. The platelets in essence are policing the endothelial layer, and with any change in the endothelial layer, say as a result of injury, the platelets get activated, which in turn starts a domino effect eventually resulting in the formation of a clot to stop the bleeding. These platelets can also get activated due to their presence in regions of high shear as is the case when the blood is flowing through narrow constrictions (for example, when a mechanical heart valve is about to close). This phenomenon is referred to as Shear Induced Platelet Activation (SIPA)[2]. The goal of this research is to study the effect of constricted geometries, high shear rates and erythrocyte-platelet interactions on platelet activation and aggregate formation, events that are critical in the initiation of thrombosis. In order to understand SIPA, one must first obtain a detailed flow in these constricted geometries. Numerous studies have been performed to obtain the flow fields of blood flowing through microchannels [3, 4]. However, the Reynolds numbers based on the characteristic length of the microchannel were in the O (1). It is worth noting that for such laminar flows confocal particle image velocimetry can be successfully applied. In this present study, the Reynolds numbers were in the O (100), rendering confocal mPIV impractical and making Micro Particle Image Velocimetry (mPIV) a clear choice.
Residual Elimination Algorithm Enhancements to Improve Foot Motion Tracking During Forward Dynamic Simulation of Gait
Authors: Jackson Jennifer N. , Hass Chris J. , Fregly Benjamin J.
Published: July 2013

During inverse dynamic simulations of human movement, inaccuracies and noise in experimental data result in residual forces and torques acting on the pelvis [1]. These quantities are physically unrealistic but are necessary to balance the equations of motion. To circumvent this problem, Remy and Thelen developed a residual elimination algorithm (REA) that employs forward dynamic simulation to produce dynamically consistent accelerations that best agree with experimental marker motion data and satisfy the whole-body equations of motion [2]. While the kinematics are dynamically consistent and the pelvis residuals effectively eliminated, the inability of REA to reproduce foot marker motion accurately is a hindrance for applications requiring precise positioning of the feet (e.g., foot-ground contact models).
Mechanotransductive Effects of Acoustic Radiation Force on Osteoblastic Primary Cilium, Cytoskeleton and Ca2+ Influx
Authors: Qin Y. X. , Zhang S. , Cheng J.
Published: July 2013

Mechanotransduction has demonstrated potentials for tissue adaptation in vivo and in vitro. It is well documented that ultrasound, as a mechanical signal, can produce a wide variety of biological effects in vitro and in vivo[1]. For example, pulsed ultrasound can be used to accelerate the rate of bone fracture healing noninvasively. Although a wide range of studies have been done, mechanism for this therapeutic effect on bone healing is currently unknown and still under active investigation. In our previous studies, we have developed methodology allowed in vitro manipulating osteoblastic cells using acoustic radiation force (ARF) generated by ultrasound without the effects of acoustic streaming and ultrasound-induced temperature rise. Furthermore, we also confirmed that ARF modulated intracellular Ca2+ transient in MC3T3-E1 osteoblast-like cells in a strain and frequency-dependent manner. A potential mechanism by which bone cells may sense ultrasound is through their structures such as primary cilia and cytoskeletons. The purpose of the current study was to evaluate the hypothesis that acoustic radiation force can regulate the activities of the primary cilium and the cytoskeleton of the cells, which act as the mechanotransductive signals to mediate Ca2+ flux, as a pathway in response to cyclic loading.
Effect of Statins and Wall Shear Stress on Endothelial Cells: Morphology and F-Actin Cytoskeleton Arrangement
Authors: Dick Melissa , Leask Richard L.
Published: July 2013

Wall shear stress and statin drugs have both been shown to influence endothelial cell function. We investigated the effect of statins on the morphology and F-actin cytoskeleton arrangement of endothelial cells with and without wall shear stress. Under static conditions, statins caused cells to become rounded and disorganized the F-actin cytoskeleton. Wall shear stress abrogated the morphological effects, but did not reverse the cytoskeleton disorganization.
In Vivo Mesenchymal Stem Cell Proliferation in Response to Dynamic Fluid Flow Stimulation
Authors: Hu M. , Yeh R. , Lien M. , Qin Y. X.
Published: July 2013

Osteoporosis is a debilitating disease characterized as decreased bone mass and structural deterioration of bone tissue. Osteoporotic bone tissue turns itself into altered structure, which leads to weaker bones that are more susceptible for fractures. While often happening in elderly, long-term bed-rest patients, e.g. spinal cord injury, and astronauts who participate in long-duration spaceflights, osteoporosis has been considered as a major public health thread and causes great medical cost impacts to the society. Mechanobiology and novel stimulation on regulating bone health have long been recognized. Loading induced bone fluid flow, as a critical mechanotransductive promoter, has been demonstrated to regulate cellular signaling, osteogenesis, and bone adaptation [4]. As one of the factors that mediate bone fluid flow, intromedullary pressure (ImP) creates a pressure gradient that further influence the magnitude of mechanotransductory signals [5]. As for a potential translational development of ImP, our group has recently introduced a novel, non-invasive dynamic hydraulic stimulation (DHS) on bone structural enhancement. Its promising effects on inhibition of disuse bone loss has been shown with 2 Hz loading through a 4-week hindlimb suspension rat study followed by microCT analysis. At the cellular level, mesenchymal stem cells (MSCs) are defined by their self-renewal ability and that to potentially differentiate into the cells that form tissues such as bone [1]. To further elucidate the cellular effects of DHS and its potential mechanism on bone quality enhancement, the objective of this study was to measure MSC quantification in response to the in vivo mechanical signals driven by DHS.
Bioheat Transfer With Ken Diller: Cellular and Tissue Transport Events Influencing Life and Death at Extreme Temperatures
Authors: Bischof John C.
Published: July 2013

This short review focuses on the contributions of Dr. Ken Diller to the field of biotransport with special focus on fundamental and applied work that has influenced other labs in the field including my own. The web of science and pubmed lists more than 260 contributions and I know of many more texts and monographs that he has contributed to this area. Specific contributions in cell biophysics, physicochemical property measurements and intravital tissue response will be highlighted as these areas have been of continuing interest to my lab.
Enhancing the Mechanical Properties of Articular Cartilage Through Enzyme-Mediated Collagen Crosslinking as Regulated by Low Oxygen Tension
Authors: Makris Eleftherios A. , Hu Jerry , Athanasiou Kyriacos A.
Published: July 2013

The poor ability of articular cartilage to repair following disease and injury makes the tissue a key target for reparative and regenerative medicine strategies. It has been shown that human knee joint resides under hypoxic conditions. Oxygen tension in healthy human synovium is between 7 and 11% and in articular cartilage may therefore be as low as 1–2.5% [1].
Locked Plating Versus Spiral Blade Retrograde Nailing in Supracondylar Femoral Fractures
Authors: Assari Soroush , Kaufman Alan , Darvish Kurosh , Rehman Saqib , Park Jung , Haw Jonathan , Safadi Fayez
Published: July 2013

Comminuted supracondylar femur fractures in the elderly are often treated with either retrograde femoral nailing or locked plating. Early weight-bearing is typically restricted after fixing supracondylar fractures, thereby impairing the patient’s mobilization. In general, surgeons are more comfortable allowing early weight-bearing of long bone fractures after nailing rather than plating, but early studies of retrograde nails for supracondylar fractures using standard distal locking showed poor fixation compared with locked plating.
Effect of Microbubble Incorporation on Local Solute Transport in Tissue Engineered Cartilage Constructs
Authors: Nover Adam B. , Durney Krista M. , Sirsi Shashank R. , Ateshian Gerard A. , Borden Mark A. , Lima Eric G. , Hung Clark T.
Published: July 2013

Previously, microbubbles have been studied for a number of different medical applications including ultrasound imaging contrast and drug delivery [1]. Microbubbles are comprised of a gas enclosed in a lipid shell. Recent research has shown that the inclusion of microbubbles in tissue engineered cartilage constructs has been shown to enhance mechanical and biochemical growth [2,3]. This modification of the tissue engineering scaffold by incorporation of gas-filled microbubbles has been shown to homogenize depth-dependent mechanical properties (Fig. 1) [3], which, in standard constructs, resembles a “U-shaped” strain profile with the stiffest regions on the edges surrounding a soft center [4]. In addition, these microbubble containing constructs are described by a higher partition coefficient than standard constructs, indicating increased solute transport [3]. These results led us to propose the hypothesis that the incorporation of microbubbles: a) increases nutrient transport upon microbubble dissolution, b) creates fluid-filled pores upon gas efflux and subsequent influx of culture media [3]. In this study, the aforementioned hypothesis is interrogated through analysis of local solute diffusivity.
A New Generation of Aortic Valve Prosthesis: Design, Manufacture and Hydrodynamic Assessment
Authors: Rahmani Benyamin , Ghanbari Hossein , Tzamtzis Spyridon , Burriesci Gaetano , Seifalian Alexander M.
Published: July 2013

Aortic valve replacement (AVR) is the second most common cardiac procedure after coronary artery bypass grafting, accounting for more than 200,000 transplantations annually worldwide [1]. Currently available mechanical and bioprosthetic heart valve replacements are not ideal as they are associated with relevant complications. The tri-leaflet polymeric heart valves (PHVs) have been widely investigated as possible alternative to these substitutes. However, the clinical application of PHVs has been limited by their suboptimal design and poor durability of available polymeric materials. This study presents a new concept of surgical aortic valve using a novel nanocomposite polymer.
Using Laser Direct-Write to Influence Embryoid Body Size on Uniform Substrates
Authors: Dias Andrew D. , Xie Yubing , Chrisey Douglas B. , Corr David T.
Published: July 2013

Embryonic stem cells (ESCs) are capable of self-renewal and have the potential to differentiate into any specialized cell type. Understanding and directing this differentiation potential is critical to producing cell sources for replacement therapies.
Material Properties Over-Estimated by Boundary Conditions in Biaxial Tension Can Be Corrected Using Finite Element Analysis
Authors: Jacobs Nathan T. , Cortes Daniel H. , Szczesny Spencer E. , Vresilovic Edward J. , Elliott Dawn M.
Published: July 2013

Tissue modeling requires an appropriate stress-strain constitutive relationship and a corresponding set of material properties. It is often the goal of experimental studies to determine these material properties. Uniaxial tension experiments are simple in experimental approach and the interpretation of results is straightforward, prompting its use in several studies. However, the freely contracting lateral edges observed in this loading modality do not mimic the in situ conditions of many fiber-reinforced soft tissues and the unconstrained fibers may also create errors.
Individual Trabecula Segmentation (ITS)-Based Plate-Rod Microstructural Finite Element Model Predicts Nonlinear Mechanical Properties of Human Trabecular Bone
Authors: Zhou Bin , Wang Ji , Sanyal Arnav , Fields Aaron J. , Wang Hong , Keaveny Tony M. , Ji Baohua , Liu X. Sherry , Guo X. Edward
Published: July 2013

Osteoporosis is a major bone disease characterized by low bone mass and microarchitecture deterioration, which affects primarily trabecular sites and leads to increased bone fragility. Trabecular bone mechanical properties have direct relations with bone fragility. High-resolution image based-finite element (FE) models with the detailed 3D microstructure have been widely utilized to assess the mechanical properties of trabecular bone. Voxel-based FE model can be generated by converting individual voxels of high resolution bone images into 8-node brick elements. A number of studies have compared mechanical properties predicted by the voxel model with those by mechanical testing and have demonstrated that the voxel FE model can accurately predict the Young’s modulus and yield strength of human trabecular bone (1). However, the computational expense of the voxel-based technique, in general, limits its clinical applications, especially the nonlinear analysis for whole bone strength. Thus, it is not applicable to apply this technique to clinical use with the respect of current computer capability. There is apparent need for an alternative modeling approach that is more computationally efficient while preserving the accuracy of the predictions.
A Microscale Collagen-Fibrin Interacting Network Model With Comparison to Experimental Results
Authors: Hyypio Jeffrey D. , Hadi Mohammad F. , Lai Victor K. , Barocas Victor H.
Published: July 2013

Many native and bioengineered soft tissues are composed of two or more types of biopolymer networks that mechanically define and support the material [1]. Modeling the response of multi-network soft tissues to mechanical loading can be difficult due to the heterogeneous nature of these materials and the large strains (>1) involved. As tissues deform, the different biopolymer networks interact with one another and determine the overall stress-strain outcome for the tissue. Capturing this interaction could help improve the accuracy of a computer model to simulate the microscale behavior of soft tissues under load. We have developed a two-network model to reflect interactions between collagen and fibrin biopolymer networks loaded in uniaxial extension. The model can help improve our understanding of native and engineered tissue mechanics.
Novel Strategy of the Determination of Mechanical Properties of Human Carotid Atherosclerotic Plaques
Authors: Boekhoven Renate W. , Lopata Richard G. P. , Rutten Marcel C. M. , van Sambeek Marc R. H. M. , van de Vosse Frans N.
Published: July 2013

Carotid endarterectomy is the procedure of choice in patients with a recent symptomatic stenosis of 70–99%. Currently, the selection of candidates eligible for carotid endarterectomy is based on stenosis size only. However, the treatment is only beneficial for patients with unstable plaques, which comprises only 16% of the patient population [1]. Hence, identifying plaque stability at an early stage would permit timely intervention, while substantially reducing overtreatment of stable plaques. The objective of this study is to distinguish between stable and unstable carotid atherosclerotic plaques by determining the plaque geometry, the plaque composition and the mechanical properties of plaque components in three dimensions (3D). Mechanical properties from healthy vessels were assessed earlier by van den Broek et al. [2] using ultrasound (US) imaging. They obtained a dynamic dataset in 2D + t. When blood pressure and vessel wall movement are known, mechanical properties can be extracted from these data using a constitutive model. However, atherosclerotic plaques are mostly asymmetric, and present calcifications will cause unfavorable acoustic shadowing when using US. In this study, the focus is on the assessment of plaque geometry, from in vitro echo-CT data, overcoming the aforementioned problems. In an experimental set-up (Fig. 1) both healthy and endarterectomy specimens were mounted, and exposed to physiological intraluminal pressures. Echo-CT was used to image the arterial segments in 3D+t. Automated geometry assessment of the arterial segments will be demonstrated and validated using microCT (μCT).
Origins, Growth, and Challenges in Bioheat Transfer
Authors: Diller Kenneth R.
Published: July 2013

Bioheat transfer is a field with origins in medical applications that date to thousands of years ago. It has long been appreciated that manipulation of temperature and energy could have significant therapeutic benefits. However, prior to the Second World War, nearly all work in this field was based on empirical studies, many of which were guided by brilliant insights of medical and life scientists. In more recent times, the principles and methods of heat transfer have been applied systematically, and often times in conjunction with highly synergistic collaborations with physicians and biologists, to achieve remarkable advances that have translated to important innovations in life science and medicine. The following discussion presents a limited range of comments concerning work accomplished by researchers associated with the ASME Bioengineering Division.
Continuous Positive Airway Pressure Impacts Cerebral Blood Flow and Cerebrospinal Fluid Motion: A Phase Contrast MRI Study
Authors: Anthikat-Albert Benedict D. , Yiallourou Theresia I. , Haba-Rubio Jose , Heinzer Raphael , Fonari Eleonora , Chevrey Nicolas , Santini Francesco , Stergiopulos Nikolaos , Martin Bryn A.
Published: July 2013

The physiological impacts of continuous positive airway pressure (CPAP) are not yet fully understood. In this study we developed an MRI protocol to assess the impact of CPAP on cerebral hemodynamics and cerebrospinal fluid (CSF) hydrodynamics in the upper cervical spine. MRI measurements were obtained on 14 healthy male subjects. The preliminary results indicated that the CSF pulsation decreased and venous outflow was altered with CPAP usage in comparison to the baseline values. Cerebral arterial flow was not impacted by CPAP usage. These findings support the hypothesis that the CSF system can act to dampen cerebral blood flow (CBF) pulsations.
Quantification of In Vivo Deformation of Healthy Lumbar Intervertebral Discs in Flexion
Authors: Nagel Tina M. , Barocas Victor H. , Nuckley David J.
Published: July 2013

Intervertebral disc (IVD) degeneration is hypothesized to be the precursor to non-specific low back pain, which is a widespread problem [1]. However, before disc degeneration can be understood, a better understanding of healthy discs must be gained. The disc is a short thick-walled cylinder with a gelatinous center, the nucleus pulposus, and a largely concentric, layered collagenous ring, the annulus fibrosus, Figure 1. The layers are referred to as lamella. The IVD is integral to the strength and flexibility of the spine. Whole disc mechanics have been widely studied, but degeneration occurs at the fiber level [2]. To understand the mechanics of degeneration, testing needs to be performed at a finer level where degenerative / injury effects occur. These effects such as tears occur in the annular lamella.
CFD Challenge: Solutions Using an In-House Spectral Element Solver, NEKTAR
Authors: Peiffer Véronique , Sherwin Spencer J.
Published: July 2013

The BioFlow Group at Imperial College London develops and uses computational and experimental techniques to study fluid dynamics in organisms with the aim of advancing healthcare applications. Within this framework our group applies Computational Fluid Dynamics (CFD) to gain a better understanding of the initiation of atherosclerotic disease. Our in-house spectral element solver has been applied to idealised [1–2] and anatomically realistic [3] geometries, including the rabbit aorta and its branches [4].
Magnetic Microtissue Stretching System to Study the Mechanobiology of 3D Fibroblast Populated Collagen Matrix
Authors: Zhao Ruogang , Boudou Thomas , Chen Christopher S. , Reich Daniel H.
Published: July 2013

The biological functions of encapsulated cells in a fibroblast populated collagen matrix (FPCM) are regulated by the mechanical properties of the surrounding matrix. Studies on the mechanobiology of encapsulated fibroblasts have adopted 3D collagen gels either tethered to a 2D substrate or free-floating as the main platforms. However, these approaches have shortcomings in that the cellular mechanical environment can only be estimated based either on the stiffness of the underlying 2D substrate or on that of the matrix before cell seeding. The real time cellular mechanical environment as the cells undergo physiological or pathological transitions is not accessible. Efforts have been made to culture FPCM into centimeter-scale tensile test specimens for mechanical property evaluation, but the bulky size of these specimens has been shown to be not optimal for biochemical intervention.
Hemodynamics Analysis of Several Stent Treatments of a Patient Specific Anterior Communicating Artery Aneurysm
Authors: Cito S. , Pallarés J. , Vernet A. , Geers A. J. , Cuesta I.
Published: July 2013

CFD predictions of the flow in cerebral aneurysms can help to analyze the mechanisms of growth and rupture and the degree of stress for a given flow conditions and to compare and to propose different stenting treatments. In this work we simulated the flow in a model of cerebral aneurysms of a real patient in six different conditions. One case corresponds to the flow conditions in the aneurysm without treatment and the other five cases correspond to different options or strategies of treatment with open cell stents (OCS) and closed cell stents (CCS) to hold the coil. The aneurysm is located in the anterior communicating artery (AComA). The effect of the treatment on the hemodynamics is quantified and reported.
Comparison of the Effects of Embolic Coils and a Low Porosity Stent on Cerebral Aneurysm Fluid Dynamics
Authors: Babiker Haithem , Roszelle Breigh , Gonzalez L. Fernando , Albuquerque Felipe , Collins Daniel , Elvikis Arius , Frakes David H.
Published: July 2013

Wide-neck cerebral aneurysms are difficult to treat with embolic coils. Concerns over the stability of coils within the aneurysmal sac often lead to incomplete filling of the sac, which may cause recurrence [1]. To overcome this challenge, clinicians may deploy a high porosity stent in a staged process to act as a supporting bridge for coils. The stent is commonly deployed 6–8 week prior to coil embolization, which lengthens the treatment period [2].
Improving Convection-Enhanced Delivery Through Photothermal Augmentation of Fluid Dispersal
Authors: Hood R. Lyle , Ecker Tobias , Rossmeisl John , Robertson John , Rylander Christopher G.
Published: July 2013

Malignant tumors of the central nervous system are the third leading cause of cancer-related deaths in adolescents and adults between the ages of 15 and 34; in children, brain tumors are the leading cause of cancer death. Convection-enhanced delivery (CED) has emerged as a promising method for the transport of high concentrations of chemotherapeutic macromolecules to brain tumors. CED is a minimally-invasive surgical procedure wherein a stereotactically-guided small-caliber catheter is inserted into the brain parenchyma, to a tumor site, for low flowrate infusion of chemotherapy [1]. This direct-delivery method bypasses obstacles to systemic chemotherapy caused by the selective impermeability of the blood-brain barrier. Although preliminary studies were favorable, CED recently failed Phase III FDA trials because clinical goals for tumor regression were not met [2]. This was primarily attributed to insufficient diffuse delivery of the drug throughout tumor masses and their surrounding margins.
Fluid Dynamic Analysis of Upper Airway of an Obstructive Sleep Apnea Patient Pre and Post Surgery
Authors: Biswas Dipankar , Loth Francis , Krauza Matthew L. , Pohle-Krauza Rachael J. , Dan Adrian G. , Zografakis John G.
Published: July 2013

The present study compares flow parameters (pressure drop, velocity, and shear stress) in the upper airway between pre- and post-bariatric surgery obstructive sleep apnea (OSA) patients. CT images of the upper airway were obtained prior to and six months post bariatric surgery in patients with a comorbid OSA. In-house software was used to reconstruct 3D geometric models of the upper airway, and fluid flow simulations were conducted using commercial computational fluid dynamics (CFD) software. Results show that pressure drop in the upper airway and velocity at the throat decrease post-surgery. Shear stress on the airway walls also decreased markedly. These trends were expected, however more patients must be analyzed and correlations must be drawn between these fluid dynamic parameters and the pathophysiology of the upper airway in OSA.
The Dispersive Characteristics of the Left Ventricle Filling Wave
Authors: Niebel Casandra , Ohara Takahiro
Published: July 2013

Left Ventricular Diastolic Dysfunction (LVDD) is impairment in the filling of the left ventricle (LV) and is presumed to affect all heart failure patients including over 50% of patients with a preserved ejection fraction. Despite drastic changes in LV filling dynamics between healthy and diseased ventricles, LVDD remains difficult to diagnose due to inherent compensatory mechanisms such as increased atrial pressure, heart rate, and LV contractility. The propagation velocity (VP) of the filling wave entering the LV is a common parameter used to assess diastolic filling. Current methods of measuring VP are not physically based and neglect much of the fluid motion entering the LV. In this work, we investigate the physics of the filling wave. We posit that it is governed by a dispersive behavior and we explore its clinical significance.
Mesenchymal Stem Cell Morphology in a Fibrous Microenvironment With Length Scales Matching the Native Meniscus
Authors: Silverstein Amy M. , Mauck Robert L.
Published: July 2013

The meniscus is a crescent shaped fibrocartilage in the knee comprised of a circumferentially aligned collagenous extracellular matrix (ECM) that functions to transmit load and enhance joint stability. The meniscus ECM varies as a function of region, where the inner meniscus is comprised of 70% collagen (60% type II vs. 40% type I), while the outer meniscus contains 80% collagen (99% type I) [1]. Similarly, cells within the inner meniscus are rounder and more ‘chondrocyte-like’, while those in the outer meniscus are elongated and ‘fibroblast-like’ [2]. Injury of the meniscus alters joint loading and hastens the onset of osteoarthritis. As meniscus healing is limited, there exists a need for functional meniscus replacements.
Assessing Rotary Stability of the Knee In Vitro Using Principal Component Analysis
Authors: Morrow Kaity , Fitzwater Fallon , Maletsky Lorin
Published: July 2013

Clinicians typically assess the functional status of the knee subjectively through manipulations to the knee’s passive connective tissue restraint under minimal load. The resulting translation or rotation at a given flexion angle is defined as the laxity of the knee which is used to suggest (in)stability. However, recent studies have shown that instability is not necessarily determined by knee laxity1. Dynamic stability at the knee is achieved through a complex interaction between soft tissue structures, neuromuscular control and articular geometry. It is during dynamic functional movements, such as walking, that patients suffer from buckling or giving way sometimes resulting in falls 2.
In Vitro Beating Heart Simulator for Minimally Invasive Heart Valve Therapy Research
Authors: Gogarty Michael B. , Dasi Lakshmi P.
Published: July 2013

Heart disease is the number one cause of death today with aortic valve stenosis (AVS) being a major contributor to the mortality rate1. Because of the invasive nature of Aortic Valve Resection (AVR), the typical treatment for AVS, between 30–60% of patients affected by severe aortic stenosis cannot be treated surgically, usually due to age and advanced comorbidities. Qualifying individuals must undergo extensive rehabilitation and of those who qualify 4.3% to 25% do not survive the first year following the procedure3,4.
Patient-Specific Finite Element Modeling of Mitral Valve Dynamic Deformation
Authors: Wang Qian , Sun Wei
Published: July 2013

Mitral valve is a two-leaflet valve that is located between the left atrium and the left ventricle of the heart. In order to successfully replace or repair mitral valve and develop effective prosthetic devices, it is critical to understand the in vivo mechanics of the normal mitral valve. Although research has been conducted to investigate animal mitral valve strains by in vivo experiments, it is still very challenging to obtain accurate in vivo stress and strain information of the human mitral valve.
CFD Challenge: Solutions Using the Commercial Finite Volume Solver, Fluent, and a pyFormex-Generated Full Hexahedral Mesh
Authors: Bols Joris , Degroote Joris , De Santis Gianluca , Trachet Bram , Segers Patrick , Vierendeels Jan
Published: July 2013

For many years, there has been a strong intra Ghent University collaboration between the IBiTech-bioMMeda research group, focusing on the application of fluid and structural mechanics for biomedical problems, and the department of Flow, Heat and Combustion Mechanics with a strong background in developing algorithms for numerical fluid mechanics and fluid-structure interaction (FSI) problems. This collaboration joins the strengths of both groups, with ongoing applications in FSI simulations of heart valves, aortic coarctation, aortic aneurysms etc., thereby integrating in vivo (human and (small) animal) hydraulic bench and numerical research.
Study of Multiple Systemic-to-Pulmonary Shunts in Single Ventricle Hearts
Authors: Moghadam Mahdi Esmaily , Hsia Tain-Yen , Murtuza Bari , Marsden Alison
Published: July 2013

For newborns diagnosed with single ventricle hearts and insufficient blood flow to the lungs, their lack of oxygen in the blood can be remedied with a modified Blalock-Taussig shunt (BTshunt) between the innominate and pulmonary artery. However, some surgeons prefer to have two systemic-to-pulmonary shunts, by either leaving the ductus arteriosus open or construct a second BT shunt, to provide additional pulmonary blood flow. There have been clinical reports of premature shunt occlusion when more than one shunt is employed, and a recent audit of shunt operations at a single institution has revealed increased mortality. There are speculation that these adverse outcomes can be due to flow competition between the two shunts, and/or having too much pulmonary blood flow. The flow dynamics and cardiopulmonary physiology in single ventricle circulations where pulmonary blood flow is supplied by more than one shunt has not been studied previously. In this study, we adopted CFD-based multi-domain simulations to compare a range of shunt configurations to examine the issue of flow competition and pulmonary overcirulation.
A Murine Model for Viable Right-Ventricular Myocardial Mechanical Behavior
Authors: Valdez-Jasso Daniela , Simon Marc A. , Sacks Michael S.
Published: July 2013

Although right-ventricular (RV) function is an important determinant of cardio-pulmonary performance in health and disease, RV myocardium biomechanical function has received little attention. In particular, no multiaxial data of the full-thickness RV have been reported for the passive or active myocardial states, for either normal or pathological conditions. Since an understanding of tissue-level biomechanical behavior is integral to connecting cellular behavior to organ-level performance, investigations into the RV myocardial stress-strain relationship are central in providing this link. For example, ventricular wall stress is considered to be a major driver of ventricular remodeling, and thus a better understanding of how wall stress and deformation are linked would provide unique insights into the mechanisms of RV function and ultimately failure in disease. Such knowledge would have direct applicability to improving methods to detect RV dysfunction, predicting response to disease-specific therapies and improving the timing of therapy if or when needed. Here, we present a murine model of viable RVFW to obtain stable and robust mechanical data suitable for structural modeling. Our study determines the of window for viability of the RVFW samples, verifies uniformity of the structure, and carries biomechanical testing to determine stability and consistency of the data.
Long Term Effect of P188 on Meniscus Preservation Following Blunt Trauma
Authors: Abraham Adam C. , Killian Megan L. , Haut Roger C. , Haut Donahue Tammy L.
Published: July 2013

Acute knee joint injury has been associated with the development and progression of secondary osteoarthritis (OA). Previous work implicates that acute damage to tissue matrix and cells of the meniscus and articular cartilage may play important roles in early-stage OA [1]. Additionally, it has been shown that articular cartilage matrix repair hinges on chondrocyte preservation [2]. Therefore, inhibition of cell death may halt tissue degeneration. Recently, the FDA-approved surfactant Poloxamer 188 (P-188) has been shown to decrease acute cell death by repair of its plasma membrane, as well as mediate p38 signaling and subsequent inflammatory and apoptotic signaling leading to a reduction in degeneration of impacted cartilage [3, 4]. Therefore, it was hypothesized that matrix glycosaminoglycans of the meniscus will be preserved in the long-term following traumatic impaction and subsequent treatment with P-188.