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differential geometry

Hossein Tavassoli, Sanaz Naghavi Alhosseini, Andy Tay, Peggy P Y Chan, Steve Kah Weng Oh, Majid Ebrahimi Warkiani
Human stem cells, including pluripotent, embryonic and mesenchymal, stem cells play pivotal roles in cell-based therapies. Over the past decades, various methods for expansion and differentiation of stem cells have been developed to satisfy the burgeoning clinical demands. One of the most widely endorsed technologies for producing large cell quantities is using microcarriers (MCs) in bioreactor culture systems. In this review, we focus on microcarriers properties that can manipulate the expansion and fate of stem cells...
July 11, 2018: Biomaterials
Shaban A Khaled, Morgan R Alexander, Derek J Irvine, Ricky D Wildman, Martin J Wallace, Sonja Sharpe, Jae Yoo, Clive J Roberts
An extrusion-based 3D printer was used to fabricate paracetamol tablets with different geometries (mesh, ring and solid) from a single paste-based formulation formed from standard pharmaceutical ingredients. The tablets demonstrate that tunable drug release profiles can be achieved from this single formulation even with high drug loading (> 80% w/w). The tablets were evaluated for drug release using a USP dissolution testing type I apparatus. The tablets showed well-defined release profiles (from immediate to sustained release) controlled by their different geometries...
August 10, 2018: AAPS PharmSciTech
André du Toit, Sholto De Wet, Jan-Hendrik S Hofmeyr, Kristian K Müller-Nedebock, Ben Loos
Autophagy failure is implicated in age-related human disease. A decrease in the rate of protein degradation through the entire autophagy pathway, i.e., autophagic flux, has been associated with the onset of cellular proteotoxity and cell death. Although the precision control of autophagy as a pharmacological intervention has received major attention, mammalian model systems that enable a dissection of the relationship between autophagic flux and pathway intermediate pool sizes remain largely underexplored. Here, we make use of a micropattern-based fluorescence life cell imaging approach, allowing a high degree of experimental control and cellular geometry constraints...
August 3, 2018: Cells
Georgia S Karanasiou, Nikolaos S Tachos, Antonios Sakellarios, Lampros K Michalis, Claire Conway, Elazer R Edelman, Dimitrios I Fotiadis
Coronary stents are expandable scaffolds that are used to widen occluded diseased arteries and restore blood flow. Because of the strain they are exposed to and forces they must resist as well as the importance of surface interactions, material properties are dominant. Indeed, a common differentiating factors amongst commercially available stents is their material. Several performance requirements relate to stent materials including radial strength for adequate arterial support post-deployment. This study investigated the effect of the stent material in three finite element models using different stents made of: (i) Cobalt-Chromium (CoCr), (ii) Stainless Steel (SS316L), and (iii) Platinum Chromium (PtCr)...
October 2017: Proceedings
Meimei Dong, Dawn P Spelke, Young Kwang Lee, Jean K Chung, Cheng-Han Yu, David V Schaffer, Jay T Groves
Interactions between EphB4 receptor tyrosine kinases and their membrane-bound ephrin-B2 ligands on apposed cells play a regulatory role in neural stem cell differentiation. With both receptor and ligand constrained to move within the membranes of their respective cells, this signaling system inevitably experiences spatial confinement and mechanical forces in conjunction with receptor-ligand binding. In this study, we reconstitute the EphB4-ephrin-B2 juxtacrine signaling geometry using a supported-lipid-bilayer system presenting laterally mobile and monomeric ephrin-B2 ligands to live neural stem cells...
July 23, 2018: Biophysical Journal
Gongping Huang, Jingdong Chen, Jacob Benesty
This letter deals with the problem of differential beamforming with microphone arrays of arbitrary planar geometry. By approximating the beampattern with the Jacobi-Anger expansion, it develops an algorithm that can form any specified frequency-invariant beampattern with a microphone array of any planar geometry as long as the sensors' coordinates are given and the spacing between neighboring sensors is smaller than the smallest wavelength. This method is rather general and it can be used to design differential beamformers with linear, circular, and concentric circular differential microphone arrays as well as differential arrays of arbitrary planar geometry where sensors are placed in any specified positions...
July 2018: Journal of the Acoustical Society of America
Mohamed Amine Chetoui, Olivier Boiron, Moncef Ghiss, Abdelwaheb Dogui, Valérie Deplano
Quantitative magnetic resonance imaging (MRI) provides useful information about intervertebral disc (IVD) biomechanical properties, especially those in relation to the fluid phase. These properties may improve IVD finite element (FE) models using data closer to physiological reality. The aim of this study is to investigate IVD degeneration-related properties using a coupling between MRI and FE modeling. To this end, proton density ([Formula: see text])-weighted MRI sequences of a porcine lumbar IVD were carried out to develop two biphasic swelling models with hyperelastic extracellular matrix behavior...
August 3, 2018: Biomechanics and Modeling in Mechanobiology
Ehsan Hendi, Asaad Y Shamseldin, Bruce W Melville, Stuart E Norris
Existing studies on sediment retention ponds (SRPs) have examined the effects of pond layout, inlet and outlet geometry and the installation of baffles on the performance of the SRPs. However, the effects of a temperature difference between the ambient water in the pond and the inflow are often neglected, and the buoyancy forces arising from these differences in temperature can potentially change the flow in the pond and hence its hydraulic performance. This study has experimentally evaluated the effect of these temperature differences on the flow field and residence time in a retention pond for a range of temperature differences...
July 2018: Water Science and Technology: a Journal of the International Association on Water Pollution Research
John K-J Li
The classic works of "On Growth and Form" and "The Problem of Relative Growth" that began a century ago have so fittingly, albeit unintentionally, become pertinent to the modern-day clinical treatment strategy of the many patients with cardiovascular disease. This chapter uses allometry, which was established for comparative biology, to explore physiological and pathological differences due to differential growth, which may lead to differing diagnostic and treatment approaches for male versus female patients...
2018: Advances in Experimental Medicine and Biology
Rami Ben-Zvi, Shidong Jiang, Harvey Scher, Brian Berkowitz
An exposition is given of a finite element method (FEM) software package to calculate solutions for the continuous time random walk (CTRW) integro-differential equation for non-Fickian (and Fickian) conservative or reactive transport in disordered media. The solutions encompass one-dimensional/two-dimensional (1D/2D) breakthrough curves and spatial concentration profiles for general geometry and grid. The velocity field, used as input to the (2D) solutions, may also be calculated by applying a compatible Darcy flow 2D solver...
July 25, 2018: Ground Water
Jarol E Molina, Alejandro Vasquez Echeverri, David C Schwartz, Juan P Hernandez-Ortiz
Electrostatic forces greatly affect the overall dynamics and diffusional activities of suspended charged particles in crowded environments. Accordingly, the concentration of counter-, or co-ions in a fluid -- ``the salt" -- determines the range, strength and order of electrostatic interactions between particles. This environment fosters engineering routes for controlling directed assembly of particles at both the micro- and nano-scale. Here, we analyzed two computational modeling schemes that considered salt within suspensions of charged particles, or polyelectrolytes: discrete and continuum...
July 25, 2018: Journal of Chemical Theory and Computation
Niels L Meereboer, Ivan Terzić, Sarah Saidi, Daniel Hermida Merino, Katja Loos
The electroactive properties of poly(vinylidene fluoride) (PVDF) are a direct consequence of its crystalline phases. Although poorly understood, nanostructuring PVDF in confined geometries can drastically change its crystallization behavior. Therefore, we synthesized a variety of PVDF-based triblock copolymers to gain a better understanding of the melt crystallization and explore how crystallization is affected by the morphology and chemical nature of the amorphous block. Differential scanning calorimetry, small-/wide-angle X-ray scattering, and transmission electron microscopy gave us excellent insights into the morphology and the corresponding crystalline phases...
July 17, 2018: ACS Macro Letters
Jinger Zang, Minjun Feng, Juan Zhao, Jianping Wang
Microemulsions are transparent, thermodynamically stable liquid mixtures of oil, water and surfactant. They typically exist in the form of micellar and bicontinuous structures, which appear to be equilibrium systems but are actually complex in structure and are difficult to characterize at the molecular level. In this work, potassium ferrocyanide [K4Fe(CN)6] and tungsten hexacarbonyl [W(CO)6] were chosen as two probe molecules for water and organic phases respectively to simultaneously explore the structures and dynamics of commonly prepared reverse micellar and bicontinuous microemulsion structures using aerosol OT (AOT) as the surfactant and isooctane as the oil phase...
August 1, 2018: Physical Chemistry Chemical Physics: PCCP
Masateru Takigawa, Atsushi Takahashi, Yasuaki Tanaka, Claire A Martin, Emiko Nakashima, Kazuya Yamao, Yuichiro Sagawa, Taishi Kuwahara, Kenji Okubo, Yoshihide Takahashi, Yuji Watari, Jun Nakajima, Katsumasa Takagi, Tadashi Fujino, Shigeki Kimura, Hiroyuki Hikita, Kenzo Hirao
BACKGROUND: Differential pacing technique to confirm mitral isthmus (MI) block is sometimes challenging due to destroyed tissues after extensive ablation. The purpose of this study is to set an endpoint of MI ablation using conduction time around the mitral annulus (MA). METHODS: Forty-five consecutive patients with persistent-AF who received MI linear ablation were included. The geometry and activation times of the left atrium (LA) around the MA were collected using a multipolar catheter before ablation...
July 17, 2018: Journal of Cardiovascular Electrophysiology
George K Latsis, Christina N Banti, Nikolaos Kourkoumelis, Constantina Papatriantafyllopoulou, Nikos Panagiotou, Anastasios Tasiopoulos, Alexios Douvalis, Angelos G Kalampounias, Thomas Bakas, Sotiris K Hadjikakou
Two known tin-based polymers of formula {[R₃Sn(CH₃COO)] n } where R = n -Bu⁻ ( 1 ) and R = Ph⁻ ( 2 ),were evaluated for their in vitro biological properties. The compounds were characterized via their physical properties and FT-IR, 119 Sn Mössbauer, and ¹H NMR spectroscopic data. The molecular structures were confirmed by single-crystal X-Ray diffraction crystallography. The geometry around the tin(IV) ion is trigonal bi-pyramidal. Variations in O⁻Sn⁻O···Sn' torsion angles lead to zig-zag and helical supramolecular assemblies for 1 and 2 , respectively...
July 14, 2018: International Journal of Molecular Sciences
Jesús Urrutia, Anuradha Roy, Samarth S Raut, Raúl Antón, Satish C Muluk, Ender A Finol
The maximum diameter criterion is the most important factor in the clinical management of abdominal aortic aneurysms (AAA). Consequently, interventional repair is recommended when an aneurysm reaches a critical diameter, typically 5.0 cm in the United States. Nevertheless, biomechanical measures of the aneurysmal abdominal aorta have long been implicated in AAA risk of rupture. The purpose of this study is to assess whether other geometric characteristics, in addition to maximum diameter, may be highly correlated with the AAA peak wall stress (PWS)...
July 10, 2018: Medical Engineering & Physics
Ji Young Choi, Jim K Lai, Zheng-Mei Xiong, Margaret Ren, Megan C Moorer, Joseph P Stains, Kan Cao
Patients with Hutchinson-Gilford progeria syndrome (HGPS) have low bone mass and an atypical skeletal geometry that manifests in a high risk of fractures. Using both in vitro and in vivo models of HGPS, we demonstrate that defects in the canonical WNT/β-catenin pathway, seemingly at the level of the efficiency of nuclear import of β-catenin, impair osteoblast differentiation and that restoring β-catenin activity rescues osteoblast differentiation and significantly improves bone mass. Specifically, we show that HGPS patient-derived iPSCs display defects in osteoblast differentiation, characterized by a decreased alkaline phosphatase activity and mineralizing capacity...
July 12, 2018: Journal of Bone and Mineral Research: the Official Journal of the American Society for Bone and Mineral Research
Benjamin B Kimia, Xiaoyan Li, Yuliang Guo, Amir Tamrakar
The vast majority of edge detection literature has aimed at improving edge recall and precision, with relatively few addressing the accuracy of edge orientation estimates which are often based on gradient. We show that first-order estimates of orientation can have significant error and this can be remedied by employing Third-Order estimates. This paper aims at estimating differential geometry attributes of an edge, namely, localization, orientation, and curvature, as well as edge topology, and develop robust numerical techniques in gray-scale and color images, applicable to a variety of popular edge detectors, such as gradient-based, gPb and SE...
June 12, 2018: IEEE Transactions on Pattern Analysis and Machine Intelligence
Menekse Ermis, Ezgi Antmen, Vasif Hasirci
Cell-substrate interactions play a crucial role in the design of better biomaterials and integration of implants with the tissues. Adhesion is the binding process of the cells to the substrate through interactions between the surface molecules of the cell membrane and the substrate. There are several factors that affect cell adhesion including substrate surface chemistry, topography, and stiffness. These factors physically and chemically guide and influence the adhesion strength, spreading, shape and fate of the cell...
September 2018: Bioactive Materials
Christopher Wilson, Joshua D Kennedy, Pierce Irby, Nathaniel Fried
Thulium fiber laser lithotripsy using smaller optical fibers may enable development of miniature ureteroscopes. Two ureteroscope distal tip prototypes were built and characterized. The first design was 4.5-French (Fr) [1.5-mm outer diameter (OD)], five channel tip, housing 200-μm inner diameter (ID) dedicated central channel for insertion of 100-μm core fibers and four surrounding channels, each with 1.5 Fr (510-μm ID) for instrumentation, irrigation, imaging, and illumination, respectively. The second design was 6...
July 2018: Journal of Biomedical Optics
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