bluuebunny/crossref_metadata_2025 huggingface dataset:
The Nano-Physiology of Mineralized Tissues
Authors: Alexander Benjamin E. , Daulton Tyrone L. , Genin Guy M. , Pasteris Jill D. , Wopenka Brigitte , Thomopoulos Stavros
Published: July 2013

The nanostructures of bone and partially mineralized tissues determine the toughness (Buehler, 2007) and stiffness (Genin et al., submitted) of these tissues. In the attachment of tendon to bone, tissue compositions and possibly nanostructures vary spatially in concert with microscopic and macroscopic variations in tissue shape, presumably to improve load transfer from tendon to bone (Thomopoulos et al., 2006). We hypothesize that undesirable stress concentrations resulting from a failure to recreate the details of this spatial grading following surgical healing may underlie the low levels of success of surgeries to repair tendon-to-bone attachments such as the rotator cuff (Galatz, 2001). Therefore, a detailed understanding of the gradients in composition and structure of the natural tendon-to-bone attachment as well as an understanding of the mechanisms of their development are critical for our efforts to synthesize surgical grafts that augment tendon-to-bone healing. As a first step towards understanding the nanometer-scale details of the tendon-to-bone attachment, we studied the nanostructure of bone using steric modeling and scanning transmission electron microscopy (STEM).
Simulating the Effects of Angiogenesis on Tumorigenesis Through Computational Modeling
Authors: Cooper Michele D. , Tanaka Martin L. , Puri Ishwar K.
Published: July 2013

Angiogenesis is a physiological process in which new blood vessels are formed from pre-existing vessels. It is one of the hallmarks of cancer and contributes greatly to the sustained growth of a tumor. Without the nutrient influx provided by newly formed capillaries, tumors growth is curtailed due to a lack of oxygen diffusion into the central region of the tumor body. Angiogenesis substantially increases the risk of developing cancer and as a result, anti-angiogenic therapies are being developed for cancer treatment.
Effects of CSF Properties on Brain Response Under Impact Loading
Authors: Chafi M. S. , Dirisala V. , Karami G. , Ziejewski M.
Published: July 2013

In the central nervous system, the subarachnoid space is the interval between the arachnoid membrane and the pia mater. It is filled with a clear, watery liquid called cerebrospinal fluid (CSF). The CSF buffers the brain against mechanical shocks and creates buoyancy to protect it from the forces of gravity. The relative motion of the brain due to a simultaneous loading is caused because the skull and brain have different densities and the CSF surrounds the brain. The impact experiments are usually carried out on cadavers with no CSF included because of the autolysis. Even in the cadaveric head impact experiments by Hardy et al. [1], where the specimens are repressurized using artificial CSF, this is not known how far this can replicate the real functionality of CSF. With such motivation, a special interest lies on how to model this feature in a finite element (FE) modeling of the human head because it is questionable if one uses in vivo CSF properties (i.e. bulk modulus of 2.19 GPa) to validate a FE human head against cadaveric experimental data.
Application of Diffusion Tensor Imaging in Modeling Diffuse Axonal Injury
Authors: Wright Rika M. , Ramesh K. T.
Published: July 2013

Traumatic brain injury (TBI) is a debilitating injury that has received a lot of attention within the past few years partly as a result of the increased number of TBI incidents arising from military conflicts. Of the incidences of TBI, diffuse axonal injury (DAI) accounts for the second largest percentage of deaths [1]. DAI is caused by sudden inertial loads to the head, and it is characterized by damage to neural cells [2]. These inertial loads at the macroscale result in functional and structural damage at the cellular level. To understand the coupling between the mechanical forces and the functional damage of neurons, an analytical model that accurately represents the mechanics of brain deformation under inertial loads must be developed. It has been shown in clinical and experimental studies that the deep white matter of the brain is highly susceptible to injury [2]. Unlike the gray matter of the brain, the white matter structures contain an organized arrangement of neural axons and therefore can be considered anisotropic (Figure 1). To account for the anisotropic nature of the white matter in finite element simulations, the orientation of the neural axons must be incorporated into a material model for brain tissue. In this study, the use of diffusion tensor imaging (DTI) as a tool to provide fiber orientation information to continuum models is investigated. By incorporating fiber orientation data into a material model for white matter, the strains experienced by neural axons in the white matter tracts of the brain are computed, and this strain is related to cellular stretch thresholds of diffuse axonal injury.
Mechanically Enhanced Precipitation of Phase-Inversion Sprayed Polyurethane Scaffold May Be Used to Match Tissue Specific Anisotropy
Authors: Kennedy James P. , Hitchcock Robert W.
Published: July 2013

Methods of creating a scaffold for tissue engineering that allow for modification of properties such as pore size, porosity, and anisotropy are essential for tissue engineering applications. For example the pore size and material anisotropy have been shown to affect cardiomyocyte elongation and alignment [1]. Phase-inversion spray polymerization (PISP) is a method for rapidly precipitating polymers onto a surface by depositing the polymer solution simultaneously with a nonsolvent, and may be used to create biocompatible scaffolds of engineered morphological and mechanical properties by varying the solubility of the polymer in the nonsolvent [2]. We report here on the fabrication of scaffolds using different nonsolvents and methods of in-process elongation that allow for control of stiffness, anisotropy ratio, porosity, and in vitro cell culture.
Fill of the Nucleus Cavity Affects Mechanical Stability in Compression, Bending and Torsion of a Spine Segment Which Has Undergone Nucleus Replacement
Authors: Arthur Amy , Cannella Marco , Keane Michael , Singhatat Wamis , Vresilovic Ed , Sarkar Sumona , Marcolongo Michele
Published: July 2013

Axial loading, rotation and bending were applied to human cadaveric lumbar segments to investigate changes in disc mechanics with denucleation and incremental delivery of a novel hydrogel nucleus replacement implant. Changes in disc height, range of motion, neutral zone, hysteresis and stiffness were examined.
In Vivo MRI of Macromolecular Transport Into the Rat Spinal Cord via Peripheral Nerve Infusion
Authors: Chen Xiaoming , Astary Garrett W. , Mareci Thomas H. , Sarntinoranont Malisa
Published: July 2013

Convection-enhanced delivery (CED), or direct infusion, of therapeutic agents into peripheral nerves is of interest since it may provide an alternative delivery route to the spinal cord (SC). This delivery method requires only minimally invasive surgery, reducing the risk of SC injury during surgery. It may also allow targeting of specific neurons entering the SC. Previous studies have shown that transport in peripheral nerves is anisotropic with a preferred direction parallel to the fiber tracts [1, 2]. A large-scale longitudinal spread of macromolecular agents may be obtained and spread of agents into the SC may be possible (Fig. 1).
A Novel Bioreactor for In Vitro Electro-Mechanical Stimulation of Cardiac Constructs
Authors: Pavesi Andrea , Vismara Riccardo , Lorenzoni Stefano , Montevecchi Franco M. , Fiore Gianfranco B.
Published: July 2013

Cardiovascular diseases are the main cause of death and disability in Europe and in fact throughout the world [1]. Tissue engineering is a rapidly growing area that aims to create, repair and/or replace tissue and organs by using combinations of cells, biomaterials and biologically active molecules.
A Microfluidic Device for Flow-Through Blood Oxygenation by Photocatalytic Action
Authors: Rasponi Marco , Ullah Tania , Gilbert Richard , Fiore Gianfranco B. , Thorsen Todd
Published: July 2013

The breakthrough work of Fujishima and Honda in 1972 [1], in which they achieved ultraviolet light-induced water cleavage with the use of titanium dioxide (TiO2) in an electrochemical cell, has drawn considerable attention in recent years to the “acceleration of a photoreaction by the presence of a catalyst” [2] or photocatalysis. Research on photocatalysis has explored the decomposition of organic pollutants and microorganisms, the superhydrophilic self-cleaning properties of surfaces, and the photosplitting of water, among other applications. Semiconductors can act as photocatalysts because of their electronic structure and TiO2, in particular, has been a popular choice. It is non-toxic and mechanically stable, can be fabricated at low-cost, and the anatase phase of TiO2 has a bandgap of approximately 3.2 eV, ideal for excitation by light in the ultraviolet range.
Development and Biocompatibility Characterization of a BioMEMS Sensor for Monitoring the Progression of Fracture Healing
Authors: Santoni Brandon G. , Melik Rohat , Unal Emre , Perkgoz Nihan Kosku , Kamstock Debra A. , Ryan Stewart D. , Dernell William S. , Demir Hilmi Volkan , Puttlitz Christian M.
Published: July 2013

Orthopaedic extremity injuries present a large medical and financial burden to the United States and world-wide communities [1]. Approximately six million long bone fractures are reported annually in the United States and approximately 10% of these fractures do not heal properly. Though the exact mechanism of impaired healing is poorly understood, many of these non-unions result when there is a communited condition that does not proceed through a stabilized healing pathway [2]. Currently, clinicians may monitor healing visually by radiographs, or via manual manipulation of the bone at the fracture [3]. Unfortunately, the course of aberrant fracture healing is not easily diagnosed in the early period when standard radiographic information of the fracture is not capable of discriminating the healing pathway. Manual assessment of fracture healing is also an inadequate diagnostic tool in the early stages of healing [4].
Thermomechanical and Hydrophobic Characterization of Shape Memory Polymers
Authors: Warren P. Daniel , Bernal Rafael R. , Harper John L. , Herlihy Rachelann N. , Vande Geest Jonathan P.
Published: July 2013

Shape memory polymers (SMPs) have generated a great amount of interest due to their capacity to recover a programmable shape under an applied stimulus, such as temperature change or light irradation [1, 2]. The SMP is initially synthesized with a specific original shape. This shape can be deformed under a mechanical load and at a temperature (TH) greater than the glass transition temperature, Tg. The application of this deformation coupled with subsequent lowering of the temperature (TC) to below the Tg, can fix the polymer in the newly altered formation even after removal of the external load. Increasing the temperature again, to a point above Tg, then activates the shape memory effect, whereby the original shape can be recovered. This shape memory ability is a direct result of specific molecular architecture. Chemical and physical crosslinks and macromolecular chain entanglements are part of this structure. Chemical crosslinks between segments give form to the original shape. Some of these segments are stimuli-sensitive, in other words, segments can become increasingly elastic with the application of thermal energy. This application of energy causes the crystalline structure of these segments to melt and be easily deformed under external load. This temporary shape can now be maintained with the removal of thermal energy leading to re-crystallization. Recoil in this state is prevented by both the new crystalline structure and entanglements of the segments caused by deformation. Physical crosslinks give the architecture permanence, since the linkages do not degrade with stimulus [3]. Different crosslinker formulations can result in varying types of chemical crosslinks. Variations in the structure lead to alterations in the material properties, such as mechanical characteristics and hydrophobicity.
Pilot Study of Irreversible Electroporation to Treat Brain Cancer
Authors: Garcia Paulo A. , Elankumaran Subbiah , Davalos Rafael V.
Published: July 2013

Non-thermal irreversible electroporation (IRE) is a promising new technique for the ablation of tissue and tumors [1–5]. This minimally invasive procedure involves placing electrodes into or around the targeted area to deliver a series of short and intense electric pulses to induce the irreversible structural changes in the cell membranes [5]. To achieve IRE, the electric field in the targeted region needs to be above a critical value which is dependent on a variety of conditions such as tissue type and pulse parameters [5]. One of its primary advantages over other ablation techniques lies in its mechanism to kill undesirable cells by primarily affecting the cell membrane without thermally damaging major blood vessels, connective tissue, nerves and the surrounding healthy tissue.
2D Analysis of Acoustic Transfer Through the Chest Cavity of Sounds Associated With Coronary Artery Disease
Authors: Cooper Daniel , Vlachos Pavlos , Roan Michael
Published: July 2013

Cardiovascular disease represents the leading cause of death in the United States, accounting for about 35% of all deaths, the majority of which are due to Coronary Artery Disease (CAD), which alone accounts for 20% of all deaths [1]. This is primarily due to the difficulty in early diagnosis of CAD; only about 20% of all cases are diagnosed prior to the patient’s first heart attack [2]. This is due to the limitations of current diagnostic techniques, which are either invasive or prohibitively expensive for use as a screening test for CAD. Phonoangiography is a technique that promises inexpensive and noninvasive diagnosis of CAD by detecting the flow noise created by turbulent flow within a stenosed coronary artery, also known as a bruit in the medical community. This technique is not currently used due to the difficulties of detecting the faint sound of a bruit in the noisy environment of the chest. To the authors’ knowledge, analysis of the acoustic transfer of cardiovascular sounds through the chest has not studied previously. We hypothesize that the acoustic transfer function at different locations on the chest surface is significantly dependent on the source location, which would provide a signal processing technique for detecting the presence of CAD.
Does Placement of the Axis of Rotation of the Cervical Spine Affect Motion Segment Mechanics During Flexion and Extension?
Authors: Kelly Brian P. , Bonin Henry , Fraysur Kyle , Sedacki Karen , DiAngelo Denis J.
Published: July 2013

Current in vitro testing methodologies remain limited in the ability to explore spinal mechanics. The gold standard of flexibility testing has traditionally focused only on evaluating rotational components of motion within a motion segment unit (MSU). While such data may be applied towards evaluation of the Center of Rotation (CoR) of a joint, many systems lack the needed sensitivity. The result is that there is currently no consensus on the location of the CoR of the spine. Further, very limited data or insight can be gathered as to the precise kinematic or dynamic state of the MSU, the influence of surgically implanted motion restoration devices, or the influence of subtle changes to an implanted device.
Remodeling and Compaction in Tissue Engineered Small Vessels
Authors: Soares Ana L. F. , Stekelenburg Maria , Baaijens Frank
Published: July 2013

Small-diameter vessels tissue engineering (TE) seeks to provide viable replacements to the native ones. The approach involves seeding autologous cells onto a biodegradable scaffold material and delivering the suitable environmental factors (biochemical and biomechanical stimuli) during culture via a conditioning protocol. Still, these replacements appear to lack the native mechanical integrity. TE protocols should then be improved and optimized.
Quasi-Static Simulation of Percutaneous Aortic Valve Leaflet Deformation
Authors: Li Kewei , Sun Wei
Published: July 2013

Aortic valve stenosis (AS) — an abnormal narrowing of the aortic valve — is the most common valvular heart disease in western world. The current standard treatment for severe AS remains the open-heart valve surgery to replace the stenotic aortic valve with a prosthetic device. However, for high-risk patients with advanced age and/or other diseases, this very invasive surgery is considered to be excessively risky. It is reported that 30% of such patients with symptomatic AS are not referred for surgery because of the high perioperative mortality rate. Recently, minimally invasive percutaneous aortic valve (PAV) replacement has been developed and tested in patients. Although significant experience has been gained through multicenter clinical trials, PAV therapy is clearly in its infancy. Various adverse effects such as device dysfunction, myocardial infarction, peripheral embolism, aortic injury, and perivalvular leakage have been reported. Furthermore, durability and safety of PAV devices need to be evaluated and studied carefully.
Alteration of Bone’s Nonlinear Elastic and Viscoelastic Nanomechanical Properties Is Triggered by Low Intensity Pulsed Ultrasound
Authors: Ferreri Suzanne , Qin Yi-Xian
Published: July 2013

Dynamic mechanotransduction, particularly under high frequency, low amplitude signals, has been proven effective in mediating bone loss and improving mechanical strength for tissues affected by estrogen deficient osteopenia. Ultrasound, which behaves as an alternating pressure wave in bone, may offer an effective, non-invasive technology for delivery of anabolic signals. In vitro, dynamic mechanical signals delivered using ultrasound have been shown to increase osteoblast proliferation [1], and in vivo studies have established ultrasound as an effective treatment for delayed and non-union fractures [2]. Previously, we showed that ultrasound signals similar to those currently used in a clinical setting for fracture healing were effective in mediating decreases in bone volume and mechanical strength at the millimeter length-scale in response to estrogen deficient osteopenia [3]. Due to bone’s inherent viscoelasticity and the dynamic nature of the applied ultrasound signals, it is particularly important to consider both elastic and viscous components of bone’s adaptive response to applied loads. In light of these findings, the goal of this study was to determine the role of therapeutic ultrasound signal intensity in modulating changes in bone’s nanoscale elastic and viscoelastic material properties associated with estrogen deficient osteopenia. We hypothesize that bone is sensitive to dynamic mechanical signals delivered via ultrasound and that bone’s tissue level nano-scale material properties, particularly nonlinear viscoelastic properties, are sensitive to ultrasound signal intensity.
Fusion of Histology and Shear Stress Based on In Vivo Images
Authors: Groen Harald C. , van Walsum Theo , Gijsen Frank J. H. , Rozie Sietske , Klein Stefan , van Gaalen Kim , van der Steen Antonius F. W. , van der Lugt Aad , Niessen Wiro J. , Wentzel Jolanda J.
Published: July 2013

Evidence is accumulating for a role of high wall shear stress (WSS) in plaque destabilization, leading to plaque rupture [1–2]. To study this in detail we can use carotid plaques that are removed during surgery. The in vivo WSS distribution can be obtained by combining 3D lumen data, derived from pre-operative CT angiography (CTA) imaging, with computational fluid dynamics. Plaque composition can be studied by means of histological processing. Accurate registration of CT imaging with histology is an essential step to study the relationship between WSS and plaque composition.
Modeling the Active Contractility of Cells Under Dynamic Loading
Authors: McGarry Patrick , Evans Anthony G. , McMeeking Robert M. , Deshpande Vikram S.
Published: July 2013

Cytoskeletal alignment and morphological changes in cells under conditions of cyclic stretching have been reported in several in-vitro studies. Of particular interest is the experimental work of Wille et al. [1] in which the contractile response of fibroblasts was isolated and quantified by testing both untreated cells and cells treated with Cytochalasin-D.
Functional Tissue Engineering of Articular Cartilage With Adult Chondrocytes
Authors: Bian Liming , Ng Kenneth W. , Lima Eric G. , Jayabalan Prakash S. , Stoker Aaron M. , Cook James L. , Ateshian Gerard A. , Hung Clark T.
Published: July 2013

The concept of cartilage functional tissue engineering (FTE) has promoted the use of physiologic loading bioreactor systems to cultivate engineered tissues with load-bearing properties [1]. Prior studies have demonstrated that culturing agarose constructs seeded with primary bovine chondrocytes from immature joints, and subjected to dynamic deformation, produced equilibrium compressive properties and proteoglycan content matching the native tissue [2]. In the process of translating these results to an adult canine animal model, it was found that protocols previously successful with immature bovine primary chondrocytes did not produce the same successful outcome when using adult canine primary chondrocytes [3]. The objective of this study was to assess the efficacy of a modified FTE protocol using adult (canine) chondrocyte-seeded hydrogel constructs and applied dynamic loading.
A Computational Model of Interstitial Transport in Murine Sarcoma With Heterogeneous Vasculature: A Sensitivity Analysis
Authors: Pishko Gregory L. , Astary Garrett W. , Mareci Thomas H. , Sarntinoranont Malisa
Published: July 2013

Extravasation of large therapeutic agents into tumor tissue following systemic injection is marked by heterogeneous distribution. Factors that contribute to this phenomenon include high interstitial fluid pressure (IFP) and non-uniform vascular permeability; they have been shown to be major obstacles delivery of macromolecules clinically [1]. Until recently, blood flow in a single vessel or capillary networks with variations in space and time has been explored using computational tumor models [2]. These studies do not account for heterogeneous tissue transport properties in regions of leakier vessels [3].
Continuous Passive Motion and Loading System Design for the Study of Pro- and Anti-Inflamatory Mediators in Articular Cartilage
Authors: Gu Xiang , Leong Daniel , Mahammud Rashal , Li Yong Hui , Sun Hui Bin , Cardoso Luis
Published: July 2013

Joint diseases are common causes of disability worldwide. Physical activity and weight bearing conditions play an important role in the regulation of joint homeostasis throughout life. The parametric characterization of deleterious and beneficial joint loading regimens influencing the homeostasis of articular cartilage is of great interest from both a basic research and clinical practice point of view. The development of in vivo animal models is critical to investigate the underlying mechanisms mediating the biological response of articular joints to external mechanical stimuli. For this purpose, the design of a device capable of accurately control the joint motion and loading in a small animal is needed. In the present work, an assisted motion system was conceived to perform continuous passive motion (CPM) and continuous loaded motion (CLM) on the knee joint of a small animal in vivo. A major purpose of this system is the study of the inflammatory and anti-inflammatory response of cartilage under several biomechanical environments. Therefore, a key design criterion was to avoid any invasive intervention (i.e. intraskeletal fixators) that may produce an intrinsic inflammatory response and then obscure/mislead the assessment of the biological markers of interest. Other important design criteria include real time control of the knee joint position, angular displacement, cyclic motion frequency and custom load magnitude applied in the axial direction along the tibia.
Bioprinted Nanoparticles for Tissue Engineering Applications
Authors: Buyukhatipoglu Kivilcim , Chang Robert , Sun Wei , Clyne Alisa Morss
Published: July 2013

Tissue engineering may require precise patterning of cells and bioactive components to recreate the complex, 3D architecture of native tissue. However, it is difficult to image and track cells and bioactive factors once they are incorporated into the tissue engineered construct. These bioactive factors and cells may also need to be moved during tissue growth in vitro or after implantation in vivo to achieve the desired tissue properties, or they may need to be removed entirely prior to implantation for biosafety concerns.
Gastrocnemius Muscle Fascicle Behavior Explored With a 3D Muscle Model
Authors: Blemker Silvia S. , Schrank Elisa S.
Published: July 2013

The gastrocnemius muscles are important for support and forward progression of movement [1], and they are commonly impaired in neurological disorders, such as stroke and cerebral palsy [2]. Currently, lumped-parameter representations [3] are used to model the gastrocnemius muscles in simulations of human movement. These representations simplify muscle architecture by assuming that all fibers are the same length, that aponeuroses behave as if they are in series with muscle fibers, and that fibers have a simple geometric arrangement. Previous studies have suggested that these simplifications may result in an overestimation of fiber length changes during movement and therefore predict that too much variation in force with joint angle (e.g., [4]).
Shear Rate Characteristics of Growing Thrombus on a Stenosis in a Coronary Sized Vessel
Authors: Bark David L. , Para Andrea N. , Ku David N.
Published: July 2013

Arterial thrombosis can lead to acute myocardial infarction or stroke. Thrombosis has been found to occur on atherosclerotic lesions and can fully occlude the blood vessel. Atheromas create a stenosis in the flow field. Thrombus forming in these regions is characteristically composed mostly of platelets with the addition of von Willebrand Factor (vWF) and polymerized fibrin. Previous studies of thrombosis under arterial-like stenotic flow conditions have shown that the thrombus growth rate increases under increasing shear rates up to 40000 s−1 [1]. The obstructive atheroma can lead to wall shear rates even greater than 40 times the average wall shear rate for an artery [2]. The shear rate dependency can be ascribed to mass transport [3]. Additionally, it can be ascribed to platelet binding mechanisms, such as vWF, that dominate at high shear, while other binding mechanisms, such as fibrinogen, bind at lower shear in the arteries [4].
An Evolution Equation for Plant Growth
Authors: O’Reilly Oliver M. , Tresierras Timothy N.
Published: July 2013

In a recent paper [1], plant growth and branching were modeled using a rod-based theory featuring Euler’s elastica. This work extended the works of Goreily et al. [2] and Silk et al. [3] on this topic. Special features of the model developed in [1] included an evolution equation for the flexural rigidity EI and intrinsic curvature νo and the use of an intermediate (growth) configuration.
Finite Element Modeling of Cerebral Angioplasty Using a Multi-Mechanism Structural Damage Model
Authors: Li Dalong , Robertson Anne M.
Published: July 2013

Percutaneous transluminal angioplasty (PTA) can lead to vascular damage when used to treat atherosclerotic obstructions and vasospasm in cerebral vessels [1–3]. In a controlled study of angioplasty in normal arteries of mongrel dogs, changes to the arterial wall due to over inflation were studied at two dilation levels (24%,50%) [4]. Damage to the wall was progressive — increasing with inflation level. At 25% inflation, localized fractures and stretching of the internal elastic lamina (IEL) were observed. Damage to the media was limited to the inner one-third of the wall. At 50% inflation, further radial damage was seen including extensive damage to the IEL, dissection of the media, distorted SMC and disorganized collagen fibers. At six months, the media exhibited signs of repair such as increased collagen content while the IEL showed no recovery.
Comparison of Numerically Modeled Knee Joint Contact Forces to Instrumented Total Knee Prosthesis Forces
Authors: Lundberg Hannah J. , Foucher Kharma C. , Andriacchi Thomas P. , Wimmer Markus A.
Published: July 2013

Total knee replacement (TKR) surgery decreases pain and increases functional mobility for patients with joint disease. As primary TKRs are implanted in patients who are younger, heavier, and more active (1), increases in wear and TKR revision rates are expected. Preclinical analysis of TKRs with mathematical models and experimental tests require accurate in vivo kinetic and kinematic input data. Kinematics can be obtained with gait analysis, but in vivo force data are just beginning to become available from instrumented TKRs from only a few patients (2). Patient gait is highly variable both within and between individuals and can be influenced by a variety of factors including the progression and history of joint disease, surgical procedure, and TKR design. Variation in patient gait and activities results in subsequent contact force and polyethylene wear variability. A validated mathematical model which calculates contact forces for alternate input data could add valuable insight for preclinical testing. A problem facing mathematical modeling is that there are too many unknowns to directly solve for contact forces. In order to approach this problem, we have developed a knee mathematical model that allows parametric variation of muscle activation levels (3) and calculates a solution space of physically possible contact forces.
A Semi-Analytical Plastic-Damage Model for Nanoindentation Contact Mechanics
Authors: Fulleringer Benjamin , Ovaert Timothy C. , Nelias Daniel
Published: July 2013

In many applications where cyclic contact loading occurs, the material may undergo progressive damage [1], resulting in a change of its mechanical properties. This can occur in biomaterials such as bone, as well as in brittle and ductile materials such as ceramics and metals, respectively.
Traumatic Brain Injury: Mechanical Response of Porcine Brain Under High Strain Rate Tests
Authors: Prabhu Raj , Horstemeyer Mark , Marin Esteban , Liao Jun , Tucker Matt , Williams Lakiesha
Published: July 2013

The brain is one of the most critical organs of the human body during life-threatening and injury sustaining accidents. Traumatic brain injury (TBI) due to mechanical insult of the head is a leading cause of death and life-long disability in the United States. The Center for Disease Control (CDC) has estimated that, on average, 1.4 million Americans sustain TBI every year, 20% of which are the result of motor vehicle-traffic accidents. Nearly 50,000 people die of TBI each year. Around 5.3 million Americans currently have long-term disabilities after sustaining a TBI. Some of these long-term disabilities are linked to functional changes affecting thinking, sensation, language and emotions [1]. Direct and indirect medical costs related to TBI amounted to an estimated $60 billion in the United States in 2000 [2]. TBIs have a deep impact on our society and require effective protective measures to curb consequent injuries and disabilities [3].
Finite Element Analysis and Validation of Brain Deformation in Linear Head Impact
Authors: Laksari Kaveh , Shafieian Mehdi , Parenti Cristina , Darvish Kurosh
Published: July 2013

The aim of this study is to present two dimensional models of human head undergoing linear acceleration and impact using finite element analysis and validating the results with dynamic impact experiments. The experimental model consisted of a cylindrical gel as brain surrogate material undergoing 55G deceleration with slip boundary condition. Two FE models were developed and compared namely, Lagrangian and Arbitrary Lagrangian Eulerian (ALE). Parameters such as the logarithmic strain and void generated in the posterior region of the head were used to validate the results.
Increased Microstructural Variability Is Associated With Decreased Structural Strength but With Increased Measures of Structural Ductility in Human Vertebrae
Authors: Yerramshetty Janardhan , Kim Do-Gyoon , Yeni Yener N.
Published: July 2013

The lack of accuracy in the prediction of vertebral fracture risk from average density measurements, all external factors being equal, may be because bone mineral density (BMD) is less than a perfect surrogate for bone strength but also because strength alone may not be sufficient to fully characterize the structural failure of a vertebra. Apart from bone quantity, organization of micro-architecture would have a role in governing mechanical properties of vertebrae. An earlier study indicated that within-vertebra variability, measured as the coefficient of variation (COV) of bone volume fraction (BV/TV) or as COV of finite element-estimated apparent modulus (EFE) correlated well with vertebral strength [1]. Therefore, as an extension to our earlier study, we investigated i) whether the relationships of vertebral strength found with COV of BV/TV and COV of EFE could be extended to the COV of other micro-structural parameters and microcomputed tomography-estimated bone mineral density (μCT-BMD) and ii) whether COV of microstructural parameters were associated with structural ductility measures.
Passive Mechanical Analysis of Engineered Myotube Fibers
Authors: Koppes Ryan A. , Schiele Nathan R. , Swank Douglas M. , Chrisey Douglas B. , Corr David T.
Published: July 2013

The loss of functional muscle as a product of genetic disease, traumatic injury, or surgical excisions results in a physiological deficiency that still remains without an effective clinical treatment [1]. Engineering of functional tissue in vitro for replacement in vivo might pose as a potential remedy for this clinical demand. By approaching tissue engineering from the bottom-up, geometrically directing myoblast growth provides a means for constructing tissue replacements cell-by-cell versus the traditional decellularized construct that remains limited by its size and ability to deliver cellular nutrients. Furthermore, geometrically controlling the growth of myoblasts allows for direct manipulation of the structural and mechanical properties inherent to muscular tissue.
Micro-PIV Measurements of an Airway Closure Model
Authors: Bian Shiyao , Zheng Ying , Takayama Shuichi , Grotberg James B.
Published: July 2013

A thin liquid layer coating the airway can be unstable and forms a plug. Airway closure usually happens at the small airways near the end of expiration, often accompanied with hypersecretion or/and surfactant deficiency in the airway in a variety of lung diseases, such as chronic obstructive pulmonary disease (COPD) and acute respiratory distress syndrome (ARDS). Modeling work by Halpern and Grotberg [1] has shown that several forces could contribute to airway closure, such as the surface tension instability and the wall compliance. Experiments in a capillary tube were conducted by Cassidy et al. [2] who found that adding surfactant increased the airway closure time and the critical film thickness. In vitro studies [3] [4] illustrated that exposure of primary human airway epithelial cells to plug propagation and rupture led to significant cell injury. Experimental studies [5] [6] on excised lungs or in vivo animal models have shown that severe tissue damage was found in surfactant-deficient lungs due to the repetitive airway reopening. However, mechanical forces induced by airway closure have not been experimentally evaluated.
A Novel Joint Loading System to Investigate the Effect of Daily Mechanical Load on a Healing Anterior Cruciate Ligament (ACL) Reconstruction
Authors: Stasiak Mark , Torzilli Peter , Imhauser Carl , Packer Jonathan , Bedi Asheesh , Brophy Robert , Kovacevic David , Fox Alice , Deng Xiang-Hua , Rodeo Scott
Published: July 2013

A novel system was developed to investigate the effect of mechanical load on tendon to bone healing, using a rat model of ACL reconstruction. A greater understanding of the effects of mechanical load may improve rehabilitation practices for the more than 100,000 ACL reconstructions each year in the US alone.[1] The purpose of this study was to assess: the accuracy of knee joint distraction, variability in fixator compliance, and ability of animals to tolerate the fixator over a typical loading protocol.
The Role of the Loading Environment on the Developing Tendon-to-Bone Insertion
Authors: Thomopoulos S. , Das R. , Kim H. M. , Zeltser D. , Kousari K. , Galatz L.
Published: July 2013

A transition zone forms at the attachment of tendon to bone during post-natal development [1]. We previously showed that this transitional tissue reduces stress concentrations at the insertion and hence reduces the risk for failure [2]. During tendon-to-bone healing, on the other hand, a transition zone does not develop at the interface [3]. Unlike development, inferior scar tissue fills the repair site and the repair is prone to rupture at the attachment. Understanding the development of the insertion will allow us to develop solutions to augment tendon-to-bone healing.
Characterizing Strains in the Tibia of Hindlimb Unloaded Rats During Combined Isometric and Eccentric Stimulated Muscle Contraction
Authors: Lucas M. W. , Swift J. M. , Shirazi-Fard Y. , Greene E. S. , Bloomfield S. A. , Hogan H. A.
Published: July 2013

We have conducted a series of studies for NASA sponsored by the NSBRI using the hindlimb unloaded (HU) rat model to simulate micro-gravity. Studies have focused on various questions related to specific effects on both bone and muscle in the unloaded limbs. In some cases, a muscle stimulation technique has been used to simulate resistive exercise as a countermeasure during HU. Results have been generally quite positive for bone but not as effective for muscle. Consequently, a series of successive alterations have been made to the muscle stimulation protocol parameters in an attempt to maintain benefits for bone while reducing the overall level of exercize in order to minimize fatigue effects on muscle.
A Dielectrophoretic Device for Studying Single Cell Mechanics
Authors: Rajendran Kavitha , Manomohan Greeshma , Clyne Alisa Morss
Published: July 2013

Mechanics plays an important role in cell function, both in normal physiology and pathological conditions. In the vasculature, the endothelial cells that line blood vessels dynamically respond to the mechanical environment. Endothelial cells sense both fluid shear stress and cyclic stretch, and alterations in these forces may contribute to vascular diseases such as atherosclerosis.
A Cell Stretching System to Measure Endothelial Cell Cyclic Strain Response on Spatially Defined Basement Membrane
Authors: Figueroa Dannielle S. , Clyne Alisa Morss
Published: July 2013

A principal concern in diabetes is the increased risk of vascular disease associated with unregulated blood glucose. Endothelial cells that line the vasculature are dysfunctional in hyperglycemia. The high glucose environment promotes basement membrane protein glycation and enhanced cross-linking, which can increase stiffness and may alter endothelial cell response to strain.
Structural and Mechanical Anisotropy Correlation via a Generalized Anisotropic Inverse Mechanics Method
Authors: Raghupathy Ramesh , Barocas Victor
Published: July 2013

Elastography, or imaging of the elastic properties of materials has emerged as an important medical diagnostics tool in the last few decades. Its primary focus has been in the area of tumor detection where such inverse methods measure the relative stiffness of regions in tissue in comparison to its surrounding [1,2]. In load-bearing tissues like tendons and blood vessels, the underlying anisotropic structure of the tissue is distinctive and essential for proper function. In diseased or damaged tissue this structure is altered. Hence the potential for a tool to quantify relative changes not just in stiffness but also directionality is high. We have developed a generalized inverse mechanics method to estimate the regional anisotropy in inhomogeneous tissue. We use a structural model for fibrous tissue with exponential stress-strain relationship to generate test data for the inverse solver. We compare the input structural anisotropy of the fiber model with the evaluated mechanical anisotropy of the constitutive parameters.
Experimentally Derived Musculotendon Parameters for the Human Soleus: Fiber Length, Pennation Angle and Isometric Force
Authors: Manal Kurt , Binder-Macleod Benjamin , Buchanan Thomas S.
Published: July 2013

The soleus is one of the strongest muscles in the human body. It is the dominant plantarflexor at the ankle and plays a key role in maintaining posture and balance [1]. The soleus has been associated with risk of falls in the elderly and it is prone to contracture resulting in reduced range of motion and potentially adverse affects on gait and balance. Accurately characterizing the force-length properties of the human soleus is important for basic clinical research and critical for those constructing musculoskeletal models if such models are to further our understanding of gait and posture in healthy and pathological populations.
An Investigation of the Coupling Function of the FDS and FDP Tendons After Ulnar Superficial Slip Resection
Authors: Graves Chris , Amirouche Farid , Barlogh Kim , Gonzalez Mark , Connor Jennifer
Published: July 2013

The goal of this study is to assess kinematic changes in the flexion pattern of a digit after resection of a single arm of the FDS tendon (ulnar superficialis slip resection or USSR). Angular joint displacement as a function of a controlled tendon excursion driven by computerized motors was used to quantify the kinematics of the finger. This series of experiments was performed on fresh-frozen cadaver hands, and data was acquired in real time using a National Instruments DAQ card and a PC running LabView software.
Biomechanical Investigation and Bone-Implant Stress Analysis of a Novel Lumbar Interspinous Spacer
Authors: Parikh Rachit , Amanesh Amanesh , Kiapour Ali , Goel Vijay K. , Abjornson Celeste
Published: July 2013

Spinal stenosis usually presents with pain radiating beyond the back to the buttocks, thighs or lower legs. The pain is worsened with extension of the lumbar spine and improves with flexion of the spine. Interspinous spacers are a relatively new treatment option that can be implanted under the minimal spinal surgical procedure. The Interspinous process devices are designed to distract (open) the foramen, where the nerve endings pass away from the center of the spinal region and into the legs. There have been many studies on the motion but stress distributions in the spine and the device are sparse.
Autonomous Control and Simulation of a Wheelchair Mounted Robotic Arm Performing Activities of Daily Living Tasks
Authors: Farelo Fabian , Alqasemi Redwan , Dubey Rajiv
Published: July 2013

A wheelchair-mounted robotic arm was designed and developed to enhance the capabilities of mobility-impaired persons with limited upper extremities limitations exceeding previous models specifications and performance [1]. The major enhancements of the wheelchair’s mechanical design are the incorporation of DC servo drive with encoders at each individual joint. The arm has seven degrees of freedom (DoF) and is side-mounted on a power wheelchair (fig 1). The control system allows coordinated Cartesian control, and offers expandability for research in combined mobility and manipulation. This paper discusses the control scheme and a virtual simulation of the existing WMRA prototype performing several activities of daily living.
Characterizing the Influence of Scaffold Anisotropy on Engineered Heart Valve Leaflet Function
Authors: Schmidt David E. , Sacks Michael S.
Published: July 2013

Tissue engineered pulmonary valves (TEPV) represent a conceptually appealing alternative to current non-viable prosthetic valves and valved conduits for the repair of congenital or acquired lesions in pediatric patients. In addition to the identification of clinically feasible cell sources, engineered soft tissues such as the TEPV require scaffolds with anisotropic mechanical properties that undergo large deformations (not possible with current PGA/PLLA non-wovens) coupled with controllable biodegradative and cell-adhesive characteristics. Electrospun PEUU (ES-PEUU) scaffolds have been produced with tensile biaxial mechanical properties remarkably similar to the native pulmonary valve (Fig. 1-a), including the ability to undergo large physiologic strains and exhibit pronounced mechanical anisotropy. Moreover, a novel cell micro-integration technique has been developed that allows for successful cell integration directly into the scaffolds at the time of fabrication, eliminating cellular penetration problems. These encouraging results suggest that ES-PEUU scaffolds micro-integrated with the appropriate cells and can serve as successful TEPV scaffolds. In the present study, we conducted a finite element based analysis of TEPV leaflets (Fig. 1-b) under quasi-static transvalvular pressure to demonstrate the impact of ES-PEUU mechanical anisotropy on scaffold strain distributions.
Modeling the Cell Type Dependency of Diffusion Limited Intracellular Ice Formation and Growth
Authors: Yang Geer , Zhang Aili , Xu Lisa X. , He Xiaoming
Published: July 2013

Modeling diffusion-limited intracellular ice formation (IIF) was first pioneered by Karlsson et al. [1]. The classical model in this work was further improved several studies later [2,3]. Nevertheless, as mentioned by Karlsson et al. in their original work [1], the approach used in the previous studies to estimate viscosity and mutual diffusion coefficient of intracellular solutions, the two most important properties that determine the rate of ice nucleation and crystal growth, is inaccurate. Moreover, the existing models are difficult to be used to study the intracellular ice nucleation and growth in different types of cells. In this study, the diffusion-limited IIF model was further improved with the capability to study the cell type dependence. The viscosity and diffusion coefficient of intracellular solution in the presence of glycerol during cryopreservation were estimated using free volume models reported in [4].
Modeling Dental Implants With Finite Element Analysis and Micro-Computed Tomography
Authors: Tsafnat Naomi
Published: July 2013

X-ray micro-computed tomography (microCT) allows us to construct three-dimensional images of specimens at the micron scale in a non-destructive manner. The digital nature of the microCT images, which are in voxel form, make them ideal candidates for use in numerical modeling and simulation [1]. Finite element analysis (FEA) is a well-known technique for modeling the structural response of a system to mechanical loading, and is most useful in modeling complex systems which cannot be analyzed analytically. MicroCT datasets can be converted into finite element models, directly incorporating both the geometry of the specimen and information about the different materials in it. This method is known as micro-finite element analysis (microFEA). It is especially useful in the study of materials with complex microstructures.
2011 Results From the Summit on Rehabilitation Engineering
Authors: Patterson Rita M. , Hefzy Mohamed Samir , Weisman Jerry
Published: July 2013

Throughout the 1960’s attempts were made to transfer sophisticated technology developed by the National Aeronautics and Space administration (NASA), the computer industry, and others into the clinical setting. However this translation was met with obstacles. In 1972 major program commitment by the Rehabilitation Service Administration (RSA) and the veterans administration was secured to create rehabilitation engineering. The broad objective of Rehabilitation Engineering is to enhance the lives of the physically handicapped through clinical involvement in a total approach to rehabilitation combining medicine, engineering, and related science and technology.