Filament Tension Research Articles

Thermo-Mechanical Behavior and Strain Rate Sensitivity of 3D-Printed Polylactic Acid (PLA) below Glass Transition Temperature (Tg).

This study investigated the thermomechanical behavior of 4D-printed polylactic acid (PLA), focusing on its response to varying temperatures and strain rates in a wide range below the glass transition temperature (Tg). The material was characterized using tension, compression, and dynamic mechanical thermal analysis (DMTA), confirming PLA's strong dependency on strain rate and temperature. The glass transition temperature of 4D-printed PLA was determined to be 65 °C using a thermal analysis (DMTA). The elastic modulus changed from 1045.7 MPa in the glassy phase to 1.2 MPa in the rubber phase, showing the great shape memory potential of 4D-printed PLA. The filament tension tests revealed that the material's yield stress strongly depended on the strain rate at room temperature, with values ranging from 56 MPa to 43 MPA as the strain rate decreased. Using a commercial FDM Ultimaker printer, cylindrical compression samples were 3D-printed and then characterized under thermo-mechanical conditions. Thermo-mechanical compression tests were conducted at strain rates ranging from 0.0001 s-1 to 0.1 s-1 and at temperatures below the glass transition temperature (Tg) at 25, 37, and 50 °C. The conducted experimental tests showed that the material had distinct yield stress, strain softening, and strain hardening at very large deformations. Clear strain rate dependence was observed, particularly at quasi-static rates, with the temperature and strain rate significantly influencing PLA's mechanical properties, including yield stress. Yield stress values varied from 110 MPa at room temperature with a strain rate of 0.1 s-1 to 42 MPa at 50 °C with a strain rate of 0.0001 s-1. This study also included thermo-mechanical adiabatic tests, which revealed that higher strain rates of 0.01 s-1 and 0.1 s-1 led to self-heating due to non-dissipated generated heat. This internal heating caused additional softening at higher strain rates and lower stress values. Thermal imaging revealed temperature increases of 15 °C and 18 °C for strain rates of 0.01 s-1 and 0.1 s-1, respectively.

Protein nanoparticles induce the activation of voltage-dependent non-selective ion channels to modulate biological osmotic pressure in cytotoxic cerebral edema.

Cytotoxic cerebral edema is a serious complication associated with cerebral ischemic stroke and is widely treated using the hypertonic dehydrant. Here, we propose, for the first time, the decrease of intracellular osmosis as a treatment strategy for alleviating cytotoxic cerebral edema. We established a fluorescence resonance energy transfer-based intermediate filament tension probe for the study and in situ evaluation of osmotic gradients, which were examined in real-time in living cells from primary cultures as well as cell lines. The MCAO rat model was used to confirm our therapy of cerebral edema. Depolymerization of microfilaments/microtubules and the production of NLRP3 inflammasome resulted in an abundance of protein nanoparticles (PNs) in the glutamate-induced swelling of astrocytes. PNs induced changes in membrane potential and intracellular second messengers, thereby contributing to hyper-osmosis and the resultant astrocyte swelling via the activation of voltage-dependent nonselective ion channels. Therefore, multiple inhibitors of PNs, sodium and chloride ion channels were screened as compound combinations, based on a decrease in cell osmosis and astrocyte swelling, which was followed by further confirmation of the effectiveness of the compound combination against alleviated cerebral edema after ischemia. The present study proposes new pathological mechanisms underlying "electrophysiology-biochemical signal-osmotic tension," which are responsible for cascade regulation in cerebral edema. It also explores various compound combinations as a potential treatment strategy for cerebral edema, which act by multi-targeting intracellular PNs and voltage-dependent nonselective ion flux to reduce astrocyte osmosis.

Intravenous Injection of Na Ions Aggravates Ang II-Induced Hypertension-Related Vascular Endothelial Injury by Increasing Transmembrane Osmotic Pressure.

Extracellular protein nanoparticles (PNs) and ions perform synergistical functions in the control of transmembrane osmotic pressure (OP) under isotonic conditions. Intravenous injection may disrupt the ion balance and alter PN levels in blood plasma, changing transmembrane OP and damaging vascular endothelial cells. Na ions were injected into AngII-induced HUVECs to simulate cell injury in vitro, and tail vein infusion of Na ions into hypertensive rats was performed to assess vascular damage. Optical measurements using an intermediate filament (IF) tension probe were conducted to detect indicators related to transmembrane OP. Immunofluorescence, Western blotting and small interfering RNA (siRNA) transfection were employed to investigate inflammasomes and the relationship between Abl2 and inflammation. Electrolyte injections with sodium ions (but not glucose and hydroxyethyl starch) induced the production of ASC and NLRP3 inflammasomes in Ang II-induced HUVECs; this in turn resulted in the disorder of calcium signals, and changes in transmembrane OP and cell permeability. Moreover, injection of Na ions into Ang II-induced HUVECs activated the mechanosensitive protein Abl2, involved in inflammation-induced transmembrane OP changes. A drug combination was identified that could induce OP recovery and block hyperpermeability induced by cytoplasmic inflammatory corpuscles in vivo and in vitro. Changes in extracellular PNs and ions following chemical stimuli (Ang II) participate in the regulation of transmembrane OP. Furthermore, injection of Na ions causes vascular endothelial injury in Ang II-induced cells in vitro and hypertension rats in vivo, suggesting it is not safe for hypertensive patients, and we propose a new drug combination as a solution.

Mechanical Stress Decreases the Amplitude of Twisting and Bending Fluctuations of Actin Filaments

A variety of biological roles of mechanical forces have been proposed in cell biology, such as cell signaling pathways for survival, development, growth, and differentiation. Mechanical forces alter the mechanical conditions within cells and their environment, which strongly influences the reorganization of the actin cytoskeleton. Single-molecule imaging studies of actin filaments have led to the hypothesis that the actin filament acts as a mechanosensor; e.g., increases in actin filament tension alter their conformation and affinity for regulatory proteins. However, our understanding of the molecular mechanisms underlying how tension modulates the mechanical behavior of a single actin filament is still incomplete. In this study, a direct measurement of the twisting and bending of a fluorescently labeled single actin filament under different tension levels by force application (0.8–3.4 pN) was performed using single-molecule fluorescence polarization (SMFP) microscopy. The results showed that the amplitude of twisting and bending fluctuations of a single actin filament decreased with increasing tension. Electron micrograph analysis of tensed filaments also revealed that the fluctuations in the crossover length of actin filaments decreased with increasing filament tension. Possible molecular mechanisms underlying these results involving the binding of actin-binding proteins, such as cofilin, to the filament are discussed.

Characterizing the Effect of Filament Moisture on Tensile Properties and Morphology of Fused Deposition Modeled Polylactic Acid/Polybutylene Succinate Parts.

Moisture absorption into hygroscopic/hydrophilic materials used in fused deposition modeling (FDM) can diminish desired mechanical properties. Sensitivity to moisture is dependent on material properties and environmental factors and needs characterization. In this article, moisture sensitivity of four grades of polylactic acid (PLA) filaments and four different ratios of PLA/polybutylene succinate (PBS) blended filaments were characterized through FDM printed American society for testing and materials (ASTM-D638) test samples after conditioning the filaments at different relative humidity levels. The tensile testing and scanning electron microscopy (SEM) of the samples' fracture surfaces revealed that PLA 4043D was the most moisture-sensitive among the chosen grades of PLA filaments. Through filament tension test and melt flow index (MFI) testing it was observed that moisture had a significant detrimental effect (20% reduction in tensile strength and 50% increase in MFI) on PLA 4043D filaments. Samples from moisture-conditioned PLA/PBS 75/25 blended filaments displayed a significant reduction (10%) in tensile strength. Moreover, the MFI of 75/25 filaments was increased with subsequent increases in moisture level. Investigation of tensile properties of ASTM samples made from four grades of PLA filaments exposed to room temperature and humidity conditions for 3 months showed an even more significant decrease in strength (ranging from 24% to 36%).

Dynamic behavior analysis of the winding system during filament reversing pushed by the traverse mechanism

The filament bundle is a kind of fiber assembly with an ultrahigh length–diameter ratio. For textiles, the filament is an intermediate product in the textile production process. For ease of storage, transportation and subsequent processing, the filament is wound to form a disc-shaped package with a certain size. During winding, the high-speed moving filament is placed precisely on the cylindrical surface of the package with the spiral shape by the traverse mechanism. Unfortunately, uneven tension of the filament during reversing is caused by the action of the traverse mechanism, which directly affects the quality of the filament package. In this article, the approach of modeling and simulating the filament winding system was proposed, of which the element model of the filament was established by the absolute node coordinate formulation, considering its viscoelasticity, as well as the effect of gravity. The contact model between the filament and the rotary vane, as well as the contact roller, was established by the Hertz law. The equations of motion for the system were derived by the Lagrange equations, and the algorithm for solving the differential-algebraic equations was further derived. Then, the dynamic behavior of the winding system during reversing was simulated and analyzed, and the results show that the moving filament is in non-contact with the rotary vane at the moment of reversing, and the small fluctuation in contact force between the rotary vane and the filament causes the large fluctuation in the filament tension. Finally, the validity is tested through an experiment.

Albumins as Extracellular Protein Nanoparticles Collaborate with Plasma Ions to Control Biological Osmotic Pressure.

IntroductionPlasma albumins as protein nanoparticles (PNs) exert essential functions in the control of biological osmotic pressure (OP), being involved in regulating water metabolism, cell morphology and cell tension. Understanding how plasma albumins and different electrolytes co-determine biological OP effects is crucial for correct interpretation of hemodynamic disorders, and practical treatment of hypo/hyper-proteinemia.MethodsOptical measurement based on intermediate filament (IF) tension probe was used for real-time evaluation of transmembrane osmotic effects in live cells. Ion fluorescent probes were employed to evaluate intracellular ion levels, and a current clamp was used to measure membrane potential, thus exploring association of electrochemical and osmotic effects.ResultsAlbumins are involved in regulation of intracellular osmolarity by a quantitative relationship. Extracellular PNs can alter membrane potentials by adsorbing counterions, induce production of intracellular PNs and further control the opening of ion channels and ion flow, contributing to electrochemical and osmotic re-equilibrium. Furthermore, various ions interplay with extracellular PNs, showing different osmotic effects: increased levels of calcium ions result in a hypotonic effect, whereas potassium ions induce hyper-osmolarity.ConclusionExtracellular PNs and Ca2+/K+ display antagonistic or synergetic effects in regulating biological OP. Live cells can spontaneously regulate osmotic effects through changing membrane potential and controlling intracellular ion content. Various plasma components need to be comprehensively analyzed, further developing a diagnostic index that considers the biological OP effects of various blood components and improves the evaluation of symptoms and diseases, such as calcium/potassium-hemodynamic disorders and edema.

Protein nanoparticle-induced osmotic pressure gradients modify pulmonary edema through hyperpermeability in acute respiratory distress syndrome

Acute respiratory distress syndrome (ARDS), caused by noncardiogenic pulmonary edema (PE), contributes significantly to Coronavirus 2019 (COVID-19)-associated morbidity and mortality. We explored the effect of transmembrane osmotic pressure (OP) gradients in PE using a fluorescence resonance energy transfer-based Intermediate filament (IF) tension optical probe. Angiotensin-II- and bradykinin-induced increases in intracellular protein nanoparticle (PN)-OP were associated with inflammasome production and cytoskeletal depolymerization. Intracellular protein nanoparticle production also resulted in cytomembrane hyperpolarization and L-VGCC-induced calcium signals, which differed from diacylglycerol-induced calcium increment via TRPC6 activation. Both pathways involve voltage-dependent cation influx and OP upregulation via SUR1-TRPM4 channels. Meanwhile, intra/extracellular PN-induced OP gradients across membranes upregulated pulmonary endothelial and alveolar barrier permeability. Attenuation of intracellular PN, calcium signals, and cation influx by drug combinations effectively relieved intracellular OP and pulmonary endothelial nonselective permeability, and improved epithelial fluid absorption and PE. Thus, PN-OP is pivotal in pulmonary edema in ARDS and COVID-19, and transmembrane OP recovery could be used to treat pulmonary edema and develop new drug targets in pulmonary injury.Graphical

Spiral waves within a bistability parameter region of an excitable medium

Spiral waves are a well-known and intensively studied dynamic phenomenon in excitable media of various types. Most studies have considered an excitable medium with a single stable resting state. However, spiral waves can be maintained in an excitable medium with bistability. Our calculations, performed using the widely used Barkley model, clearly show that spiral waves in the bistability region exhibit unique properties. For example, a spiral wave can either rotate around a core that is in an unexcited state, or the tip of the spiral wave describes a circular trajectory located inside an excited region. The boundaries of the parameter regions with positive and ‘negative’ cores have been defined numerically and analytically evaluated. It is also shown that the creation of a positive or ‘negative’ core may depend on the initial conditions, which leads to hysteresis of spiral waves. In addition, the influence of gradient flow on the dynamics of the spiral wave, which is related to the tension of the scroll wave filaments in a three-dimensional medium, is studied.

Scroll wave with negative filament tension in a model of the left ventricle of the human heart and its overdrive pacing.

Nonlinear waves of electrical excitation initiate cardiac contraction. Abnormal wave propagation in the heart, e.g., spiral waves, can lead to sudden cardiac arrest. This study analyzed the dynamics of spiral waves under the influence of an instability called negative filament tension, and examined how the spiral waves can be eliminated through high-frequency pacing. A generic anatomical model of the left ventricle of the human heart and the Aliev-Panfilov model for cardiac tissue were used. The study showed that the source of such arrhythmia is elongated filaments with lengths that can be 10-20 times greater than the characteristic thickness of the heart wall. In anisotropic tissue, the filament elongated before it was annihilated at the base of the heart. The spiral waves were eliminated through overdrive pacing with stimulation periods from 0.8 to 0.95 relative to the spiral wave period. The minimum time for the expulsion was about 10s.

High-frequency pacing of scroll waves in a three-dimensional slab model of cardiac tissue.

Vortices in excitable media underlie dangerous cardiac arrhythmias. One way to eliminate them is by stimulating the excitable medium with a period smaller than the period of the vortex. So far, this phenomenon has been studied mostly for two-dimensional vortices known as spiral waves. Here we present a first study of this phenomenon for three-dimensional vortices, or scroll waves, in a slab. We consider two main types of scroll waves dynamics: with positive filament tension and with negative filament tension and show that such elimination is possible for some values of the period in all cases. However, in the case of negative filament tension for relatively long stimulation periods, three-dimensional instabilities occur and make elimination impossible. We derive equations of motion for the drift of paced filaments and identify a bifurcation parameter that determines whether the filaments orient themselves perpendicular to the impeding wave train or not.

Cofilin Protects Contractile Rings from Bridging Instabilities

Significant experimental evidence from fission yeast studies suggests the major structural challenge faced by the cytokinetic contractile ring is bridging instability. When uncontrolled, this instability causes sections of the actomyosin ring to pull away from the membrane into straight bridges. Such straight bridges were observed in rings with the myosin-II mutant myo2-E1, which binds actin weakly (Laplante et al., 2015). Bridges have also been observed in rings with the ADF/cofilin mutants adf1-M2 and adf1-M3 (Cheffings et al., 2019), which impair cofilin-mediated severing of filamentous actin. Bridges contained actin and myosin II Myp2, leaving myosin II Myo2 behind on the plasma membrane. More bridging occurred in regions of lower Myo2 density. To examine the origin of bridging, and the role of ADF/cofilin in stabilizing the ring, we used simulations of the fission yeast ring. In simulations, the ∼400-800 pN ring tensions generated high centripetal (“Laplace”) forces tending to unanchor the ring from the membrane. These were opposed primarily by binding of membrane-anchored Myo2 to the tense actin filaments, drastically weakened in the myo2-E1 mutant. Simulations of myo2-E1 rings accurately reproduced the bridging phenotype (Laplante et al., 2015). Simulations also reproduced the bridging phenotype in rings with the ADF/cofilin mutants. Impaired cofilin-mediated severing increased actin filament lengths, thus increasing the ring tension and hence the Laplace forces. Bridging occurred when Laplace forces exceeded the Myo2-actin unbinding threshold. The filament tension was proportional to its length, as longer filaments were pulled by more myosin II heads. In ADF/cofilin mutants filaments grew ∼3-fold longer and had ∼ 3-fold normal tension. Bridges peeled away from the plasma membrane at locations where inward Laplace forces exceeded the local anchoring force from Myo2. Bridging was therefore most likely in regions with low Myo2 density, as observed (Cheffings et al., 2019).

Clusters of a Few Bound Cofilins Sever Actin Filaments

Cofilin is an essential actin filament severing protein that accelerates the assembly dynamics and turnover of actin networks by increasing the number of filament ends where subunits add and dissociate. It binds filament subunits stoichiometrically and cooperatively, forming clusters of contiguously-bound cofilin at sub-saturating occupancies. Filaments partially occupied with cofilin sever at boundaries between bare and cofilin-decorated segments. Imaging studies concluded that bound clusters must reach a critical size (Cc) of 13–100 cofilins to sever filaments. In contrast, structural and modeling studies suggest that a few or even a single cofilin can sever filaments, possibly with different severing rate constants. How clusters grow through the cooperative incorporation of additional cofilin molecules, specifically if they elongate asymmetrically or uniformly from both ends and if they are modulated by filament shape and external force, also lacks consensus. Here, using hydrodynamic flow to visualize individual actin filaments with TIRF microscopy, we found that neither flow-induced filament bending, tension, nor surface attachment conditions substantially affected the kinetics of cofilin binding to actin filaments. Clusters of bound cofilin preferentially extended toward filament pointed ends and displayed severing competency at small sizes (Cc < 3), with no detectable severing dependence on cluster size. These data support models in which small clusters of cofilin introduce local, but asymmetric, structural changes in actin filaments that promote filament severing with a rate constant that depends weakly on the size of the cluster.

Stabilizing meandering scroll waves and ordering scroll wave turbulence by a circularly polarized electric field in highly excitable media

Scroll waves could demonstrate meandering behaviors and even break up into scroll wave turbulence. Significantly differing from the instability induced by negative filament tension occurring often in weakly excitable media, breakup of scroll waves in highly excitable media typically involves the interaction of fronts with refractory tail of the wave. How to stabilize scroll waves and suppress scroll wave turbulence caused by such a mechanism is understudied as previous works are largely limited to the case of the negative filament tension. Here we perform a computational study to show that application of a circularly polarized electric field in highly excitable media could not only effectively force a meandering scroll wave to a rigidly rotating one via a phase-locking mechanism, but also prevent breakup of scroll waves and convert scroll wave turbulence to stable rotating scroll waves. The application of our findings in chemical systems is also discussed.

Termination of Scroll Waves by Surface Impacts.

Three-dimensional scroll waves direct cell movement and gene expression, and induce chaos in the brain and heart. We found an approach to terminate multiple three-dimensional scrolls. A pulse of a properly configured electric field detaches scroll filaments from the surface. They shrink due to filament tension and disappear. Since wave emission from small heterogeneities is not used, this approach requires a much lower electric field. It is not sensitive to the details of the excitable medium. It may affect future studies of low-energy chaos termination in the heart.

Mechanical Strength Analysis of Pulsed Alternator Air-Core Rotor

As a high-speed, high-energy rotating machine, a compulsator is subjected to a high centrifugal force and large mechanical shocks during discharge. The use of composite material components fabricated by filament winding significantly improves the compulsator's performance. However, the composite components' relatively low radial and shear strength pose problems from a mechanical stability viewpoint. This paper presents a mechanical strength analysis for a compensated pulsed alternator (CPA) rotor with a bowl-shaped support. The mechanical model of the rotor was established. From the interior to the exterior, the rotor was divided into the bowl-shaped support, composite yoke, field winding, and composite banding. The radial and tangential stress distributions of the composite yoke were determined using analytical methods. The composite yoke and banding were fabricated using filament tension winding and modeled using the multiring interference fit analytical method. The interference fit for each layer was calculated and the mechanical analysis of the CPA rotor during discharge is presented. Two bowl-shaped carbon fiber epoxy resin supports were analyzed and compared.

Numerical analysis of the tension and twist of staple strands in embeddable and locatable spinning

This study reports a numerical analysis on embeddable and locatable spinning systems. The finite element method is used to quantify the relationship between the tension and twist of staple strands and the spinning parameters. The model was constructed using the three-dimensional beam element, which is capable of simulating the stretching, bending and torsion behavior of the filament and the staple strand. It was found that the staple strand shares far less load (around 13.8%) than the filament during the spinning process. The twist is mainly distributed on the composite yarns and less on other zones. The pretension of the filament, the filament–strand distance ratio, the twist of the composite yarn and the material fed-in velocity were investigated for their influence on the tension and twist of the staple strand. Numerical predictions showed that higher filament tension and filament–strand ratio lead to less load and more twist on the staple strand. This is beneficial in producing stronger and smoother yarns and avoiding end breakages. It was also determined that strand tension and twist increase with an increase in composite yarn twist and a decrease in material fed-in velocity.

Expansion of scroll wave filaments induced by chiral mismatch.

In three-dimensional excitable systems, scroll waves are rotating vortex states that consist of smoothly stacked spirals. This stacking occurs along one-dimensional phase singularities called filaments. If the system has a positive filament tension, these curves either straighten or collapse over time. The collapse can be prevented if the filament pins to a nonreactive object or a group of objects, but even in this case, the filament length does not typically grow. Using numerical simulations, we provide examples of filament growth induced by pinning, such as a scroll ring pinning to an inert trefoil knot, and explain the mechanism of this growth. Surprisingly, the corresponding filament loop thus not only persists in time but also steadily extends far from the pinning object.

On the development of a filament winding robotic system

This paper reports on the design, manufacture, control and implementation of a robotic head for filament winding, typically carbon, glass etc. employed in shell-like part manufacturing with composite materials. The head is attached to a 6 axis industrial robot collaborating with a rotary axis on which a die is secured. Concept development and preliminary study of the head and its assembly on the robot were performed on a CAD system with motion analysis. Two alternative winding heads were studied and the one with embedded filament tension control was implemented. The winding path is planned by exploiting CAD-based kinematic simulation or analytical calculation. Control of the system was performed using the robot’s inbuilt capabilities via programming in V+ language interfaced with a micro-processor controlling die rotation according to the open loop paradigm. Cylindrical and conical winding were successfully performed paving the way for expansion to non-symmetrical winding patterns.

Filament Tension and Phase Locking of Meandering Scroll Waves.

Meandering spiral waves are often observed in excitable media such as the Belousov-Zhabotinsky reaction and cardiac tissue. We derive a theory for drift dynamics of meandering rotors in general reaction-diffusion systems and apply it to two types of external disturbances: an external field and curvature-induced drift in three dimensions. We find two distinct regimes: with small filament curvature, meandering scroll waves exhibit filament tension, whose sign determines the stability and drift direction. In the regimes of strong external fields or meandering motion close to resonance, however, phase locking of the meander pattern is predicted and observed.