Gecko-inspired van der Waals force-based adhesion technology demonstrates significant potential for robotic operations.While superior adhesion is achieved under parallel contact during testing,engineering operations o...Gecko-inspired van der Waals force-based adhesion technology demonstrates significant potential for robotic operations.While superior adhesion is achieved under parallel contact during testing,engineering operations often involve non-parallel contact,weakening adhesion,and compromising task stability and efficiency.Stable attachment under such non-parallel contacts remains challenging.Inspired by the soft muscle and rigid bone in the gecko’s sole,this study proposes a self-adaptive core-shell dry adhesive by embedding a thin,rigid piece into a soft,thick elastomer comprising a top adhesion tip with a mushroom-like geometry for interfacial adhesion based on the van der Waals force and a bottom core-shell configuration for interface stress regulation.Unlike traditional core-shell structures with a fixed“dead core,”the proposed“live core”rotates within the soft shell,mimicking skeletal joints.This enables stress equalization at the interface and facilitates adaptive contact to macroscopic interfacial angle errors.This innovative core-shell configuration demonstrates an adhesion strength 100 times higher than conventional homogeneous structures under non-parallel contact and offers anti-overturning ability by mitigating torsional effects.The proposed strategy can advance the development of gecko-inspired adhesion-based devices and systems.展开更多
Self-cleaning surfaces are desirable in many engineering applications where low energy consumption,reusability and sustainability are of the biggest concerns.Inspired by the gecko’s unique ’dry selfcleaning’ hierar...Self-cleaning surfaces are desirable in many engineering applications where low energy consumption,reusability and sustainability are of the biggest concerns.Inspired by the gecko’s unique ’dry selfcleaning’ hierarchical structures.Here we fabricated artificial Fe304/PDMS composites that show robust self-cleaning capabilities.The enhanced adhesion performance is attributable to the decrease of PDMS polymerization degree and the load transfer between PDMS matrix and Fe304 magnetic particles.The self-cleaning surfaces showed up to 24.3% self-cleaning rate with as few as 4 steps.Simulation result indicated that the changing of cross linking between Fe304 and PDMS is the main reason for the enhanced self-cleaning surfaces.This work reveals an alternative route of making high-performance self-cleaning smart surfaces that are applicable in the textile industry,robotic locomotion/gripping technology,outerspace explorations and tissue engineering.展开更多
In dry attachment systems of spiders and geckos, van der Waals forces mediate attraction between substrate and animal tarsus. In particular, the scopula of Evarcha arcuata spiders allows for reversible attachment and ...In dry attachment systems of spiders and geckos, van der Waals forces mediate attraction between substrate and animal tarsus. In particular, the scopula of Evarcha arcuata spiders allows for reversible attachment and easy detachment to a broad range of surfaces. Hence, reproducing the scopula's roughness compatibility while maintaining anti-bunching features and dirt particle repellence behavior is a central task for a biomimetic transfer to an engineered model. In the present work we model the scopula of E. arcuata from a mechano-elastic point of view analyzing the influence of its hierarchical structure on the attachment behavior. By considering biological data of the gecko and spider, and the simulation results, the adhesive capabilities of the two animals are compared and important confirmations and new directives in order to reproduce the overall structure are found. Moreover, a possible suggestion of how the spider detaches in an easy and fast manner is proposed and supported by the results.展开更多
Gecko has the ability to climb flexibly on various natural surfaces because of its fine layered adhesion system of foot,which has motivated researchers to carry out a lot of researches on it.Significant progresses hav...Gecko has the ability to climb flexibly on various natural surfaces because of its fine layered adhesion system of foot,which has motivated researchers to carry out a lot of researches on it.Significant progresses have been made in the gecko-like dry adhesive surfaces in the past 2 decades,such as the mechanical measurement of adhesive characteristics,the theoretical modeling of adhesive mechanism and the production of synthetic dry adhesive surfaces.Relevant application researches have been carried out as well.This paper focuses on the investigations made in recent years on the gecko-like dry adhesive surfaces,so as to lay the foundation for further research breakthroughs.First,the adhesion system of gecko’s foot and its excellent adhesive characteristics are reviewed,and the adhesive models describing the gecko adhesion are summarily reviewed according to the diff erent contact modes.Then,some gecko-like dry adhesive surfaces with outstanding adhesive characteristics are presented.Next,some application researches based on the gecko-like dry adhesive surfaces are introduced.Finally,the full text is summarized and the problems to be solved on the gecko-like dry adhesive surfaces are prospected.展开更多
Transfer printing based on switchable adhesive is essential for developing unconventional systems,including flexible electronics,stretchable electronics,and micro light-emitting diode(LED)displays.Here we report a des...Transfer printing based on switchable adhesive is essential for developing unconventional systems,including flexible electronics,stretchable electronics,and micro light-emitting diode(LED)displays.Here we report a design of switchable dry adhesive based on shape memory polymer(SMP)with hemispherical indenters,which offers a continuously tunable and reversible adhesion through the combination of the preloading effect and the thermal actuation of SMP.Experimental and numerical studies reveal the fundamental aspects of design,fabrication,and operation of the switchable dry adhesive.Demonstrations of this adhesive concept in transfer printing of flat objects(e.g.,silicon wafers),three-dimensional(3D)objects(e.g.,stainless steel balls),and rough objects(e.g.,frosted glasses)in two-dimensional(2D)or 3D layouts illustrate its unusual manipulation capabilities in heterogeneous material integration applications.展开更多
Inspired by the excellent adhesion performances of setae structure from organisms,micro/nano-pillar array has become one of the paradigms for adhesive surfaces.The micropillar arrays are composed of the resin pillars ...Inspired by the excellent adhesion performances of setae structure from organisms,micro/nano-pillar array has become one of the paradigms for adhesive surfaces.The micropillar arrays are composed of the resin pillars for adhesion and the substrate with different elastic modulus for supporting.The stress singularity at the bi-material corner between the pillars and the substrate can induce the failure of the micropillar-substrate corner and further hinder the fabrication and application of micropillar arrays,yet the design for the stability of the micropillar array lacks systematical and quantitative guides.In this work,we develop a semi-analytical method to provide the full expressions for the stress distribution within the bi-material corner combining analytical derivations and numerical calculations.The predictions for the stress within the singularity field can be obtained based on the full expressions of the stress.The good agreement between the predictions and the FEM results demonstrates the high reliability of our method.By adopting the strain energy density factor approach,the stability of the pillar-substrate corner is assessed by predicting the failure at the corner.For the elastic mismatch between the pillar and substrate given in this paper,the stability can be improved by increasing the ratio of the shear modulus of the substrate to that of the micropillar.Our study provides accurate predictions for the stress distribution at the bi-material corner and can guide the optimization of material combinations of the pillars and the substrate for more stable bioinspired dry adhesives.展开更多
The remarkable ability of geckos to climb and run rapidly on walls and ceilings has recently received considerable interest from many researchers.Significant progress has been made in understanding the attachment and ...The remarkable ability of geckos to climb and run rapidly on walls and ceilings has recently received considerable interest from many researchers.Significant progress has been made in understanding the attachment and detachment mechanisms and the fabrication of articulated gecko-inspired adhesives and structured surfaces.This article reviews the direct experiments that have investigated the properties of gecko hierarchical structures,i.e.,the feet,toes,setae,and spatulae,and the corresponding models to ascertain the mechanical principles involved.Included in this review are reports on gecko-inspired surfaces and structures with strong adhesion forces,high ratios of adhesion and friction forces,anisotropic hierarchical structures that give rise to directional adhesion and friction,and“intelligent”attachment and detachment motions.展开更多
Bionic adhesives with tip-expanded microstructural arrays have attracted considerable interest owing to their high adhesive performance at low preloads.Their mainstream manufacturing method is molding.Due to most mold...Bionic adhesives with tip-expanded microstructural arrays have attracted considerable interest owing to their high adhesive performance at low preloads.Their mainstream manufacturing method is molding.Due to most molds are made of silicon or silicon-based soft templates,and have poor wear resistant or vulnerability to high temperature,limiting their use in large-scale manufacturing.Nickel is widely used as an embossing mold in the micro/nano-imprint industrial process owing to its good mechanical properties.However,the processing of metal molds for the fabrication of tip-expanded microstructural arrays is extremely challenging.In this study,using electrodeposition techniques,the shape of the micropores is modified to obtain end-controlled pores.The effect of the non-uniformity of the electric field on the microporous morphology in the electrodeposition process is systematically investigated.Furthermore,the mechanism of non-uniformity evolution of the microporous morphology is revealed.The optimized microporous metal array is used as a mold to investigate the cavity evolution laws of the elastic cushions under pre-load during the manufacturing process.As a result,typical bionic adhesives with tip-expansion are obtained.Moreover,corresponding adhesion mechanics are analyzed.The results show that electrochemical modifications have broad application prospects in the fabrication of tip-expanded microstructures,providing a new method for the large-scale fabrication of bionic adhesives based on metal molds.展开更多
Climbing robots are of potential use for surveillance, inspection and exploration in different environments. In particular, the use of climbing robots for space exploration can allow scientists to explore environments...Climbing robots are of potential use for surveillance, inspection and exploration in different environments. In particular, the use of climbing robots for space exploration can allow scientists to explore environments too challenging for traditional wheeled designs. To adhere to surfaces, biomimetic dry adhesives based on gecko feet have been proposed. These biomimetic dry adhesives work by using multi-scale compliant mechanisms to make intimate contact with different surfaces and adhere by using Van der Waals forces. Fabrication of these adhesives has frequently been challenging however, due to the difficulty in combining macro, micro and nanoscale compliance. We present an all polymer foot design for use with a hexapod climbing robot and a fabrication method to improve reliability and yield. A high strength, low-modulus silicone, TC-5005, is used to form the foot base and microscale fibres in one piece by using a two part mold. A macroscale foot design is produced using a 3D printer to produce a base mold, while lithographic definition of microscale fibres in a thick photoresist forms the ＇hairs＇ of the polymer foot. The adhesion of the silicone fibres by themselves or attached to the macro foot is examined to determine best strategies for placement and removal of feet to maximize adhesion. Results demonstrate the successful integration of micro and macro compliant feet for use in climbing on a variety of surfaces.展开更多
Synthetic dry adhesives inspired by the nano-and micro-scale hairs found on the feet of geckos and some spiders have beendeveloped for almost a decade. Elastomeric single level micro-scale mushroom shaped fibres are c...Synthetic dry adhesives inspired by the nano-and micro-scale hairs found on the feet of geckos and some spiders have beendeveloped for almost a decade. Elastomeric single level micro-scale mushroom shaped fibres are currently able to function evenbetter than natural dry adhesives on smooth surfaces under normal loading. However, the adhesion of these single level syntheticdry adhesives on rough surfaces is still not optimal because of the reduced contact surface area. In nature, contact area ismaximized by hierarchically structuring different scales of fibres capable of conforming surface roughness. In this paper, weadapt the nature’s solution arid propose a novel dual-level hierarchical adhesive design using Polydimethylsiloxane (PDMS),which is tested under peel loading at different orientations. A negative macro-scale mold is manufactured by using a laser cutterto define holes in a Poly(methyl methacrylate) (PMMA) plate. After casting PDMS macro-scale fibres by using the obtainedPMMA mold, a previously prepared micro-fibre adhesive is bonded to the macro-scale fibre substrate. Once the bondingpolymer is cured, the micro-fibre adhesive is cut to form macro scale mushroom caps. Each macro-fibre of the resulting hierarchicaladhesive is able to conform to loads applied in different directions. The dual-level structure enhances the peel strengthon smooth surfaces compared to a single-level dry adhesive, but also weakens the shear strength of the adhesive for a given areain contact. The adhesive appears to be very performance sensitive to the specific size of the fibre tips, and experiments indicatethat designing hierarchical structures is not as simple as placing multiple scales of fibres on top of one another, but can requiresignificant design optimization to enhance the contact mechanics and adhesion strength.展开更多
Smart dry adhesives,a rapidly growing class of intelligent materials and structures,are engineered to provide strong,robust adhesion when needed while also allowing for controlled,easy detachment in response to specif...Smart dry adhesives,a rapidly growing class of intelligent materials and structures,are engineered to provide strong,robust adhesion when needed while also allowing for controlled,easy detachment in response to specific stimuli.Traditional smart adhesives,often exemplified by fibrillar structures made of elastomers,face a number of challenges.These include limitations on maximum adhesion strength imposed by microstructural dimensions,restricted adaptability to surfaces with varying degrees of roughness,and an inherent trade-off between adhesion strength and switchability.This review explores how shape memory polymers(SMPs)can address these challenges and,through their rubber-to-glass(R2G)transition capability,provide a powerful foundation for the next generation of smart dry adhesives.Specifically,we summarize and elucidate the mechanisms by which SMPs enhance adhesion strength and switchability through material characteristics such as tunable stiffness,shape-locking,and shape-memory effects.Additionally,we discuss a wide range of innovative designs and applications of SMP adhesives,offering insights into the ongoing challenges and emerging opportunities in this rapidly evolving field.展开更多
Switchable adhesives have attracted widespread attention due to their strong reusability and adaptability to operate stably in complex environments.However,the simple fabrication of adhesive structures and reliable co...Switchable adhesives have attracted widespread attention due to their strong reusability and adaptability to operate stably in complex environments.However,the simple fabrication of adhesive structures and reliable control of adhesion remain challenging.Here,we developed a neodymium iron boron/polydimethylsiloxane(NdFeB/PDMS)magnetic composite with optimal mechanical and magnetic performance.Then we fabricated lamellar structures and setal arrays using a molding and magnetic field-induced process,imitating the multi-level adhesion system of gecko feet.The lamellar can be deformed under the action of a magnetic field to control the adhesion,the setal array is used to enhance adhesion and provide self-cleanability to the adhering surface.Switchable adhesion was realized by applying an external magnetic field,where the maximum adhesion strength was 5.1 kPa,the switchable range was within 40%.Through finite element analysis simulations and experimental verification,it was proved that the adhesion force variation was ascribed to the magnetic field-induced surface deformation.Finally,we installed the adhesive on the end of the robotic arm,realizing the transfer of the target object.This work provides a simple method to fabricate a gecko-like surface and a practical strategy to realize switchable adhesion,which sheds light on broad application potential in production lines,medical products,more.展开更多
Mechanically flexible surface structures with embedded conductive electrodes are attractive in contact-based devices,such as those used in reversible dry/adhesion and tactile sensing.Geometrical shapes of the surface ...Mechanically flexible surface structures with embedded conductive electrodes are attractive in contact-based devices,such as those used in reversible dry/adhesion and tactile sensing.Geometrical shapes of the surface structures strongly determine the contact behavior and therefore the resulting adhesion and sensing functionalities;however,available features are often restricted by fabrication techniques.Here,we additively manufacture elastomeric structure arrays with diverse angles,shapes,and sizes;this is followed by integration of conductive nanowire electrodes.The fabricated flexible three-dimensional(3D)surface electrodes are mechanically compliant and electrically conductive,providing multifunctional ability to sense touch and to switch adhesion via a combined effect of shear-and electro adhesives.We designed soft,anisotropic flexible structures to mimic the gecko’s reversible adhesion,which is governed by van der Waals forces;we integrated nanowires to further manipulate the localized electric field among the adjacent flexible 3D surface electrodes to provide additional means to digitally tune the electrostatic attraction at the contact interface.In addition,the composite surface can sense the contact force via capacitive sensing.Using our flexible 3D surface electrodes,we demonstrate a complete soft gripper that can grasp diverse convex objects,including metal,ceramic,and plastic products,as well as fresh fruits,and that exhibits 72%greater electroadhesive gripping force when voltage is applied.展开更多
Recently,the intelligent strategies for adapting to multiple challengeable surfaces of electroactive programmable materials integrated with bio-inspired architectures offer expanded directions beyond traditional limit...Recently,the intelligent strategies for adapting to multiple challengeable surfaces of electroactive programmable materials integrated with bio-inspired architectures offer expanded directions beyond traditional limitations in soft grippers,medical mobile robots,and XR(Extended Reality)interfaces.These electroactive programmable adhesive materials are adaptively designed for a variety of complex surfaces,including soft,wet,non-flat,or contamination-susceptible feature such as bio-surfaces and vulnerable objects.They can be produced via solution-based methods of replica coating or 3/4-dimensional printing.The integration of electroactive programmable materials and intelligent adhesive architecture enables super-adaptive switchable adhesion to a variety of complex surfaces through control of physical deformation and mechanical properties at the adhesive interface,presenting a breakthrough in soft electro-robotics and extended reality(XR)Haptic interfaces technology.These surface-adaptive platform can provide multiple functionalities that can efficiently control physical deformations of soft bioinspired architectures or transfer physical energy(heat,vibration,pressure)into the engaged surfaces in a lightweight and human-friendly form.This review focuses on intelligent strategies,principles,design,and fabrication methods of super-adaptive electroactive programmable materials intelligently combined with bioinspired switchable adhesives for next-generation human–robot interaction devices,along with current challenges and prospects.展开更多
Autonomously self-healing, reversible, and soft adhesive microarchitecturesand structured electric elements could be important features in stable and versatilebioelectronic devices adhere to complex surfaces of the hu...Autonomously self-healing, reversible, and soft adhesive microarchitecturesand structured electric elements could be important features in stable and versatilebioelectronic devices adhere to complex surfaces of the human body(rough, dry, wet, and vulnerable). In this study, we propose an autonomousself-healing multi-layered adhesive patch inspired by the octopus, which possessself-healing and robust adhesion properties in dry/underwater conditions.To implement autonomously self-healing octopus-inspired architectures, adynamic polymer reflow model based on structural and material design suggestscriteria for three-dimensional patterning self-healing elastomers. In addition,self-healing multi-layered microstructures with different moduli endowsefficient self-healing ability, human-friendly reversible bio-adhesion, and stablemechanical deformability. Through programmed molecular behavior ofmicrolevel hybrid multiscale architectures, the bioinspired adhesive patchexhibited robust adhesion against rough skin surface under both dry andunderwater conditions while enabling autonomous adhesion restoring performanceafter damaged (over 95% healing efficiency under both conditions for24 h at 30℃). Finally, we developed a self-healing skin-mountable adhesiveelectronics with repeated attachment and minimal skin irritation by laminatingthin gold electrodes on octopus-like structures. Based on the robust adhesionand intimate contact with skin, we successfully obtained reliable measurements during dynamic motion under dry, wet, and damagedconditions.展开更多
基金supported by the National Natural Science Foundation(52025055,52175546,and 52405624)the Shaanxi University Youth Innovation Team.
文摘Gecko-inspired van der Waals force-based adhesion technology demonstrates significant potential for robotic operations.While superior adhesion is achieved under parallel contact during testing,engineering operations often involve non-parallel contact,weakening adhesion,and compromising task stability and efficiency.Stable attachment under such non-parallel contacts remains challenging.Inspired by the soft muscle and rigid bone in the gecko’s sole,this study proposes a self-adaptive core-shell dry adhesive by embedding a thin,rigid piece into a soft,thick elastomer comprising a top adhesion tip with a mushroom-like geometry for interfacial adhesion based on the van der Waals force and a bottom core-shell configuration for interface stress regulation.Unlike traditional core-shell structures with a fixed“dead core,”the proposed“live core”rotates within the soft shell,mimicking skeletal joints.This enables stress equalization at the interface and facilitates adaptive contact to macroscopic interfacial angle errors.This innovative core-shell configuration demonstrates an adhesion strength 100 times higher than conventional homogeneous structures under non-parallel contact and offers anti-overturning ability by mitigating torsional effects.The proposed strategy can advance the development of gecko-inspired adhesion-based devices and systems.
基金supported by the National Natural Science Foundation of China (Nos.51575528,51875577,51704243)Beijing Nova Program (No.Z171100001117058)+1 种基金Tribology Science Fund of State Key Laboratory of Tribology (No.SKLTKF16A06)Science Foundation of China University of Petroleum (No.2462019QNXZ02)
文摘Self-cleaning surfaces are desirable in many engineering applications where low energy consumption,reusability and sustainability are of the biggest concerns.Inspired by the gecko’s unique ’dry selfcleaning’ hierarchical structures.Here we fabricated artificial Fe304/PDMS composites that show robust self-cleaning capabilities.The enhanced adhesion performance is attributable to the decrease of PDMS polymerization degree and the load transfer between PDMS matrix and Fe304 magnetic particles.The self-cleaning surfaces showed up to 24.3% self-cleaning rate with as few as 4 steps.Simulation result indicated that the changing of cross linking between Fe304 and PDMS is the main reason for the enhanced self-cleaning surfaces.This work reveals an alternative route of making high-performance self-cleaning smart surfaces that are applicable in the textile industry,robotic locomotion/gripping technology,outerspace explorations and tissue engineering.
基金supported by the ARIADNA scheme (study ID 06/6201) of the European Space Agency
文摘In dry attachment systems of spiders and geckos, van der Waals forces mediate attraction between substrate and animal tarsus. In particular, the scopula of Evarcha arcuata spiders allows for reversible attachment and easy detachment to a broad range of surfaces. Hence, reproducing the scopula's roughness compatibility while maintaining anti-bunching features and dirt particle repellence behavior is a central task for a biomimetic transfer to an engineered model. In the present work we model the scopula of E. arcuata from a mechano-elastic point of view analyzing the influence of its hierarchical structure on the attachment behavior. By considering biological data of the gecko and spider, and the simulation results, the adhesive capabilities of the two animals are compared and important confirmations and new directives in order to reproduce the overall structure are found. Moreover, a possible suggestion of how the spider detaches in an easy and fast manner is proposed and supported by the results.
基金supported by the Major Research Plan of the National Natural Science Foundation of China[Grant number 91848202]supported by the Self-Planned Task of State Key Laboratory of Robotics and System(HIT)[Grant number SKLRS202106B].
文摘Gecko has the ability to climb flexibly on various natural surfaces because of its fine layered adhesion system of foot,which has motivated researchers to carry out a lot of researches on it.Significant progresses have been made in the gecko-like dry adhesive surfaces in the past 2 decades,such as the mechanical measurement of adhesive characteristics,the theoretical modeling of adhesive mechanism and the production of synthetic dry adhesive surfaces.Relevant application researches have been carried out as well.This paper focuses on the investigations made in recent years on the gecko-like dry adhesive surfaces,so as to lay the foundation for further research breakthroughs.First,the adhesion system of gecko’s foot and its excellent adhesive characteristics are reviewed,and the adhesive models describing the gecko adhesion are summarily reviewed according to the diff erent contact modes.Then,some gecko-like dry adhesive surfaces with outstanding adhesive characteristics are presented.Next,some application researches based on the gecko-like dry adhesive surfaces are introduced.Finally,the full text is summarized and the problems to be solved on the gecko-like dry adhesive surfaces are prospected.
基金The authors acknowledge the supports of the National Natural Science Foundation of China(Grant Nos.11872331 and U20A6001)Zhejiang University K.P.Chao’s High Technology Development Foundation.
文摘Transfer printing based on switchable adhesive is essential for developing unconventional systems,including flexible electronics,stretchable electronics,and micro light-emitting diode(LED)displays.Here we report a design of switchable dry adhesive based on shape memory polymer(SMP)with hemispherical indenters,which offers a continuously tunable and reversible adhesion through the combination of the preloading effect and the thermal actuation of SMP.Experimental and numerical studies reveal the fundamental aspects of design,fabrication,and operation of the switchable dry adhesive.Demonstrations of this adhesive concept in transfer printing of flat objects(e.g.,silicon wafers),three-dimensional(3D)objects(e.g.,stainless steel balls),and rough objects(e.g.,frosted glasses)in two-dimensional(2D)or 3D layouts illustrate its unusual manipulation capabilities in heterogeneous material integration applications.
基金supported by the National Natural Science Foundation of China(Grant No.12272276)the Fundamental Research Funds for the Central Universities(Grant No.2042023kf0194)the Shenzhen Science and Technology Program(Grant No.JCYJ20220530140606013)。
文摘Inspired by the excellent adhesion performances of setae structure from organisms,micro/nano-pillar array has become one of the paradigms for adhesive surfaces.The micropillar arrays are composed of the resin pillars for adhesion and the substrate with different elastic modulus for supporting.The stress singularity at the bi-material corner between the pillars and the substrate can induce the failure of the micropillar-substrate corner and further hinder the fabrication and application of micropillar arrays,yet the design for the stability of the micropillar array lacks systematical and quantitative guides.In this work,we develop a semi-analytical method to provide the full expressions for the stress distribution within the bi-material corner combining analytical derivations and numerical calculations.The predictions for the stress within the singularity field can be obtained based on the full expressions of the stress.The good agreement between the predictions and the FEM results demonstrates the high reliability of our method.By adopting the strain energy density factor approach,the stability of the pillar-substrate corner is assessed by predicting the failure at the corner.For the elastic mismatch between the pillar and substrate given in this paper,the stability can be improved by increasing the ratio of the shear modulus of the substrate to that of the micropillar.Our study provides accurate predictions for the stress distribution at the bi-material corner and can guide the optimization of material combinations of the pillars and the substrate for more stable bioinspired dry adhesives.
基金the Natural Science Foundation of China(Grant Nos.51175281 and 51021064)。
文摘The remarkable ability of geckos to climb and run rapidly on walls and ceilings has recently received considerable interest from many researchers.Significant progress has been made in understanding the attachment and detachment mechanisms and the fabrication of articulated gecko-inspired adhesives and structured surfaces.This article reviews the direct experiments that have investigated the properties of gecko hierarchical structures,i.e.,the feet,toes,setae,and spatulae,and the corresponding models to ascertain the mechanical principles involved.Included in this review are reports on gecko-inspired surfaces and structures with strong adhesion forces,high ratios of adhesion and friction forces,anisotropic hierarchical structures that give rise to directional adhesion and friction,and“intelligent”attachment and detachment motions.
基金the Natural Science Foundation of Jiangsu Province of China(No.BK20170796)the foundation of‘‘Jiangsu Provincial Key Laboratory of Bionic Functional Materials”of China(No.NJ2020026)+1 种基金the foundation of National Defense Key Laboratory of China(No.6142004190204)the National Natural Science Foundation of China(No.52075249)。
文摘Bionic adhesives with tip-expanded microstructural arrays have attracted considerable interest owing to their high adhesive performance at low preloads.Their mainstream manufacturing method is molding.Due to most molds are made of silicon or silicon-based soft templates,and have poor wear resistant or vulnerability to high temperature,limiting their use in large-scale manufacturing.Nickel is widely used as an embossing mold in the micro/nano-imprint industrial process owing to its good mechanical properties.However,the processing of metal molds for the fabrication of tip-expanded microstructural arrays is extremely challenging.In this study,using electrodeposition techniques,the shape of the micropores is modified to obtain end-controlled pores.The effect of the non-uniformity of the electric field on the microporous morphology in the electrodeposition process is systematically investigated.Furthermore,the mechanism of non-uniformity evolution of the microporous morphology is revealed.The optimized microporous metal array is used as a mold to investigate the cavity evolution laws of the elastic cushions under pre-load during the manufacturing process.As a result,typical bionic adhesives with tip-expansion are obtained.Moreover,corresponding adhesion mechanics are analyzed.The results show that electrochemical modifications have broad application prospects in the fabrication of tip-expanded microstructures,providing a new method for the large-scale fabrication of bionic adhesives based on metal molds.
文摘Climbing robots are of potential use for surveillance, inspection and exploration in different environments. In particular, the use of climbing robots for space exploration can allow scientists to explore environments too challenging for traditional wheeled designs. To adhere to surfaces, biomimetic dry adhesives based on gecko feet have been proposed. These biomimetic dry adhesives work by using multi-scale compliant mechanisms to make intimate contact with different surfaces and adhere by using Van der Waals forces. Fabrication of these adhesives has frequently been challenging however, due to the difficulty in combining macro, micro and nanoscale compliance. We present an all polymer foot design for use with a hexapod climbing robot and a fabrication method to improve reliability and yield. A high strength, low-modulus silicone, TC-5005, is used to form the foot base and microscale fibres in one piece by using a two part mold. A macroscale foot design is produced using a 3D printer to produce a base mold, while lithographic definition of microscale fibres in a thick photoresist forms the ＇hairs＇ of the polymer foot. The adhesion of the silicone fibres by themselves or attached to the macro foot is examined to determine best strategies for placement and removal of feet to maximize adhesion. Results demonstrate the successful integration of micro and macro compliant feet for use in climbing on a variety of surfaces.
基金Finallcial support was provided by the Natural Sciences and Engineering Research Council of Canada(NSERC)the European Space Agency(ESA)
文摘Synthetic dry adhesives inspired by the nano-and micro-scale hairs found on the feet of geckos and some spiders have beendeveloped for almost a decade. Elastomeric single level micro-scale mushroom shaped fibres are currently able to function evenbetter than natural dry adhesives on smooth surfaces under normal loading. However, the adhesion of these single level syntheticdry adhesives on rough surfaces is still not optimal because of the reduced contact surface area. In nature, contact area ismaximized by hierarchically structuring different scales of fibres capable of conforming surface roughness. In this paper, weadapt the nature’s solution arid propose a novel dual-level hierarchical adhesive design using Polydimethylsiloxane (PDMS),which is tested under peel loading at different orientations. A negative macro-scale mold is manufactured by using a laser cutterto define holes in a Poly(methyl methacrylate) (PMMA) plate. After casting PDMS macro-scale fibres by using the obtainedPMMA mold, a previously prepared micro-fibre adhesive is bonded to the macro-scale fibre substrate. Once the bondingpolymer is cured, the micro-fibre adhesive is cut to form macro scale mushroom caps. Each macro-fibre of the resulting hierarchicaladhesive is able to conform to loads applied in different directions. The dual-level structure enhances the peel strengthon smooth surfaces compared to a single-level dry adhesive, but also weakens the shear strength of the adhesive for a given areain contact. The adhesive appears to be very performance sensitive to the specific size of the fibre tips, and experiments indicatethat designing hierarchical structures is not as simple as placing multiple scales of fibres on top of one another, but can requiresignificant design optimization to enhance the contact mechanics and adhesion strength.
基金support from the Ministry of Education(MOE)of Singapore under the Academic Research Fund Tier 2[MOE-T2EP50122-0001]support from the National Key R&D Program of China[2022YFB3805700]+1 种基金support from the National Natural Science Foundation of China[U23A20412]support from the China Scholarship Council program[202406120073].
文摘Smart dry adhesives,a rapidly growing class of intelligent materials and structures,are engineered to provide strong,robust adhesion when needed while also allowing for controlled,easy detachment in response to specific stimuli.Traditional smart adhesives,often exemplified by fibrillar structures made of elastomers,face a number of challenges.These include limitations on maximum adhesion strength imposed by microstructural dimensions,restricted adaptability to surfaces with varying degrees of roughness,and an inherent trade-off between adhesion strength and switchability.This review explores how shape memory polymers(SMPs)can address these challenges and,through their rubber-to-glass(R2G)transition capability,provide a powerful foundation for the next generation of smart dry adhesives.Specifically,we summarize and elucidate the mechanisms by which SMPs enhance adhesion strength and switchability through material characteristics such as tunable stiffness,shape-locking,and shape-memory effects.Additionally,we discuss a wide range of innovative designs and applications of SMP adhesives,offering insights into the ongoing challenges and emerging opportunities in this rapidly evolving field.
基金the National Nature Science Foundation of China(No.52275210)the Natural Science Foundation of Shaanxi Province(No.2022JM-175)+1 种基金the Fundamental Research Funds for the Central UniversitiesSEM facility of Instrument Analysis Center of Xi'an Jiaotong University,China.
文摘Switchable adhesives have attracted widespread attention due to their strong reusability and adaptability to operate stably in complex environments.However,the simple fabrication of adhesive structures and reliable control of adhesion remain challenging.Here,we developed a neodymium iron boron/polydimethylsiloxane(NdFeB/PDMS)magnetic composite with optimal mechanical and magnetic performance.Then we fabricated lamellar structures and setal arrays using a molding and magnetic field-induced process,imitating the multi-level adhesion system of gecko feet.The lamellar can be deformed under the action of a magnetic field to control the adhesion,the setal array is used to enhance adhesion and provide self-cleanability to the adhering surface.Switchable adhesion was realized by applying an external magnetic field,where the maximum adhesion strength was 5.1 kPa,the switchable range was within 40%.Through finite element analysis simulations and experimental verification,it was proved that the adhesion force variation was ascribed to the magnetic field-induced surface deformation.Finally,we installed the adhesive on the end of the robotic arm,realizing the transfer of the target object.This work provides a simple method to fabricate a gecko-like surface and a practical strategy to realize switchable adhesion,which sheds light on broad application potential in production lines,medical products,more.
基金This work was supported by a National Research Foundation of Korea(NRF)(2018R1C1B5086570 and 2022R1A2C400211511)Korea Institute for Advancement of Technology(KIAT)grant(P0017006,The Competency Development Program for Industry Specialist)funded by the Korean government at Korea Advanced Institute of Science and Technology(KAIST),and by the Toyota Research Institute at MIT.
文摘Mechanically flexible surface structures with embedded conductive electrodes are attractive in contact-based devices,such as those used in reversible dry/adhesion and tactile sensing.Geometrical shapes of the surface structures strongly determine the contact behavior and therefore the resulting adhesion and sensing functionalities;however,available features are often restricted by fabrication techniques.Here,we additively manufacture elastomeric structure arrays with diverse angles,shapes,and sizes;this is followed by integration of conductive nanowire electrodes.The fabricated flexible three-dimensional(3D)surface electrodes are mechanically compliant and electrically conductive,providing multifunctional ability to sense touch and to switch adhesion via a combined effect of shear-and electro adhesives.We designed soft,anisotropic flexible structures to mimic the gecko’s reversible adhesion,which is governed by van der Waals forces;we integrated nanowires to further manipulate the localized electric field among the adjacent flexible 3D surface electrodes to provide additional means to digitally tune the electrostatic attraction at the contact interface.In addition,the composite surface can sense the contact force via capacitive sensing.Using our flexible 3D surface electrodes,we demonstrate a complete soft gripper that can grasp diverse convex objects,including metal,ceramic,and plastic products,as well as fresh fruits,and that exhibits 72%greater electroadhesive gripping force when voltage is applied.
基金National Research Foundation of Korea,Grant/Award Numbers:NRF-2022R1A4A3032923,RS-2023-00214236,RS-2024-00352352South Korean Ministry of Trade,Industry and Energy,Grant/Award Number:RS-2022-00154781National Research Council of Science and Technology,Grant/Award Number:CRC230231-000。
文摘Recently,the intelligent strategies for adapting to multiple challengeable surfaces of electroactive programmable materials integrated with bio-inspired architectures offer expanded directions beyond traditional limitations in soft grippers,medical mobile robots,and XR(Extended Reality)interfaces.These electroactive programmable adhesive materials are adaptively designed for a variety of complex surfaces,including soft,wet,non-flat,or contamination-susceptible feature such as bio-surfaces and vulnerable objects.They can be produced via solution-based methods of replica coating or 3/4-dimensional printing.The integration of electroactive programmable materials and intelligent adhesive architecture enables super-adaptive switchable adhesion to a variety of complex surfaces through control of physical deformation and mechanical properties at the adhesive interface,presenting a breakthrough in soft electro-robotics and extended reality(XR)Haptic interfaces technology.These surface-adaptive platform can provide multiple functionalities that can efficiently control physical deformations of soft bioinspired architectures or transfer physical energy(heat,vibration,pressure)into the engaged surfaces in a lightweight and human-friendly form.This review focuses on intelligent strategies,principles,design,and fabrication methods of super-adaptive electroactive programmable materials intelligently combined with bioinspired switchable adhesives for next-generation human–robot interaction devices,along with current challenges and prospects.
基金National Research Foundation of Korea,Grant/Award Numbers: NRF-2021R1C1C1009925,2020R1A6A1A03048004, RS-2023-00214236Ministry of Trade,Industry & Energy (MOTIE, Korea),Grant/Award Number: RS-2022-00154781National Research Council of Science &Technology, Grant/Award Number:CRC230231-000。
文摘Autonomously self-healing, reversible, and soft adhesive microarchitecturesand structured electric elements could be important features in stable and versatilebioelectronic devices adhere to complex surfaces of the human body(rough, dry, wet, and vulnerable). In this study, we propose an autonomousself-healing multi-layered adhesive patch inspired by the octopus, which possessself-healing and robust adhesion properties in dry/underwater conditions.To implement autonomously self-healing octopus-inspired architectures, adynamic polymer reflow model based on structural and material design suggestscriteria for three-dimensional patterning self-healing elastomers. In addition,self-healing multi-layered microstructures with different moduli endowsefficient self-healing ability, human-friendly reversible bio-adhesion, and stablemechanical deformability. Through programmed molecular behavior ofmicrolevel hybrid multiscale architectures, the bioinspired adhesive patchexhibited robust adhesion against rough skin surface under both dry andunderwater conditions while enabling autonomous adhesion restoring performanceafter damaged (over 95% healing efficiency under both conditions for24 h at 30℃). Finally, we developed a self-healing skin-mountable adhesiveelectronics with repeated attachment and minimal skin irritation by laminatingthin gold electrodes on octopus-like structures. Based on the robust adhesionand intimate contact with skin, we successfully obtained reliable measurements during dynamic motion under dry, wet, and damagedconditions.
