Bionic Double-layer Structure Design And Actuation Mechanism Research Based On Responsive Hydrogel

Intelligence is the trend of the development of human civilization and modern science,and it is the attribute that things can actively meet all kinds of human needs with the support of new technology.In particular,soft robots based on intelligent materials can realize dexterous operation and quick response under the stimulation of external environment such as force,heat,light,electricity,magnetism and chemistry.They are widely used in national life,industrial and agricultural production,aerospace and military industry,biomedicine,basic science and other fields.Different from the motor actuate of traditional rigid robots,the actuating mode of soft robots based on soft materials depends on the intelligent materials used,which has the advantages of large deformation,multiple degrees of freedom,flexible contact,selectivity,simple structure and process,and low cost.As a typical intelligent soft material,responsive hydrogel has many excellent characteristics,such as rich variety,biology-like flexibility,selectable multi-response,easy processing,low cost,biological compatibility,etc.,and has become a research hotspot in soft robot field.However,in the face of complex and diverse practical application environments,responsive hydrogels have some defects,such as relatively complex processing,relatively slow response,single response mode,response law to be summarized,stability degradation with time,and poor application adaptability.Therefore,how to give consideration to simple preparation,fast response,multi-mode response,suitable scenario adaptability and in-depth discussion of actuation deformation law has become the bottleneck problem that restricts the development of responsive hydrogels.There are many kinds of stimulus response systems in nature,such as chameleon’s discoloration camouflage,mimosa’s vibration motion,Venus flytrap’s flexing mutation preying,and redbud pod’s automatic seeding.In particular,the aquatic plant,Aldrovanda vesiculosa,can achieve ultra-fast underwater prey movement in milliseconds by using its striped layered structure under the change of external environment,which provides a key bionics inspiration for the research of bionic double-layer structure design and actuating mechanism based on responsive hydrogel.In this paper,based on the characteristics of rapid underwater actuate and microstructure of aldrovanda vesiculosa,the bionic double-layer structure model is extracted.In response to complex and diverse water environment and special external stimuli,external stimuli such as temperature,solvent,ion and pH and corresponding responsive hydrogels are selected to construct a multi-stimulus responsive hydrogel/air-laid paper system with bionic double-layer structure,and explore its multi-response mode,fast drive and programmable deformation behavior.The actuating principle is revealed by combining theoretical analysis and experimental verification.Through parameter regulation and data analysis of hydrogel layer,air-laid paper layer and solution,the performance is optimized and the actuating law is summarized.Design valve device based on bionic double-layer structure,and explore its selectable,one-way flow,liquid shunt and other functions.This effective unification of bionic structure design,theoretical prediction,experimental parameter regulation,data analysis and rule summary provides a fruitful research idea for the development of soft actuater field.The specific research contents and main conclusions are as follows:(1)Based on the underwater predatory mechanism and microstructure characteristics of aldrovanda vesiculosa,bionic double-layer structure model with striped structure and layered structure is extracted by using bionics principle.The design concept of responsive hydrogel as the active layer and air-laid paper as the passive layer realizes bionic double-layer structure.The influence of hydrogel layer,air-laid paper layer and solution on the actuating performance of bionic double-layer structure is predicted by using geometric relationship,Euler-Bernoulli beam theory and finite element analysis,and the driving behavior of bionic double-layer structure is effectively controlled.(2)Based on the bionic double-layer structure model and design concept,a temperature responsive hydrogel with bionic double-layer structure is designed by choosing PNIPAM hydrogel as the active layer and air-laid paper as the passive layer.By adjusting nano-clay content and relative thickness of hydrogel layer,the fringe angle and tensile properties of paper layer,the bionic double-layer structure can be actuation quickly.The correctness of theoretical analysis and prediction is verified by data analysis.Combined with the structural design,the multifunctionality including universality,photothermal actuate and reproducibility is realized,and programmable deformation such as gripper application and letter deformation is accomplished.(3)Based on bionic double-layer structure model and the design concept,in order to cope with the diversity and complexity of responding to natural water body environment,selected solvent(gelatin),ion(gelatin),acidic pH(P(AAm-co-VI)),alkaline pH(PAAc)hydrogel for active layer,and air-laid paper is passive layer.Design for four types of bionic double-layer structure response hydrogel,and those can be actuated quickly under external stimulation such as solvent,ion and pH.The response behavior of the solve-responsive double-layer structure to as many as 11 solvents is successfully realized,and the actuation performance basically conforms to the dielectric constant sequence relationship.The response ability of the ion-responsive double-layer structure to 13 anions and 3 cations is verified successfully,and the actuating performance basically conforms to the Hofmeister sequence relationship.Combined with the data analysis,the correctness of the theoretical analysis and prediction is verified,and the programmable deformation behavior is studied.(4)Based on the experimental results of a variety of bilayer responsive hydrogels with bionic bilayer structure,a spiral deaformation law and an effective actuating force formula are proposed for the first time by means of observation,theoretical analysis and data fitting.The spiral deaformation law refers to that the bending state of the responsive hydrogel system with bionic double-layer structure presents a spiral shape under external stimuli,and the terminal trajectory(bending angle-time relationship)conforms to the exponential function relationship in the plane cartesian coordinate system,and also conforms to the logarithmic spiral characteristics in polar coordinates,meanwhile,the influence of different experimental parameters on actuating performance also conforms to a certain functional relationship.The effective actuating force formula can be used to qualitatively analyze the bending direction and actuating performance.(5)A series of valve devices based on double-layer structure are designed and verified,including five single-pass type,six double-pass type,two three-pass type and one four-pass type,with selectable one-way flow,liquid shunt and other functional characteristics.A valve regulation law based on spiral deaformation law is proposed through data analysis.In conclusion,through the design and actuation mechanism research of the bionic double-layer structure based on responsive hydrogel,the control of water flow behavior of hydrogel-based flexible structure in complex liquid environment and its application potential in simple valve device are expanded.