Helical Bending Research Articles

Climbing Plant‐Inspired Multi‐Responsive Biomimetic Actuator with Transitioning Complex Surfaces

AbstractBionic robots have great potential in healthcare, rescue, and surveillance. However, most soft actuators can only realize one or two deformation modes, which largely limit the application in complex environments. This study develops electric/Infrared (IR) light/magnetic multi‐field coupling soft actuators by combining liquid crystal elastomers (LCE), liquid metal (LM) and magnetic Ecoflex (Mecoflex). Originated from the synergistic effect of the differed thermal expansion and the liquid crystal phase transition, the actuator can realize outstanding large deformations (bending angle > 300°) at ultra‐low voltages (1.0 V). In addition, by designing the molecular orientation in the LCE layer and programming the magnetization in the Mecoflex layer, the bending or helical bending deformations can be controlled under electric/magnetic and IR light/magnetic coupling actuation. Based on the complex deformation capability, bionic climbing plants and two kinds of quadrupedal robots are developed. With the structural design of the quadrupedal robots, they can flexibly switch deformations to pass through complex environments by controlling the externally applied coupling fields, which demonstrates their broad potential in practical applications.

Study on the effect of geometry and material property on collapse pressure of a helical steam generator tube under external pressure

In this paper, a numerical study was conducted to analyze the effect of the geometry (tube thickness, ovality, and helical diameter) and material properties of once through steam generator tubes subjected to external pressure on collapse pressure. The outer diameter of the steam generator tube was fixed at 17 mm, and the tube thickness was changed to 2.5 mm, 2.29 mm, and 1.27 mm. Ovality was considered for three cases of 0 %, 4 %, and 8 %, and three cases for helical diameter were considered: 577 mm, 937 mm, and 1297 mm. As material properties, elastic perfectly plastic property that ignores plastic hardening and real material property that reflect plastic hardening were considered. At the helical diameter (Dm/do ≥ 34) considered in this paper, the effect of collapse pressure due to helical bending did not appear on ovalities and both material properties. On the other hand, the wall thickness affected the collapse pressures according to the material properties when ovality occurred (>0 %). This is explained because the collapse mechanism varies depending on the thickness.

Functionality optimization for effective singlet fission coupling screening in the full-dimensional molecular and intermolecular coordinate space.

In computational chemistry, accurately predicting molecular configurations that exhibit specific properties remains a critical challenge. Its intricacies become especially evident in the study of molecular aggregates, where the light-induced functionality is tied to highly structure-dependent electronic couplings between molecules. Here, we present an efficient strategy for the targeted screening of the structural space employing a "functionality optimization" technique, in which a chosen descriptor, constrained by the ground state energy expression, is optimized. The chosen algorithmic differentiation (AD) framework allows one to automatically obtain gradients without its tedious implementation. We demonstrate the effectiveness of the approach by identifying perylene bisimide (PBI) dimer motifs with enhanced effective SF coupling. Our findings reveal that certain structural modifications of the PBI monomer, such as helical twisting and bending as well as slipped-rotated packing arrangements, can significantly increase the effective SF coupling.

Capturing heterogeneous conformers of cobalamin riboswitch by cryo-EM.

RNA conformational heterogeneity often hampers its high-resolution structure determination, especially for large and flexible RNAs devoid of stabilizing proteins or ligands. The adenosylcobalamin riboswitch exhibits heterogeneous conformations under 1 mM Mg2+ concentration and ligand binding reduces conformational flexibility. Among all conformers, we determined one apo (5.3 Å) and four holo cryo-electron microscopy structures (overall 3.0-3.5 Å, binding pocket 2.9-3.2 Å). The holo dimers exhibit global motions of helical twisting and bending around the dimer interface. A backbone comparison of the apo and holo states reveals a large structural difference in the P6 extension position. The central strand of the binding pocket, junction 6/3, changes from an 'S'- to a 'U'-shaped conformation to accommodate ligand. Furthermore, the binding pocket can partially form under 1 mM Mg2+ and fully form under 10 mM Mg2+ within the bound-like structure in the absence of ligand. Our results not only demonstrate the stabilizing ligand-induced conformational changes in and around the binding pocket but may also provide further insight into the role of the P6 extension in ligand binding and selectivity.

From amyloid fibrils to microfiber condensates: Tuning microfluidic coextrusion of food-grade β-lactoglobulin-pectin core-shell fibers by changes of protein structure

Protein-based microfibers have potential applications in bioengineering and food but preserving and utilizing the unique nanomechanical properties of their protein building blocks at the micrometer scale remains a challenge. This study investigates the bottom-up fabrication of core-shell fibers by coaxial microfluidic spinning of pectin and β-lactoglobulin in different conformational states (monomeric, amyloid fibrils, shortened amyloid fibrils in their isotropic/nematic phases), gelled in CaCl2 solution. Fiber diameters ranged between 478 and 855 μm (wet state) and 107–135 μm (dry state). They showed clear core-shell cross-sections, except pectin-β-lactoglobulin monomer fibers where the compact protein is presumably understood to diffuse through the pectin matrix. The molecular orientation of the fiber building blocks was expressed as order parameters representing the alignment of pectin chains and amyloid fibrils parallel to the fiber axis calculated from synchrotron wide-angle X-ray scattering (WAXS) with a spatial resolution of 20 μm. Introduction of amyloid fibrils as the protein core increased the Young's modulus from 3.3 to 6.4 GPa and tensile strength from 117 to 182 MPa compared to pure pectin fibers. Increasing the protein core flow rate from 1 to 2 mL/h, however, caused helical bending of the core jet, a decrease in order, and ultimately worsened mechanical performance. Overall, full length amyloid fibrils proved to be more beneficial to the mechanical properties than shortened amyloid fibrils. By providing insight into the relationship between protein conformation, spinning flow rate, and resulting mechanical properties of core-shell microfibers, these results may contribute to the field of novel fibrous protein-based materials.

Study of Vibration Strength of D16 Aluminum Alloy Joints Welded Applying Resistance Spot Welding

Purpose of research is to develop and test a technique and perform an experimental study of the vibration strength of D16 aluminum alloy joints welded applying resistance spot welding.Methods. Test coupons were made from 1 mm thick D16 aluminum alloy sheet blanks applying resistance spot welding. A feature of the proposed test is the implementation of a symmetrical loading cycle. During the tests, the number of cycles to failure depending on the range of vibrations was recorded. Annealing and thermomechanical straightening were carried out to exclude helical bending after cutout. After deburring and root facing, the surface of the coupons was prepared for welding using chemical etching. The coupons were welded using a TECNA 8214N spot welding machine. The welding current was 30 kA, the welding duration was 0.1 s, the electrodes force was 180 daN. The static shear strength of the welded joint was studied using a UTS 110M-5 1-U tensile testing machine. The breaking force was 3.66 kN. The peculiarity of the proposed test is the implementation of a symmetrical loading cycle. During the tests, the number of cycles to failure depending on the range of vibrations was recorded.Results. As a result of the statistical analysis of the study results, a linear mathematical relationship between the logarithms of the number of cycles to failure and the amplitude of vibrations was obtained. Depending on the range of vibrations, characteristic zones of destruction were revealed. To provide the possibility of comparing the results of vibration obtained under different conditions of fixing the samples, it is proposed to use the range of vibration displacement per unit length of the work[iece as the ordinate.Conclusion. A technique or studying the vibrational strength of joints welded by resistance spot welding under conditions of a symmetrical loading cycle is proposed and tested. For the studied coupons, the equality of the welded joint to the base metal is achieved at the value of the logarithm of the ratio of the range of vibration displacement per unit length of the coupons equal to 0.01.

Helical bending waves superimposed on large helical waves of an extremely long sperm flagellum of Drosophila melanogaster

Insect sperm flagella show wide variety of their internal structures and beating patterns. Accurate description of the features will provide important information for understanding the mechanism of axonemal structure and the corresponding bending wave generation. Here, we focus on spermatozoa of Drosophila melanogaster, which has an extremely long flagellum with a length of 2 millimeters. Its internal structure, axoneme has 9+9+2 architecture, distinct from conventional 9+2 axoneme. Unlike axonemes from the flagella of Chlamydomonas or sea urchins, the constituent proteins of axonemes of Drosophila sperm have not been well characterized. Nevertheless, Drosophila axonemes have many advantages over axonemes from other sources. (1) Drosophila is one of the best-established laboratory animals. It has a short life cycle and is easy to breed. (2) Complete genome information is available. (3) A vast number of mutants have been created, natural or transgenic, and many of them are available from stock centers worldwide. Taking these advantages, here, we isolated spermatozoa from the testes and recorded their movement with a high-speed camera. The spermatozoon swims in a spiral pathway in the radius of a few hundred micrometers, and the beating wave consists of minor waves (20-30 Hz, wavelength = ca. 30 μm) superimposed on major waves. Although its physiological significance is unclear, the double-wave nature of the beating pattern could be related to the 9 + 9 + 2 architecture. When combined with the genetic resource of Drosophila, the precise observation will provide a powerful clue for studying the structure-function relationship of eukaryotic flagella in general. This work was supported by JSPS KAKENHI, 26440089 and 17K07376 to K.O., JP16H06280, the Takeda Science Foundation (K.O.) and Hyogo Science and Technology Association (K.O.).

Multimaterial Embedded 3D Printing of Composite Reinforced Soft Actuators.

Soft pneumatic actuators (SPAs) have attracted enormous attention in the growing field of robotics. Among different SPAs, composite reinforced actuators (CRAs) are widely used because of their simple structure and high controllability. However, multistep molding, a time-consuming method, is still the predominant fabrication method. Here, we propose a multimaterial embedded printing method (ME3P) to fabricate CRAs. In comparison with other 3-dimensional printing methods, our method improves fabrication flexibility greatly. Via the design and fabrication of the reinforced composites' patterns and different geometries of the soft body, we demonstrate actuators with programmable responses (elongation, contraction, twisting, bending, and helical and omnidirectional bending). Finite element analysis is employed for the prediction of pneumatic responses and the inverse design of actuators based on specific actuation needs. Lastly, we use tube-crawling robots as a model system to demonstrate our ability to fabricate complex soft robots for practical applications. This work demonstrates the versatility of ME3P for the future manufacturing of CRA-based soft robots.

Tapered, Twisted Bundled-Tube Locomotive Devices for Stepped Pipe Inspection.

The twisted bundled-tube locomotive device is an elongated soft robot that moves inside a pipe in a helical bending motion. This motion mimics the behavior of microorganisms called spirochetes. This device is inexpensive and easy to miniaturize because of its simple structure, which consists of three inflatable tubes twisted together. It can move in pipes of various diameters without a change in design. Therefore, it has a high capacity for water pipe inspection. However, it has not yet been shown to pass through step parts wherein the diameter of the pipes decreases. In this study, we developed a device that was deformed into a tapered shape by changing the pitch of the spirals at each location. The prototype device was able to move from a pipe with an inside diameter of 52.9 mm to a pipe with an inside diameter of 21.6 mm for horizontally fixed pipes, and from a pipe with an inside diameter of 41.6 mm to a pipe with an inside diameter of 21.6 mm for vertically fixed pipes.

Molecular Dynamics Simulations of the Apo and Holo States of the Copper Binding Protein CueR Reveal Principal Bending and Twisting Motions.

Copper is essential for proper functioning of cells but is dangerous in unregulated concentrations. One of the members in the bacterial system responsible for facilitating copper homeostasis is the copper efflux regulator (CueR) protein. Upon copper binding, CueR induces transcription of additional copper homeostasis proteins via a cascade of events. There are some available crystal structures of CueR, in the holo (copper-bound), active (copper- and DNA-bound), and repressed (only DNA-bound) states, and these structures suggest that transcription initiation involves a distortion in the promoter DNA strand. In this work, we study the dynamic behavior of the protein, using molecular dynamics simulations, and compare with available electron paramagnetic resonance measurements for validation. We develop simple force-field parameters to describe the copper-binding motif, thus enabling the use of simplified, classical physics equations. This enabled us to access reasonable simulation times that illustrate global motions of the protein. Both in the holo and apo states of CueR, we observed large-scale helical bending motions that could be involved in the bending of a bound DNA molecule so that transcription activation can take place. Additionally, copper binding might afford increased rigidification of the active state via helix α6.

The many modes of flagellar and ciliary beating: Insights from a physical analysis

The mechanism that allows the axoneme of eukaryotic cilia and flagella to produce both helical and planar beating is an enduring puzzle. The nine outer doublets of eukaryotic cilia and flagella are arranged in a circle. Therefore, each doublet pair with its associated dynein motors, should produce torque to bend the flagellum in a different direction. Sequential activation of each doublet pair should, therefore result in a helical bending wave. In reality, most cilia and flagella have a well‐defined bending plane and many exhibit an almost perfectly flat (planar) beating pattern. In this analysis we examine the physics that governs flagellar bending, and arrive at two distinct possibilities that could explain the mechanism of planar beating. Of these, the mechanism with the best observational support is that the flagellum behaves as two ribbons of doublets interacting with a central partition. We also examine the physics of torsion in flagella and conclude that torsion could play a role in transitioning from a planar to a helical beating modality in long flagella. Lastly, we suggest some tests that would provide theoretical and/or experimental evaluation of our proposals.

A Solvent Molecule Driven Pure PEDOT:PSS Actuator

AbstractActuators which mechanically respond to various external stimuli are promising for diverse applications including soft robots, energy generators, artificial muscles, and sensors. Herein, a PEDOT:PSS film based vapor‐driven soft actuator by using H2SO4 treated process is presented. This actuator exhibits rapid (0.24 s for one actuation) and robust (>1000 times without obvious fatigue) responses to stimuli of various organic solvents with reversible large‐shape deformations. By coating gold on the one side of the PEDOT:PSS film with subsequent generation of specific patterns, the designed bilayer‐structured actuator achieves controllable actuation including vertical and helical bending. Furthermore, a walking robot and a vapor‐driven generator are successfully constructed with remarkable performances upon vapor stimuli using the proposed PEDOT:PSS film based actuator. The achievement presented here opens a new avenue for a new generation of robots and smart sensors.

Analytic springback prediction in cylindrical tube bending for helical tube steam generator

This paper newly proposes an efficient analytic springback prediction method to predict the final dimensions of bent cylindrical tubes for a helical tube steam generator in a small modular reactor. Three-dimensional bending procedure is treated as a two-dimensional in-plane bending procedure by integrating the Euler beam theory. To enhance the accuracy of the springback prediction, mathematical representations of flow stress and elastic modulus for unloading are systematically integrated into the analytic prediction model. This technique not only precisely predicts the final dimensions of the bent helical tube after a springback, but also effectively predicts the various target radii. Numerical validations were performed for five different radii of helical tube bending by comparing the final radius after a springback.

Curvature and force measurement of soft manipulator based on stretchable helical optic fibre

Abstract The soft surgical manipulator is a scientific frontier in the fields of minimally invasive surgery and robotics, and it is crucial for improving the performance of surgery. However, owing to its narrow and confined environment in minimally invasive surgeries, some existing methods have not solved its problem of accurate measurement, which limits its application. This paper demonstrates the curvature and force measurement of a hyper-elastic soft manipulator with helically embedded stretchable fibre Bragg grating (FBG)-based fibre optic sensor. Unlike a straight FBG embedding configuration, this unique helical configuration prevents sensor dislocation, supports stretchability, and facilitates the detection of various movements of the soft manipulator. First, the design of the soft manipulator embedded with a stretchable helical optic fibre is described. Second, the sensing theory of the soft manipulator was analysed, and the stretchable helical FBG sensing model was established. Finally, to verify the effectiveness of this design and sensing technique based on the stretchable helical optic fibre, some compression and bending experiments of the soft manipulator were conducted. The results showed that the errors between theoretical and experimental measurements are less than 5%, and the helical structure enables 10% of compression in length, thus facilitating in the measurement of tension and bending curvature of the soft manipulator.

A three-dimensional model of flagellar swimming in a Brinkman fluid

We investigate three-dimensional flagellar swimming in a fluid with a sparse network of stationary obstacles or fibres. The Brinkman equation is used to model the average fluid flow where a flow-dependent term, including a resistance parameter that is inversely proportional to the permeability, captures the effects of the fibres on the fluid. To solve for the local linear and angular velocities that are coupled to the flagellar motion, we extend the method of regularized Brinkmanlets to incorporate a Kirchhoff rod, discretized as point forces and torques along a centreline. Representing a flagellum as a Kirchhoff rod, we investigate emergent waveforms for different preferred strain and twist functions. Since the Kirchhoff rod formulation allows for out-of-plane motion, in addition to studying a preferred planar sine wave configuration, we also study a preferred helical configuration. Our numerical method is validated by comparing results to asymptotic swimming speeds derived for an infinite-length cylinder propagating planar or helical waves. Similar to the asymptotic analysis for both planar and helical bending, we observe that with small amplitude bending, swimming speed is always enhanced relative to the case with no fibres in the fluid (Stokes) as the resistance parameter is increased. For regimes not accounted for with asymptotic analysis, i.e. large amplitude planar and helical bending, our model results show a non-monotonic change in swimming speed with respect to the resistance parameter; a maximum swimming speed is observed when the resistance parameter is near one. The non-monotonic behaviour is due to the emergent waveforms; as the resistance parameter increases, the swimmer becomes incapable of achieving the amplitude of its preferred configuration. We also show how simulation results of slower swimming speeds for larger resistance parameters are actually consistent with the asymptotic swimming speeds if work in the system is fixed.

Emergent three-dimensional sperm motility: coupling calcium dynamics and preferred curvature in a Kirchhoff rod model.

Changes in calcium concentration along the sperm flagellum regulate sperm motility and hyperactivation, characterized by an increased flagellar bend amplitude and beat asymmetry, enabling the sperm to reach and penetrate the ovum (egg). The signalling pathways by which calcium increases within the flagellum are well established. However, the exact mechanisms of how calcium regulates flagellar bending are still under investigation. We extend our previous model of planar flagellar bending by developing a fluid-structure interaction model that couples the 3D motion of the flagellum in a viscous Newtonian fluid with the evolving calcium concentration. The flagellum is modelled as a Kirchhoff rod: an elastic rod with preferred curvature and twist. The calcium dynamics are represented as a 1D reaction-diffusion model on a moving domain, the flagellum. The two models are coupled assuming that the preferred curvature and twist of the sperm flagellum depend on the local calcium concentration. To investigate the effect of calcium on sperm motility, we compare model results of flagellar bend amplitude and swimming speed for three cases: planar, helical (spiral with equal amplitude in both directions), and quasi-planar (spiral with small amplitude in one direction). We observe that for the same parameters, the planar swimmer is faster and a turning motion is more clearly observed when calcium coupling is accounted for in the model. In the case of flagellar bending coupled to the calcium concentration, we observe emergent trajectories that can be characterized as a hypotrochoid for both quasi-planar and helical bending.

Helix Angle Effect on the Helical Gear Load Carrying Capacity

The aim of this study is to investigate the helix angle effect on the helical gear load carrying capacity, including the bending and contact load carrying capacity. During the simulation, the transverse contact ratio is calculated with respect to the constant pressure angle. By changing the helix angle, both the overlap contact ratio and total contact ratio are calculated and simulated. The bending stress and contact stress of a helical gear are calculated and simulated with respect to the helix angle. Solid (CAD) modelling of a pinion gear was obtained using SOLIDWORKS software. The analytically obtained results and finite elements method results are compared. It is observed that increasing the helix angle causes an increase of the contact ratio of the helical gear. Furthermore, increasing the contact ratio reduces the bending stress and contact stress of the helical gear. However, with a constant transverse contact ratio, it is possible to improve the total contact ratio depending on the helix angle. It is concluded that a higher helix angle increases the helical gear bending and contact load carrying capacity.

Conformational dynamics of the essential sensor histidine kinase WalK.

Two-component systems (TCSs) are key elements in bacterial signal transduction in response to environmental stresses. TCSs generally consist of sensor histidine kinases (SKs) and their cognate response regulators (RRs). Many SKs exhibit autokinase, phosphoryltransferase and phosphatase activities, which regulate RR activity through a phosphorylation and dephosphorylation cycle. However, how SKs perform different enzymatic activities is poorly understood. Here, several crystal structures of the minimal catalytic region of WalK, an essential SK from Lactobacillus plantarum that shares 60% sequence identity with its homologue VicK from Streptococcus mutans, are presented. WalK adopts an asymmetrical closed structure in the presence of ATP or ADP, in which one of the CA domains is positioned close to the DHp domain, thus leading both the β- and γ-phosphates of ATP/ADP to form hydrogen bonds to the ℇ- but not the δ-nitrogen of the phosphorylatable histidine in the DHp domain. In addition, the DHp domain in the ATP/ADP-bound state has a 25.7° asymmetrical helical bending coordinated with the repositioning of the CA domain; these processes are mutually exclusive and alternate in response to helicity changes that are possibly regulated by upstream signals. In the absence of ATP or ADP, however, WalK adopts a completely symmetric open structure with its DHp domain centred between two outward-reaching CA domains. In summary, these structures of WalK reveal the intrinsic dynamic properties of an SK structure as a molecular basis for multifunctionality.

Study of the Influence of Helical Bending Strain and Perpendicular Self-Field on Critical Current Degradation for Multilayer YBCO Tapes

An experimental investigation of the critical current (I c ) degradation of multilayer twisted yttrium barium copper oxide (YBCO) tapes in self-field was performed. The influence of the number of tape layers (N) and twist pitch (P) on critical current was researched. The results showed that the influence of helical bending strain and perpendicular self-field on critical current degradation was a comprehensive process. No critical current degradation was found when there was just one layer and the twist pitch was over 20 mm. However, the situation would change when the number of tape layers increased. The critical current degradation would increase with increase in helical bending strain or perpendicular self-field. The critical current degradation can reach a maximum of 24.6% when the helical bending strain was 0.23% and the number of tape layers was 5. A mathematic formula was set up to express the comprehensive influence of helical bending strain and perpendicular self-field on critical current degradation. The results can provide an important theoretical foundation for the application of high temperature superconducting tapes and the design of YBCO cables.

Structural features of influenza A virus panhandle RNA enabling the activation of RIG-I independently of 5'-triphosphate.

Retinoic acid-inducible gene I (RIG-I) recognizes specific molecular patterns of viral RNAs for inducing type I interferon. The C-terminal domain (CTD) of RIG-I binds to double-stranded RNA (dsRNA) with the 5′-triphosphate (5′-PPP), which induces a conformational change in RIG-I to an active form. It has been suggested that RIG-I detects infection of influenza A virus by recognizing the 5′-triphosphorylated panhandle structure of the viral RNA genome. Influenza panhandle RNA has a unique structure with a sharp helical bending. In spite of extensive studies of how viral RNAs activate RIG-I, whether the structural elements of the influenza panhandle RNA confer the ability to activate RIG-I signaling has been poorly explored. Here, we investigated the dynamics of the influenza panhandle RNA in complex with RIG-I CTD using NMR spectroscopy and showed that the bending structure of the panhandle RNA negates the requirement of a 5′-PPP moiety for RIG-I activation.