Bioinspired Multifunctional Self-Sensing Actuated Gradient Hydrogel for Soft-Hard Robot Remote Interaction

The development of bioinspired gradient hydrogels with self-sensing actuated capabilities for remote interaction with soft-hard robots remains a challenging endeavor. Here, we propose a novel multifunctional self-sensing actuated gradient hydrogel that combines ultrafast actuation and high sensitivity for remote interaction with robotic hand. The gradient network structure, achieved through a wettability difference method involving the rapid precipitation of MoO_(2) nanosheets, introduces hydrophilic disparities between two sides within hydrogel. This distinctive approach bestows the hydrogel with ultrafast thermo-responsive actuation(21° s^(-1)) and enhanced photothermal efficiency(increase by 3.7 ℃ s^(-1) under 808 nm near-infrared). Moreover, the local cross-linking of sodium alginate with Ca^(2+) endows the hydrogel with programmable deformability and information display capabilities. Additionally, the hydrogel exhibits high sensitivity(gauge factor 3.94 within a wide strain range of 600%), fast response times(140 ms) and good cycling stability. Leveraging these exceptional properties, we incorporate the hydrogel into various soft actuators, including soft gripper, artificial iris, and bioinspired jellyfish, as well as wearable electronics capable of precise human motion and physiological signal detection. Furthermore, through the synergistic combination of remarkable actuation and sensitivity, we realize a self-sensing touch bioinspired tongue. Notably, by employing quantitative analysis of actuation-sensing, we realize remote interaction between soft-hard robot via the Internet of Things. The multifunctional self-sensing actuated gradient hydrogel presented in this study provides a new insight for advanced somatosensory materials, self-feedback intelligent soft robots and human–machine interactions.

Bioinspired directional structures for inhibiting wetting on super-melt-philic surfaces above 1200°C

Over the past two decades,superhydrophobic surfaces that are easily created have aroused considerable attention for their superior performances in various applications at room temperature.Nowadays,there is a growing demand in special fields for the development of surfaces that can resist wetting by high-temperature molten droplets(>1200°C)using facile design and fabrication strategies.Herein,bioinspired directional structures(BDSs)were prepared on Y2O3-stabilized ZrO2(YSZ)surfaces using femtosecond laser ablation.Benefiting from the anisotropic energy barriers,the BDSs featured with no additional modifiers showed a remarkable increase from 9.2°to 60°in the contact angle of CaO–MgO–Al2O3–SiO2(CMAS)melt and a 70.1%reduction in the spreading area of CMAS at 1250°C,compared with polished super-CMAS-melt-philic YSZ surfaces.Moreover,the BDSs demonstrated exceptional wetting inhibition even at 1400°C,with an increase from 3.3°to 31.3°in contact angle and a 67.9%decrease in spreading area.This work provides valuable insight and a facile preparation strategy for effectively inhibiting the wetting of molten droplets on super-melt-philic surfaces at extremely high temperatures.

MXenes for Bioinspired Soft Actuators:Advancements in Angle-Independent Structural Colors and Beyond

Soft actuators have garnered substantial attention in current years in view of their potential appliances in diverse domains like robotics,biomedical devices,and biomimetic systems.These actuators mimic the natural movements of living organisms,aiming to attain enhanced flexibility,adaptability,and versatility.On the other hand,angle-independent structural color has been achieved through innovative design strategies and engineering approaches.By carefully controlling the size,shape,and arrangement of nanostructures,researchers have been able to create materials exhibiting consistent colors regardless of the viewing angle.One promising class of materials that holds great potential for bioinspired soft actuators is MXenes in view of their exceptional mechanical,electrical,and optical properties.The integration of MXenes for bioinspired soft actuators with angle-independent structural color offers exciting possibilities.Overcoming material compatibility issues,improving color reproducibility,scalability,durability,power supply efficiency,and cost-effectiveness will play vital roles in advancing these technologies.This perspective appraises the development of bioinspired MXene-centered soft actuators with angleindependent structural color in soft robotics.

Predicting the Mechanical Behavior of a Bioinspired Nanocomposite through Machine Learning

The bioinspired nacre or bone structure represents a remarkable example of tough,strong,lightweight,and multifunctional structures in biological materials that can be an inspiration to design bioinspired high-performance materials.The bioinspired structure consists of hard grains and soft material interfaces.While the material interface has a very low volume percentage,its property has the ability to determine the bulk material response.Machine learning technology nowadays is widely used in material science.A machine learning model was utilized to predict the material response based on the material interface properties in a bioinspired nanocomposite.This model was trained on a comprehensive dataset of material response and interface properties,allowing it to make accurate predictions.The results of this study demonstrate the efficiency and high accuracy of the machine learning model.The successful application of machine learning into the material property prediction process has the potential to greatly enhance both the efficiency and accuracy of the material design process.

Bioinspired All‑Fibrous Directional Moisture‑Wicking Electronic Skins for Biomechanical Energy Harvesting and All‑Range Health Sensing

Electronic skins can monitor minute physiological signal variations in the human skins and represent the body’s state,showing an emerging trend for alternative medical diagnostics and human-machine interfaces.In this study,we designed a bioinspired directional moisture-wicking electronic skin(DMWES)based on the construction of heterogeneous fibrous membranes and the conductive MXene/CNTs electrospraying layer.Unidirectional moisture transfer was successfully realized by surface energy gradient and push-pull effect via the design of distinct hydrophobic-hydrophilic difference,which can spontaneously absorb sweat from the skin.The DMWES membrane showed excellent comprehensive pressure sensing performance,high sensitivity(maximum sensitivity of 548.09 kPa^(−1)),wide linear range,rapid response and recovery time.In addition,the single-electrode triboelectric nanogenerator based on the DMWES can deliver a high areal power density of 21.6μW m^(−2) and good cycling stability in high pressure energy harvesting.Moreover,the superior pressure sensing and triboelectric performance enabled the DMWES for all-range healthcare sensing,including accurate pulse monitoring,voice recognition,and gait recognition.This work will help to boost the development of the next-generation breathable electronic skins in the applications of AI,human-machine interaction,and soft robots.

Developing super-hydrophobic and corrosion-resistant coating on magnesium-lithium alloy via one-step hydrothermal processing

Formation of super-hydrophobic and corrosion-resistant coatings can provide significant corrosion protection to magnesium alloys.However,it remains a grand challenge to produce such coatings for magnesium-lithium alloys due to their high chemical reactivity.Herein,a one-step hydrothermal processing was developed using a stearic-acid-based precursor medium,which enables the hydrothermal conversion and the formation of low surface energy materials concurrently to produce the super-hydrophobic and corrosion-resistant coating.The multiscale microstructures with nanoscale stacks and microscale spheres on the surface,as well as the through-thickness stearates,lead to the super-hydrophobicity and excellent corrosion resistance of the obtained coating.

Bioinspired MXene-Based Soft Actuators Exhibiting Angle-Independent Structural Color

In nature,many living organisms exhibiting unique structural coloration and soft-bodied actuation have inspired scientists to develop advanced structural colored soft actuators toward biomimetic soft robots.However,it is challenging to simultaneously biomimic the angle-independent structural color and shape-morphing capabilities found in the plum-throated cotinga flying bird.Herein,we report biomimetic MXene-based soft actuators with angle-independent structural color that are fabricated through controlled self-assembly of colloidal SiO_(2) nanoparticles onto highly aligned MXene films followed by vacuum-assisted infiltration of polyvinylidene fluoride into the interstices.The resulting soft actuators are found to exhibit brilliant,angle-independent structural color,as well as ultrafast actuation and recovery speeds(a maximum curvature of 0.52 mm−1 can be achieved within 1.16 s,and a recovery time of~0.24 s)in response to acetone vapor.As proof-of-concept illustrations,structural colored soft actuators are applied to demonstrate a blue gripper-like bird’s claw that can capture the target,artificial green tendrils that can twine around tree branches,and an artificial multicolored butterfly that can flutter its wings upon cyclic exposure to acetone vapor.The strategy is expected to offer new insights into the development of biomimetic multifunctional soft actuators for somatosensory soft robotics and next-generation intelligent machines.

Bioinspired fish-scale-like magnesium composites strengthened by contextures of continuous titanium fibers:Lessons from nature

Natural fish scales demonstrate outstanding mechanical efficiency owing to their elaborate architectures and thereby may serve as ideal prototypes for the architectural design of man-made materials.Here bioinspired magnesium composites with fish-scale-like orthogonal plywood and double-Bouligand architectures were developed by pressureless infiltration of a magnesium melt into the woven contextures of continuous titanium fibers.The composites exhibit enhanced strength and work-hardening ability compared to those estimated from a simple mixture of their constituents at ambient to elevated temperatures.In particular,the double-Bouligand architecture can effectively deflect cracking paths,alleviate strain localization,and adaptively reorient titanium fibers within the magnesium matrix during the deformation of the composite,representing a successful implementation of the property-optimizing mechanisms in fish scales.The strength of the composites,specifically the effect of their bioinspired architectures,was interpreted based on the adaptation of classical laminate theory.This study may offer a feasible approach for developing new bioinspired metal-matrix composites with improved performance and provide theoretical guidance for their architectural designs.

DEM Numerical Simulation of Abrasive Wear Characteristics of a Bioinspired Ridged Surface

This paper presents numerical investigations into a ridged surface whose design is inspired by the geometry of a Farrer’sscallop.The objective of the performed research is to assess if the proposed Bioinspired Ridged Surface (BRS) can potentiallyimprove wear resistance of soil-engaging components used in agricultural machinery and to validate numerical simulationsperformed using software based on the Discrete Element Method (DEM).The wear performance of the BRS is experimentallydetermined and also compared with a conventional flat surface.Different size of soil particles and relative velocities between theabrasive sand and the testing surfaces are used.Comparative results show that the numerical simulations are in agreement withthe experimental results and support the hypothesis that abrasive wear is greatly reduced by substituting a conventional flatsurface with the BRS.

Super-hydrophobic characteristics of butterfly wing surface

Many biological surface are hydrophobic because of their complicated composition and surface microstructure. Eleven species (four families) of butterflies were selected to study their micro-, nano-structure and super-hydrophobic characteristic by means of Confocal Light Microscopy, Scanning Electron Microscopy and Contact Angle Measurement. The contact an- gles of water droplets on the butterfly wing surface were consistently measured to be about 150 ? and 100 ? with and without the squamas, respectively. The dust on the surface can be easily cleaned by moving spherical droplets when the inclining angle is larger than 3 ?. It can be concluded that the butterfly wing surface possess a super-hydrophobic, water-repellent, self-cleaning, or “Lotus-effect”characteristic. The contact angle measurement of water droplets on the wing surface with and without the squamas showed that the water-repellent characteristic is a consequence of the microstructure of the squamas. Each water droplet (diameter 2 mm) can cover about 700 squamas with a size of 40 m×80 m of each squama. The regular riblets with a width of 1000 nm to 1500 nm are clearly observed on each single squama. Such nanostructure should play a very important role in their super-hydrophobic and self-cleaning characteristic.

NANO-TRIBOLOGICAL STUDY ON A SUPER-HYDROPHOBIC FILM FORMED ON ROUGH ALUMINUM SUBSTRATES

A novel super-hydrophobic stearic acid(STA)film with a water contact angle of 166° was prepared by chemical adsorption on aluminum wafer coated with polyethyleneimine(PEI)film. The micro-tribological behavior of the super-hydrophobic STA monolayer was compared with that of the polished and PEI-coated Al surfaces.The effect of relative humidity on the adhesion and friction was investigated as well.It was found that the STA monolayer showed decreased friction,while the adhesive force was greatly decreased by increasing the surface roughness of the Al wafer to reduce the contact area between the atomic force microscope(AFM)tip and the sample surface to be tested.Thus the friction and adhesion of the Al wafer was effectively decreased by generating the STA monolayer, which indicated that it could be feasible and rational to prepare a surface with good adhesion resistance and lubricity by properly controlling the surface morphology and the chemical composition.Both the adhesion and friction decreased as the relative humidity was lowered from 65% to 10%,though the decrease extent became insignificant for the STA monolayer.

Femtosecond laser micro/nano fabrication for bioinspired superhydrophobic or underwater superoleophobic surfaces

The preparation of superhydrophobic or underwater superoleophobic interface materials has become a research hotspot because of their wide application in self-cleaning, drag reduction, oil-water separation, anti-oil pollution and so on. The unique wettability of organisms gives inspiration to design and create new interface materials. This review focuses on the recent research progress of femtosecond laser micro/nano fabrication for bioinspired superhydrophobic or underwater superoleophobic surfaces. This review starts with a presentation of the related background including the advantages of femtosecond laser and wettability theoretical basis. Then, organisms with unique wettability in nature, the preparation of superhydrophobic or underwater superoleophobic surfaces by femtosecond lasers on different materials, and their related important applications are introduced. Finally, the current challenges and future prospects with regard to this field are provided.

Super-hydrophobic and super-lipophilic functionalized graphene oxide/polyurethane sponge applied for oil/water separation

Nowadays, oil spills have led to a serious environmental crisis of the world. To deal with this problem, inspired from super-hydrophobic lotus leaf, this study fabricated super-hydrophobic and super-lipophilic functionalized graphene oxide/polyurethane （FGP） sponge by a simple and inexpensive dip coating method. The resulting FGP sponge was characterized by infrared spectroscopy, X-ray diffraction, scanning electron microscopy and water contact angle. The results expressed that FGP sponge exhibited a similar surface structure to that of a lotus leaf, and possessed the super-hydrophobic characteristic with the water contact angle （WAC） of 152°± 1 °. The absorption capacity and reusability were also investigated. It can be seen that, the FGP sponge can remove a wide range of oils and organic solvents from water with good absorption capacities （up to 35 times of its own mass）. Significantly, after 10 cycles the absorption capacity of the oils and organic solvents was higher than 90°; for the reused FGP sponge, demonstrating the good reusability of the FGP sponge. Therefore, this study probably provided a simole way to remove the pollutions ofoil spills and toxic organism from water.

Bioinspired Injectable Self-Healing Hydrogel Sealant with Fault-Tolerant and Repeated Thermo-Responsive Adhesion for Sutureless Post-Wound-Closure and Wound Healing

Hydrogels with multifunctionalities,including sufficient bonding strength,injectability and self-healing capacity,responsive-adhesive ability,fault-tolerant and repeated tissue adhesion,are urgently demanded for invasive wound closure and wound healing.Motivated by the adhesive mechanism of mussel and brown algae,bioinspired dynamic bonds cross-linked multifunctional hydrogel adhesive is designed based on sodium alginate(SA),gelatin(GT)and protocatechualdehyde,with ferric ions added,for sutureless post-wound-closure.The dynamic hydrogel cross-linked through Schiff base bond,catechol-Fe coordinate bond and the strong interaction between GT with temperature-dependent phase transition and SA,endows the resulting hydrogel with sufficient mechanical and adhesive strength for efficient wound closure,injectability and self-healing capacity,and repeated closure of reopened wounds.Moreover,the temperature-dependent adhesive properties endowed mispositioning hydrogel to be removed/repositioned,which is conducive for the fault-tolerant adhesion of the hydrogel adhesives during surgery.Besides,the hydrogels present good biocompatibility,near-infrared-assisted photothermal antibacterial activity,antioxidation and repeated thermo-responsive reversible adhesion and good hemostatic effect.The in vivo incision closure evaluation demonstrated their capability to promote the post-wound-closure and wound healing of the incisions,indicating that the developed reversible adhesive hydrogel dressing could serve as versatile tissue sealant.

Bioinspired soft actuators with highly ordered skeletal muscle structures

Mammals such as humans develop skeletal muscles composed of muscle fibers and connective tissue,which have mechanical properties that enable power output with three-dimensional motion when activated.Artificial muscle-like actuators developed to date,such as the McKibben artificial muscle,often focus sole contractile elements and have rarely addressed the contribution of flexible connective tissue that forms an integral part of the structure and morphology of biological muscle.Herein,we present a class of pneumatic muscle-like actuators,termed highly mimetic skeletal muscle(HimiSK)actuator,that consist of parallelly arranged contractile units in a flexible matrix inspired by ultrasonic measurements on skeletal muscle.The contractile units act as a muscle fiber to produce active shortening force,and the flexible matrix functions as connective tissue to generate passive deformation.The application of positive pressure to the contractile units can produce a linear contraction and force.In this actuator,we assign different flexible materials as contractile units and a flexible matrix,thus forming five mold actuators.These actuators feature three-dimensional motion on activation and present both intrinsic force-velocity and force-length characteristics that closely resebmle those of a biological muscle.High output and tetanic force produced by harder contractile units improve the maximum output force by up to about 41.3%and the tetanic force by up to about 168%.Moreover,high displacement and velocity can be generated by a softer flexible matrix,with the improvement of maximum displacement up to about 33.3%and velocity up to about 73%.The results demonstrate that contractile units play a crucial role in force generation,while the flexible matrix has a significant impact on force transmission and deformation;the final force,velocity,displacement,and three-dimensional motion results from the interplay of contractile units,fluid and flexible matrix.Our approach introduces a model of the presented HimiSK actuators to better understand the mechanical behaviors,force generation,and transmission in bioinspired soft actuators,and highlights the importance of using flexible connective tissue to form a structure and configuration similar to that of skeletal muscle,which has potential usefulness in the design of effective artificial muscle.

Experimental research on friction-reduction with super-hydrophobic surfaces

Many recent studies have confirmed the existence of liquid slip over particular types of solid surfaces, and these so-called super-hydrophobic surfaces have been shown to generate effective liquid slip because of the air trapped between the surface structures. In this paper, based on boundary layer theory, the microscopic structure of the super-hydrophobic surface is analyzed. The liquid slip effect on friction-reduction over super-hydrophobic surfaces under various flow conditions is investigated by experiments with a flume and water tunnel. The experimental results show that the greatest amount of drag-reduction that can be achieved is 8.76% at a low Re.

Self-Exfoliation of Flake Graphite for Bioinspired Compositing with Aramid Nanofiber toward Integration of Mechanical and Thermoconductive Properties

Flexible yet highly thermoconductive materials are essential for the development of next-generation flexible electronic devices.Herein,we report a bioinspired nanostructured film with the integration of large ductility and high thermal conductivity based on self-exfoliated pristine graphene and three-dimensional aramid nanofiber network.A self-grinding strategy to directly exfoliate flake graphite into few-layer and few-defect pristine graphene is successfully developed through mutual shear friction between graphite particles,generating largely enhanced yield and productivity in comparison to normal liquid-based exfoliation strategies,such as ultrasonication,high-shear mixing and ball milling.Inspired by nacre,a new bioinspired layered structural design model containing three-dimensional nanofiber network is proposed and implemented with an interconnected aramid nanofiber network and high-loading graphene nanosheets by a developed continuous assembly strategy of sol-gel-film transformation.It is revealed that the bioinspired film not only exhibits nacre-like ductile deformation behavior by releasing the hidden length of curved aramid nanofibers,but also possesses good thermal transport ability by directionally conducting heat along pristine graphene nanosheets.

Self-shaping of bioinspired chiral composites

Self-shaping materials such as shape memory polymers have recently drawn considerable attention owing to their high shape-changing ability in response to changes in ambient conditions, and thereby have promising applications in the biomedical, biosensing, soft robotics and aerospace fields. Their design is a crucial issue of both theoretical and technological interest. Motivated by the shape-changing ability of Towel Gourd tendril helices during swelling/deswelling, we present a strategy for realizing self-shaping function through the deformation of micro/nanohelices. To guide the design and fabrication of selfshaping materials, the shape equations of bent configurations, twisted belts, and helices of slender chiral composite are developed using the variation method. Furthermore, it is numerically shown that the shape changes of a chiral composite can be tuned by the deformation of micro/nanohelices and the fabricated fiber directions. This work paves a new way to create self-shaping composites.

Bioinspired micro/nanostructured surfaces prepared by femtosecond laser direct writing for multi-functional applications

manufacturing of biomimetic micro/nanostructures due to its specific advantages including high precision,simplicity,and compatibility for diverse materials in comparison with other methods(e.g.ion etching,sol-gel process,chemical vapor deposition,template method,and self-assembly).These biomimetic micro/nanostructured surfaces are of significant interest for academic and industrial research due to their wide range of potential applications,including self-cleaning surfaces,oil-water separation,and fog collection.This review presents the inherent relationship between natural organisms,fabrication methods,micro/nanostructures and their potential applications.Thereafter,we throw a list of current fabrication strategies so as to highlight the advantages of FLDW in manufacturing bioinspired microstructured surfaces.Subsequently,we summarize a variety of typical bioinspired designs(e.g.lotus leaf,pitcher plant,rice leaf,butterfly wings,etc)for diverse multifunctional micro/nanostructures through extreme femtosecond laser processing technology.Based on the principle of interfacial chemistry and geometrical optics,we discuss the potential applications of these functional micro/nanostructures and assess the underlying challenges and opportunities in the extreme fabrication of bioinspired micro/nanostructures by FLDW.This review concludes with a follow up and an outlook of femtosecond laser processing in biomimetic domains.

Mechanics of bioinspired imaging systems

Imaging systems in nature have attracted a lot of research interest due to their superior optical and imaging characteristics, Recent advancements in materials science, mechanics, and stretchable electronics have led to successful development of bioinspired cameras that resemble the structures and functions of biological light-sensing organs. In this review, we discuss some recent progresses in mechanics of bioinspired imaging systems, including tunable hemispherical eyeball camera and artificial compound eye camera. The mechanics models and results reviewed in this article can provide efficient tools for design and optimization of such systems, as well as other related optoelectronic systems that combine rigid elements with soft substrates.