adhesive forces
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eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Titas Sengupta ◽  
Noelle L Koonce ◽  
Nabor Vázquez-Martínez ◽  
Mark W Moyle ◽  
Leighton H Duncan ◽  
...  

During development, neurites and synapses segregate into specific neighborhoods or layers within nerve bundles. The developmental programs guiding placement of neurites in specific layers, and hence their incorporation into specific circuits, are not well understood. We implement novel imaging methods and quantitative models to document the embryonic development of the C. elegans brain neuropil, and discover that differential adhesion mechanisms control precise placement of single neurites onto specific layers. Differential adhesion is orchestrated via developmentally-regulated expression of the IgCAM SYG-1, and its partner ligand SYG-2. Changes in SYG-1 expression across neuropil layers result in changes in adhesive forces, which sort SYG-2-expressing neurons. Sorting to layers occurs, not via outgrowth from the neurite tip, but via an alternate mechanism of retrograde zippering, involving interactions between neurite shafts. Our study indicates that biophysical principles from differential adhesion govern neurite placement and synaptic specificity in vivo in developing neuropil bundles.


Author(s):  
Pranav Sudersan ◽  
Michael Kappl ◽  
Bat-El Pinchasik ◽  
Hans-Jürgen Butt ◽  
Thomas Endlein

Many insects can climb smooth surfaces using hairy adhesive pads on their legs mediated by tarsal fluid secretions. It was previously shown that a terrestrial beetle can even adhere and walk underwater. The naturally hydrophobic hairs trap an air bubble around the pads, allowing the hairs to make contact to the substrate like in air. However, it remained unclear to what extent such an air bubble is necessary for underwater adhesion. To investigate the role of the bubble, we measured the adhesive forces inindividual legs of live but constrained ladybug beetles underwater in the presence and absence of a trapped bubble and compared it with its adhesion in air. Our experiments revealed that on a hydrophobic substrate, even without a bubble, the pads show adhesion comparable to that in air. On a hydrophilic substrate, underwater adhesion is significantly reduced, with or without a trapped bubble. We modelled the adhesion of a hairy pad using capillary forces. Coherent with our experiments, the model demonstrates that the wetting properties of the tarsal fluid alone can determine the ladybugs’ adhesion to smooth surfaces in both air and underwater conditions and that an air bubble is not a prerequisite for their underwater adhesion. The study highlights how such a mediating fluid can serve as a potential strategy to achieve underwater adhesion via capillary forces, which could inspire artificial adhesives for underwater applications.


Author(s):  
Yicen Lin ◽  
Gergely Maróti ◽  
Mikael Lenz Strube ◽  
Ákos T. Kovács

AbstractBacillus cereus group (Bacillus cereus sensu lato) has a diverse ecology, including various species that produce biofilms on abiotic and biotic surfaces. While genetic and morphological diversification enable the adaptation of multicellular communities, this area remains largely unknown in the Bacillus cereus group. In this work, we dissected the experimental evolution of Bacillus thuringiensis 407 Cry-during continuous recolonization of plastic beads. We observed the evolution of a distinct colony morphotype that we named fuzzy spreader (FS) variant. Most multicellular traits of the FS variant displayed higher competitive ability versus the ancestral strain, suggesting an important role for diversification in the adaptation of B. thuringiensis to the biofilm lifestyle. Further genetic characterization of FS variant revealed the disruption of a guanylyltransferase gene by an insertion sequence (IS) element, which could be similarly observed in the genome of a natural isolate. The evolved FS and the deletion mutant in the guanylyltransferase gene (Bt407ΔrfbM) displayed similarly altered aggregation and hydrophobicity compared to the ancestor strain, suggesting that adaptation process highly depends on the physical adhesive forces.


2021 ◽  
Author(s):  
Raghvendra Singh

Abstract There are four known fundamental forces of nature and there is a need to combine them into a unified theory. Progress has been made toward this goal but gravity remains an issue. However, the four forces are body forces that act on points. They together do not make the universe a closed system. Here, I identify a surface force, which acts outward normal to the surface of the universe. Further, using water drop hanging in a vacuum as a model, I provide a formula to find the magnitude of this force. The fifth force is generated by surface tension, a property of dark energy. On the other hand, matter particles interact with each other through cohesive forces and with dark matter through adhesive forces. I give a range of functional forms of all cohesive and adhesive forces and present an equation that unifies all the forces of nature.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Marta Targosz-Korecka ◽  
Agata Kubisiak ◽  
Damian Kloska ◽  
Aleksandra Kopacz ◽  
Anna Grochot-Przeczek ◽  
...  

AbstractEndothelial cells (ECs) play a crucial role in the development and propagation of the severe COVID-19 stage as well as multiorgan dysfunction. It remains, however, controversial whether COVID-19-induced endothelial injury is caused directly by the infection of ECs with SARS-CoV-2 or via indirect mechanisms. One of the major concerns is raised by the contradictory data supporting or denying the presence of ACE2, the SARS-CoV-2 binding receptor, on the EC surface. Here, we show that primary human pulmonary artery ECs possess ACE2 capable of interaction with the viral Spike protein (S-protein) and demonstrate the crucial role of the endothelial glycocalyx in the regulation of the S-protein binding to ACE2 on ECs. Using force spectroscopy method, we directly measured ACE2- and glycocalyx-dependent adhesive forces between S-protein and ECs and characterized the nanomechanical parameters of the cells exposed to S-protein. We revealed that the intact glycocalyx strongly binds S-protein but screens its interaction with ACE2. Reduction of glycocalyx layer exposes ACE2 receptors and promotes their interaction with S-protein. These results indicate that the susceptibility of ECs to COVID-19 infection may depend on the glycocalyx condition.


2021 ◽  
Author(s):  
Raghvendra Singh

Abstract There are four known fundamental forces of nature and there is a need to combine them into a unified theory. Progress has been made toward this goal but gravity remains an issue. However, the four forces are body forces that act on points. They together do not make the universe a closed system. Here, I identify a surface force, which acts outward normal to the surface of the universe. Further, using water drop hanging in a vacuum as a model, I provide a formula to find the magnitude of this force. The fifth force is generated by the surface tension, a property of dark energy. On the other hand, matter particles interact with each other through a cohesive force and with dark matter through an adhesive force. I give a range of the functional forms of all cohesive and adhesive forces and present an equation that unifies all the forces of nature.


Plasma ◽  
2021 ◽  
Vol 4 (2) ◽  
pp. 201-213
Author(s):  
Alexander V. Zakharov ◽  
Eugene V. Rosenfeld

Dust particles on a nonconductive surface are known to acquire electric charge and detach from the surface under plasma conditions and/or when affected by ultraviolet radiation. Similar phenomena occur as a result of electrostatic surface cleaning (shedding) as well as in nature, e.g., when observing levitation of dust particles above the lunar surface. A detachment of dust particles from the surface should occur when the electrostatic forces of their repulsion Fc exceed the sum of the gravitation Fg forces and the adhesive van der Waals FvdW forces acting on the particle on a nonconducting surface. However, a paradoxical situation usually arises: the three primary forces of different nature Fc, Fg, and FvdW, acting on a speck of dust with a characteristic size of the order of hundreds or thousands of nanometers, are completely incomparable in magnitude, herewith Fc << Fg << FvdW. In the last decade, numerous attempts have been made to explain how a particle on a nonconducting surface can acquire a charge sufficient for the electrostatic forces that arise to approach the adhesive forces’ values. However, despite some successes, many questions remain unanswered. This article presents a brief analysis of the charge appearance process on a solitary dust speck and a speck lying on the surface. To explain the detachment of dust particles from the surface caused by electrostatic forces and the accumulation of a charge on those particles sufficient for levitation, one should take into account the charge density fluctuations on the surface.


Author(s):  
E. M. Rossi ◽  
P. Sudharshan Phani ◽  
R. Guillemet ◽  
Julie Cholet ◽  
Doriane Jussey ◽  
...  

Abstract Surface Free Energy (SFE) has become a relevant design parameter to produce materials and devices with controlled wettability. The non-destructive measurement of SFE in nanopatterned super-hydrophobic hard surfaces is a challenge in both research and industry since in most cases time-consuming contact angle measurements are not feasible. In this work, we present a novel nanoindentation based method for the measurement of pull-off adhesive forces by carefully controlling environmental and instrumentation issues. The method is found to measure SFE over five orders of magnitude, covering hydrophilic to super-hydrophobic surfaces, and has been validated with contact angle measurements. Its limitations and shortcomings are critically discussed, with a specific focus on the experimental issues that could affect the reliability and reproducibility of the results. Finally, the potential applications of the newly developed methodology include fast non-destructive mapping of SFE over heterogeneous surfaces with spatially controlled wettability. Graphic abstract


2021 ◽  
Author(s):  
Joseph M. Monti ◽  
Antoine Sanner ◽  
Lars Pastewka

Abstract Understanding the distribution of interfacial separations between contacting rough surfaces is integral for providing quantitative estimates for adhesive forces between them. Assuming nonadhesive, frictionless contact of self-affine surfaces, we derive the distribution of separations p(g) between surfaces near the contact edge. The distribution diverges as g-1/3 for small gaps, and we use numerical simulations with fine resolution to confirm the scaling. The characteristic scale over which the prediction persists is h0' drep, the product of the rms surface slope and the mean diameter of contacting regions. We show that these results remain valid for weakly adhesive contacts and connect these observations to recent theories for adhesion between rough surfaces.


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