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Articles 1 - 21 of 21
Full-Text Articles in Biomedical Engineering and Bioengineering
Reviewing The American University Law Review On Extraterritoriality: A Critical Response To Viki Economides, Note, Tianrui Group Co. V. Itc: The Dubious Status Of Extraterritoriality And The Domestic Industry Requirement Requirement Of Section 337(Link), Jonathan R. K. Stroud
Jonathan R. K. Stroud
Recently, the Federal Circuit upheld the Commission’s decision to exclude goods based on a trade secret violation that largely happened abroad. The American University Law Review critiqued that decision on two grounds: First, that a presumption against extraterritorial application of U.S. law applied; and second, that licensing alone could not establish a domestic industry. The American University Law Review's critique remains incomplete, however, as the Federal Circuit correctly decided the case for at least two reasons. first, the Federal Circuit correctly applied the “extraterritorial presumption” canon of construction; and second, the recent Federal Circuit decision in InterDigital Communications LLC v. …
Effects Of Electrostatic Correlations On Electrokinetic Phenomena, Brian Storey, Martin Bazant
Effects Of Electrostatic Correlations On Electrokinetic Phenomena, Brian Storey, Martin Bazant
Brian Storey
The classical theory of electrokinetic phenomena is based on the mean-field approximation that the electric field acting on an individual ion is self-consistently determined by the local mean charge density. This paper considers situations, such as concentrated electrolytes, multivalent electrolytes, or solvent-free ionic liquids, where the mean-field approximation breaks down. A fourth-order modified Poisson equation is developed that captures the essential features in a simple continuum framework. The model is derived as a gradient approximation for nonlocal electrostatics of interacting effective charges, where the permittivity becomes a differential operator, scaled by a correlation length. The theory is able to capture …
Effect Of Applied Uniaxial Stress On Rate And Mechanical Effects Of Cross-Linking In Tissue-Derived Biomaterials, Debbie Chachra, Paul Gratzer, Christopher Pereira, J. Lee
Effect Of Applied Uniaxial Stress On Rate And Mechanical Effects Of Cross-Linking In Tissue-Derived Biomaterials, Debbie Chachra, Paul Gratzer, Christopher Pereira, J. Lee
Debbie Chachra
Conformational changes in collagen fibrils, and indeed the triple helix, can be produced by application of mechanical stress or strain. We have demonstrated that the rate of cross-linking in glutaraldehyde and epoxide homobifunctional reagents can be modulated by uniaxial stress (strain). Two poly(glycidyl ether) epoxides were used: Denacol® EX-810 (a small bifunctional reagent), and Denacol EX-512 (a large polyfunctional reagent). To prevent any possible effect from being masked by saturation of cross-linking sites, bovine pericardium was cross-linked to such an extent that the increase in collagen denaturation temperature, Td, was one-half of the maximal rise achievable with …
Shelf-Life Of Bioprosthetic Heart Valves: A Structural And Mechanical Study, Maryse Julien, Dany Letouneau, Yves Marois, Alain Cardou, Martin King, Robert Guidoin, Debbie Chachra, J. Lee
Shelf-Life Of Bioprosthetic Heart Valves: A Structural And Mechanical Study, Maryse Julien, Dany Letouneau, Yves Marois, Alain Cardou, Martin King, Robert Guidoin, Debbie Chachra, J. Lee
Debbie Chachra
This study was undertaken to evaluate the influence of storage conditions on the shelf-life of porcine bioprosthetic valves. Fifty-five unimplanted porcine bioprostheses have been evaluated. The valves were stored in 0.5% buffered glutaraldehyde solution for different periods of time (7, 23 and 32 months). Twenty-eight valves were refrigerated while the remaining valves were stored at room temperature. The pH of the glutaraldehyde solution at room temperature decreased with time of storage, while that kept in the refrigerator remained stable over the course of the study. Macroscopic observations showed that the valve tissues kept at room temperature, especially for the periods …
Fluoride Treatment Increased Serum Igf-1, Bone Turnover, And Bone Mass, But Not Bone Strength, In Rabbits, C. Turner, L. Garetto, A. Dunipace, W. Zhang, M. Wilson, Marc Grynpas, Debbie Chachra, R. Mcclintock, M. Peacock, G. Stookey
Fluoride Treatment Increased Serum Igf-1, Bone Turnover, And Bone Mass, But Not Bone Strength, In Rabbits, C. Turner, L. Garetto, A. Dunipace, W. Zhang, M. Wilson, Marc Grynpas, Debbie Chachra, R. Mcclintock, M. Peacock, G. Stookey
Debbie Chachra
We hypothesized that fluoride partly acts by changing the levels of circulating calcium-regulating hormones and skeletal growth factors. The effects of oral fluoride on 24 female, Dutch-Belted, young adult rabbits were studied. The rabbits were divided into two study groups, one control and the other receiving about 16 mg fluoride/rabbit/day in their drinking water. After 6 months of fluoride dosing, all rabbits were euthanized and bone and blood samples were taken for analyses. Fluoride treatment increased serum and bone fluoride levels by over an order of magnitude (P < 0.001), but did not affect body weight or the following serum biochemical variables: urea, creatinine, phosphorus, total protein, albumin, bilirubin, SGOT, or total alkaline phosphatase. No skeletal fluorosis or osteomalacia was observed histologically, nor did fluoride affect serum PTH or Vitamin D metabolites (P > 0.4). BAP was increased 37% (P < 0.05) by fluoride; serum TRAP was increased 42% (P < 0.05); serum IGF-1 was increased 40% (P < 0.05). Fluoride increased the vertebral BV/TV by 35% (P …
The Effect Of Different Hormone Replacement Therapy Regimens On The Mechanical Properties Of Rat Vertebrae, Debbie Chachra, M. Kasra, Carla Vanin, N. Maclusky, R. Casper, Marc Grynpas
The Effect Of Different Hormone Replacement Therapy Regimens On The Mechanical Properties Of Rat Vertebrae, Debbie Chachra, M. Kasra, Carla Vanin, N. Maclusky, R. Casper, Marc Grynpas
Debbie Chachra
The purpose of this study was to examine the effects of estrogen replacement, in concert with three different progestin regimens, on the mechanical properties of rat lumbar vertebrae. Ninety-two Sprague-Dawley rats (11 months old) were divided into six groups for treatment. The first group was an intact control, the second group (OVX) was ovariectomized only, and the third group (estrogen-only) was ovariectomized and received continuous estrogen through a 17-estradiol implant. The remaining groups were ovariectomized and received estrogen and progestin (norethindrone, NET) therapy; 3 g of NET was injected daily (estrogen plus continuous NET), or 6 g of NET was …
Stability Of A Microvessel Subject To Structural Adaptation Of Diameter And Wall Thickness, Alisha Sarang-Sieminski, John Geddes, Ilari Shafer, Rachel Nancollas, Morgan Boes
Stability Of A Microvessel Subject To Structural Adaptation Of Diameter And Wall Thickness, Alisha Sarang-Sieminski, John Geddes, Ilari Shafer, Rachel Nancollas, Morgan Boes
John B. Geddes
Vascular adaptation—or structural changes of microvessels in response to physical and metabolic stresses—can influence physiological processes like angiogenesis and hypertension. To better understand the influence of these stresses on adaptation, Pries et al. (1998, 2001a,b, 2005) have developed a computational model for microvascular adaptation. Here, we reformulate this model in a way that is conducive to a dynamical systems analysis. Using th ese analytic methods, we determine the equilibrium geometries of a single vessel under different conditions and classify its type of stability. We demonstrate that our closed-form solution for vessel geometry exhibits the same regions of stability as the …
Directed 3d Cell Alignment And Elongation In Microengineered Hydrogels, Alisha Sarang-Sieminski, Hug Aubin, Jason Nichol, Ché Hutson, Hojae Bae, Donald Cropek, Payam Akhyari, Ali Khademhosseini
Directed 3d Cell Alignment And Elongation In Microengineered Hydrogels, Alisha Sarang-Sieminski, Hug Aubin, Jason Nichol, Ché Hutson, Hojae Bae, Donald Cropek, Payam Akhyari, Ali Khademhosseini
Alisha L. Sarang-Sieminski
Organized cellular alignment is critical to controlling tissue microarchitecture and biological function. Although a multitude of techniques have been described to control cellular alignment in 2D, recapitulating the cellular alignment of highly organized native tissues in 3D engineered tissues remains a challenge. While cellular alignment in engineered tissues can be induced through the use of external physical stimuli, there are few simple techniques for microscale control of cell behavior that are largely cell-driven. In this study we present a simple and direct method to control the alignment and elongation of fibroblasts, myoblasts, endothelial cells and cardiac stem cells encapsulated in …
Igf-I And Mechanical Environment Interact To Modulate Engineered Cartilage Development, Keith Gooch, Torsten Blunk, D. Courter, Alisha Sarang-Sieminski, Predrag Bursac, Gordana Vunjak-Novakovic, Lisa Freed
Igf-I And Mechanical Environment Interact To Modulate Engineered Cartilage Development, Keith Gooch, Torsten Blunk, D. Courter, Alisha Sarang-Sieminski, Predrag Bursac, Gordana Vunjak-Novakovic, Lisa Freed
Alisha L. Sarang-Sieminski
Bovine calf articular chondrocytes were seeded onto biodegradable polyglycolic acid scaffolds and cultured for four weeks using in vitro systems providing different mechanical environments (static and mixed Petri dishes, static and mixed flasks, and rotating vessels) and different biochemical environments (medium with and without supplemental insulin-like growth factor I, IGF-I). Under all conditions, the resulting engineered tissue histologically resembled cartilage and contained its major constituents: glycosaminoglycans, collagen, and cells. The mechanical environment and supplemental IGF-I (a) independently modulated tissue morphology, growth, biochemical composition, and mechanical properties (equilibrium modulus) of engineered cartilage as previously reported; (b) interacted additively or in some …
Engineering Strategies To Recapitulate Epithelial Morphogenesis Within Synthetic Three-Dimensional Extracellular Matrix With Tunable Mechanical Properties, Alisha Sarang-Sieminski, Yekaterina Miroshnikova, D Jorgens, L Spirio, M Auer, V Weaver
Engineering Strategies To Recapitulate Epithelial Morphogenesis Within Synthetic Three-Dimensional Extracellular Matrix With Tunable Mechanical Properties, Alisha Sarang-Sieminski, Yekaterina Miroshnikova, D Jorgens, L Spirio, M Auer, V Weaver
Alisha L. Sarang-Sieminski
The mechanical properties (e.g. stiffness) of the extracellular matrix (ECM) influence cell fate and tissue morphogenesis and contribute to disease progression. Nevertheless, our understanding of the mechanisms by which ECM rigidity modulates cell behavior and fate remains rudimentary. To address this issue, a number of two and three-dimensional (3D) hydrogel systems have been used to explore the effects of the mechanical properties of the ECM on cell behavior. Unfortunately, many of these systems have limited application because fiber architecture, adhesiveness and/or pore size often change in parallel when gel elasticity is varied. Here we describe the use of ECM-adsorbed, synthetic, …
Self-Assembling Short Oligopeptides And The Promotion Of Angiogenesis, Alisha Sarang-Sieminski, Daria Narmoneva, Olumuyiwa Oni, Shugang Zhang, Jonathan Gertler, Roger Kamm, Richard Lee
Self-Assembling Short Oligopeptides And The Promotion Of Angiogenesis, Alisha Sarang-Sieminski, Daria Narmoneva, Olumuyiwa Oni, Shugang Zhang, Jonathan Gertler, Roger Kamm, Richard Lee
Alisha L. Sarang-Sieminski
Because an adequate blood supply to and within tissues is an essential factor for successful tissue regeneration, promoting a functional microvasculature is a crucial factor for biomaterials. In this study, we demonstrate that short self-assembling peptides form scaffolds that provide an angiogenic environment promoting long-term cell survival and capillary-like network formation in three-dimensional cultures of human microvascular endothelial cells. Our data show that, in contrast to collagen type I, the peptide scaffold inhibits endothelial cell apoptosis in the absence of added angiogenic factors, accompanied by enhanced gene expression of the angiogenic factor VEGF. In addition, our results suggest that the …
Primary Sequence Of Ionic Self-Assembling Peptide Gels Affects Endothelial Cell Adhesion And Capillary Morphogenesis, Alisha Sarang-Sieminski, C. Semino, Haiyan Gong, Roger Kamm
Primary Sequence Of Ionic Self-Assembling Peptide Gels Affects Endothelial Cell Adhesion And Capillary Morphogenesis, Alisha Sarang-Sieminski, C. Semino, Haiyan Gong, Roger Kamm
Alisha L. Sarang-Sieminski
Appropriate choice of biomaterial supports is critical for the study of capillary morphogenesis in vitro as well as to support vascularization of engineered tissues in vivo. Self-assembling peptides are a class of synthetic, ionic, oligopeptides that spontaneously assemble into gels with an ECM-like microarchitecture when exposed to salt. In this paper, the ability of four different self-assembling peptide gels to promote endothelial cell adhesion and capillary morphogenesis is explored. Human umbilical vein endothelial cells (HUVECs) were cultured within ionic self-assembling peptide family members, RAD16-I ((RADA)4), RAD16-II ((RARADADA)2), KFE-8 ((FKFE)2), or KLD-12 ((KLDL)3). …
Biomaterial-Microvasculature Interactions, Alisha Sarang-Sieminski, Keith Gooch
Biomaterial-Microvasculature Interactions, Alisha Sarang-Sieminski, Keith Gooch
Alisha L. Sarang-Sieminski
The utility of implanted sensors, drug-delivery systems, immunoisolation devices, engineered cells, and engineered tissues can be limited by inadequate transport to and from the circulation. As the primary function of the microvasculature is to facilitate transport between the circulation and the surrounding tissue, interactionsbetween biomaterials and the microvasculature have been explored to understand the mechanisms controlling transport to implanted objects and ultimately improve it. This review surveys work on biomaterial-microvasculature interactions with a focus on the use of biomaterials to regulate the structure and function of the microvasculature. Several applications in which biomaterial-microvasculature interactions play a crucial role are briefly …
The Relative Magnitudes Of Endothelial Force Generation And Matrix Stiffness Modulate Capillary Morphogenesis In Vitro, Alisha Sarang-Sieminski, Robert Hebbel, Keith Gooch
The Relative Magnitudes Of Endothelial Force Generation And Matrix Stiffness Modulate Capillary Morphogenesis In Vitro, Alisha Sarang-Sieminski, Robert Hebbel, Keith Gooch
Alisha L. Sarang-Sieminski
When suspended in collagen gels, endothelial cells elongate and form capillary-like networks containing lumens. Human blood outgrowth endothelial cells (HBOEC) suspended in relatively rigid 3 mg/ml floating collagen gels, formed in vivo-like, thin, branched multi-cellular structures with small, thick-walled lumens, while human umbilical vein endothelial cells (HUVEC) formed fewer multi-cellular structures, had a spread appearance, and had larger lumens. HBOEC exert more traction on collagen gels than HUVEC as evidenced by greater contraction of floating gels. When the stiffness of floating gels was decreased by decreasing the collagen concentration from 3 to 1.5 mg/ml, HUVEC contracted gels more and formed …
The Stiffness Of Three-Dimensional Ionic Self-Assembling Peptide Gels Affects The Extent Of Capillary-Like Network Formation, Alisha Sarang-Sieminski, A Was, G Kim, Haiyan Gong, Roger Kamm
The Stiffness Of Three-Dimensional Ionic Self-Assembling Peptide Gels Affects The Extent Of Capillary-Like Network Formation, Alisha Sarang-Sieminski, A Was, G Kim, Haiyan Gong, Roger Kamm
Alisha L. Sarang-Sieminski
Improving our ability to control capillary morphogenesis has implications for not only better understanding of basic biology, but also for applications in tissue engineering and in vitro testing. Numerous biomaterials have been investigated as cellular supports for these applications and the biophysical environment biomaterials provide to cells has been increasingly recognized as an important factor in directing cell function. Here, the ability of ionic self-assembling peptide gels to support capillary morphogenesis and the effect of their mechanical properties is investigated. When placed in a physiological salt solution, these oligopeptides spontaneously self-assemble into gels with an extracellular matrix (ECM)-like microarchitecture. To …
Vasp Involvement In Force-Mediated Adherens Junction Strengthening, Alisha Sarang-Sieminski, Anita Kris, Roger Kamm
Vasp Involvement In Force-Mediated Adherens Junction Strengthening, Alisha Sarang-Sieminski, Anita Kris, Roger Kamm
Alisha L. Sarang-Sieminski
Strengthening of cell-matrix adhesions in response to applied force has been well documented. However, while implied by various lines of evidence, the force-mediated strengthening of cell–cell adhesions has not been directly demonstrated. In the current study, we present results consistent with force strengthening in adherens junctions, obtained by application of different force profiles to VE-cadherin-coated magnetic beads attached to endothelial cells. When force is ramped from a low to high value over time, fewer beads detach than with the immediate application of high force. Cells treated with cytochalasin D or lacking Ena/VASP activity show similar levels of detachment relative to …
Differential Effects Of Ovariectomy On The Mechanical Properties Of Cortical And Cancellous Bone In Rat Femora And Vertebrae, Debbie Chachra, J.M. Lee, M. Kasra, Marc Grynpas
Differential Effects Of Ovariectomy On The Mechanical Properties Of Cortical And Cancellous Bone In Rat Femora And Vertebrae, Debbie Chachra, J.M. Lee, M. Kasra, Marc Grynpas
Debbie Chachra
The purpose of this study was to evaluate the effects of ovariectomy on the mechanical properties of bone in the aged Sprague-Dawley rat model of osteoporosis. Eight female rats were sacrificed at the start of the study, at the age of four months. Twenty-four remaining rats were then bilaterally ovariectomized (OVX), and another twenty-four served as controls. Eight rats from each group were sacrificed at five, ten or fifteen weeks. The mean density of L1 vertebral bodies from OVX rats was lower than in their control counterparts, as was the compressive modulus, the ultimate compressive stress and the toughness. The …
Bone Quality In Animal Models Of Osteoporosis, Marc Grynpas, Debbie Chachra, Kathleen Lundon
Bone Quality In Animal Models Of Osteoporosis, Marc Grynpas, Debbie Chachra, Kathleen Lundon
Debbie Chachra
The use of animal models is a very powerful tool for the preclinical assessment of potential therapies for osteoporosis. However, the effective use of animal models has two prerequisites. The first is the use of appropriate techniques to assess the overall effects of therapy on bone. As spontaneous fractures do not occur in any species other than humans, the efficacy of a therapy cannot be assessed by its impact on fracture incidence. Instead, a suite of parameters (collectively referred to as ‘bone quality’), including bone architecture, mineralization and mechanical properties, is examined. While techniques such as histomorphometry and dual-energy x-ray …
Post-Cmos Fabrication Of Working Electrodes For On-Chip Recordings Of Transmitter Release, Sunitha Ayers, Khajak Berberian, Kevin Gillis, Manfred Lindau, Bradley Minch
Post-Cmos Fabrication Of Working Electrodes For On-Chip Recordings Of Transmitter Release, Sunitha Ayers, Khajak Berberian, Kevin Gillis, Manfred Lindau, Bradley Minch
Bradley Minch
The release of neurotransmitters and hormones from secretory vesicles plays a fundamental role in the function of the nervous system including neuronal communication. High-throughput testing of drugs modulating transmitter release is becoming an increasingly important area in the fields of cell biology, neurobiology, and neurology. Carbon-fiber amperometry provides high-resolution measurements of amount and time course of the transmitter release from single vesicles, and their modulation by drugs and molecular manipulations. However, these methods do not enable the rapid collection of data from a large number of cells. To allow this testing, we have developed a complementary metal-oxide semiconductor (CMOS) potentiostat …
Fluoride And Mineralized Tissues, Debbie Chachra, Anya Vieira, Marc Grynpas
Fluoride And Mineralized Tissues, Debbie Chachra, Anya Vieira, Marc Grynpas
Debbie Chachra
This review focuses on the interaction of fluoride with the material properties of bone and teeth, which is of clinical, scientific, and public health interest. These tissues are composed primarily of collagen (protein) and hydroxyapatite (mineral), and their mechanical function depends on the properties of the constituents, their proportions, the interface, and the three-dimensional structure. Changing any of these may have clinical consequences. Fluoride interacts with mineralized tissues in a number of ways. At low doses, the fluoride may be passively incorporated into the mineral, stabilizing it against dissolution; this is one of the mechanisms by which municipally fluoridated water …
A New Tool To Assess The Mechanical Properties Of Bone Due To Collagen Degradation, C. Wynnyckyj, S. Omelon, K. Savage, M. Damani, Debbie Chachra, Marc Grynpas
A New Tool To Assess The Mechanical Properties Of Bone Due To Collagen Degradation, C. Wynnyckyj, S. Omelon, K. Savage, M. Damani, Debbie Chachra, Marc Grynpas
Debbie Chachra
Current clinical tools for evaluating fracture risk focus only on the mineral phase of bone. However, changes in the collagen matrix may affect bone mechanical properties, increasing fracture risk while remaining undetected by conventional screening methods such as dual energy x-ray absorptiometry (DXA) and quantitative ultrasound (QUS). The mechanical response tissue analyzer (MRTA) is a non-invasive, radiation-free potential clinical tool for evaluating fracture risk. The objectives of this study were two-fold: to investigate the ability of the MRTA to detect changes in mechanical properties of bone as a result of treatment with 1 M potassium hydroxide (KOH) and to evaluate …