bluuebunny/crossref_metadata_2025 huggingface dataset:
Biomechanical Effect of Lumbar Disc Degeneration Under Flexion/Extension: A Finite Element Model Study
Authors: Ruberté Lissette M. , Natarajan Raghu , Andersson Gunnar B. J.
Published: March 2014

Degenerative disc disease (DDD) is a progressive pathological condition observed in 60 to 80% of the population [1]. It involves changes in both the biochemistry and morphology of the intervertebral disc and is associated with chronic low back pain, sciatica and adult scoliosis [2,3]. The most accepted theory of the effects of DDD on the kinematics of the spine is that proposed by Kirkaldy-Willis and Farfan which states that the condition initiates as a temporary dysfunction, followed by instability and then re-stabilization as the disease progresses [4]. Although there is no clear relationship between disc degeneration and the mechanical behavior of the lumbar spine, abnormal motion patterns either in the form of increased motion or erratic motion have been reported from studies on human cadaveric motion segments [5,6]. To date however no study has looked at how disc degeneration affects the adjacent segment mechanics. IN vivo testing is difficult for these purposes given that specimens are generally obtained from people at the later stages of life and consequently often display multiple pathologies. A finite element model is a viable alternative to study the mechanics of the segments adjacent to the diseased disc. It is hypothesized that moderate degeneration at one level will alter the kinematics of the whole lumbar spine.
Finite Element Modeling of the Lamina Cribrosa Microarchitecture in the Normal and Early Glaucoma Monkey Optic Nerve Head
Authors: Downs J. Crawford , Roberts Michael D. , Burgoyne Claude F. , Hart Richard T.
Published: March 2014

Glaucoma is the second leading cause of blindness in the US and is usually associated with elevated intraocular pressure (IOP). Glaucomatous damage is believed to occur at the optic nerve head (ONH) where the retinal ganglion cell axons pass through an opening in the back of the eye wall on their path to the brain. This opening is spanned by the lamina cribrosa, a fenestrated connective tissue structure that provides structural and nutritional support for the axons as they pass through the eye wall.
Effects of Short Duration Overpressure on Astrocytes: An In Vitro Study
Authors: Leung Lai Yee , VandeVord Pamela J. , Hardy Warren , De Guzman Roche , Yang King H. , King Albert I.
Published: March 2014

Blast wave overpressure from detonations can injure physiological systems ‘silently.’ Experimental and clinical studies have revealed the damaging effects of shock waves on different physiological systems, such as ears, lungs and gastrointestinal tracts [1, 2]. Despite the improved helmet and body armor, many veterans returning from wars suffered from neurological disorders that are being diagnosed as mild traumatic brain injury. Warden (2006) reported that most of these veterans were exposed to blast [3]. In vivo study illustrated neuronal degeneration in the brain after exposure to blast waves [4]. As with many neuronal diseases, blast-induced neuronal injury may be related to microglia and astrocyte activation. However, the underlying mechanism is not clearly understood. This study was aimed at investigating the effects of short duration overpressure on astrocytes, in terms of cell proliferation and mRNA expression of several apoptotic genes and glial fibrillary acidic protein (GFAP).
Analytic and Computational Comparison of Poroelastic and Elastic Biomechanical Models for Soft Ocular Tissues
Authors: Mortazavi Ariane , Vande Geest Jonathan P. , Simon Bruce R. , Park Robert I.
Published: March 2014

Current investigations into the cause of glaucoma reveal the importance and influence of biomechanical properties and response in ocular tissue [1–4]. Finite element models (FEMs) supported by experimental data are essential in quantifying stress, strain and displacement values at vulnerable locations in the eye; (e.g., the optic nerve head (ONH, lamina cribrosa (LC), etc); associated with normal and elevated intraocular pressures (IOP). In order to create such FEMs, our analysis shows the importance of extending elastic to poroelastic (PE) material models in FEMs used to describe ocular structures. The current study investigates the quantitative differences between elastic and PE representations of material behavior and compares the accuracy of analytical results with computational results from a PE FEM. Such differences may be important when investigating the pathophysiology and diagnosis of ocular diseases.
Airway Reopening: The Pulsatile Propagation of a Finger of Air Through a Fluid-Occluded Cylindrical Tube
Authors: Smith Bradford J. , Gaver Donald P.
Published: March 2014

We computationally investigate the unsteady pulsatile propagation of a finger of air through a liquid-filled rigid cylindrical tube. This study is relevant to acute respiratory distress syndrome (ARDS), which is characterized by pulmonary airway collapse and fluid occlusion. Subsequent airway reopening, driven by mechanical ventilation, may generate damaging mechanical stresses on the airway walls that can result in ventilator-induced lung injury (VILI). We hypothesize that unsteady flows accompanied by dynamic surfactant transport may reduce the incidence of VILI. Herein we investigate the flow-field under constant surface tension to develop a fundamental understanding of unsteady flows in this system, and to identify the parametric ranges over which transport may be optimized to minimize pulmonary atelectrauma.
The Critical Buckling Pressure of Arteries
Authors: Fierro Cesar A. , Johnson Kurtis , Han Hai-Chao
Published: March 2014

Artery stability is essential to normal arterial functions. This study examined the critical internal pressure at which arteries buckle. The critical pressure was found to be strongly related to the axial strain in the arteries.
Quantification of Three-Dimensional Motion of the Renal Arteries Using Image-Based Modeling Techniques
Authors: Suh Ga Young , Choi Gilwoo , Draney Blomme Mary , Taylor Charles A.
Published: March 2014

Stents implanted to treat renal artery stenosis are vulnerable to stent fracture and thrombosis [1–3]. We hypothesize that the motion of the renal arteries during respiration is a possible cause of stent fracture or in-stent restenosis. However, the respiratory motion of the renal arteries and the kidneys is poorly understood. Using magnetic resonance imaging data we previously quantified the two-dimensional deformation of the renal arteries and demonstrated that respiration-induced kidney motion results in vessel bending near the ostia [4]. In this study we quantified the complex three-dimensional motion of the renal arteries and kidneys over the respiratory cycle using magnetic resonance angiography data and imaged-based modeling methods. We provide quantitative information on anatomic changes to the renal arteries that may provide data to design improved pre-clinical, benchtop tests for renal stents.
Nonlinear Finite Element Modeling of Monkey Posterior Sclera Under Intraocular Pressure
Authors: Girard Michaël , Downs Crawford J. , Burgoyne Claude F. , Bottlang Michael , Suh Jun-Kyo F.
Published: March 2014

We hypothesize that the mechanical properties of posterior sclera play a central role in the development of glaucomatous vision loss.
A New Versatile Mechanistic Collagen Remodeling Algorithm
Authors: van Donkelaar C. C. , Wilson W.
Published: March 2014

To appropriately tissue engineer load-bearing soft tissues requires reproducing the tissues mechanical structure. The most important mechanical component is collagen, which forms a cross-linked fiber network. Soft tissues adapt their structures to their functions, by aligning the predominant fiber orientation with the loading direction.
What Molecular Dynamics Simulations Can Tell Us About Mechanical Properties of Kinesin and Its Interaction With Tubulin
Authors: Aprodu Iuliana , Gautieri Alfonso , Montevecchi Franco M. , Redaelli Alberto , Soncini Monica
Published: March 2014

Kinesin is a processive molecular motor found in various cells including neurons, that transports membrane-bound vesicles and organelles along the microtubule. Kinesin typically consists of three distinct domains: two large globular heads that attach to the microtubule, a central coiled region, and a light-chain that attaches to the cellular cargo. The metabolic energy that drives kinesins is provided in the form of ATP. The energy released by ATP hydrolysis is converted into direct movement after kinesin binds strongly to the microtubule. Two mechanisms were proposed to explain the movement of kinesin along microtubules: the “hand over hand” model in which the two heads alternate in the role of leading and the “inchworm” model in which one head always leads.
Automated Segmentation and Morphometric Measurement of a Human Airway Tree From Multi-Detector CT Images Toward the Numerical Analysis of Pulmonary Flow Dynamics
Authors: Nakamura Masanori , Shimada Yasuhiro , Miki Takahito , Imai Yohsuke , Suda Yuji , Tamura Gen , Wada Shigeo
Published: March 2014

Advancement in imaging technologies has shortened scan time of computed-tomography (CT). Recently introduced to a clinical market, 64-detector CT is capable of acquiring 64 simultaneous 0.5-mm slices with each 400-ms gantry revolution, yielding precise isotropic imaging of even peripheral airways within a single breath hold.
Pressure Induced Strain at Femoral Artery Bypass Graft Junctions
Authors: Campbell Triona , Cole Reena , O’Donnell Michael
Published: March 2014

Femoral or femoropopliteal artery bypass graft junctions have a predilection for failure due to restenosis. It has been clinically proven that vascular reconstructions tend to restenose within a short period of time [1]. Extensive studies have cited wall shear stresses as being primarily responsible and definite correlations between hydrodynamic stresses in the arterial wall and arterial disease have been shown [2,3]. However intensive investigations into wall shear stresses have lead to conflicting arguments on the proliferation and propagation of stenoses. It was concluded by Freidman [4] that the intima at sites exposed to relatively high or unidirectional shears thickened initially, but as time progressed the greatest thicknesses were ultimately achieved at sites exposed to lower or more oscillatory shear environments. A contradicting view was expressed by Nazemi [5] that low wall shear stress contributed to the onset of atherosclerotic plaque formation, whilst high wall shear stress encouraging plaque growth. A number of studies have however established a statistically significant correlation between pressure and intimal hyperplasia and concluded that blood pressure and not blood flow is the primary factor responsible for the localization of atherosclerosis [6–8].
Mechanical Behaviour of the Subcutaneous Fat Layer
Authors: Geerligs M. , Peters G. W. M. , Oomens C. W. J. , Ackermans P. , Baaijens F. P. T.
Published: March 2014

A very important function of the human subcutaneous fat layer is to act as a mechanical cushion. However, prolonged loading may result in damage such as pressure ulcers. Depending on the severity and origin of the ulcer, skin, subcutaneous fat and muscle can be affected. The aetiology of pressure ulcers is still poorly understood; it is not even clear whether wounds start to develop in skin, in the fat layer or even in deeper layers [1]. One of the tools used to better understand the way mechanical loading affects tissues is mechanical modeling. The success of a mechanical model strongly depends on the constitutive equations that are used to describe the mechanical properties obtained with experimental work. For skin and muscle much is already known, but a tremendous lack of data is found regarding the properties of adipose tissue. In the case of the subcutaneous fat tissue, very few of the mechanical properties have been determined experimentally.
3D Reconstruction of Patient-Specific Abdominal Aortic Aneurysms: From CT Scan to Silicone Model
Authors: Doyle Barry J. , Morris Liam G. , Callanan Anthony , Kavanagh Eamon , Kelly Pat , Vorp David A. , McGloughlin Tim M.
Published: March 2014

Abdominal aortic aneurysm (AAA) is a local, permanent, irreversible dilation of the infrarenal section of the aorta that risks rupture until treated. AAA is defined as an infrarenal diameter 1.5 times the normal diameter. Currently, surgeons intervene when the aneurysm reaches a maximum diameter of 50mm [1]. 200,000 new cases are diagnosed each year in the US, with 500,000 new cases diagnosed worldwide [2]. This results in 15,000 deaths each year from AAA rupture in the US alone [3], with 8,000 deaths per year in the UK [4]. Literature supports the theory that small aneurysms may be as likely to rupture as larger aneurysms [5–7], and therefore, the need for a more reliable predictor of AAA rupture may have clinical importance.
Hemodynamics and the Natural History of Cerebral Aneurysms
Authors: Cebral Juan R. , Castro Marcelo A. , Putman Christopher M.
Published: March 2014

The mechanisms responsible for the evolution and rupture of cerebral aneurysms are not well understood. This is a multi-factorial problem, and previous studies [1–3] have identified the major factors involved: a) arterial hemodynamics, b) mechanobiology and wall biomechanics, and c) peri-aneurysmal environment. In this paper we present recent results based on patient-specific computational hemodynamics models of a number of cerebral aneurysms that indicate that hemodynamics plays an important role both in the progression and rupture of intracranial aneurysms. In particular, the data seems to support the idea that mechanisms associated to high wall shear stress may be responsible for the evolution and rupture of these aneurysms [4].
Combined Effect of Glycosaminoglycan and Mechanical Stimulation on the In Vitro Biomechanics of Tissue Engineered Tendon Constructs
Authors: Kinneberg Kirsten R. C. , Nirmalanandhan Victor S. , Powell Heather M. , Boyce Steven T. , Butler David L.
Published: March 2014

Tissue engineering offers an attractive alternative to direct repair or reconstruction of injuries to tendons, ligaments and capsular structures that represent almost 45% of the 32 million musculoskeletal injuries that occur each year in the United States [1]. Mesenchymal stem cell (MSC)-seeded collagen constructs are currently being used by our group to repair tendon injuries in the rabbit model [2, 3]. Although these cell-assisted repairs exhibit 50% greater maximum force and stiffness at 12 weeks compared to values for natural repair, tissues often lack the maximum force sufficient to resist the peak in vivo forces acting on the repair site [3]. Our laboratory has previously demonstrated that in vitro construct stiffness and repair stiffness at 12 weeks post surgery are positively correlated [4]. Therefore, in an effort to further improve the repair outcome using tissue engineering, we continue our investigation of scaffold materials to create stiffer MSC-collagen constructs. Our group has recently evaluated two scaffold materials, type I collagen sponges fabricated within the Engineered Skin Lab (ESL, Shriners Hospitals for Children) by a freezing and lyophilization process with and without glycosaminoglycan (chondroitin-6-sulfate; GAG) [5] and found the ESL sponges to significantly improve biomechanical properties of the constructs compared to sponges we currently use in the lab (P1076, Kensey Nash Corporation, Exton, PA). This study also demonstrated that GAG significantly upregulates collagen type I, decorin, and fibronectin gene expression (unpublished results).
Mineral Composition at the Tendon-to-Bone Insertion and Its Role in Stress Transfer
Authors: Thomopoulos Stavros , Kent Alistair , Birman Victor , Das Rosalina , Wopenka Brigitte , Pasteris Jill , Genin Guy
Published: March 2014

Musculoskeletal injuries are a common cause of pain and disability, and result in significant health care costs. Rotator cuff injuries, which make up the majority of soft tissue injuries to the upper extremity, commonly require surgical repair to the humeral head. At the rotator cuff, for example, the recurrence of tears to surgically repaired tendons has been reported to be as high as 94% [1]. The most dramatic feature of the failed tendon-to-bone healing scenarios is the lack of a transition zone between the tendon and bone that existed before the injury [2].
Differences Between Principal Strain Directions and Muscle Fiber Directions in the Contracting Biceps Bracii Measured With CPC-MRI
Authors: Zhou Hehe , Novotny John E.
Published: March 2014

Skeletal muscle exhibit non-uniform internal architectures and our research goals are to relate these to their internal mechanics during contraction to provide a better understanding of muscle function, verify muscle models and permit more sophisticated interpretation of the functional effects of injury. Our previous studies have developed a novel method to calculate 2D Lagrangian strain field of skeletal muscle from the CPC-MRI [1]. The objective of this study is to apply CPC-MRI to derive Lagrangian strain fields for the normal biceps brachii and to determine its minimum principal strain directions in vivo during contraction. We will then compare them to the muscle fiber directions or pennation angles measured by a parallel ultrasound study. If we assume the muscle force is mainly transmitted along fiber directions, we would expect that the minimum principal strain directions are the same as fiber directions. Comparisons between different regions of the muscle and flexion angles will also be made.
A Computational Investigation of Blood Flow in Realistic AAA Stent-Grafts
Authors: Molony David S. , Doyle Barry J. , Callanan Anthony , Morris Liam G. , Walsh Michael , McGloughlin Tim M.
Published: March 2014

Abdominal aortic aneurysm (AAA) is treated with two methods — open repair and endovascular repair. The endovascular method has many advantages over open repair, such as shorter hospital stays, non-invasiveness and shorter recovery times but there have been several reported problems with these devices, including graft migration, endoleaks and limb occlusion. Graft migration occurs in approximately 10% of grafts [1] while limb occlusion occurs in 11% of cases [2]. The consequence of endoleaks and migration not being treated may be the ultimate rupture of the aneurysm. The occlusion of iliac graft limbs can lead to peripheral vascular problems such as ischemia and gangrene. Some of the influencing factors on migration, occlusion and endoleaks are fluid, drag, stent-graft angulation and flow characteristics such as Deans flow.
Evolution of Scar Mechanical Properties During Myocardial Infarct Healing in Rat
Authors: Fomovsky Gregory M. , Holmes Jeffrey W.
Published: March 2014

The mechanics of healing myocardial infarcts are an important determinant of post-infarction left ventricular (LV) function and remodeling. Large animal infarct models are well studied; healing infarct scars have been shown to be mechanically and structurally anisotropic [1], and this anisotropy may help preserve LV function during some stages of healing [2]. At the same time, it has been suggested that the rat model of myocardial infarction is more similar to humans in the range of infarct sizes and observed LV dysfunction [3]. However, in the rat model, infarct mechanics and their effect on the overall LV function have not been described so far.
Use of Computational Fluid Dynamics for the Replication of Clinical Blood Flow and Pressure Measurements and Characterization of Hemodynamics in the Normal Ascending and Thoracic Aorta
Authors: LaDisa John F. , Figueroa C. Alberto , Vignon-Clementel Irene E. , Chan Frandics P. , Feinstein Jeffrey A. , Taylor Charles A.
Published: March 2014

Complications associated with abnormalities of the ascending and thoracic aorta are directly influenced by mechanical forces. To understand hemodynamic alterations associated with diseases in this region, however, we must first characterize related indices during normal conditions. Computational fluid dynamics (CFD) models of the ascending and thoracic aorta to date have only provided descriptions of the velocity field using idealized representations of the vasculature, a single patient data set, and outlet boundary conditions that do not replicate physiologic blood flow and pressure. Importantly, the complexity of aortic flow patterns, limited availability of methods for implementing appropriate boundary conditions, and ability to replicate vascular anatomy all contribute to the difficulty of the problem and, likely, the scarcity of more detailed studies.
Stress Analysis of Carotid Arterial Stenosis With 3-D Fluid-Structure Interaction Simulations
Authors: Fabbri Giulia , Long Quan , Gao Hao , Koenig Carola , Collins Michael W. , Pinelli Michele
Published: March 2014

Atherosclerotic plaques may rupture without warning and cause subsequential acute syndromes such as myocardial infarction and cerebral stroke. Plaque disruption tends to occur at points where the plaque surface is weakest i.e. at points where biomechanical stresses caused by the pulsatile blood flow are concentrated. Therefore, both plaque vulnerability (intrinsic disease) and rupture triggers (extrinsic forces) are important for plaque disruption [1]. The former predisposes the plaque to rupture while the latter may precipitate it.
One Dimensional Model of the Systemic Arterial Tree Including Cerebral Circulation
Authors: Reymond Philippe , Merenda Fabrice , Perren Fabienne , Rüfenacht Daniel , Stergiopulos Nikos
Published: March 2014

The aim of this study is to develop a distributed model of the entire systemic arterial tree, coupled to a heart model and including a detailed description of the cerebral arteries. Distributed models of the arterial tree have been studied extensively in the past (Avolio [1]; Cassot et al [2]; Meister [3]; Schaaf and Abbrecht [4]; Stergiopulos et al [5]; Westerhof et al [6]; Zagzoule and Marc-Vergnes [7]), however, no model has been developed so far that offers a physiologically relevant coupling to the heart and includes the entire cerebral artery network.
Hand Grasping Kinematics
Authors: Patterson Rita M. , Abreu Beatriz C. , Viegas Steven F. , Buford William L. , Andersen Clark , Ottenbacher Kenneth
Published: March 2014

Grasping involves precise and coordinated movement between the wrist complex and digits. The overall objective of this study was to examine variations in overall hand posture and finger coordination among persons with brain injury (BI) during a grasping activity to identify stereotypical prehension patterns within the study group.
Constitutive Model of Biodegradable Non-Linear Polymeric Materials for Applications in the Biomedical Field
Authors: Soares Joao S. , Moore James E. , Rajagopal Kumbakonam R.
Published: March 2014

Synthetic biodegradable polymers have seen a dramatic increase in their availability and utilization over the last few decades. The first reported biomedical application of biodegradable polymers was during the 70s in biodegradable sutures and to date, it remains as the most widespread usage of this family of materials. Biodegradable polymers have also been proven to be effective carriers in local drug delivery therapies and are widely used as a primary constituent of scaffolds in tissue engineering applications.
Enhanced Cellular Infiltration With Removal of Sacrificial Fibers From a Dual-Polymer Nanofibrous Scaffold
Authors: Metter Robert B. , Baker Brendon M. , Burdick Jason A. , Mauck Robert L.
Published: March 2014

The meniscus is a wedge-shaped, fibrocartilaginous tissue that stabilizes the knee joint by transmitting and distributing loads from the rounded femur to the flat tibial plateau [1]. With normal use, the meniscus experiences large tensile stresses along its circumferentially oriented collagen fibers [2]. Interruption of these fibers with injury inhibits load transfer and precipitates the early onset of osteoarthritis in the adjacent articular surfaces. Endogenous healing of the avascular region of the meniscus is limited, and restoration of fiber architecture is difficult to achieve [3]. The current, standard treatment of partial meniscectomy alleviates symptoms but does not restore mechanical function.
A Skeletalized Representation of the Total Cavopulmonary Connection
Authors: Krishnankuttyrema Resmi , Dasi Lakshmi Prasad , Pekkan Kerem , Sundareswaran Kartik , Kitajima Hiroumi D. , Yoganathan Ajit P.
Published: March 2014

Single ventricle congenital heart problems are reported for 2 out of every 1000 live births in the USA. In these cases, mixing of oxygenated and deoxygenated blood occurs in the heart causing severe cyanosis. The Fontan repair is a 3-stage palliative surgical correction technique performed during infancy. Its aim is to restore normal oxygen saturation by directly connecting the systemic venous return to the lungs and bypassing the right heart [1].
Deformation-Dependent Enzyme Cleavage of Collagen
Authors: Wyatt Karla E.-K. , Bourne Jonathan W. , Torzilli Peter A.
Published: March 2014

Collagen degradation is a mechanism for normal musculoskeletal development and extracellular matrix (ECM) maintenance, and in response to trauma, disease and inflammation. Matrix metalloproteinases (MMP-1, 8, and 13, the collagenases) are the primary enzymes that act to degrade collagen. These MMPs gain access to the collagen triple helix by binding to the enzyme’s attachment domain along the α-chains, followed by separation (unwinding) of the α-chains to expose the 3/4–1/4 cleavage site, and then cleavage of the α-chain by the enzyme’s catalytic domain [3, 5].
Changes in Camera Visibility Affect Measured Marker Motion
Authors: Kuxhaus Laurel , Schimoler Patrick J. , Vipperman Jeffrey S. , Baratz Mark E. , Miller Mark Carl
Published: March 2014

Motion analysis is an important tool for biomechanical studies and its accuracy and reliability for large-volume applications, such as gait labs, is well-established. Previous work has offered a comparison of commercially available systems.[1] No work to date has quantified the error in position of a given tracking marker caused by its removal from the view of one or more cameras, either by obstruction or by the data being removed during the image reconstruction process. This issue is critical to the tracking of extremely fine movements such as the travel of the radial head on the capitellum during elbow motion. Due to anatomical constraints, markers must frequently be placed a distance away from the body of interest and must be smaller than those conventionally used in gross motion analysis. The nature of the motion may not permit all cameras to view all markers all of the time. For example, a specimen may itself obstruct a camera’s view during certain motions.
Extraction and Selection of Characteristics in Skin Lesions Images Using Wavelets in Multiresolution Analysis
Authors: Soares Heliana Bezerra , Neto Adrião Duarte D. , de Carvalho Marco Antônio G.
Published: March 2014

The incidence of skin cancer have increased quickly in the last few years. Although it is an illness potentially fatal, if detected and removed precociously, it has 100% of cure. The clinical diagnosis is based on the ABCD system, which is a list of parameters (asymmetry, edge, color and dimension) that had been introduced to help in the tumors diagnosis [1, 5].
3D Finite Strains in Bovine Annulus Fibrosus Tissue
Authors: Huyghe J. M. , Jongeneelen C. J. M. , Kraaijeveld F. , Schroeder Y.
Published: March 2014

Intervertebral disc tissue consists of a fluid-filled extra-cellular matrix, in which living cells are sparsely dispersed. The mechanical function is highly dependent on the composition of the extra-cellular matrix, which primary consists of collagen fibrils and negatively charged proteoglycans. Due to the fixed charges of the proteoglycans (PG’s), the cation concentration inside the tissue is higher than physiological. This excess of ion particles leads to an osmotic pressure difference, which causes swelling of the tissue [1]. Because the intervertebral disc is gripped between two vertebrae, the swelling is constrained in vivo, resulting in a intradiscal pressure of 0.1 to 0.2 MPa in supine position. It has been shown that the osmotic pressure inside cartilaginous tissues is much higher than would be expected based on its FCD [2]. This is because part of the water in the tissue is absorbed by the collagen fibers. The proteoglycan molecules, because of their large size, are excluded from this intra-fibrillar space. This means that their effective concentrations are much higher in the extra-fibrillar space than if they were distributed uniformly throughout the entire matrix. Hence, the effective fixed charge density is higher than if computed from total tissue water content. A recent study demonstrates that intrafibrillar water increases osmolarity within the annulus fibrosus substantially [3]. On the other hand, Wognum et al. [4] showed by means of a physical and a numerical model of the disc that high osmolarity within the disc has a protective effect against crack propagation within the disc. Hence, the decrease in osmolarity associated with degeneration may be an explanation of (1) the growing number of cracks observed in the degenerating disc as well as (2) the poor correlation between external loading and crack propagation [5]. The purpose of the present study is to test the hypothesis of Wognum et al. [4] through direct observation of the deformation of annulus fibrosus tissue around discontinuities within its collagen network.
Towards the Prediction and Minimization of Device Failure for Endolvascular Grafts in Abdominal Aortic Aneurysms
Authors: Layman Ron , Missoum Samy , Vande Geest Jonathan
Published: March 2014

The local dilation of the infrarenal aorta, termed an abdominal aortic aneurysm (AAA), occurs over several years and may eventually lead to rupture, an event currently ranked the 15th leading cause of death in the United States [1, 2]. AAA can often remain quiescent and asymptomatic, making the diagnosis and treatment of AAA patients a clinical challenge. For patients whose AAAs dilate to a critical diameter there are two standard treatments: open surgical resection and endovascular repair (EVAR). EVAR involves inserting an endovascular graft into the aneurysm to prevent pressurization of the AAA cavity.
Biaxial Mechanics of Musculoskeletal Tissue and Fiber-Reinforced Scaffolds
Authors: O’Connell Grace D. , Sen Sounok , Baker Brendon M. , Mauck Robert L. , Elliott Dawn M.
Published: March 2014

Biaxial tensile testing is the primary experiment used to functionally evaluate cardiovascular fiber-reinforced tissues [1, 2], but has not been widely applied to musculoskeletal tissues. The in situ geometry of many musculoskeletal tissues does not meet uniaxial tensile boundary conditions of freely contracting edges and large aspect ratios. In addition, biaxial tests load the sample through a larger domain of strain configurations as are experienced in situ. In contrast, uniaxial tests represent just a single path within that domain. It has been shown in cardiac tissue and grafts that model parameters determined from biaxial experiments can be used to predict uniaxial behavior, but that uniaxial tests do not predict the biaxial behavior well [1, 2]. Therefore, biaxial mechanical testing is important to address musculoskeletal tissue function.
A Comparative Study of Mechanical Properties of Fresh and Elastic-Network Only Proximal Artery Tissues
Authors: Kao Philip , Qi H. Jerry , Lammers Steve , Shandas Robin
Published: March 2014

The contribution of the elastic network to the mechanical behavior of arterial tissues is not well quantified. This paper focuses on the quantification of the behavior of fresh and elastic-network-only (digested) calf arterial tissues in uniaxial deformation using the anisotropic hyperelastic model proposed by Bischoff et al. ([1]). This model characterizes an orthotropic, hyperelastic response, which is well-suited for the modeling of arterial tissues ([2],[3]). For this paper, we attempt to match the material constants associated with the Bischoff-Arruda anisotropic hyperelastic model to our experimental data from arterial tissues including the ascending aortic arch, descending aorta, main, left, and right pulmonary arteries, using a least-squares method. The material parameters obtained from the data fit provide a quantitative comparison of mechanical properties of fresh artery tissues and elastin networks.
Effects of Glycerol on the Thermal Properties of Phosphate Buffered Saline and Porcine Liver at Subzero Temperatures
Authors: Choi Jeung H. , Bischof John C.
Published: March 2014

Improvements in the prediction of thermal behavior during cryosurgery and cryopreservation can help improve the outcome of these cryobiological applications. The accuracy of the models depends on numerous factors including the kinetics and energy release during phase change phenomena and knowledge of thermal properties. Furthermore, connecting the thermal properties to crystalline, amorphous, and other phases adds an important mechanistic dimension that can also improve and direct an outcome. However, insufficient data for thermal properties in the subzero domain result in reliance on property estimations based usually upon tabulated water-ice data or weight averaged values from known materials primarily in temperature ranges above −40 °C [1]. This study focused on expanding the thermal properties database for both solutions and tissues. Results for Phosphate Buffered Saline (PBS) and porcine liver with glycerol at subzero temperatures (−150 ∼ 0 °C) are reported. The shifting of thermal property values due to sample crystallization, amorphous phase transition, and melting is discussed.
Effect of Stretch on Bladder Smooth Muscle Cells in Three-Dimensional Culture
Authors: Roby Tiffany S. , Nagatomi Jiro
Published: March 2014

The bladder is routinely subjected to mechanical stretch from filling cycles; however, abnormal bladder distention can result from pathological conditions such as bladder outlet obstruction. It has been suggested that abnormal mechanical environments in the bladder trigger cellular and molecular changes, such as smooth muscle cell hyperplasia or hypertrophy and alteration of the extracellular matrix (ECM). These cellular and ECM changes can, in turn, deteriorate the function of the bladder by decreasing the contractility and compliance of the tissue [1, 3, 5].
The Effects of Culture Conditions and Implantation on the Structural and Mechanical Characteristics of a Tissue Engineered Urethral Wrap
Authors: Haworth Donna J. , Chew Douglas W. , Kim Dae Kyung , Miyazato Minoru , Yoshimura Naoki , Chancellor Michael B. , Vorp David A.
Published: March 2014

Urethral dysfunction is a common complication of diabetes mellitus, spinal cord injury, vaginal childbirth, and pelvic trauma. Stress urinary incontinence (SUI) is the involuntary loss of urine due to the inability of the urethral sphincter to maintain a tight seal during the storage phase, and is a disease that physically and emotionally affects 25 million American women annually [1]. There are currently several treatments for SUI including surgery, Kegel exercises, and electrical stimulation, each accompanied by limited effectiveness and/or complications [2–3]. We believe that regenerative medicine techniques applied to the native urethra may aid in improving the function and support of the diseased urethra. Thus, we have begun the development of a tissue engineered urethral wrap (TEUW) for placement as a cuff around the native urethra and integration with the host tissue. The goal of this work was to determine optimized culture conditions for TEUWs and to determine if their use in vivo improves urethral function.
Elasticity of Cartilage Measured by Large Strain, Non-Hertzian AFM Nanoindentation
Authors: Lin David C. , Dimitriadis Emilios K. , Horkay Ferenc
Published: March 2014

The raster scanning and nanoindentation capabilities of the AFM are exploited in force spectroscopy, a valuable quantitative technique for mapping the elastic properties of materials down to nanometer resolution. When the probe is of well-defined geometry and the indentation behavior can be represented by established contact mechanics models, the force maps can be transformed to elastic modulus maps to facilitate comparison. This is especially important in biological specimens, where sample-to-sample variability is usually high.
Development of a Thrombus Mimic in Abdominal Aortic Aneurysms
Authors: Ashton John H. , Vande Geest Jonathan P.
Published: March 2014

Abdominal aortic aneurysms (AAAs) represent a significant disease in the western world as rupture of AAA is currently the 15th leading cause of death in the United States [1,2]. The rate of incidence of this disease is also thought to be increasing given the aging population. While AAA rupture is attributed to the gradual weakening of the wall, the mechanisms of aneurysm initiation, growth, and development remain relatively unclear. The role of biomechanics in the diagnosis and prevention of AAA rupture has been reported [3].
Viscoelastic Characterization of Perfused Liver: Indentation Testing and Preliminary Modeling
Authors: Kerdok Amy E. , Howe Robert D. , Socrate Simona
Published: March 2014

Computer-aided medical technologies are currently restricted by the limited understanding of the mechanical response of solid abdominal organs to finite loading conditions typical of surgical manipulation [5]. This limitation is a result of the difficulty in acquiring the necessary data on whole organs. To develop a constitutive model capable of predicting complex surgical scenarios, multiple testing modalities need to be simultaneously obtained to capture the fundamental nature of the tissue’s behavior under such conditions. In vivo tests are essential to obtain a realistic response, but their inherent difficulty and unknown boundary conditions makes them an impractical approach. Ex vivo tests are easy to control, but the response is unrealistic. A perfusion apparatus was previously developed that obtained near in vivo conditions for whole livers while allowing the ease of ex vivo testing [3]. This work presents the results from complete viscoelastic testing of whole-perfused livers with surgically relevant time-dependant indentation loading profiles to 35% nominal strain. These results will aid in the development of a constitutive model for the liver whose parameters can be related to the physical constituents of the tissue. As an intermediate modeling step, a 1D rheological modeling tool was used to identify the form and initial parameters for a constitutive model.
In-Vivo Tibiofemoral Contact Stress in the Knee After TKA
Authors: Suggs Jeremy F. , Hanson George R. , Li Guoan
Published: March 2014

Polyethylene wear is a leading cause of failure in total knee arthroplasty (TKA). Knowing the stresses experienced by the polyethylene would be pivotal information for efforts to improve polyethylene longevity. Previous investigations into the stress and wear of the polyethylene have required estimates of in-vivo conditions [1]. This work investigates the feasibility of using actual in-vivo kinematics obtained using dual fluoroscopy as boundary conditions for finite element analysis of the polyethylene.
Turbulent vs. Vortex Ring Energy Losses in the Left Ventricle
Authors: Pierrakos Olga , Vlachos Pavlos
Published: March 2014

Left ventricular flows in the human heart are very complex due to the intricate geometry, the pulsatile character of the flow, the interaction of the jets with the LV flexible walls, and the unsteady motion of the leaflets, which generate intrinsically complicated flow structures. Furthermore, although mechanical heart valves (MHV) have received universal recognition, their performance is still unmatched to that of the natural valves. The flow past MHVs induces a combination of flow characteristics, which are clearly dependent on the specific valve design and valve orientation. Traditionally, valve performance and hemodynamics have been quantified using effective orifice size and pressure gradients. However, quality and direction of flow, often overlooked, are also important aspects of valvular function and relate to valve design and orientation. One of the key characteristics in LV flows is the shear layers shedding past heart valves which generate vortex ring formation resulting into energy entrapment, thus reducing the efficiency of the heart.
In Vivo Tissue-Level Thresholds for Spinal Cord Injury
Authors: Maikos Jason , Elias Ragi , Qian Zhen , Metaxas Dimitris , Shreiber David
Published: March 2014

Traumatic loading conditions, such as those experienced during car accidents or falls, can lead to spinal cord injury (SCI), resulting in permanent functional damage [1]. A better understanding of the biomechanical causes of SCI and knowledge of the tolerance of spinal cord tissue to mechanical loading is critical in understanding how mechanisms of injury lead to neurologic deficits, as well as designing methods to prevent SCI. Finite element analysis (FEA) has become an important and cost effective tool to investigate the biomechanics of trauma. FEA has been used to study a variety of biomechanical analyses of trauma, including brain injury and spine injury biomechanics, but there have been limited analyses on spinal cord injury (SCI) [2–5]. In fact, despite the prevalence of small animal models in the neuroscience community used to study SCI, there have been no published analyses of in vivo models of SCI.
The Digital Leaflet: Quantitative Image Analysis and 3-D Digital Reconstruction of the Aortic Valve Leaflet
Authors: Stella John A. , Sacks Michael S.
Published: March 2014

Current efforts in tissue engineering center on designing viable replacements to resolve limitations that arise in existing medical technologies such as mechanical and biological valvular prosthetic devices. The realization of such tasks is complicated by the intricate, regionally variant structural and mechanical properties observed in the native aortic valve leaflet (AVL) [1–2, 4]. To design and construct such a valve, a detailed understanding of native leaflet microstructure and function is required. As such, creating a computational framework incorporating structural and functional characteristics spanning from the cell to organ level would be highly valued [3, 6]. The current study utilizes histological sectioning techniques to evaluate and reconstruct the 3D microstructure of the complete AVL. In addition to gaining further insight into leaflet structure function relationships, the current study will lay the basis for the development of analytical tools involving physiologically accurate 3D finite element representations.
Biological Markers of Atherogenesis Correlate With Both Shear and Mural Stress in Perfused Arterial Segments Exposed to Cyclic Axial Stretching Ex Vivo
Authors: VanEpps J. Scott , Chew Douglas W. , Vorp David A.
Published: March 2014

While documented risk factors (e.g., hypertension, diabetes, etc.) for atherosclerosis are systemic in nature, atherosclerotic plaques appear in a heterogeneous distribution in the vasculature [1]. Certain arteries (e.g., coronary arteries) are exposed to cyclic deformations such as stretching, bending, and twisting due to their being tethered to surrounding tissue beds [2]. Such stimuli likely results in spatially-varying biomechanical stresses and may be a key modulator of atherosclerotic lesion localization [3]. We have developed a unique methodology for combining ex vivo experimental perfusion of arterial segments with computational modeling. Using this methodology we examined the hypothesis that local variations in shear and mural stress associated with cyclic axial stretch of arterial segments influence the distribution of endothelial permeability and the expression of various genes associated with atherogenesis.
A Compressible, Transversely Isotropic, Hyperelastic Constitutive Model of the Guinea Pig Spinal Cord White Matter
Authors: Galle Beth , Ouyang Hui , Shi Riyi , Nauman Eric A.
Published: March 2014

Slow compression spinal cord injuries occur when the spinal canal narrows, the consequence of degenerative, infective, or oncologic legion growth, and exerts pressure throughout the spinal cord. Transverse tissue compression results in an amalgamation of mechanical insults at the cellular level [1]. However, the mechanism of cellular injury has yet to be elucidated. We have recently developed a hyperelastic, isotropic plane strain finite element model (FEM) of the guinea pig spinal cord white matter response to transverse compression based on force-deformation curves measured in vitro. The strongest correlation with in vitro axonal injury density was the combination of the in-plane shear stress with the in- and out-of-plane normal stresses quantified using the FEM [2]. However, we hypothesize that the guinea pig spinal cord white matter is a transversely isotropic material. Material anisotropy must be incorporated into the FEM to achieve enhanced model accuracy, specifically, the prediction of axial stresses within the spinal cord parenchyma during transverse tissue compression. Therefore, the objective of the present study was to propose a compressible, transversely isotropic, hyperelastic constitutive model of the guinea pig spinal cord white matter.
Poroviscoelastic Properties of Mouse Cartilage From Inverse Finite Elements and Indentation
Authors: Chiravarambath Sidharth , Simha Narendra K. , Lewis Jack L.
Published: March 2014

Transgenic mice offer a novel way to probe structure function relationships in healthy and osteoarthritic cartilage. Indentation is a convenient method to measure mechanical properties of cartilage in the mouse. In order to reduce test data to material properties, test model geometry along with a material model needs to be assumed. Most recent developments support the use of a poroviscoelastic (PVE) model for cartilage. However, using this model makes separation of the flow-dependent and flow-independent viscoelastic parameters challenging. For cartilage from larger animals, Huang [1] showed that tensile tests have negligible flow-dependent response and hence can identify the flow-independent material parameters. A compression experiment can then be used to find only the flow-dependent parameters. However, limited cartilage volumes in mouse do not allow for tension tests, so mouse cartilage is primarily tested by indentation. Mak [2] has shown that fluid flow occurs mainly for times comparable to the gel diffusion time T = a2/Hκ where a is the tip size, H is the aggregate modulus and κ is permeability. Consequently, we propose use of two different sized indenters to separate flow-independent and dependent effects in mouse cartilage. One tip is small enough to make T negligible (say <0.1 s), then relaxation data will probe only the flow-independent response, whereas a second considerably larger tip will probe both flow-dependent and fluid flow effects. The data from the small indenter can be used to fit the flow-independent parameters; the data from the large indenter, in conjunction with parameters from the first fit, can be used to fit the flow-dependent parameters.
Improving the Anisotropy of Collagen by Electric Field Increases Its Toughness by Two-Fold
Authors: Cheng Xingguo , Wasserman Nicholas , Akkus Ozan
Published: March 2014

Collagen is the major structural protein in the connective tissues such as skin, bone, ligaments, and tendons. The specific hierarchical organization of collagen molecules determines the unique properties of each specific tissue. For example, in tendon, the parallel alignment of collagen molecules, fibrils, fibril bundles, fascicles and tendon units gives tendon good mechanical properties. Thus, in vitro engineering of collagen molecules hold great promise as a tissue regeneration material. However, there is a need for mechanically superior collagenous structures, which currently cannot be provided by isotropic gels which lack defined orientation. Increasing the anisotropy of gels would increase the strength of collagenous constructs tremendously.