Asymmetric Contraction Research Articles

Biomimetic shape-morphing actuators with controlled bending deformation and photo-mediated 3D shape programming for flexible smart devices

Biomimetic soft actuators with programmable morphing behaviors and remote actuations have drawn significant attention in recent years. In this work, we present the network architecture of a four-arm crystalline shape memory polymer actuator via efficient thiol-acrylate coupling of polycaprolactone precursor bearing crosslinkable methacrylate end-groups with pentaerythritol, followed by post-approach surface chemistry of polydopamine (PDA) nanospheres coating. The excellent photothermal transfer efficiency of the coated PDA can enable rapid temperature increase over the transition temperature of polymeric matrix and optically drive the shape morphings. Combined with built-in internal stress, anisotropic polymer chain relaxation of the strained thin actuator film would generate asymmetric contractions and thus causes controlled bending deformations via surface directing of an 532 nm green laser. Beyond this, the dynamic nature of transesterification reaction also provides the actuator film with reprogrammability. Remarkably, the morphing behaviors of a flexible plane film into various soft robots including 3D airplane and chiral helix were achieved under a 300 mW/cm2 simulated light irradiation. The results presented in this study clearly provide a new method for designing actuators with spatiotemporally programmable morphing behaviors and will pave way for the construction of flexible smart devices.

Biodegradable photo-crosslinked polycaprolactone/polydopamine elastomers with excellent light driven programmable shape memory and chemical degradation properties

Fabrication of biodegradable shape memory polymer with remotely controllable shape actuation is of great significance in the biomedical field but remains challenging. Herein, we present a simple strategy to fabricate a monolayer-based stretchable and mechanically robust polycaprolactone/polydopamine elastomer via efficient thiol-ene click chemistry. The resultant elastomers exhibit desirable photothermal transfer efficiency and can enable rapid temperature increase over the melting temperature of polymeric matrix, and quantitative results demonstrate that the crosslinked film exhibited excellent shape memory properties with shape fixity (Rf) and shape recovery ratios (Rr) approaching 92.3 % and 95.6 %, respectively. Combined with photo stimuli, anisotropic polymer chain relaxation of the prestretched film can generate asymmetric contractions and eventually give rise to ut out-of-plane bending actuations upon photo stimulation, meanwhile, numerical simulation reveals the interaction mechanism of light with film. Beyond this, we further demonstrate that the bending angle is correlated with the parameters of prestretch strain, film thickness as well as irradiation time, and the maximum value can reach 158° with prestretch strain of 200 % and film thickness of 0.3 mm. In particular, the bent structures could be reversibly deformed into plane state via photo-directed corresponding opposite surfaces. Remarkably, the in vitro degradation properties of the elastomers on PBS-T buffer solutions demonstrated that the degradation was composed of induction stage and acceleration stage. This work will pave way for designing biodegradable light-induced shape memory materials toward biomedical device fields and so on.

Programming Motion into Materials Using Electricity-Driven Liquid Crystal Elastomer Actuators.

As thermally driven smart materials capable of large reversible deformations, liquid crystal elastomers (LCEs) have great potential for applications in bionic soft robots, artificial muscles, controllable actuators, and flexible sensors due to their ability to program controllable motion into materials. In this article, we introduce conductive LCE actuators using a liquid metal electrothermal layer and a polyethylene terephthalate substrate. Our LCE actuators can be stimulated at low currents from 2 to 4 A and produce a maximum work density of 9.4 . We illustrate the potential applications of this system by designing a palm-activated artificial muscle gripper, which can be used to grasp soft objects ranging from 5 to 55 mm in size, and even ring-shaped workpieces with precise external or internal support. Furthermore, inspired by the movement of fruit fly larvae, we designed a new soft robot capable of bioinspired crawling and turning by inducing anisotropic friction with an asymmetric design. Finally, we illustrate advanced motional control by designing an autonomously rotating wheel based on the asymmetric contraction of its spokes. To assist in the production of autonomously moving robots, we provide a thorough characterization of its motion dynamics.

Bioinspired self-coiling Janus microfiber actuators for micro-lifter and humidity sensing

Many soft coiled actuators are mimic the desirable structures of plant tendril. Here, we present a facile microfluidic spinning method to fabricate self-coiling Janus microfiber actuator with tunable morphology, spontaneous coiling performance and reversible traction property. By adjusting the component of hydrogel Janus fiber in a microfluidic spinning device with theta-shaped channels, tens of hundreds of homogeneous coils can be spontaneously and rapidly generated due to asymmetric contraction upon dehydration process, and three different forms of coiled fibers with various screw diameters are presented. Furthermore, the coiled Janus microfiber with hygroscopic properties possesses a reversible coiling/uncoiling performance under humidity gradients, which can serve as a micro-actuator to lift a certain weight with enough tensile strain and long-range tractive displacement. In addition, local reversible coiling/uncoiling morphing is achieved under water contact and near infrared light optothermal stimulations. As a verification of this coiled microfiber actuator, a smart switch is designed to control different colored LED lights for sensing an ambient moisture content.

Mechanics of tensegrity cell units incorporating asymmetry and insights into mollitaxis.

The mechanical response of a contractile cell anchored to the substrate through focal adhesions is studied by means of an asymmetric pre-strained tensegrity structure obeying a neo-Hookean stress-strain law. The aim is to assess the influence of overall asymmetric contraction on the cell durotaxis and on the growth of the focal adhesion plaque. The asymmetric kinematics of the system is obtained in two ways, that is by assuming a gradient of the substrate stiffness and through asymmetric buckling. Equivalent springs are purposely considered to represent the stiffness of the ensemble formed by the substrate, the focal adhesion plaque and the integrin ligands. Then, contraction results from elastic strains induced by competing polymerization and actomyosin contraction. The cell mechanical response in terms of durotaxis and its coupling with focal adhesion plaque growth is finally analysed with respect to the effects of asymmetry, gaining some insights into how this asymmetry could participate to redirect cell migration, both in terms of durotaxis and mollitaxis.

A synoptic bridge linking sea salt aerosol concentrations in East Antarctic snowfall to Australian rainfall

Previous research has shown that aerosol sea salt concentrations (Southern Ocean wind proxy) preserved in the Law Dome ice core (East Antarctica) correlate significantly with subtropical eastern Australian rainfall. However, physical mechanisms underpinning this connection have not been established. Here we use synoptic typing to show that an atmospheric bridge links East Antarctica to subtropical eastern Australia. Increased ice core sea salt concentrations and wetter conditions in eastern Australia are associated with a regional, asymmetric contraction of the mid-latitude westerlies. Decreased ice core sea salt concentrations and drier eastern Australia conditions are associated with an equatorward shift in the mid-latitude westerlies, suggesting greater broad-scale control of eastern Australia climate by southern hemisphere variability than previously assumed. This relationship explains double the rainfall variance compared to El Niño-Southern Oscillation during late spring-summer, highlighting the importance of the Law Dome ice core record as a 2000-year proxy of eastern Australia rainfall variability.

Spatial correction improves accuracy of catheter positioning during ablation of premature ventricular contractions: differences between ventricular outflow tracts and other localizations

BackgroundHybrid activation mapping is a novel tool to correct for spatial displacement of the mapping catheter due to asymmetrical contraction of myocardium during premature ventricular contractions (PVC). The aim of this study is to describe and improve our understanding of spatial displacement during PVC mapping as well as options for correction using hybrid activation mapping.Methods and resultsWe analyzed 5798 hybrid mapping points in 40 acquired hybrid maps of 22 consecutive patients (age 63 ± 16 years, 45% female) treated for premature ventricular contractions (PVCs). Median PVC-coupling interval was 552 ms (IQR 83 ms). Spatial displacement was determined by measuring the dislocation of the catheter tip during PVC compared to the preceding sinus beat. Mean spatial displacement was 3.8 ± 1.5 mm for all maps. The displacement was 1.3 ± 0.4 mm larger for PVCs with non-outflow-tract origin compared to PVCs originating from the ventricular outflow tracts (RVOT/LVOT; p = 0.045). Demographic parameters, PVC-coupling-interval and chamber of origin had no significant influence on the extent of spatial displacement.ConclusionEctopic activation of the ventricular myocardium during PVCs results in spatial displacement of mapping points that is significantly larger for PVCs with non-outflow-tract origin. The correction for spatial displacement may improve accuracy of radiofrequency current (RFC)-application in catheter ablation of PVCs.

Insight into the graphitization mechanism of the interface between iron and diamond: A DFT study

It is an important topic in the manufacturing research field to understand the mechanisms for the wear of diamond surfaces. The density functional theory (DFT) methods have served as useful tools for studying chemical reaction mechanisms in processing. In this work, we studied the changes in the diamond structure during the interface contact between the iron and diamond. The iron-diamond contact area is simplified to different coverage rates of Fe atom, corresponding to different numbers of adatom. With the different numbers of the Fe adatoms, the interlayer CC bonds have different changes. Below the Fe adatom region, the interlayer CC bonds are strengthened, inhibiting the graphitization. It is noteworthy that the CC bonds became significantly weakened or even broken at the boundary of the interface contact. Moreover, the interface sliding simulation verifies that the graphitization preferentially occurs at the edge of the interface between iron and diamond. The actual cause of graphitization is the synergistic effect of the charge transfer of the FeC bonds and the asymmetric contraction and stretching on the diamond surface. Our work provides a theoretical basis for suppressing excessive diamond tool wear and polishing the diamond surfaces.

PP2A-Cdc55 phosphatase regulates actomyosin ring contraction and septum formation during cytokinesis

Eukaryotic cells divide and separate all their components after chromosome segregation by a process called cytokinesis to complete cell division. Cytokinesis is highly regulated by the recruitment of the components to the division site and through post-translational modifications such as phosphorylations. The budding yeast mitotic kinases Cdc28-Clb2, Cdc5, and Dbf2-Mob1 phosphorylate several cytokinetic proteins contributing to the regulation of cytokinesis. The PP2A-Cdc55 phosphatase regulates mitosis counteracting Cdk1- and Cdc5-dependent phosphorylation. This prompted us to propose that PP2A-Cdc55 could also be counteracting the mitotic kinases during cytokinesis. Here we show that in the absence of Cdc55, AMR contraction and the primary septum formation occur asymmetrically to one side of the bud neck supporting a role for PP2A-Cdc55 in cytokinesis regulation. In addition, by in vivo and in vitro assays, we show that PP2A-Cdc55 dephosphorylates the chitin synthase II (Chs2 in budding yeast) a component of the Ingression Progression Complexes (IPCs) involved in cytokinesis. Interestingly, the non-phosphorylable version of Chs2 rescues the asymmetric AMR contraction and the defective septa formation observed in cdc55∆ mutant cells. Therefore, timely dephosphorylation of the Chs2 by PP2A-Cdc55 is crucial for proper actomyosin ring contraction. These findings reveal a new mechanism of cytokinesis regulation by the PP2A-Cdc55 phosphatase and extend our knowledge of the involvement of multiple phosphatases during cytokinesis.

Thirst for money: External guarantees and stock price crash risk

We evaluate the financial risk and explore the potential motivation behind the pervasive external guarantee activities of listed firms in China from 2008 to 2017. We find that external guarantee intensity is positively associated with stock price crash risk. Further analysis shows that the negative consequences are driven by external guarantee activities with strong information asymmetry. Asymmetric contracts and guarantee relationships produce crash risk. The management hide guarantee risk, whereas analysts reveal crash risk. In addition, external guarantees strengthen bank-firm relationships. Overall, firms are motivated by accessing loans from related banks and by concealing potential risks associated with external guarantees.

Asymmetric Group Loan Contracts: Experimental Evidence

We design an experiment to study the role of (a)symmetry in the context of group lending with joint liability. The performance of joint-liability contracts crucially hinges on borrowers engaging in peer monitoring. We find that asymmetric contracts, in which monitoring is a dominant strategy for one borrower, increase the monitoring rate, and thus the repayment rate and performance. Moreover, symmetric contracting also increases expected profits of the lending institution. Overall, our results suggest that asymmetric joint-liability contracts are worth considering as part of a policy to maintain financial stability.

Experimental study on inertial focusing pattern in asymmetric contraction–expansion array microchannel

Experimental study on inertial focusing pattern in asymmetric contraction–expansion array microchannel

A Biologically Inspired Ring-Shaped Soft Pneumatic Actuator for Large Deformations.

Biomimicry of the stomach's peristaltic contractions can be challenging in the design, modeling, and control of a soft actuator. The mimicking of organ contractions advances our knowledge of the digestive system and analyzes the biological behavior by testing with a physical robot. This article proposes a ring-shaped soft pneumatic actuator (RiSPA) as a segment of the digestive tract. RiSPA is made of a ring frame with embedded bellow actuators that generate contractive motions. An embedded sensory system measures the contraction using range sensors. The kinematics and dynamics of RiSPA's contraction are modeled and simulated, while a state feedback algorithm is applied to them. The simulation results are validated experimentally by comparing the RiSPA measurements with desired applied signals. The proposed actuator provides controllable symmetrical and asymmetrical contractions analog to the human stomach. The results of RiSPA validate the prediction performance of the simulation and controller with applied sinusoidal signals as a peristaltic wave. RiSPA contractions can be applied to a broad range of applications, such as imitating the esophagus and intestine contractions.

Unconstrained 3D Shape Programming with Light‐Induced Stress Gradient

Programming 2D sheets to form 3D shapes is significant for flexible electronics, soft robots, and biomedical devices. Stress regulation is one of the most used methods, during which external force is usually needed to keep the stress, leading to complex processing setups. Here, by introducing dynamic diselenide bonds into shape-memory materials, unconstrained shape programming with light is achieved. The material could hold and release internal stress by themselves through the shape-memory effect, simplifying programming setups. The fixed stress could be relaxed by light to form stress gradients, leading to out-of-plane deformations through asymmetric contractions. Benefiting from the variability of light irradiation, complex 3D configurations can be obtained conveniently from 2D polymer sheets. Besides, remotely controlled "4D assembly" and actuation, including object transportation and self-lifting, can be achieved by sequential deformation. Taking advantage of the high spatial resolution of light, this material can also produce 3D microscopic patterns. The light-induced stress gradients significantly simplify 3D shape programming procedures with improved resolution and complexity and have great potential in soft robots, smart actuators, and anti-counterfeiting techniques.

The One21 Technique: An Individualized Treatment for Glabellar Lines Based on Clinical and Anatomical Landmarks.

PurposeBotulinum toxin type A is an effective treatment for glabellar dynamic wrinkles. As the muscular group involved in the contraction of the glabella varies among people, individualized treatment can achieve optimal results. This study evaluates a customized assessment for the treatment of glabellar lines with Incobotulinumtoxin-A, leading to an individualized points distribution and dosage.Patients and MethodsA single-center, evaluator-blinded, therapeutic cohort study enrolled 130 women with moderate or severe glabellar wrinkles. They underwent Incobotulinumtoxin-A injection following the standard 5-point injection at the glabellar muscles (n = 65) or an individualized assessment and scheme treatment based on anatomical references of contraction, the One21 technique (n = 65). All the patients were photographed under maximum contraction before treatment (T0) and after 4 weeks (T28). The photos were randomly assessed by two blinded, experienced raters to consensually grade the severity according to the Merz Aesthetics Scales (MAS). The primary clinical efficacy was defined as a 2-point reduction in the MAS score, on Day 28.ResultsThe groups were homogeneous regarding age, phototype, and baseline MAS scores. On Day 28 (T28), 64 (98.5%) patients from the One21 group and 52 (80%) from the 5-point group reduced the MAS score by at least two points (p < 0.01). When adjusted by age and phototype, both groups reduced the MAS score at T28 (p < 0.01); nevertheless, patients from the One21 group significantly performed better (p < 0.01), with a much higher rate response rate at T28, in comparison to the 5-point group. Of patients enrolled in the 5-point group, 83.1% utilized muscle groups other than the procerus and corrugator in glabellar wrinkle formation, and 17 (24.6%) presented asymmetrical contraction. Patients from the 5-point group with glabellar asymmetry and those who utilized the frontalis and orbicularis presented inferior performance (p < 0.05), reinforcing the importance of an individualized assessment and treatment plan.ConclusionThe One21 technique yielded better results than the standard 5-point treatment in reducing glabellar dynamic lines with Incobotulinumtoxin-A, especially for asymmetric lines of the glabella or the involvement of muscle groups other than the procerus and corrugator.

Fabrication of a Dual Stimuli-Responsive Assorted Film Comprising Magnetic- and Gold-Nanoparticles with a Self-Assembly Protein of α-Synuclein.

Development of sensing elements for controllable soft materials is crucial to improve their responsiveness toward remotely provided external stimuli. Magnetic nanoparticles (MNPs) and gold nanoparticles (AuNPs) have been coassembled into a flexible free-floating 2D film to produce a shape deformable mobile structure in the presence of magnetic field and light irradiation by employing a self-assembly protein of α-synuclein (αS). αS was demonstrated to be essential for the preparation of a multisensory system because the intrinsically disordered protein led to a complete dispersion of MNPs to an average size of 10 nm in aqueous solution, pH-dependent closely packed single layer adsorption of αS-MNPs, and α-helix-mediated free-floating MNP monolayer film formation upon dissolving the underlying polycarbonate substrate with chloroform. As AuNPs were incorporated into the assorted hybrid film in the presence of MNPs, however, the β-sheet component became prominent. By placing the assorted film between a spin-coated thin layer of thermoresponsive P(AAc-co-NIPAAm) hydrogel comprising acrylic acid and N-isopropylacrylamide and a passive layer of silicone elastomer, the resulting triply structure exhibited not only magnet-induced locomotion but also shape deformation due to asymmetric contraction of the sandwiching two layers caused by the heat generated by AuNPs upon near IR irradiation. In fact, two adjoining planar layers of another triply structure were shown to form a three-dimensional lotus flower with the light. This multisensory system is suggested to be further functionalized by modifying the αS molecules and incorporating additional nanoparticles to react to diverse stimuli, which would make the system be utilized in the areas of not only soft robotics but also foldable electronics, high-performance sensors/actuators, and medical/wearable applications.

Asymmetric Group Loan Contracts: Experimental Evidence

We design an experiment to study the role of (a)symmetry in the context of group lending with joint liability. The performance of joint-liability contracts crucially hinges on borrowers engaging in peer monitoring. We find that asymmetric contracts, in which monitoring is a dominant strategy for one borrower, increase the monitoring rate, and thus the repayment rate and performance. Moreover, symmetric contracting also increases expected profits of the lending institution. Overall, our results suggest that asymmetric joint-liability contracts are worth considering as part of a policy to maintain financial stability.

Rotatory nystagmus after granisetron administration

Background: Granisetron is a popular antiemetic medication used in the emergency department to control nausea and vomiting with an excellent side effect profile among adults and pediatric, in both healthy and oncology patients. Case Presentation: Our patient received granisetron for nausea and vomiting then developed torsional nystagmus, asymmetrical abnormal muscle contractions, and electrocardiography showed QTc prolongation 487 ms. The patient did improve after IV lorazepam and magnesium sulphate administration. Conclusion: QTc prolongation increases the risk of developing Torsades de Pointes and sudden death. Extrapyramidal syndrome caused by granisetron is rare and should not be confused with seizure. Both are significant effects associated with 5-HT3 antagonists administration to be aware of and if they occurred, should be managed in a timely fashion.

Asymmetric Input Contracts with Price Leadership and Capacity Constraints

This paper considers a vertically related industry where an upstream supplier simultaneously negotiates with two downstream retailers endowed with (possibly) asymmetric bargaining powers, over the purchase of an input. Downstream firms have asymmetric capacities and downstream competition has a price leadership structure. Under linear tariffs, an increase in the upstream supplier's bargaining power towards the large firm induces a positive externality on the small firm's tariff. Under two-part tariff, instead, cross effects vanish. In both regimes, we obtain that, a priori the small firm may end up i) demanding a larger stock of the input and ii) paying less for it. Our model also proves useful to show that the well-known countervailing buyer power hypothesis may not hold because an integrated downstream firm might negotiate a better input price without any pass-through to the final consumers. We mainly relate our analysis to the UK grocery market and to the recent empirical evidence regarding its functioning.

Factors of Postural Asymmetry (FPA) At The Pre- and Subclinical Stages of the Develop-ment of 3D Deformity of the Vertebral Complex

In the pathogenesis of typical scoliosis, as a three-dimensional deformation, the process of formation of its horizontal component is of particular interest. From the point of view of the functional anatomy of the vertebral complex, appearance of this component is directly related to the work of the transverso-spinal muscles. Thus, their contraction on the left side results in a rotational displacement of the vertebral bodies to the right, and the same phenomenon on the right causes a left-sided rotation of the main bone elements of the supporting column of the spine. It has already been shown that longterm asymmetric contraction of these muscles is a key at the subclinical stage of the transition of a healthy spine to the “scoliotic” status [1-3]. The method of blood serum bioassay (BT SC) has confirmed our assumption that among the participants in the pathogenesis of progressive scoliosis there are so-called neuropeptide factors of postural asymmetry (FPA), which have an ability to lateralize the activity of motor neurons in the spinal cord. These were natural regulators - oxytocin and arginine-8-vasopressin, and this ability appears in a case of a multiple increase in their concentration. Determination of their quantitative characteristics using ELISA showed high correlations between the levels of these factors and the process of spinal column deformation at the pre-and subclinical stages of scoliosis development.