Bioinspired strategies for biomimetic actuators from ultrafast to ultraslow

Motile plant tissues can control their configurations and regulate their motion speed according to their specific requirements,which offer various protypes for biomimetic actuators with controlled motion speed.In this perspective,we focus on the speed control of plant tissues and the bioinspired strategies for speed regulation of artificial actuators.We begin with a summary to the strategies and mechanisms of motile plant tissues for controlling motion speed,ranging from ultrafast to ultraslow.We then exemplify the models for fabricating bioinspired artificial actuators and briefly discuss current application scenarios of actuators with varying speeds from ultrafast to ultraslow.Finally,we propose potential strategies for the speed regulation of actuators.

Overhead-free Noise-tolerant Federated Learning: A New Baseline

Federated learning (FL) is a promising decentralized machine learning approach that enables multiple distributed clients to train a model jointly while keeping their data private. However, in real-world scenarios, the supervised training data stored in local clients inevitably suffer from imperfect annotations, resulting in subjective, inconsistent and biased labels. These noisy labels can harm the collaborative aggregation process of FL by inducing inconsistent decision boundaries. Unfortunately, few attempts have been made towards noise-tolerant federated learning, with most of them relying on the strategy of transmitting overhead messages to assist noisy labels detection and correction, which increases the communication burden as well as privacy risks. In this paper, we propose a simple yet effective method for noise-tolerant FL based on the well-established co-training framework. Our method leverages the inherent discrepancy in the learning ability of the local and global models in FL, which can be regarded as two complementary views. By iteratively exchanging samples with their high confident predictions, the two models “teach each other” to suppress the influence of noisy labels. The proposed scheme enjoys the benefit of overhead cost-free and can serve as a robust and efficient baseline for noise-tolerant federated learning. Experimental results demonstrate that our method outperforms existing approaches, highlighting the superiority of our method.

Temperature-Dependent Tearing Behavior of Rubber Materials:Characterization and Modeling

With the increasingly widespread application of rubber in many fields,there is a growing demand for quantitative characterization of temperature-dependent mechanical properties in high-temperature service environments.The critical tearing energy is an important criterion for determining whether rubber materials will experience tearing instability,while tear strength is a key parameter for rubber materials to resist tearing.It is necessary to quantitatively characterize their evolution with temperature.Current theoretical research mainly relies on fitting a large amount of experimental data,which is not convenient for engineering applications.Therefore,in this work,a temperature-dependent critical tearing energy model is firstly developed based on the force-heat equivalence energy density principle.This model considers the equivalent relationship between the critical tearing energy required for crack instability propagation and the thermal energy stored in the rubber material.It is demonstrated that our model has higher prediction accuracy when compared to other models.Furthermore,combining with the Griffith fracture theory,temperature-dependent tear strength models applicable to three different crack modes are separately established.These models are validated using experimental data for Mode I opening cracks and ModeⅢtearing cracks,and good consistency is achieved.Additionally,a quantitative analysis of the influence of elastic modulus on tear strength at different temperatures is conducted.This work provides a reliable way for predicting temperature-dependent tearing instability behavior and offers beneficial suggestions for improving the tear strength of rubber materials at different temperatures.

Water-Excluding Underwater Glue Induced by Marangoni Effect

Marangoni effect at the two-phase interface with different surface tension as a unique mass transfer phenomenon has been widely used in daily life and industrialmanufacture.However,their marvelous liquid-driving capability between miscible liquids has long been ignored,especially in water environments.Here,we first reveal a distinct underwater Marangoni effect between the solvent of glues and the water layer on solid surfaces.Driven by the Marangoni effect,organic solvents with water solubility,high dielectric constant,and low diffusivity could effectively exclude the interfacial water layer,enabling direct and effective contact between glues and solid surfaces.Our experimental results and theoretical simulation proved that a relatively large ratio of the Marangoni number in the horizontal direction and to the vertical direction ensured an effective underwater adhesion of the water-excluding glue.This surface engineering approach provides an alternative to the traditional methods of molecular engineering for realizing underwater adhesion.

Resilient conductive membrane synthesized by in-situ polymerisation for wearable non-invasive electronics on moving appendages of cyborg insect

By leveraging their high mobility and small size,insects have been combined with microcontrollers to build up cyborg insects for various practical applications.Unfortunately,all current cyborg insects rely on implanted electrodes to control their movement,which causes irreversible damage to their organs and muscles.Here,we develop a non-invasive method for cyborg insects to address above issues,using a conformal electrode with an in-situ polymerized ion-conducting layer and an electron-conducting layer.The neural and locomotion responses to the electrical inductions verify the efficient communication between insects and controllers by the non-invasive method.The precise“S”line following of the cyborg insect further demonstrates its potential in practical navigation.The conformal non-invasive electrodes keep the intactness of the insects while controlling their motion.With the antennae,important olfactory organs of insects preserved,the cyborg insect,in the future,may be endowed with abilities to detect the surrounding environment.

Author Correction:Resilient conductive membrane synthesized by in-situ polymerisation for wearable noninvasive electronics on moving appendages of cyborg insect

In the version of this article initially published,the subfigures in the Fig.3 were in the wrong order and has been corrected on the HTML and PDF versions of the article.

Recent Progress of Mussel-Inspired Underwater Adhesives

Underwater adhesion is greatly desired in tissue transplantation, medical treatment, ocean transportation, and so on. However, common commercial polymeric adhesives are rather weakened and easily destroyed in water envi- ronment. In nature, some marine organisms, such as mussels, barnacles, or tube worms, exhibiting excellent under- water adhesion up to robust bonding on the rock of sea floor, can give exciting solutions to address the problem. Among these marine organisms, mussels exhibit unique underwater adhesion via the foot proteins of byssus. It has been verified that the catechol groups from the side chain of the mussel foot proteins is the main contribution to the unique underwater adhesion. Hence, inspired by the mussels＇ underwater adhesion, many mussel-mimetic polymers with catechol as end chains or side chains have been developed in the past decades. Here, we review recent progress of mussel-inspired underwater adhesives polymers from their catechol-functional design to their potential applica- tions in intermediates, anti-biofouling, self-healing of hydrogels, biological adhesives, and drug delivery. The re- view may provide basis and help for the development of the commercial underwater adhesives.

Engineering subcellular-patterned biointerfaces to regulate the surface wetting of multicellular spheroids

Studying the wetting behaviors of multicellular spheroids is crucial in the fields of embryo implantation, cancer propagation, and tissue repair. Existing strategies for controlling the wetting of multicellular spheroids mainly focus on surface chemistry and substrate rigidity. Although topography is another important feature in the biological micro-environment, its effect on multicellular spheroid wetting has seldom been explored. In this study, the influence of topography on the surface wetting of multicellular spheroids was investigated using subcellular- patterned opal films with controllable colloidal particle diameters （from 200 to 1,500 nm）. The wetting of hepatoma carcinoma cellular （Hep G2） spheroids was impaired on opal films compared with that on flat substrates, and the wetting rate decreased as colloidal particle diameter increased. The decrement reached 48.5% when the colloidal particle diameter was 1,500 nm. The subcellular-patterned topography in opal films drastically reduced the cellular mobility in precursor films, especially the frontier cells in the leading edge. The frontier cells failed to form mature focal adhesions and stress fibers on micro-patterned opal films. This was due to gaps between colloidal particles leaving adhesion vacancies, causing weak cell-substrate adhesion and consequent retarded migration of Hep G2 spheroids. Our study manifests the inhibiting effects of subcellular-patterned topography on the wetting behaviors of multicellular spheroids, providing new insight into tissue wetting-associated treatments and biomaterial design.

Directional transport of centimeter-scale object on anisotropic microcilia surface under water

Natural organisms such as cactus spines or trachea cilia have unique directional transport ability, owing to their anisotropic surface structures or asymmetric motion.However, most artificial interfacial materials are incapable of transporting macroscale object underwater. Herein, we report that anisotropic microcilia arrays, composed of cobalt fine powder and PDMS, can successfully transport the centimeterscale hydrogel underwater by periodically asymmetric stroke under alternative magnetic field. Reciprocal collective stroke of anisotropic microcilia can generate directional flow, propelling the centimeter-scale hydrogel slice forward. Accompanying computational simulation results are consistent with the directional transport behaviors observed in our experiments. This study provides a clue to design artificial anisotropic interfacial materials with capability of transporting macroscale object at low Reynolds number.

Flexible Dry Hydrogel with Lamella-Like Structure Engineered via Dehydration in Poor Solvent

Hydrogels are among the most promising biologic materials in recent technology with numerous desired applications,including serving as biosensors,drug delivery vehicles,and tissue-engineered products for cell matrices.However,they often dehydrate,and become stiff and brittle in air,causing loss of flexibility and functions.Several layered structures have been proven to increase the strength,toughness,and even flexibility of these materials,which might provide a new clue for the sustenance of the flexibility of drying gels.Herein,we report a novel solvent-dehydrated hydrogel engineering approach,aimed to change the inner structure and keep the flexibility of a dehydrated hydrogel in the air via solvent-induced dehydration,for example,acetonedehydrated polyacrylic acid hydrogel.This flexible dry gel could be folded,twisted,and stretched without any damage due to the assumed lamella-like structures,contrary to dry gels without these microstructures or those with porous structures,which retain brittle consistency.The flexible dry gel also exhibited excellent self-healing capability with the assistance of solvents.Fascinatingly,this flexible gel film displayed strain-visualizing paper writing/erasing performance properties,with water acting as invisible ink.Thus,this fabricated flexible hydrogel film might function as confidential information storage material.Our current approach is versatile,hence applicable to other hydrogels,and provides insight into the engineering of other functional gels for extended future applications.

Regulatable interfacial adhesion between stamp and ink for transfer printing

As an emerging processing technology,transfer printing enables the assembly of functional material arrays(called inks)on various substrates with micro/nanoscale resolution and has been widely used in the fabrication of flexible electronics and display systems.The critical steps in transfer printing are the ink pick-up and printing processes governed by the switching of adhesion states at the stamp/ink interface.In this review,we first introduce the history of transfer printing in terms of the transfer methods,transferred materials,and applications.Then,the fundamental characteristics of the transfer printing system and typical strategies for regulating the stamp/ink interfacial adhesion strength are summarized and exemplified.Finally,future challenges and opportunities for developing the novel stamps,inks,and substrates with intelligent adhesion capability are discussed,aiming to inspire the innovation in the design of transfer printing systems.