scholarly journals Filament Rigidity and Connectivity Tune the Deformation Modes of Active Biopolymer Networks

2017 ◽  
Author(s):  
Samantha Stam ◽  
Simon L. Freedman ◽  
Shiladitya Banerjee ◽  
Kimberly L. Weirich ◽  
Aaron R. Dinner ◽  
...  
Keyword(s):  
Molecular Motors ◽  
The Self ◽  
Self Organization ◽  
Cross Linking ◽  
Physical Parameters ◽  
Active Materials ◽  
Wide Range ◽  
Filament Bundles ◽  
Deformation Modes ◽  
Insight Into

ABSTRACTMolecular motors embedded within collections of actin and microtubule filaments underlie the dynamic behaviors of cytoskeletal assemblies. Understanding the physics of such motor-filament materials is critical to developing a physical model of the cytoskeleton and the design of biomimetic active materials. Here, we demonstrate through experiments and simulations that the rigidity and connectivity of filaments in active biopolymer networks regulates the anisotropy and the length scale of the underlying deformations, yielding materials with varying contractility. Semi-flexible filaments that can be compressed and bent by motor stresses undergo deformations that are predominantly biaxial. By contrast, rigid filament bundles contract via actomyosin sliding deformations that are predominantly uniaxial. Networks dominated by filament buckling are robustly contractile under a wide range of connectivities, while networks dominated by actomyosin sliding can be tuned from contractile to extensile through reduced connectivity via cross-linking. These results identify physical parameters that control the forces generated within motor-filament arrays, and provide insight into the self-organization and mechanics of cytoskeletal assemblies.

scholarly journals Filament rigidity and connectivity tune the deformation modes of active biopolymer networks

2017 ◽  
Vol 114 (47) ◽  
pp. E10037-E10045 ◽  
Author(s):  
Samantha Stam ◽  
Simon L. Freedman ◽  
Shiladitya Banerjee ◽  
Kimberly L. Weirich ◽  
Aaron R. Dinner ◽  
...  
Keyword(s):  
Molecular Motors ◽  
The Self ◽  
Self Organization ◽  
Cross Linking ◽  
Physical Parameters ◽  
Active Materials ◽  
Wide Range ◽  
Filament Bundles ◽  
Deformation Modes ◽  
Insight Into

Molecular motors embedded within collections of actin and microtubule filaments underlie the dynamics of cytoskeletal assemblies. Understanding the physics of such motor-filament materials is critical to developing a physical model of the cytoskeleton and designing biomimetic active materials. Here, we demonstrate through experiments and simulations that the rigidity and connectivity of filaments in active biopolymer networks regulates the anisotropy and the length scale of the underlying deformations, yielding materials with variable contractility. We find that semiflexible filaments can be compressed and bent by motor stresses, yielding materials that undergo predominantly biaxial deformations. By contrast, rigid filament bundles slide without bending under motor stress, yielding materials that undergo predominantly uniaxial deformations. Networks dominated by biaxial deformations are robustly contractile over a wide range of connectivities, while networks dominated by uniaxial deformations can be tuned from extensile to contractile through cross-linking. These results identify physical parameters that control the forces generated within motor-filament arrays and provide insight into the self-organization and mechanics of cytoskeletal assemblies.

scholarly journals Serotonergic Axons as Fractional Brownian Motion Paths: Insights into the Self-organization of Regional Densities

2019 ◽  
Author(s):  
Skirmantas Janušonis ◽  
Nils Detering ◽  
Ralf Metzler ◽  
Thomas Vojta
Keyword(s):  
Brownian Motion ◽  
Fractional Brownian Motion ◽  
Adult Brain ◽  
The Self ◽  
Self Organization ◽  
Dense Matrix ◽  
Two Dimensional ◽  
Wide Range ◽  
Motion Paths ◽  
Key Features

ABSTRACTAll vertebrate brains contain a dense matrix of thin fibers that release serotonin (5-hydroxytryptamine), a neurotransmitter that modulates a wide range of neural, glial, and vascular processes. Perturbations in the density of this matrix have been associated with a number of mental disorders, including autism and depression, but its self-organization and plasticity remain poorly understood. We introduce a model based on reflected Fractional Brownian Motion (FBM), a rigorously defined stochastic process, and show that it recapitulates some key features of regional serotonergic fiber densities. Specifically, we use supercomputing simulations to model fibers as FBM-paths in two-dimensional brain-like domains and demonstrate that the resultant steady state distributions approximate the fiber distributions in physical brain sections immunostained for the serotonin transporter (a marker for serotonergic axons in the adult brain). We suggest that this framework can support predictive descriptions and manipulations of the serotonergic matrix and that it can be further extended to incorporate the detailed physical properties of the fibers and their environment.

scholarly journals A physical perspective on cytoplasmic streaming

2015 ◽  
Vol 5 (4) ◽  
pp. 20150030 ◽  
Author(s):  
Raymond E. Goldstein ◽  
Jan-Willem van de Meent
Keyword(s):  
Molecular Motors ◽  
Cytoplasmic Streaming ◽  
Aquatic Plant ◽  
Broad Class ◽  
Self Organization ◽  
Cell Periphery ◽  
Wide Range ◽  
Streaming Transport ◽  
Eukaryotic Organisms

Organisms show a remarkable range of sizes, yet the dimensions of a single cell rarely exceed 100 µm. While the physical and biological origins of this constraint remain poorly understood, exceptions to this rule give valuable insights. A well-known counterexample is the aquatic plant Chara , whose cells can exceed 10 cm in length and 1 mm in diameter. Two spiralling bands of molecular motors at the cell periphery drive the cellular fluid up and down at speeds up to 100 µm s −1 , motion that has been hypothesized to mitigate the slowness of metabolite transport on these scales and to aid in homeostasis. This is the most organized instance of a broad class of continuous motions known as ‘cytoplasmic streaming’, found in a wide range of eukaryotic organisms—algae, plants, amoebae, nematodes and flies—often in unusually large cells. In this overview of the physics of this phenomenon, we examine the interplay between streaming, transport and cell size and discuss the possible role of self-organization phenomena in establishing the observed patterns of streaming.

scholarly journals A gelation transition enables the self-organization of bipolar metaphase spindles

2021 ◽  
Author(s):  
Benjamin A. Dalton ◽  
David Oriola ◽  
Franziska Decker ◽  
Frank Jülicher ◽  
Jan Brugués
Keyword(s):  
Molecular Motors ◽  
Mitotic Spindle ◽  
Large Scale ◽  
Relaxation Times ◽  
Network Connectivity ◽  
The Self ◽  
Self Organization ◽  
Bipolar Structure ◽  
Microtubule Polarity ◽  
Microtubule Transport

The mitotic spindle is a highly dynamic bipolar structure that emerges from the self-organization of microtubules, molecular motors, and other proteins. Sustained motor-driven poleward flows of short dynamic microtubules play a key role in the bipolar organization of spindles. However, it is not understood how the local activity of motor proteins generates these large-scale coherent poleward flows. Here, we combine experiments and simulations to show that a gelation transition enables long-ranged microtubule transport causing spindles to self-organize into two oppositely polarized microtubule gels. Laser ablation experiments reveal that local active stresses generated at the spindle midplane propagate through the structure thereby driving global coherent microtubule flows. Simulations show that microtubule gels undergoing rapid turnover can exhibit long stress relaxation times, in agreement with the long-ranged flows observed in experiments. Finally, we show that either disrupting such flows or decreasing the network connectivity can lead to a microtubule polarity reversal in spindles both in the simulations and in the experiments. Thus, we uncover an unexpected connection between spindle rheology and architecture in spindle self-organization.

scholarly journals On the Role of the Excitation/Inhibition Balance of Homeostatic Artificial Neural Networks

Entropy ◽  
2021 ◽  
Vol 23 (12) ◽  
pp. 1681
Author(s):  
Maximilian Brütt ◽  
Christian Kaernbach
Keyword(s):  
Neural Networks ◽  
Artificial Neural Networks ◽  
Intracellular Calcium ◽  
Cell Activity ◽  
Cortical Cell ◽  
Threshold Value ◽  
The Self ◽  
Self Organization ◽  
Wide Range ◽  
Artificial Neural

Homeostatic models of artificial neural networks have been developed to explain the self-organization of a stable dynamical connectivity between the neurons of the net. These models are typically two-population models, with excitatory and inhibitory cells. In these models, connectivity is a means to regulate cell activity, and in consequence, intracellular calcium levels towards a desired target level. The excitation/inhibition (E/I) balance is usually set to 80:20, a value characteristic for cortical cell distributions. We study the behavior of these homeostatic models outside of the physiological range of the E/I balance, and we find a pronounced bifurcation at about the physiological value of this balance. Lower inhibition values lead to sparsely connected networks. At a certain threshold value, the neurons develop a reasonably connected network that can fulfill the homeostasis criteria in a stable way. Beyond the threshold, the behavior of the artificial neural network changes drastically, with failing homeostasis and in consequence with an exploding number of connections. While the exact value of the balance at the bifurcation point is subject to the parameters of the model, the existence of this bifurcation might explain the stability of a certain E/I balance across a wide range of biological neural networks. Assuming that this class of models describes the self-organization of biological network connectivity reasonably realistically, the omnipresent physiological balance might represent a case of self-organized criticality in order to obtain a good connectivity while allowing for a stable intracellular calcium homeostasis.

scholarly journals A model for the self-organization of microtubules driven by molecular motors

2000 ◽  
Vol 15 (3) ◽  
pp. 483-492 ◽  
Author(s):  
B. Bassetti ◽  
M. Cosentino Lagomarsino ◽  
P. Jona
Keyword(s):  
Molecular Motors ◽  
The Self ◽  
Self Organization

scholarly journals Electromigration-induced formation of percolating adsorbate islands during condensation from the gaseous phase: a computational study

2021 ◽  
Vol 12 ◽  
pp. 694-703
Author(s):  
Alina V Dvornichenko ◽  
Vasyl O Kharchenko ◽  
Dmitrii O Kharchenko
Keyword(s):  
Thin Film ◽  
Gaseous Phase ◽  
Computational Study ◽  
Critical Value ◽  
The Self ◽  
Self Organization ◽  
Control Parameters ◽  
Electrical Field ◽  
Applied Electrical Field ◽  
Insight Into

We provide a computational study of a change in the morphology of a growing thin film during condensation caused by electromigration effects. It will be shown, that separated circular adsorbate islands, realized in an isotropic system, become elongated in the direction of the applied electrical field. We discuss the dependence of the critical value of the strength of the applied electrical field, responsible for the formation of percolating adsorbate islands, on main control parameters. This study provides insight into details of electromigration effects during the self-organization of adatoms into percolating adsorbate islands during condensation from the gaseous phase. We will show that the elongated morphology of adsorbate islands remains stable if the electric field is turned off.

Sentence-Based Experience Logging in New Hearing Aid Users

2020 ◽  
Vol 29 (3S) ◽  
pp. 631-637
Author(s):  
Katja Lund ◽  
Rodrigo Ordoñez ◽  
Jens Bo Nielsen ◽  
Dorte Hammershøi
Keyword(s):  
Hearing Aid ◽  
Patient Experiences ◽  
Online Tool ◽  
Rehabilitation Process ◽  
Hearing Rehabilitation ◽  
Clinical Observations ◽  
Hearing Aid Use ◽  
Wide Range ◽  
Insight Into ◽  
Shed Light

Purpose The aim of this study was to develop a tool to gain insight into the daily experiences of new hearing aid users and to shed light on aspects of aided performance that may not be unveiled through standard questionnaires. Method The tool is developed based on clinical observations, patient experiences, expert involvement, and existing validated hearing rehabilitation questionnaires. Results An online tool for collecting data related to hearing aid use was developed. The tool is based on 453 prefabricated sentences representing experiences within 13 categories related to hearing aid use. Conclusions The tool has the potential to reflect a wide range of individual experiences with hearing aid use, including auditory and nonauditory aspects. These experiences may hold important knowledge for both the patient and the professional in the hearing rehabilitation process.

The Relationship between Seeker and Spiritual Guide as portrayed in contemporary Western Sufi Autobiographies

2011 ◽  
Vol 5 (2) ◽  
pp. 297-332
Author(s):  
Kate Zebiri
Keyword(s):  
Life Writing ◽  
New Age ◽  
The Self ◽  
Individual Autonomy ◽  
Religious Authority ◽  
The Face ◽  
The Relationship ◽  
Insight Into ◽  
Continuity And Discontinuity

This article aims to explore the Shaykh-mur?d (disciple) or teacher-pupil relationship as portrayed in Western Sufi life writing in recent decades, observing elements of continuity and discontinuity with classical Sufism. Additionally, it traces the influence on the texts of certain developments in religiosity in contemporary Western societies, especially New Age understandings of religious authority. Studying these works will provide an insight into the diversity of expressions of contemporary Sufism, while shedding light on a phenomenon which seems to fly in the face of contemporary social and religious trends which deemphasize external authority and promote the authority of the self or individual autonomy.

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