bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling Pressure Losses at Arterial Junctions With Application to Junctions of the Fetal Ductus Arteriosus
Authors: Mynard Jonathan P. , Davidson Malcolm R. , Penny Daniel J. , Smolich Joseph J.
Published: July 2013

In one-dimensional (1D) models of arterial networks, branch junctions are represented by flow and mechanical energy (or total pressure, i.e. p + 1/2ρu2) coupling conditions. The flow condition simply ensures conservation of mass, but the pressure condition is less trivial because pressure losses are known to occur in the vicinity of junctions, caused by regions of complex flow that depend on the vascular geometry and prevailing flow patterns. These losses are commonly ignored in 1D models under the assumption that area ratios and branching angles of arterial junctions are optimally designed. However, one setting where pressure losses are likely to be important is the junction of the ductus arteriosus (DA) with the aorta in the fetus, considering the high kinetic energy of blood in the DA [1], the acute angle between the aortic isthmus (Aols) and DA, and the redirection of DA blood flow towards the descending aorta (DAo, Figure 1). Previously, pressure losses have been approximated in 1D models by enforcing continuity of static (rather than total) pressure [2] or by using empirical loss coefficients obtained from experiments in 90 degree T-tubes [3]. In the current study, we implemented a loss formulation described by Bassett et al [4] for 1D gas dynamics simulations, which unlike previous methods, can be used to model junctions with any number of branches and any orientation of branch angles, and explicitly accounts for the influence of area and flow ratios on pressure losses. Results of the model are validated against high fidelity measurements in fetal lambs.
Simulations of Flow Through Bileaflet Mechanical Heart Valves With Asymmetric Leaflet Motion
Authors: Yun B. Min , Dasi Lakshmi P. , Aidun Cyrus K. , Yoganathan Ajit P.
Published: July 2013

Prosthetic heart valves have been used for over 50 years to replace diseased native valves but still lead to severe complications such as platelet aggregation and thromboembolic events. The most widely implanted design is the bileaflet mechanical heart valve (BMHV). Most modern BMHV designs have better flow hemodynamics and blood damage performance than earlier-generation counterparts. However, blood element trauma and thromboembolic events still remain as major complications of current BMHV designs. These problems have been linked to blood damage caused by non-physiological stresses. These stresses are caused by the complex flow fields that arise due to prosthetic heart valve design. In order to reduce the severity of these complications, the blood damage that occurs in flows through prosthetic heart valves must be well understood.
Realizations of Experimental Hydrocephalus Data Through the Analytical Model of Poroviscoelastic Brain Tissue
Authors: Mehrabian Amin , Abousleiman Younane
Published: July 2013

Despite recent advances in hydro-mechanical characterization of brain tissue [1], existing models remain inadequate due to complexities associated with the brain’s geometry and rheological properties [2] as well as limited knowledge on the mechanisms which control the CerebroSpinal Fluid (CSF) absorption or formation and their impact on the extracellular fluid content changes inside parenchyma [3].
Comparison of Methods to Predict Scapular Notching From Radiographs After Reverse Total Shoulder Arthroplasty
Authors: Henninger Heath B. , Harris Michael D. , Petersen Kristen R. , Burks Robert T. , Tashjian Robert Z.
Published: July 2013

Scapular notching is a complication of reverse total shoulder arthroplasty (rTSA) that results in bone loss on the lateral border of the scapula. Notching has been reported in up to 86% of patients at 5 year follow-up [1], and is graded 1–4 as a function of progressive bone loss [2]. Notching may arise from impingement, erosion, periprosthetic osteolysis, stress shielding or a combination of these [1]. Glenosphere position can mitigate notching by limiting hardware impingement [3–5], but may increase the forces required to abduct the arm [6]. Clinicians might optimize patient range of motion and function via implant placement if susceptibility to notching was known a-priori.
Fluid Structural Interaction of a Patient Specific Congenital Bicuspid Aortic Valve
Authors: Govindarajan V. , Udaykumar H. S. , Vigmostad S. , Levack M. M. , Gorman J. H. , Jackson B. M. , Gorman R. C. , Chandran K. B.
Published: July 2013

Congenital Bicuspid Aortic Valve (BAV) is a valvular anomaly where a patient is born with a valve with two leaflets instead of a normal tri-leaflet valve. It has also been reported that BAVs are prone to progressive calcification and also other complications such as ascending aortic dilatation, dissection and rupture [1]. The geometrical variations with the BAV may be a factor in altering the deformation and stresses on the leaflets resulting in calcification of the leaflets earlier than with normal tri-leaflet aortic valves. Altered flow patterns past BAV into the ascending aorta can also be anticipated. Analysis of flow dynamics during the opening phase, and the resultant fluid forces on the aortic root could improve our understanding of aortic aneurysms and dissections observed in patients with BAV [2]. In this study, the valvular deformation and the flow across a patient-specific BAV and root are simulated using the method of fluid structural interaction analysis. The patient-specific geometry is obtained employing 3D ultrasound images segmented as point cloud data and surfaces are constructed with commercial software GAMBIT using NURBS based connectivity. The opening phase of the valve is simulated under flow with physiological Reynolds number and with realistic material properties for the leaflets and the aortic root. Such an analysis on the dynamics of BAV with patient-specific geometry may be a useful tool in stratifying BAV patients that may be at risk in developing valvular and ascending aortic pathology.
The Effects of Shoe Architecture on Impact Forces During Gait: A Continuation Study
Authors: Powell Bethany , Post Ryan , Williams Bruce , Sevener Kathleen , Goehler Craig M.
Published: July 2013

In the current athletic footwear market, there exists a wide range of shoe architectures that offer a variety of options in terms of flexibility and support. The importance of footwear type has proved to be significant in the prevention of an assortment of injuries, including knee osteoarthritis [1, 2]. Footwear type has also been shown to affect the lower extremity kinematics as well as the regulation of leg stiffness for a subject during dynamic activities [3]. An important attribute used to categorize athletic footwear architecture is the inherent flexibility of the shoe. The natural flex observed in the sole of the shoe determines the level of flexibility; a more flexible shoe will flex closer to the mid-foot region while a shoe designed for stability will flex closer to the ball of the shoe.
Influence of Vertebra Stiffness in the Finite Element Analysis of the Intervertebral Disc
Authors: Díaz Carlos A. , García Jose J. , Puttlitz Christian M.
Published: July 2013

Spine finite element models are an essential tool to study the degeneration of the intervertebral disc (IVD). Due to the complex geometry of the vertebras, the anisotropy and heterogeneity of the tissues, and the contact and material nonlinearities [1], spine models demand high computational resources. Considering the relatively low stiffness of the IVD compared to that of the vertebrae, we hypothesized that finite element stress and stress distributions of the IVD do not change substantially if the vertebras are modeled as rigid bodies. This simplification in spine models may considerably reduce the solution time when the interest is the analysis of the IVD.
Comprehensive Identification of Tibiofemoral Joint Anatomy and Mechanical Response: Pathway to Multiscale Characterization
Authors: Chokhandre Snehal , Bennetts Craig , Halloran Jason , Colbrunn Robb , Bonner Tara , Jones Morgan H. , Erdemir Ahmet
Published: July 2013

The human knee joint is a complex multi-body structure, whose substructures greatly affect its mechanical response. An understanding of the multiscale mechanics of the joint is essential for the prevention and treatment of knee joint injuries and pathologies. Due to the limitations associated with in vivo experimentation, mechanical characterization of the knee joint has commonly relied on in vitro experimentation [1,2]. Predictive and descriptive studies of the mechanical function of the knee and its substructures have commonly employed computational modeling, in particular finite element (FE) analysis, which can be driven by experimental data. With the recent focus on the use of FE models of the knee joint for scientific and clinical purposes [3–5], data for model development, verification, and validation became increasingly important, especially when relying on FE analysis for decision making. An adequate representation of a joint not only depends on the specimen-specific anatomy but may also need to be informed by specimen-specific tissue properties for model development, and specimen-specific joint/tissue response to confirm model response.
Image Based Modeling of Biotransport Through Complex Moving Geometries
Authors: Dillard Seth I. , Udaykumar H. S. , Buchholz James H. J.
Published: July 2013

One of the major challenges to realistically modeling biotransport phenomena in computational fluid dynamics simulations lies with the difficulty of accurately describing the tortuous geometries and motions exhibited by organs and organ systems. Descriptions must be created in a manner that is amenable to definition within some operative computational domain, while at the same time capturing the essence of what is desired to be understood.
Using Vortex Coreline Detection to Characterize Aneurysmal Flow Activity
Authors: Byrne Greg , Mut Fernando , Cebral Juan R.
Published: July 2013

Assessing the risk of rupture of cerebral aneurysms is important for planning elective interventions. Since hemodynamics is thought to play a fundamental role in the mechanisms governing aneurysm progression and rupture, numerous investigations have tried to connect aneurysm hemodynamic conditions and rupture. In our previous work aneurysm flow patterns were qualitatively classified into simple / complex and stable / unstable categories by looking at the number of vortices within the aneurysm and their persistence during the cardiac cycle [1, 2]. The purpose of this work is to propose objective hemodynamic metrics that can capture these flow characteristics with the goal of relating them to aneurysm rupture.
Design of an Eye Tracking System Enabling Communication for TBI and SCI Patients
Authors: Evans Jeff , Neilson Peter , Rath Jordan , DeWitt John , Laz Peter , Mahoor Mohammad
Published: July 2013

Some patients who have suffered a traumatic brain injury (TBI) or a spinal cord injury (SCI) lose the ability to operate a computer via traditional methods (mouse and keyboard) or common alternative methods (voice control). The inability to move or speak makes it extremely difficult to communicate. Currently patients must rely on blinking yes or no to a series of questions that the caretaker asks in order to communicate their wants and needs. This system relies on the caretaker anticipating the patient’s needs in a timely manner which is not ideal. The purpose of this Senior Capstone Design project is to develop an eye tracking system to allow TBI and SCI patients to operate a computer exclusively using eye movements. Occupational Therapists at Craig Hospital, a recognized leader in TBI and SCI patient care, have provided the design team with access to a focus group of patients and insight into the needs and constraints of their patient population. With the ability to operate a computer, the patient will have the ability to more fully engage in communication by typing words on a screen for their caretakers to read and in a broader sense: e-mail and instant message family and friends as well as engage in social networking sites. The ability to control a computer allows for choices in entertainment from music to television to newspapers and magazines.
Nanotopography Directs Fate of Human Embryonic Stem Cells
Authors: Chen Weiqiang , Villa-Diaz Luis G. , Sun Yubing , Weng Shinuo , Kim Jin Koo , Krebsbach Paul H. , Fu Jianping
Published: July 2013

Human embryonic stem cells (hESCs) have remarkable potentials for breakthroughs in future cell-based therapeutics owing to their self-renewal capability and pluripotency [1–2]. However, their intrinsic mechanosensitivity to biophysical signals from the local cellular microenvironment is not well characterized [3–4]. In this work, we introduced a simple, yet precise, microfabrication strategy for accurate control and patterning of local nanoroughness on glass surfaces using photolithography and reactive ion etching (RIE). Our results demonstrated that nanoscale topological features could provide a potent regulatory signal over a diverse array of hESC behaviors, including their morphology, adhesion, proliferation and clonal expansion, and differentiation.
Bioengineered Fascicle-Like Skeletal Muscle Tissue Constructs
Authors: Neal Devin , Sakar Mahmut Selman , Asada H. Harry
Published: July 2013

Tissue engineered skeletal muscle constructs have and will continue to be valuable in treating, and testing various muscle injuries and diseases. However a significant drawback to numerous methods of producing 3D skeletal muscle constructs grown in vitro is that muscle cell density as a fraction of total volume or mass, is often significantly lower than muscle found in vivo. Therefore a method to increase muscle cell density within a construct is needed.
Double-Layer Representation of Model Microorganisms by a Boundary Element Method
Authors: Kyoya Kohei , Imai Yohsuke , Yamaguchi Takami , Ishikawa Takuji
Published: July 2013

Analysis of a suspension of microorganisms is important in environmental and biomedical engineering. Previous studies had problems of high computational load in simulating many-body interaction of non-spherical swimmers. In this study, we propose a boundary element method (BEM), based on the double-layer representation, for calculating interactions of two squirmers in Stokes flow regime. By comparing the trajectories of squirmers calculated by both single- and double-layer representations, we show the accuracy of the method. The developed method has potential to deal with many-body interactions of non-spherical microorganisms.
Residual Stresses in Solid Tumors: Implications to Tumor Growth and Drug Delivery
Authors: Stylianopoulos Triantafyllos , Martin John D. , Chauhan Vikash P. , Munn Lance L. , Jain Rakesh K.
Published: July 2013

The uncontrolled growth of cancer cells within a confined tissue space generates residual stresses in solid tumors [1,2]. These stresses contribute to tumor progression, pathological cellular behavior, and compression of lymphatic and blood vessels [3–5]. A major consequence of vascular compression is a decrease in pathways available for blood flow and delivery of diagnostic and therapeutic agents, resulting in insufficient and heterogeneous delivery of chemotherapy and nanomedicine. The reduced perfusion also causes hypoxia and acidity — two important barriers to treatment efficacy and promoters of malignancy. In this work, we developed a strategy to quantify growth-induced residual stresses in tumors and investigate whether stress levels affect tumor growth rate and delivery of therapeutic agents. We found that stress levels are elevated in solid tumors and are sufficient to cause the collapse of blood vessels. In addition high stress levels were correlated to slower tumor growth.
An EMG-Controlled Device Managing Transition From Passive to Active Exercise in the Acute Rehabilitation of the Ankle Joint
Authors: Viscuso Stefano , Pittaccio Simone
Published: July 2013

The capacity of flexing one’s ankle is an indispensible segment of gait re-learning, as imbalance, wrong compensatory use of other joints and risk of falling may depend on the so-called drop-foot. The rehabilitation of ankle dorsiflexion may be achieved through active exercising of the relevant musculature (especially tibialis anterior, TA). This can be troublesome for patients affected by weakness and flaccid paresis. Thus, as needs evolve during patient’s improvements, a therapeutic device should be able to guide and sustain gradual recovery by providing commensurate aid. This includes exploiting even initial attempts at voluntary motion and turn those into effective workout. This paper presents an active orthosis powered by two rotary actuators containing shape memory alloy (SMA) wire that promote passive ankle dorsiflexion. A computer routine that analyses the electromyographic (sEMG) signal from TA muscle is used to control the orthosis and trigger its activation when appropriate sEMG signal is recorded.
Simulating In-Vivo Tibiofemoral Loads With the Aid of a Customised LifeModeler Musculoskeletal System
Authors: Muller J. H.
Published: July 2013

The major drawback of musculoskeletal models, independent of the platform used, is uncertainty in the accuracy of the predictions, whether qualitative or quantitative, from the analysis on the computational model. Body motion, predicted muscle activation and the environment reaction forces can be validated in a motion laboratory. Unfortunately, this dataset provides little to no information on the joint loads and muscle tensions that are difficult to measure. The challenge to predict in-vivo knee loads, while the actual loads are available for comparison, provides the opportunity to evaluate the viability of the strategy to set up and analyze the computational musculoskeletal model.
Hemodynamics in Ascending and Abdominal Aorta Aneurysm Formation in the ApoE−/− Angiotensin II Mouse Model
Authors: Trachet Bram , Renard Marjolijn , Bols Joris , Staelens Steven , Loeys Bart , Segers Patrick
Published: July 2013

Aortic aneurysm is a pathological dilatation of the aorta that can be life-threatening when it ruptures. Aneurysms occur throughout the entire aorta but there is a predisposition for the ascending and the abdominal aorta, an observation that cannot be fully explained by the current knowledge of the disease pathophysiology. ApoE −/− mice infused with angiotensin II have recently been reported to develop not only abdominal [1], but also ascending aortic aneurysms [2]. These animals thus provide the perfect model to compare aneurysm progression in both aortic locations and to investigate whether disturbed hemodynamics play a role in the initial phase of aneurysm growth. In this study, both imaging and computational biomechanics techniques were used to elucidate the flow field at the location of the aneurysm prior to onset of the disease.
Eye Vessel Compliance as a Function of Intraocular and Arterial Pressure and Eye Compliance
Authors: Villamarin Adan , Roy Sylvain , Stergiopulos Nikolaos
Published: July 2013

Age-related macular degeneration (AMD) is a disease affecting the eye and is likely related to an increase in eye vascular rigidity. Developing methodologies to measure eye vessels compliance is of interest, as this may prove useful in diagnosing retinal diseases such as AMD. In vitro and in vivo experiments were conducted on rabbit eyes to validate the methodology proposed. Therefore the compliance of the eye vessels was estimated indirectly from the measurements of intraocular pressure (IOP), blood pressure and the compliance of the eyeball (OC) and compared to the pressure-volume curve. The method to estimate the vascular compliance of the eye was then tested under normal conditions and after administration of norepinephrine in vivo, which induced a vasoconstriction leading to reduction in vascular compliance. In vitro comparison of direct versus indirect estimates of compliance showed a difference that was not significant (0.075 vs. 0.077 μl/mmHg, p = 0.86). Results from the in vivo study indicated that norepinephrine significantly increased the arterial pulse pressure amplitude while compliance of vascular network of the eye decreased from 0.18 ± 0.12 μl/mmHg to 0.10 ± 0.08 μl/mmHg (p = 0.001). These results indicate that the compliance of the vascular network can be predicted using the IOP, the arterial pressure and the OC of the eyeball.
The Importance of Biarticular Torque Generators in Torque-Driven Simulation Models
Authors: King Mark , Lewis Martin
Published: July 2013

Forward-dynamics computer simulation models of human movement are typically driven by individual muscle models, or torque generators. In muscle-driven models, muscle parameters are typically determined from experimental data in the literature. While in torque-driven models, subject-specific torque parameters can be determined from torque measurements collected on an isovelocity dynamometer. Such a method avoids some of the errors encountered with individual muscle models by determining strength parameters directly from torque measurements. The disadvantage of existing subject-specific torque generator models over individual muscle models has been that the torque exerted at a joint has been represented by a function of the kinematics of the primary joint. As such torque generator models may not accurately represent the torques exerted by biarticular muscles where the kinematics of a primary and secondary joint may be important.
Stress-Fiber Remodeling in 3D: ‘Contact Guidance vs Stretch Avoidance’
Authors: Foolen Jasper , Deshpande Vikram , Baaijens Frank
Published: July 2013

When engineering fibrous tissues in vitro, appropriate matrix anisotropy is considered important for long term functionality and durability in vivo. However, it is not fully understood how to guide, maintain and control matrix anisotropy. Experiments suggest that collagen anisotropy is affected by actin-mediated cell traction and associated cellular orientation [1]. Although cellular orientation in 2D can be manipulated via imposed uniaxial cyclic stretch [2], 3D data are lacking. We questioned how uniaxial cyclic stretch influences actin and collagen orientation in 3D constructs.
Effects of Head Orientation on the Intracranial Pressure of Rats Exposed to Shock Waves
Authors: Dal Cengio Leonardi Alessandra , Keane Nickolas , Bir Cynthia , VandeVord Pamela
Published: July 2013

With the increasing number of military personnel returning from conflicts with neurological manifestations of traumatic brain injury (TBI), there has been a great focus on the effects resulting from blast exposure (Okie 2005; Hicks et al. 2010). Recently, experimental studies have been reported which investigated the biomechanical response of the rat head exposed to a shock wave. The results indicated that the imparted shock wave may induce multiple response modes of the skull, including global flexure, which may have a significant contribution to the mechanism of injury (Bolander et al. 2011; Dal Cengio Leonardi et al. 2011). However, the question of whether head orientation could play a role in the level of energy imparted on the brain is still of concern. This study quantitatively measured the effect of head orientation on intracranial pressure (ICP) of rats exposed to a shock wave. Furthermore, the study examined how skull maturity affects ICP response at various orientations. It was hypothesized firstly that skull flexural modes dominate the ICP response, hence varying head orientation would be expected to alter this imparted stress waveform. The head orientation affects not only the shape and size of the “presented area” exposed to the incident wave, but the degree and nature of the response of the individual skull plate elements due to the variance of skull physiology. As such, this has a significant influence on the stress that the shock wave imparts on the brain due to changes in skull dynamics.
Hyperelastic Model of Collagen Fiber Orientation in the Fetal Growth Restricted Carotid Artery
Authors: Dodson Reuben Blair , Rozance Paul J. , Reina-Romo Esther , Ferguson Virginia L. , Hunter Kendall S.
Published: July 2013

Intrauterine growth restriction (IUGR) is a common complication that is associated with hypertension in the developing fetal sheep [1]. Hypertension reduces arterial compliance, introducing health problems such as increased overall hydraulic impedance and cardiac workload [2, 3]. Both organ resistance and vascular compliance are critical factors in the progression of cardiovascular diseases (CVD) [3–5] with IUGR infants showing high incidence of CVD as adults [6]. Changes in circulation and the associated intrinsic hemodynamic forces during critical gestation influence the formation of the vessels, creating stiffer, less compliant arteries. While IUGR vessels are significantly stiffer than controls, the structural remodeling in response to hypertension is not biochemically quantitative and is believed to be due to fiber alignment [7].
A Coupled Overlapping Domain Method for the Computation of Transitional Flow Through Artificial Heart Valves
Authors: Verkaik A. C. , Bogaerds A. C. B. , Storti F. , van de Vosse F. N.
Published: July 2013

When blood is pumped through the aortic valves, it has a time dependent flow with a relatively high speed, resulting in Reynolds numbers between 1500 and 3000. Hence, flow is in the transitional regime between laminar and turbulent flow. Transitional flow contains small scale fluctuations, see Figure 1, and may result in local high deformation rates.
A Non-Invasive Study Using MR-Derived Wave Intensity Analysis to Highlight the Effect of Surgical Arch Reconstruction on Ventriculo-Arterial Coupling in Patients With Hypoplastic Left Heart Syndrome
Authors: Biglino Giovanni , Ntsinjana Hopewell , Steeden Jennifer A. , Baker Catriona , Schievano Silvia , Khambadkone Sachin , Hsia Tain-Yen , Taylor Andrew M. , Giardini Alessandro
Published: July 2013

Hypoplastic left heart syndrome (HLHS) is a congenital heart disease whose staged surgical palliation aims to progressively separate the systemic and pulmonary circulations. The first stage or Norwood procedure [1] involves surgical reconstruction of the aortic arch, usually with pulmonary homograft patch [2]. Recent evidence suggested that, because of this extensive reconstruction, HLHS patients have abnormal elastic properties [3] and reduced distensibility [4,5] of the ascending aorta. However, the impact of the reconstructed aorta and its abnormal elastic properties on ventricular mechanics, i.e. ventriculo-arterial coupling mismatch, has not been assessed. In the light of this mismatch, a change in impedance on the arterial side will reflect on the ventricular side and quantification of this phenomenon may provide mechano-energetic information for further understanding a complex physiology such as palliated HLHS with aortic arch surgical reconstruction. In this study we suggest that wave intensity analysis (WIA) is a valid method for studying ventriculo-arterial coupling, as WIA is a hemodynamic index able to assess the performance of the heart and its interaction with arterial system. Previously, distensibility quantification necessitated either of invasive [5] or cuff [4] arterial pressure monitoring, or multiple magnetic resonance (MR) images acquisitions for transit time wave speed calculation [6]. Instead, here we propose a non-invasive and semi-automated method based only on MR images analysis, with single slice analysis for estimate of local distensibility. The method, including WIA, was developed as a plug-in for DICOM viewer OsiriX, and applied to two cohorts of single ventricle patients.
Comparing Pre-Operative Predictions and Post-Operative Fontan Hemodynamic Outcomes: Implications for Computer-Based Surgery Planning
Authors: Haggerty Christopher M. , de Zélicourt Diane A. , Restrepo Maria , Rossignac Jarek , Spray Thomas L. , Kanter Kirk R. , Fogel Mark A. , Yoganathan Ajit P.
Published: July 2013

Computer-based surgical planning of cardiothoracic surgery is a new paradigm that uses engineering tools to model and evaluate patient-specific surgical options and thus provide insights on the hemodynamic implications of a given design. In this study, the total cavopulmonary palliation of single ventricle defects serves as a test-bed for such techniques by comparing the output of pre-operative modeling to hemodynamic outcomes derived from post-operative imaging. The resulting accuracy of the models demonstrates that, despite the inherent challenges, surgical planning is a viable reality in single ventricle cardiothoracic surgery that can potentially deliver significant clinical impact.
Investigation of Mechanoresponsive Behaviors of Human Embryonic Stem Cells Using Microfabricated Elastomeric Post Arrays
Authors: Sun Yubing , Villa-Diaz Luis G. , Lam Raymond H. W. , Chen Weiqiang , Krebsbach Paul H. , Fu Jianping
Published: July 2013

Much effort has been recently directed to investigate how soluble factors in the local cellular microenvironment of embryonic stem cells (ESCs) regulate their fate decisions [1]; however, effects of mechanical signals in the local cellular microenvironment on the fates of ESCs are still not yet well understood. Early experimental evidence established in recent years has shown that mechanical signals and external forces experienced through interactions with extracellular matrix (ECM) mechanics can play critical roles in regulating survival, proliferation and differentiation of ESCs. However, there is still limited knowledge of how mechanical signals in the local cellular microenvironment regulate the fate decisions of human ESCs (hESCs), and advancing such knowledge will be critical for both fundamental understanding and clinical applications of hESCs. This work was thus set to explicitly investigate the mechanosensitive properties of hESCs.
Stem Cell Fate Within 3D Hydrogels is Mediated by Network Structure-Dependent Traction Generation
Authors: Khetan Sudhir , Legant Wesley R. , Chen Christopher S. , Burdick Jason A.
Published: July 2013

A continuing goal in biomaterials research is to understand how cell adhesion to the surrounding materials and/or matrix regulates cell behavior in 3D. Advanced understanding of these processes may aid the development of synthetic biomaterials for tissue engineering applications, as well as to help understand basic cellular processes. The majority of past work, however, has focused on cell behavior atop 2D substrates that poorly recapitulate the 3D in vivo microenvironment [1]. Recent reports have suggested that within 3D hydrogels, encapsulated human mesenchymal stem cell (hMSC) fate is not determined by cell morphology or matrix mechanics alone [2], but by gel-structure dependent traction force generation [3]. As hMSCs represent a promising cell source for regenerative applications [4], it is critical to better develop our understanding of the link between cell fate and microenvironmental physical and biochemical cues in 3D, with a focus on the range of materials used in regenerative medicine. In the current work, hMSCs were encapsulated within degradable and non-degradable hyaluronic acid (HA) hydrogels of similar elastic moduli to assess the influence of hydrogel remodeling and cellular traction generation on differentiation lineage specification.
In Vivo Evaluation of Wrist Cartilage Integrity Using T2 Relaxation Time After Scapholunate Ligament Injury and Surgical Repair
Authors: Chappell Isaac D. , Lee Phil , McIff Terence E. , Toby E. Bruce , Fischer Kenneth J.
Published: July 2013

Osteoarthritis (OA) is a serious and frequently occuring outcome of untreated scapholunate dissocation, the most common form of carpal instability in the wrist [1]. As cartilage degenerates, the water content of surrounding tissue becomes less bound. Magnetic resonance imaging (MRI) T2 relaxation time is longer when water content is less bound [2]. MRI offers the advantageous combination of detailed images of soft tissues such as cartilage with the ability to evaluate free water content. Contrasting the various T2 relaxation times found in the cartilage of healthy wrist surfaces with those of injured wrists is thereby proposed as a method of evaluating cartilage degeneration. We hypothesized that T2 values obtained would be longer for the cartilage of the injured wrists. Though surgical treatment may relieve pain and restore some function to the wrist, it is hypothesized that T2 relaxation time will remain increased after surgery as cartilage regeneration is a very slow process, if it happens at all. The goal of this research is to provide a method to evaluate the biochemical and infer the biomechanical integrity of cartilage for various cartilage surfaces in a wrist after injury.
Numerical Simulation of Cell Motility at Low Reynolds Number
Authors: Scherr Thomas F. , Wu Chunliang , Monroe W. Todd , Nandakumar Krishnaswamy
Published: July 2013

As length scales decrease to microns, the mechanism for swimming becomes unfortunately counter-intuitive. In the macro-world, where human intuition has developed, we swim by accelerating the liquid around us. For microorganisms, which swim at Reynolds numbers much less than unity, Stokes law does not permit accelerations. As such, the fluid movement is governed entirely by the local boundaries of the microorganism and the fluid viscosity dampens velocity fluctuations rapidly as distance away from the swimmer increases. A well known byproduct of this, Purcell’s “Scallop Theorem”, forbids reciprocal motions to generate net forward movement [1]. To overcome this, flagella propagate waves down their length and cilia have asymmetric beats. This type of motility has been described as zero-thrust swimming since the net force on the organism-fluid system must be zero [2].
Different Finite Element Strategies to Satisfy Clinical and Engineering Requirements in Modeling a Novel Percutaneous Device
Authors: Capelli Claudio , Biglino Giovanni , Petrini Lorenza , Migliavacca Francesco , Bonhoeffer Philipp , Taylor Andrew M. , Schievano Silvia
Published: July 2013

By taking into account patient-specific properties, finite element (FE) models can aid in the optimization of the devices’ mechanical performances, accelerating the time of development and reducing testing costs. Patient-specific cardiovascular modeling can also drive the development of novel devices [1], by means of anatomical elements that are more representative than animal surrogates [2], and integrating standard in vitro tests with patient-specific loading conditions [3]. Transcatheter heart valve implantation can particularly benefit from a modeling approach. In the field of treatment of valve dysfunctions, percutaneous techniques are relatively new or under development, and modeling tools can contribute to improve these procedures (e.g. design modifications or different routes for device insertion) and increase patient safety in the early introduction of new devices into clinical practice. For a feasible clinical application, computational methods need to be fully validated against physical data, to take into account patient-specific properties, and to provide results in a short time. Instead, from an engineering perspective, models can cost-effectively aid the design phase by improving preclinical testing with more realistic loading conditions for accurate simulation of mechanical behaviour and prediction of durability. This study aims to identify optimal modeling strategies to respond to both clinical and engineering requirements. As a case study, simulations were conducted on a new percutaneous pulmonary valve implantation (PPVI) device [4] tested within a patient-specific right ventricular outflow tract model.
Tunable Hyaluronic Acid Hydrogels to Alter and Understand Left Ventricular Remodeling
Authors: Tous Elena , Ifkovits Jamie L. , Dorsey Shauna M. , Szczesny Spencer E. , Koomalsingh Kevin J. , Shuto Takashi , Soeda Toru , Gorman Joseph H. , Elliott Dawn M. , Gorman Robert C. , Burdick Jason A.
Published: July 2013

Heart disease causes about 15% of deaths in the United States; about two thirds of these cases are due to coronary artery disease [1]. Post myocardial infarction (MI), left ventricular (LV) remodeling ensues and leads to geometric changes that result in dilation and thinning of the myocardial wall. This increases stress in the infarct and healthy tissue and ultimately results in heart failure. Injectable bulking agents have recently emerged as a promising therapy to address these maladaptive changes. As suggested by the Law of Laplace, thickening of the myocardium should decrease stress on the heart and potentially attenuate the negative effects of LV remodeling [2].
Fluid-Structure Interaction Simulation of the Edge-to-Edge Repair of the Mitral Valve in Functional and Degenerative States
Authors: Lau K. D. , Burriesci G. , Díaz-Zuccarini V.
Published: July 2013

The most common dysfunction of the mitral valve (MV) is mitral valve regurgitation (MVR) which accounts for approximately 70% of native MV dysfunction [1]. During closure, abnormal amounts of retrograde flow enter the left atrium altering ventricular haemodynamics, an issue which can lead to cardiac related pathologies. MVR is caused by a variety of different mechanisms which are either degenerative (myxomatous degeneration) or functional (annular dilation or papillary muscle displacement) [2]. Correction of MVR is performed by repairing existing valve anatomy or replacement with a prosthetic substitute, however repair is preferred as mortality rates are reduced (2.0% against 6.1% for replacement) along with other valve related complications [3]. A common and popular method of repair is the edge-to-edge repair (ETER), which aims to correct MVR by surgically connecting the regurgitant region through reducing the inter-leaflet distance. Although MV function is improved in systole, induced stresses are significantly increased in diastole where the MV is typically in a low state of stress. In order to assess the effect of this technique in diastole, where the dynamics of both the MV and ventricular filling are disrupted it is required to use fluid-structure interaction (FSI) modelling techniques. Here a FSI model of the of the MV has been described, using this model the resulting induced stresses from the ETER in both functional and degenerative states of the MV have been simulated and assessed using the explicit finite element code LS-DYNA.
Prediction of TKR Function Using Specimen Specific Robotically Calibrated Knee Models
Authors: Siggelkow Eik , Sauerberg Iris , Benazzo Francesco , Bandi Marc
Published: July 2013

Passive knee kinematics and kinetics following total knee replacement (TKR) are dependent on the topology of the component joint surfaces as well as the properties of the passive soft tissue structures (ligaments and capsule). Recently, explicit computer models have been used for the prediction of knee joint kinematics based on experimental investigations [1]. However, most of these models replicate experimental knee simulators [2], which simulate soft tissue structures using springs or elastomeric structures. New generations of experimental setups deploy industrial robots for measuring kinematics and kinetics in six degrees of freedom as well as the contribution of soft tissue structures. Based on these experiments, accurate soft tissue properties are available for use in computer models to aid more realistic predictions of kinematics. Final evidence of the quality of the kinematic predictions from these computer models can be provided by direct validation of the models against experimental data. Therefore, the objective of this study was to use in vitro robotic test data to develop, verify, and validate specimen specific virtual models suitable for predicting laxity and kinematics of the reconstructed knee.
OCT Detects Collagen Fiber Alignment in Human Cadaveric Lumbar Facet Capsular Ligament During Mechanical Loading
Authors: Claeson Amy A. , Yeh Yi-Jou , Akkin Taner , Winkelstein Beth A. , Nuckley David J. , Barocas Victor H.
Published: July 2013

The lumbar facet capsular ligament (FCL) is a highly collagenous structure that functions to constrain lumbar spinal motion. Two FCLs are found at each level of the spine, flanking the spinous process. The ligament spans from the inferior articular process (IAP) of the superior vertebra to the superior articular process (SAP) of the inferior vertebra forming the posterior portion of the facet capsule (Figure 1). Along with the anteriorly located ligamentum flavum, the FCL contains the synovial fluid that lubricates the facet joint. The facet capsule is highly innervated [1] and may be involved in low back pain or proprioception. Thus, changes in collagen fiber alignment from mechanical loading may activate mechanoreceptors leading to proprioception or nociceptors leading to pain.
A Nondestructive Fiber-Based Imaging System to Assess Tissue-Engineered Vascular Grafts
Authors: Whited Bryce M. , Hofmann Matthias C. , Lu Peng , Rylander Christopher G. , Soker Shay , Wang Ge , Xu Yong , Rylander Marissa Nichole
Published: July 2013

The clinical need for alternatives to autologous vein and artery grafts for small-diameter vascular reconstruction have led researches to a tissue-engineering approach. Bioengineered vascular grafts provide a mechanically robust conduit for blood flow while implanted autologous cells remodel the construct to form a fully functional vessel [1]. A typical tissue-engineering approach involves fabricating a vascular scaffold from natural or synthetic materials, seeding the lumen of a vessel with endothelial cells (EC) and the vessel wall with smooth muscle cells or fibroblasts to mimic the functional properties of a native vessel. The cell-seeded vascular scaffold is then preconditioned in vitro using a pulsatile bioreactor to mimic in vivo conditions to enhance vessel maturation before implantation (Fig. 1).
Design of a Multi-Function Walker/Cane for Enhanced Assistive Function
Authors: Burns Thomas , Finn Thomas , Garrant Emily , Hemsing Frank , Lewicki Kathleen , Pane Ryan , Kuxhaus Laurel , Fite Kevin
Published: July 2013

In the United States over 4 million people use canes and over 1.5 million people use walkers [1]. Of those walker users 77% are 65 years or older. Over 47,000 emergency room visits each year are a result of falls involving walkers and canes. Injuries from walker accidents are seven times more prevalent than cane accidents [2,3]. Many of these injuries result from the unavailability of a suitable assistive device for a patient’s current environment. For example, a walker may not allow patients to maneuver around a living room. Patients often resort to the dangerous practice of furniture walking (using surrounding objects to aid in balance) when environmental factors such as insufficient space preclude the use of a walker-type assistive device. Narrow passageways are particularly challenging to navigate for those individuals using a walker.
Quantitative Crash Injury Risk Predictions by Body Region: Is Risk Sensitive to New Vehicle Safety Features?
Authors: Kusano Kristofer D. , Gabler Hampton C.
Published: July 2013

Retrospective examinations of real-world injury data is often used to evaluate injury risk for exposure to hazards, e.g. car crashes. In studying injury resulting from passenger vehicle crashes, there are several sources of real-world data that contain information about the crashes (e.g. vehicle damage, impact speeds) as well as occupant injury outcome. These real-world crash databases are used, for example, to study risk of traumatic brain injury, countermeasure opportunities for far-side occupants in side impact, and spleen injury for different restraint types [1–3].
CFD Challenge: Solutions Using the Commercial Finite Volume Solver, Fluent
Authors: Kalsi Hardeep S. , Long Quan
Published: July 2013

Mr. Kalsi is currently reading 3rd year Aerospace Engineering at Brunei University, London, this CFD challenge was undertaken as a final year dissertation project under the supervision of Dr. Quan Long at the Brunel Institute for Bioengineering (BIB). Simulations were carried out using the finite volume solver package ANSYS Fluent through the educational license available at Brunel University.
Finite Element Analysis Demonstrates Splinting in the Porcine Mandibular Condyle Causes Changes in Bone Volume Fraction and Stiffness Anisotropy
Authors: Zaylor William , Sindelar Betty , Cotton John R.
Published: July 2013

Currently about 10 million Americans report signs and symptoms of TMJ dysfunction. One form of treatment for TMJ dysfunction is dental splints which reorient the jaw during mastication. This presumably changes the direction, magnitude and location of mechanical loads on the mandibular condyle of the temporomandibular joint (TMJ). The precise nature of load changes and their effect on the underlying condylar trabecular bone have not been reported.
Influence of False Vocal Folds Gap on the Glottal Jet Flow
Authors: Farahani Mehrdad H. , Mousel John , Alipour Fariborz , Vigmostad Sarah
Published: July 2013

Despite the large incidence of speech problems in the modern life, our knowledge about the effect of supraglottic laryngeal structures on human phonation is lacking. These structures are mainly consisting of aryepiglottic folds, epiglottis, arytenoids, and false folds (ventricular folds). Shape and size of these structures depends on several factors including race, gender, age, and laryngeal abnormalities.
The Ability of a Residual Reduction Algorithm to Account for Handrail Use During Gait Analysis
Authors: Knarr Brian A. , Higginson Jill S.
Published: July 2013

Subjects with significant gait impairments may require the use of external support to safely walk during motion capture collections [1]. Development of musculoskeletal simulations in the OpenSim environment, however, is complicated by external forces beyond ground reaction forces. Measured ground reaction forces and moments may be dynamically inconsistent with model kinematics due to modeling assumptions and experimental error [2]. With the addition of external forces applied using handrails, a harness support system or other loads, prediction of muscle forces and contribution to movement may be inaccurate, especially if all external forces are not able to be measured and included in the model.
Pseudomonas Aeruginosa Cells Alter Environment to Efficiently Colonize Surfaces Using Fluid Dynamics
Authors: Du Huijing , Xu Zhiliang , Anyan Morgen , Kim Oleg , Leevy W. Matthew , Shrout Joshua D. , Alber Mark
Published: July 2013

Many bacteria use motility described as swarming to colonize surfaces and form biofilm. Swarming motility has been shown important to biofilm formation [1], where cells act not as individuals but as coordinated groups to move across surfaces, often within a thin-liquid film [2]. Production of a surfactant during swarm improves bacterial motility by lowering surface tension of the liquid film [2]. The mechanism of cell motion during swarming are currently best described for Escherichia coli and Paenibacillus spp., which spread as monolayers of motile cells [3,4]. For Pseudomonas aeruginosa (P. aeruginosa), which does not swarm as a monolayer, the cell and fluid patterns are difficult to discern using current experimental methods. It is not yet known if swarming P. aeruginosa cells behave solely as swimming cells [5] or if twitching, sliding, or walking motility [6] are also important to swarming.