Tension Propagation Research Articles

Dissecting cell membrane tension dynamics and its effect on Piezo1-mediated cellular mechanosensitivity using force-controlled nanopipettes

The dynamics of cellular membrane tension and its role in mechanosensing, which is the ability of cells to respond to physical stimuli, remain incompletely understood, mainly due to the lack of appropriate tools. Here, we report a force-controlled nanopipette-based method that combines fluidic force microscopy with fluorescence imaging for precise manipulation of the cellular membrane tension while monitoring the impact on single-cell mechanosensitivity. The force-controlled nanopipette enables control of the indentation force imposed on the cell cortex as well as of the aspiration pressure applied to the plasma membrane. We show that this setup can be used to concurrently monitor the activation of Piezo1 mechanosensitive ion channels via calcium imaging. Moreover, the spatiotemporal behavior of the tension propagation is assessed with the fluorescent membrane tension probe Flipper-TR, and further dissected using molecular dynamics modeling. Finally, we demonstrate that aspiration and indentation act independently on the cellular mechanobiological machinery, that indentation induces a local pre-tension in the membrane, and that membrane tension stays confined by links to the cytoskeleton.

Model based precise register control method for shaft-driven Roll-to-Roll(R2R) systems

Shaft-driven Roll-to-Roll (R2R) printing systems have advantages in keeping the printing rolls synchronously rotating, thereby reducing the register errors of R2R printing systems. However, tension oscillations and propagation are still inevitable due to other factors such as disturbances, which lead to the fluctuation of register errors. In this paper, a new mechanical model is established for the shaft-driven R2R systems. Then, a model-based precise control (MBPC) method is proposed, in which an implicit coupling algorithm is designed for the cooperate actions of the dancer rolls to rapidly suppress the tension oscillations and propagation. The stability of the proposed control system is proved via Lyapunov analysis. Moreover, the effectiveness of the proposed modeling and control method is verified via an industrial example. The results indicate that the proposed model can accurately characterize the dynamics of the R2R systems, and the MBPC can effectively eliminate the register errors caused by the tension oscillations and propagation, through the implicit coupling algorithm. Additionally, the results also demonstrate that the MBPC can increase the register precision of package manufacturing R2R systems into ±40 micrometers, which is superior to the existing control method.

Cooperative compensate register control for mechanical shaft driven roll-to-roll printing system with dancer rolls

In mechanical shaft driven roll-to-roll (R2R) printing systems, tension propagation caused by the regulation of dancer rolls increase the control difficulty of the whole system. In this paper, a cooperative compensate control (CoComC) method is proposed for the R2R printing systems to attenuate tension fluctuation and reduce the register errors. Specifically, a mechanical model is established to quantify the relationship among the web tension, linear velocity of dancer roll and register error. Based on the model, a well-tuned feedback control law is designed for each dancer roll, and a cooperative matrix is proposed to coordinate the feedback control to attenuate the tension fluctuation and reduce the register error in the corresponding printing unit. Further, the stability and convergence condition of the proposed control system are provided and proved via Lyapunov stability theory. The effectiveness of the proposed control method is demonstrated by experiments. Comparisons of the existing control method are carried out to show the superior performance of CoComC, i.e., higher register accuracy, superior fluctuation attenuation performance and less waste of printing material.

Forced and spontaneous translocation dynamics of a semiflexible active polymer in two dimensions.

Polymer translocation is a fundamental topic in non-equilibrium physics and is crucially important to many biological processes in life. In the present work, we adopt two-dimensional Langevin dynamics simulations to study the forced and spontaneous translocation dynamics of an active filament. The influence of polymer stiffness on the underlying dynamics is explicitly analyzed. For the forced translocation, the results show a robust stiffness-induced inhibition, and the translocation time exhibits a dual-exponent scaling relationship with the bending modulus. Tension propagation (TP) is also examined, where we find prominent modifications in terms of both activity and stiffness. For spontaneous translocation into a pure solvent, the translocation time is almost independent of the polymer stiffness. However, when the polymer is translocated into a porous medium, an intriguing non-monotonic alteration of translocation time with increasing chain stiffness is demonstrated. The semiflexible chain is beneficial for translocation while the rigid chain is not conducive. Stiffness regulation on the diffusion dynamics of the polymer in porous media shows a consistent scenario. The interplay of activity, stiffness, and porous crowding provides a new mechanism for understanding the non-trivial translocation dynamics of an active filament in complex environments.

Translocation Dynamics of an Active Filament through a Long-Length Scale Channel.

Active filament translocation through a confined space is crucial for diverse biological processes. By using Langevin dynamics simulations, we investigate the translocation dynamics of an axially self-propelled chain through a channel. First, results show a suggestive reciprocal scaling of translocation time versus active force. Second, in the case of a long channel, we demonstrate a very intriguing nonmonotonic change of translocation time with increasing channel width. The driving force shows a similar trend, providing a consistent picture to understand the unexpected channel width effect. In particular, in a moderately broad channel, the disordered chain conformation results in a loss of driving force and thus inhibits translocation dynamics. Chain adsorption might occur in a wide channel, which accounts for a facilitated translocation. Lastly, we connect the translocation process to tension propagation (TP). A modified TP picture is proposed to interpret the waiting time distribution. Our work highlights the new phenomenology owing to the crucial interplay of activity and spacial confinement, which drives the translocation dynamics, going beyond the traditional entropic barrier scenario.

Cell protrusions and contractions generate long-range membrane tension propagation

Membrane tension is thought to be a long-range integrator of cell physiology. Membrane tension has been proposed to enable cell polarity during migration through front-back coordination and long-range protrusion competition. These roles necessitate effective tension transmission across the cell. However, conflicting observations have left the field divided as to whether cell membranes support or resist tension propagation. This discrepancy likely originates from the use of exogenous forces that may not accurately mimic endogenous forces. We overcome this complication by leveraging optogenetics to directly control localized actin-based protrusions or actomyosin contractions while simultaneously monitoring the propagation of membrane tension using dual-trap optical tweezers. Surprisingly, actin-driven protrusions and actomyosin contractions both elicit rapid global membrane tension propagation, whereas forces applied to cell membranes alone do not. We present a simple unifying mechanical model in which mechanical forces that engage the actin cortex drive rapid, robust membrane tension propagation through long-range membrane flows.

Do cell membranes support or resist tension propagation?

In cell migration, protrusions have been proposed to communicate with one another via long-range membrane tension propagation for the winner-take-all, thereby establishing the axis of cell movement. This coordination among protrusions necessitates rapid propagation of membrane tension across the cell. However, several prominent studies suggested otherwise, reporting that cell membranes resist tension propagation and challenging the role of membrane tension as a global integrator in cell physiology. The field hence remains largely divided over the debate of tension propagation, and one source of disagreement stems from differences in methodology. Experiments showing global tension propagation relied on endogenous mechanical perturbations from the cell, while others unable to detect propagation employed exogenous force applications to mimic endogenous counterparts.

Experimental investigation of the forces dictating polymer translocation through solid-state nanopores.

After realizing direct long-read DNA and RNA sequencing, nanopores show also potential for decoding information on other polymers, including proteins and nanostructured DNA. Understanding the process by which these biopolymers are captured and traverse nanopores however remains a challenging task due to the complex nature of the non-equilibrium translocation dynamics which occur on multiple timescales and are dictated mainly by forces over which full experimental control is challenging. This unfortunately also makes verification of theoretical ideas difficult. In this work, we present solid-state nanopore data of DNA fragments for a wide range of experimental conditions in hopes of showcasing the various underlying forces and processes during capture and translocation. Namely, we specifically attempt to establish the absolute and relative magnitude of electrophoretic forces, and frictional contributions originating from hydrodynamic interactions both inside and outside nanopores. This is achieved by studying the dependence of translocation times on nanopore size (3-20 nm diameter) and DNA length (500-45,000 bp), and by measuring the time-dependent translocation velocity of DNA nanostructures, which consists of a linear DNA polymer with three helix-bundle (3HB) sub-structures patterned along its contour. The velocity profile of the patterned nanostructure is measured under different applied voltages (0.1-1 V), in different salt concentrations (0.5-4 M LiCl), and in different pore geometry. The data allow us to corroborate the predictions of tension propagation and consolidate previously published observations regarding measurements of electrophoretic pulling force and pore-polymer interactions in nanopore systems. In addition to bridging nanopore experiment and theory, these results can be used to inform and design several biosensing and digital storage applications.

Recoil Measurements in Drosophila Embryos: from Mounting to Image Analysis.

Tension and force propagation play a central role in tissue morphogenesis, as they enable sub- and supra-cellular shape changes required for the generation of new structures. Force is often generated by the cytoskeleton, which forms complex meshworks that reach cell-cell or cell-extracellular matrix junctions to induce cellular rearrangements. These mechanical properties can be measured through laser microdissection, which concentrates energy in the tissue of interest, disrupting its cytoskeleton. If the tissue is undergoing tension, this cut will induce a recoil in the surrounding regions of the cut. This protocol describes how one can perform laser microdissection experiments and subsequently measure the recoil speed of the sample of interest. While we explain how to carry out these experiments in Drosophila embryos, the recoil calibration and downstream analyses can be applied to other types of preparations. Key features Allows measuring tension in live Drosophila embryos with a relatively simple approach. Describes a quick way to mount a high number of embryos. Includes a segmentation-free recoil quantification that reduces bias and speeds up analysis. Graphical overview.

Preprint Highlight: Actin-driven protrusions generate rapid long-range membrane tension propagation in cells.

The distribution of long-range membrane tension across a cell is controversial. Previous studies find either that cell membranes do not propagate tension or that membrane tension propagation is potentially coupled to protrusions. Further, it is unclear whether the actin cortex resists or contributes to membrane tension. This work combined optogenetic activation of actin-driven membrane protrusions for generating local endogenous tension with dual-optical trapping for measuring and manipulating exogenous membrane tension. This powerful combination of techniques showed that the plasma membrane and actin cortex are integrated in long-range membrane tension propagation. The authors developed a composite mechanical model that predicts this integration and was experimentally validated. This study demonstrates that cell membrane tension is intrinsically coupled to actin cytoskeleton dynamics and challenges previous findings.

Membrane tension propagation couples axon growth and collateral branching.

Neuronal axons must navigate a mechanically heterogeneous environment to reach their targets, but the biophysical mechanisms coupling mechanosensation, growth, and branching are not fully understood. Here, we show that local changes in membrane tension propagate along axons at approximately 20 μm/s, more than 1000-fold faster than in most other nonmotile cells where this property has been measured. Local perturbations to tension decay along the axon with a length constant of approximately 41 μm. This rapid and long-range mechanical signaling mediates bidirectional competition between axonal branch initiation and growth cone extension. Our data suggest a mechanism by which mechanical cues at one part of a growing axon can affect growth dynamics remotely.

Elucidating the dynamics of polymer transport through nanopores using asymmetric salt concentrations

While notable progress has been made in recent years both experimentally and theoretically in understanding the highly complex dynamics of polymer capture and transport through nanopores, there remains significant disagreement between experimental observation and theoretical prediction that needs to be resolved. Asymmetric salt concentrations, where the concentrations of ions on each side of the membrane are different, can be used to enhance capture rates and prolong translocation times of electrophoretically driven polymers translocating through a nanopore from the low salt concentration reservoir, which are both attractive features for single-molecule analysis. However, since asymmetric salt concentrations affect the electrophoretic pull inside and outside the pore differently, it also offers a useful control parameter to elucidate the otherwise inseparable physics of the capture and translocation process. In this work, we attempt to paint a complete picture of the dynamics of polymer capture and translocation in both symmetric and asymmetric salt concentration conditions by reporting the dependence of multiple translocation metrics on voltage, polymer length, and salt concentration gradient. Using asymmetric salt concentration conditions, we experimentally observe the predictions of tension propagation theory, and infer the significant impact of the electric field outside the pore in capturing polymers and in altering polymer conformations prior to translocation.

Discriminating protein tags on a dsDNA construct using a Dual Nanopore Device

We report Brownian dynamics simulation results with the specific goal to identify key parameters controlling the experimentally measurable characteristics of protein tags on a dsDNA construct translocating through a double nanopore setup. First, we validate the simulation scheme in silico by reproducing and explaining the physical origin of the asymmetric experimental dwell time distributions of the oligonucleotide flap markers on a 48 kbp long dsDNA at the left and the right pore. We study the effect of the electric field inside and beyond the pores, critical to discriminate the protein tags based on their effective charges and masses revealed through a generic power-law dependence of the average dwell time at each pore. The simulation protocols monitor piecewise dynamics at a sub-nanometer length scale and explain the disparate velocity using the concepts of nonequilibrium tension propagation theory. We further justify the model and the chosen simulation parameters by calculating the Péclet number which is in close agreement with the experiment. We demonstrate that our carefully chosen simulation strategies can serve as a powerful tool to discriminate different types of neutral and charged tags of different origins on a dsDNA construct in terms of their physical characteristics and can provide insights to increase both the efficiency and accuracy of an experimental dual-nanopore setup.

Driven polymer translocation into a channel: Isoflux tension propagation theory and Langevin dynamics simulations

Isoflux tension propagation (IFTP) theory and Langevin dynamics (LD) simulations are employed to study the dynamics of channel-driven polymer translocation in which a polymer translocates into a narrow channel and the monomers in the channel experience a driving force ${f}_{\mathrm{c}}$. In the high driving force limit, regardless of the channel width, IFTP theory predicts $\ensuremath{\tau}\ensuremath{\propto}{f}_{\text{c}}^{\ensuremath{\beta}}$ for the translocation time, where $\ensuremath{\beta}=\ensuremath{-}1$ is the force scaling exponent. Moreover, LD data show that for a very narrow channel fitting only a single file of monomers, the entropic force due to the subchain inside the channel does not play a significant role in the translocation dynamics and the force exponent $\ensuremath{\beta}=\ensuremath{-}1$ regardless of the force magnitude. As the channel width increases the number of possible spatial configurations of the subchain inside the channel becomes significant and the resulting entropic force causes the force exponent to drop below unity.

Crack Growth and Delamination Analysis in GFRP Composite Materials

The modeling of the structural behavior of composite materials is an interesting but complex task since the response of the material to loading structural may be difficult to predict, and the failure may be manifested in different forms. In cross-ply fiber-reinforced composites, the major failure mechanisms include: (i) the failure of the matrix material (transverse cracking), (ii) delamination and (iii) the breakage of the fibers. The process of the transverse cracking is a well studied damage mechanism and can be used in numerical simulations, in order to study the effects of various parameters on the crack density. In this paper, the finite element modeling of a cross-ply composite under uniaxial loading in tension is performed using ABAQUS software, considering all the potential damage mechanisms. The model takes into account shear-lag effect for the determination of the stress transfer and furthermore it adopts a homogenization procedure for the calculation of elastic and viscoelastic material properties. Stochasticity is introduced by assigning various interfacial strengths that follow a Gaussian distribution, so as to predict the cracking sequence up to saturation in the transverse to the 0∘ layers. The results are directly compared with available experimental measurements showing reasonable agreement. Finally, a cross-ply RVE model was created and loaded in uniaxial tension and crack propagation is modelled with the Extended Finite Element Method (XFEM). The stress concentration calculations around the crack tips are in agreement with the mesoscale model.

Dynamics of driven polymer transport through a nanopore

The transport of polymers across nanoscale pores underpins many biological processes, such as the ejection of bacteriophage DNA into a host cell and the transfer of genes between bacteria. The movement of polymers into and out of confinement is also the basis for a wide range of sensing technologies used for single-molecule detection and sequencing. Acquiring an accurate understanding of the translocation dynamics is an essential step in the quantitative analysis of polymer structure, including the localization of binding sites or sequences. Here we use synthetic nanopores and nanostructured DNA molecules to directly measure the velocity profile of driven polymer translocation through synthetic nanopores. Our results reveal a two-stage behaviour in which the translocation initially slows with time before accelerating close to the end of the process. We also find distinct local velocity correlations as the DNA polymer chain passes through the nanopore. Brownian dynamics simulations show that the two-stage behaviour is associated with tension propagation, with correlations arising from the random-walk conformation in which the DNA begins.

Fault detection for recycled rubber and glass material implementation via digital image processing

The study exhibits to understand the cracks generation and propagation inside the material as a source of the identification. The research is based primarily on the assessment of deflection, tension, and fracture propagation in structures through digital image processing (DIP) and its correlation. The DIP is a non-destructive assessment technique to capture microstructure pictures and loading in various loading scenarios. In order to monitor features and assign their position to a defined coordinate system, photogrammetry concepts are applied. The generated displacement data represents the typical movement present concerning the initial location in the centre of the tiny sub-images employed in the analysis. Aerial or satellite photos collected before and after the earthquake may currently be analyzed in techniques to deduce co-seismic terrain malformations with sub-pixel correlation. Due to the intrinsic diversity of natural faults and deformations, the interpretation of this data is not straightforward. The study of the correlation with either program clearly shows the relative shifts, the friction interface, the rupture arrest on the border, and wing fractures. The observations of displacement collected are transformed into strains using non-local denoising algorithms. This work is the first step in combining the digital picture association approach with high-speed photography to record transient dynamic rupture events. For measuring surface movement and tension in concrete, the DIP technology and the MATLAB® Program tracking have been employed.

DNA barcodes using a double nanopore system

The potential of a double nanopore system to determine DNA barcodes has been demonstrated experimentally. By carrying out Brownian dynamics simulation on a coarse-grained model DNA with protein tag (barcodes) at known locations along the chain backbone, we demonstrate that due to large variation of velocities of the chain segments between the tags, it is inevitable to under/overestimate the genetic lengths from the experimental current blockade and time of flight data. We demonstrate that it is the tension propagation along the chain’s backbone that governs the motion of the entire chain and is the key element to explain the non uniformity and disparate velocities of the tags and DNA monomers under translocation that introduce errors in measurement of the length segments between protein tags. Using simulation data we further demonstrate that it is important to consider the dynamics of the entire chain and suggest methods to accurately decipher barcodes. We introduce and validate an interpolation scheme using simulation data for a broad distribution of tag separations and suggest how to implement the scheme experimentally.

Polymer translocation through a nanopore assisted by an environment of active rods

We use a combination of computer simulations and iso-flux tension propagation (IFTP) theory to investigate translocation dynamics of a flexible linear polymer through a nanopore into an environment composed of repulsive active rods in 2D. We demonstrate that the rod activity induces a crowding effect on the polymer, leading to a time-dependent net force that facilitates translocation into the active environment. Incorporating this force into the IFTP theory for pore-driven translocation allows us to characterise translocation dynamics in detail and derive a scaling form for the average translocation time as $\tilde{\tau} \sim \tilde{L}_{\textrm{r}}^{\nu} / \tilde{F}_{\textrm{SP}} $, where $\tilde{L}_{\textrm{r}}$ and $\tilde{F}_{\textrm{SP}}$ are the rod length and self-propelling force acting on the rods, respectively, and $\nu$ is the Flory exponent.

Pulling a folded polymer through a nanopore

We investigate the translocation dynamics of a folded linear polymer which is pulled through a nanopore by an external force. To this end, we generalize the iso-flux tension propagation theory for end-pulled polymer translocation to include the case of two segments of the folded polymer traversing simultaneously trough the pore. Our theory is extensively benchmarked with corresponding molecular dynamics (MD) simulations. The translocation process for a folded polymer can be divided into two main stages. In the first stage, both branches are traversing the pore and their dynamics is coupled. If the branches are not of equal length, there is a second stage where translocation of the shorter branch has been completed. Using the assumption of equal monomer flux of both branches confirmed by MD simulations, we analytically derive the equations of motion for both branches and characterize the translocation dynamics in detail from the average waiting time and its scaling form.