scholarly journals Self-organized patterning and morphogenesis in embryonic epithelia from antagonistic signals and fiber networks

2015 ◽  
Author(s):  
F.W. Cummings ◽  
Kai Lu
Keyword(s):  
Signaling Pathways ◽  
Growth Phase ◽  
Fiber Network ◽  
Fiber Networks ◽  
General Ability ◽  
Self Organized ◽  
Ability To Regenerate ◽  
Gene Patterning ◽  
Fiber Mesh ◽  
Organ Sizes

AbstractA number of universals can be observed in the developing embryos of all phyla. An attempt is made here to describe some of these with a simple model, one consisting of two mutually repelling regions of gene patterning produced by signaling pathways, two acting at each growth phase. The diffusion of ligands is short range, nearest or near neighbors, but the transcription patterns extend over many cellular diameters. The universals discussed are: gastrulation, formation of a blastopore, patterning of stem cells as surrounding compartments (propagating anew with each growth phase, to the adult), the origin of bilaterality, the prevalence of segmentation, and the general ability to regenerate and duplicate. The origin of organ sizes are determined by the parameters of the signaling pathways involved, independent of cell sizes or numbers. The important fiber mesh, or fiber network that can also extend over many cell diameters is also briefly discussed, and is seen as a partner with the signaling pathways in the overall patterning.

scholarly journals Reconfigurable optical multiplexer based on liquid crystals for polymer optical fiber networks

2006 ◽  
Vol 14 (4) ◽  
Author(s):  
P. Lallana ◽  
C. Vázquez ◽  
J. Pena ◽  
R. Vergaz
Keyword(s):  
Optical Fiber ◽  
Wavelength Division Multiplexing ◽  
Optical Sensors ◽  
Integrated Circuit ◽  
Electronic System ◽  
Polymer Optical Fiber ◽  
Fiber Network ◽  
Fiber Networks ◽  
Graded Index ◽  
Optical Fiber Networks

AbstractIn this work, different novel 3×1 multiplexer structures for being used in polymer optical fiber networks are proposed. Designs are compact, scalable, and of low consumption, capable of operating in a large wavelength range simultaneously 660, 850, and 1300 nm, due to the use of nematic liquid crystal cells. Light that comes from each input port is handled independently and eight operation modes are possible.Control electronics has been made using a programmable integrated circuit. Electronic system makes available the managing of the optical stage using a computer. An additional four optical sensors have been included for allowing the optical status checking.Finally, a polarization independent multiplexer has been implemented and tested. Insertion losses less than 4 dB and isolation better than 23 dB have been measured. In addition, 30-ms and 15-ms setup and rise times have been obtained. The proposed multiplexer can be used in any polymer optical fiber network, even in perfluorinated graded index one, and it can be specially useful in optical sensor networks, or in coarse wavelength division multiplexing networks.

Relating Network Topology to Network Mechanics

2012 ◽  
Author(s):  
Eric M. Christiansen ◽  
Mohammad F. Hadi ◽  
Victor H. Barocas
Keyword(s):  
Mechanical Properties ◽  
Network Topology ◽  
Soft Tissues ◽  
Topological Properties ◽  
Fiber Network ◽  
Fiber Networks ◽  
Protein Fiber ◽  
Network Topologies

Soft tissues are comprised of underlying fiber networks of collagen and other fibrous proteins and biopolymers. Thus, the ability to model the deformation of fiber networks is critical to understanding the mechanics of tissues in vivo and in vitro [1]. Complicating the issue, protein fiber networks are comprised of a range of different topologies that behave differently under load. There is a clear need for a method to derive network parameters that characterize the network and allow for the prediction of their behavior. In this study, we characterized several different random fiber network types based on their intrinsic mechanical and topological properties. Such characterization would improve our ability to select microscale network topologies that match the mechanical properties we observe in healthy and diseased native tissues [2]. It would also improve our ability to discern the outcome of microstructural changes in tissues (such as from remodeling or injury) on their overall mechanics.

scholarly journals Drosophila as a Model System to Study Cell Signaling in Organ Regeneration

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Sara Ahmed-de-Prado ◽  
Antonio Baonza
Keyword(s):  
Drosophila Melanogaster ◽  
Signaling Pathways ◽  
Cell Fate ◽  
Cellular Responses ◽  
Model System ◽  
Signaling Networks ◽  
Cellular Processes ◽  
Organ Regeneration ◽  
Ability To Regenerate ◽  
Genetic Mechanisms

Regeneration is a fascinating phenomenon that allows organisms to replace or repair damaged organs or tissues. This ability occurs to varying extents among metazoans. The rebuilding of the damaged structure depends on regenerative proliferation that must be accompanied by proper cell fate respecification and patterning. These cellular processes are regulated by the action of different signaling pathways that are activated in response to the damage. The imaginal discs of Drosophila melanogaster have the ability to regenerate and have been extensively used as a model system to study regeneration. Drosophila provides an opportunity to use powerful genetic tools to address fundamental problems about the genetic mechanisms involved in organ regeneration. Different studies in Drosophila have helped to elucidate the genes and signaling pathways that initiate regeneration, promote regenerative growth, and induce cell fate respecification. Here we review the signaling networks involved in regulating the variety of cellular responses that are required for discs regeneration.

scholarly journals Single-Line Bidirectional Optical Add/Drop Multiplexer for Ring Topology Optical Fiber Networks

Sensors ◽  
2021 ◽  
Vol 21 (8) ◽  
pp. 2641
Author(s):  
Chung-Yi Li ◽  
Ching-Hung Chang ◽  
Zih-Guei Lin
Keyword(s):  
Optical Fiber ◽  
Optical Network ◽  
Optimal Solution ◽  
Single Line ◽  
Ring Topology ◽  
Fiber Network ◽  
Fiber Networks ◽  
Optical Fiber Networks ◽  
New Type ◽  
The Stability

A new type of passive single-line bidirectional optical add/drop multiplexer (SBOADM) is proposed and experimentally demonstrated. When the proposed SBOADM is placed as a node of a ring topology optical fiber network, the special routing function of the SBOADM can always drop down the desired downstream signals whether the signals are injected into the SBOADM in either the clockwise (CW) or counterclockwise (CCW) direction and can upload and send back the upstream signals via the reversed optical pathway of the downstream signals. Once fiber link failure occurs in the optical network, the blocked network connections can be recovered immediately by sending out the downstream signals in both the CW and CCW directions of the fiber ring. As in all passive devices, the SBOADM needs no power supply or complicated network management to achieve the bidirectional function. Thus, the proposed device is an optimal solution to enhance the stability and reliability of rapidly developed optical fiber networks.

Personalized Fiber-Reinforcement Networks for Meniscus Reconstruction

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Jay M. Patel ◽  
Andrzej Brzezinski ◽  
Salim A. Ghodbane ◽  
Rae Tarapore ◽  
Tyler M. Lu ◽  
...  
Keyword(s):  
Contact Stress ◽  
Load Distribution ◽  
Fiber Reinforcement ◽  
Distribution Analysis ◽  
Stress Distributions ◽  
Fiber Network ◽  
Fiber Networks ◽  
Length Width ◽  
Post Traumatic

Abstract The menisci are fibrocartilaginous tissues that are crucial to the load-sharing and stability of the knee, and when injured, these properties are compromised. Meniscus replacement scaffolds have utilized the circumferential alignment of fibers to recapitulate the microstructure of the native meniscus; however, specific consideration of size, shape, and morphology has been largely overlooked. The purpose of this study was to personalize the fiber-reinforcement network of a meniscus reconstruction scaffold. Human cadaveric menisci were measured for a host of tissue (length, width) and subtissue (regional widths, root locations) properties, which all showed considerable variability between donors. Next, the asymmetrical fiber network was optimized to minimize the error between the dimensions of measured menisci and predicted fiber networks, providing a 51.0% decrease (p = 0.0091) in root-mean-square (RMS) error. Finally, a separate set of human cadaveric knees was obtained, and donor-specific fiber-reinforced scaffolds were fabricated. Under cyclic loading for load-distribution analysis, in situ implantation of personalized scaffolds following total meniscectomy restored contact area (253.0 mm2 to 488.9 mm2, p = 0.0060) and decreased contact stress (1.96 MPa to 1.03 MPa, p = 0.0025) to near-native values (597.4 mm2 and 0.83 MPa). Clinical use of personalized meniscus devices that restore physiologic contact stress distributions may prevent the development of post-traumatic osteoarthritis following meniscal injury.

scholarly journals Compression Strength Mechanisms of Low-Density Fibrous Materials

Materials ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 384 ◽  
Author(s):  
Jukka Ketoja ◽  
Sara Paunonen ◽  
Petri Jetsu ◽  
Elina Pääkkönen
Keyword(s):  
High Speed ◽  
Image Correlation ◽  
Regenerated Cellulose ◽  
Low Density ◽  
Fibrous Materials ◽  
High Speed Imaging ◽  
Fiber Network ◽  
Fiber Networks ◽  
Fiber Materials ◽  
Heterogeneous Deformation

In this work we challenge some earlier theoretical ideas on the strength of lightweight fiber materials by analyzing an extensive set of foam-formed fiber networks. The experimental samples included various different material densities and different types of natural and regenerated cellulose fibers. Characterization of the samples was performed by macroscopic mechanical testing, supported by simultaneous high-speed imaging of local deformations inside a fiber network. The imaging showed extremely heterogeneous deformation behavior inside a sample, with both rapidly proceeding deformation fronts and comparatively still regions. Moreover, image correlation analysis revealed frequent local fiber dislocations throughout the compression cycle, not only for low or moderate compressive strains. A new buckling theory including a statistical distribution of free-span lengths is proposed and tested against the experimental data. The theory predicts universal ratios between stresses at different compression levels for low-density random fiber networks. The mean ratio of stresses at 50% and 10% compression levels measured over 57 different trial points, 5.42 ± 0.43, agrees very well with the theoretical value of 5.374. Moreover, the model predicts well the effect of material density, and can be used in developing the properties of lightweight materials in novel applications.

On Structure and Elastic Fields of Random Fiber Networks

2010 ◽  
Author(s):  
Hamed Hatami-Marbini ◽  
Catalin R. Picu
Keyword(s):  
Structural Parameters ◽  
Upper And Lower Bounds ◽  
Segment Length ◽  
Complex Deformation ◽  
Fiber Network ◽  
Scaling Properties ◽  
Fiber Networks ◽  
Long Range Correlations ◽  
Elastic Fields ◽  
Box Counting Method

Random filamentous networks and their response to the applied load can be considered as a model to study the mechanical properties of biological systems such as cytoskeleton of a cell and connective tissues. A mathematical model for the actual and complex deformation of these networks under stress is developed using a micromechanics approach. We recently studied the effect of various micro-structural parameters such as fiber length, mean segment length and fiber flexibility on the network deformation field at various length scales. The network elasticity is mapped into a two dimensional heterogeneous continuum domain in order to show that the elastic fields of dense fiber networks show long range correlations over a range of scales for which we gave the upper and lower bounds. It is concluded that the deformation of random networks is similar to that of highly heterogeneous continuum domains with stochastic distribution of moduli. We employed the stochastic finite element method to solve boundary value problems defined on the random fiber network domain. Here, we present a brief review of this methodology and report new results on scaling properties of the structure of fiber networks using box-counting method.

Stability of Fiber Networks Under Biaxial Stretching

1995 ◽  
Vol 62 (2) ◽  
pp. 398-406 ◽  
Author(s):  
Xiaoping Liu ◽  
R. D. James
Keyword(s):  
Energy Function ◽  
Anisotropic Materials ◽  
Variational Calculation ◽  
Constitutive Behavior ◽  
Dead Load ◽  
Fiber Network ◽  
Fiber Networks ◽  
Biaxial Stretching ◽  
Dead Loading ◽  
Related Observation

This paper is concerned with the constitutive behavior of a particular orthogonal fiber network under biaxial dead loading. We also describe a new kind of biaxial, dead-loading machine which is applicable to anisotropic materials. The machine does not require that the loads are exerted along symmetry axes of the material. A specimen of the cloth was loaded by different loading paths to the same equibiaxial dead-load, and two different final deformations were observed. A related observation was reported by Treloar for rubber in 1948. In order to understand this instability, we experimentally determined the energy function for the cloth. The energy function is then used in a variational calculation to explain this instability.

Understanding extensibility of paper: Role of fiber elongation and fiber bonding

TAPPI Journal ◽  
2020 ◽  
Vol 19 (3) ◽  
pp. 125-135
Author(s):  
JARMO KOUKO ◽  
TUOMAS TURPEINEN ◽  
ARTEM KULACHENKO ◽  
ULRICH HIRN ◽  
ELIAS RETULAINEN
Keyword(s):  
Strain Curve ◽  
Tensile Tests ◽  
Pulp Fibers ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Fiber Network ◽  
Fiber Networks ◽  
Strain Behavior ◽  
Softwood Kraft Pulp ◽  
Random Fiber Networks

The tensile tests of individual bleached softwood kraft pulp fibers and sheets, as well as the micro-mechanical simulation of the fiber network, suggest that only a part of the elongation potential of individual fibers is utilized in the elongation of the sheet. The stress-strain curves of two actual individual pulp fibers and one mimicked classic stress-strain behavior of fiber were applied to a micromechanical simulation of random fiber networks. Both the experimental results and the micromechanical simulations indicated that fiber bonding has an important role not only in determining the strength but also the elongation of fiber networks. Additionally, the results indicate that the shape of the stress-strain curve of individual pulp fibers may have a significant influence on the shape of the stress-strain curve of a paper sheet. A large increase in elongation and strength of paper can be reached only by strength-ening fiber-fiber bonding, as demonstrated by the experimental handsheets containing starch and cellulose microfi-brils and by the micromechanical simulations. The key conclusion related to this investigation was that simulated uniform inter-fiber bond strength does not influence the shape of the stress-strain curve of the fiber network until the bonds fail, whereas the number of bonds has an influence on the activation of the fiber network and on the shape of the whole stress-strain curve.

scholarly journals YAP1 Regulates the Self-organized Fate Patterning of hESCs-Derived Gastruloids

2021 ◽  
Author(s):  
Servando Giraldez ◽  
Eleonora Stronati ◽  
Ling Huang ◽  
Hui-Ting Hsu ◽  
Elizabeth Abraham ◽  
...  
Keyword(s):  
Signaling Pathways ◽  
Cell Fate ◽  
Embryonic Stem ◽  
Chromatin Accessibility ◽  
The Self ◽  
Germ Layer ◽  
Nodal Signaling ◽  
Rna Seq ◽  
Self Organized

ABSTRACTDuring gastrulation, the coordinated activity of BMP, WNT and NODAL signaling pathways guide the differentiation of the pluripotent epiblast into the three germinal layers. Recent studies underline the role of the Hippo-effector YAP1 regulating WNT and NODAL signaling pathways and repressing mesoendodermal differentiation in human embryonic stem cells (hESCs). However, the contribution of YAP1 to the cell-fate patterning decisions that transform the epiblast in a three-germ layer gastrula remains unknown. We address this question by analyzing micropatterned 2D-gastruloids derived from hESCs, in the presence and absence of YAP1. Our findings show that YAP1 is necessary for gastrulation. YAP1 KO-gastruloids display reduced ectoderm layer and enlarged mesoderm and endoderm layers, compared to WT. Furthermore, YAP1 regulates the self-organized patterning of the hESCs, as the discrete position of the three germ layers is altered in the YAP1 KO-gastruloids. Our epigenome (single-nuclei ATACseq) and transcriptome (RNA-seq) analysis revealed that YAP1 directly represses the chromatin accessibility and transcription of key genes in the NODAL pathway, including the NODAL and FOXH1 genes. In WT gastruloids, a gradient of NODAL: SMAD2.3 signaling from the periphery to the center of the colony regulates the exit of pluripotency toward endoderm, mesoderm and ectoderm, respectively. Hence, in the absence of YAP1, a hyperactive NODAL signaling retains SMAD2.3 in the nuclei impeding the self-organized differentiation of hESCs. Accordingly, the partial inhibition of NODAL signaling is sufficient to rescue the differentiation and pattern -defective phenotypes of the YAP1 KO gastruloids. Our work revealed that YAP1 is a master regulator of NODAL signaling, essential to instruct germ layer fate patterning in human gastruloids.

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