Design,fabrication,and Application Of Hydrogel-Based Hard Magnetic Soft Machines

In recent years,with the continuous development of soft robotics,remotely-driven,magnetically-responsive soft machines have gradually become a research hotspot.Hard-magnetic soft machines can achieve complex deformation through magnetic domain programming and thus have attracted great attention.However,currently reported hard-magnetic soft machines are either simple in structure or challenging to implement with magnetic domain programming methods.Their matrix materials are often silicone elastomers rather than hydrogels with better biocompatibility.Magnetic hydrogels,on the other hand,often suffer from poor mechanical properties and simple magnetic response,and cannot undergo rapid and complex deformation.In view of the above problems,starting from the material synthesis of hard-magnetic hydrogels,this paper proposes a biomimetic structure design and magnetic domain reprogramming method for hard magnetic soft robots.This paper further uses a magnetic hydrogel soft machine to explore its biomedical applications preliminarily.This paper aims to provide new methods and ideas for the design,manufacture,and application of magnetic soft machines,and further promote magnetic soft machines in practical engineering and medical treatment.This paper mainly conducts the following research:Firstly,a synthesis strategy of hard-magnetic hydrogel materials is proposed.By introducing the microgel-reinforcement system,the thickening of the hydrogel prepolymer solution and the enhancement of the mechanical properties of the magnetic hydrogel are achieved at the same time.Moreover,a hydrogel prepolymer solution with a magnetic particle content of up to 50 wt%and a uniform distribution is obtained.The prepolymer solution has suitable rheological properties,and can be employed to fabricate three-dimensional magnetic structures by extrusion-based 3D printing.The microgel-reinforced magnetic hydrogel has very strong and tough mechanical properties,the ultimate stretch reaches more than 15,and the fracture toughness reaches 15000J/m~2.Taking advantage of the large remanence of the hard-magnetic material,the magnetic domain programming of the printed magnetic hydrogel structure is achieved,and the fast,reversible,programmable deformation behavior driven by an external magnetic field is demonstrated.Secondly,based on the concept of biomimetics,the joint design of the magnetic soft machine is proposed.Through experiments and finite element simulations,it is proved that the magnetic soft machine with joint structures consumes less energy in the process of magnetic field-driven deformation,and can achieve larger deformation under the same magnetic field.A variety of magnetic soft machines with joint structures are fabricated by 3D printing,demonstrating their ability to perform multimodal deformation.An experiment of removing a foreign object using a six-armed magnetic millirobot is proposed.The foreign object removal experiments are carried out in animal organs ex vivo.The remote control of the target object is realized with the help of an external magnetic field and endoscopic imaging.Finally,based on the magnetothermal effect,a facile method for reprogramming the magnetic domains of hard-magnetic soft machines is proposed.The magnetization distribution and the corresponding deformation response of the magnetic soft machines are studied,and the model of magnetothermal heating process in alternating magnetic field is established through experiments and simulations.The reconfigurable deformation of magnetic soft machines introduced by magnetic domain reprogramming is demonstrated on both one-dimensional and two-dimensional models.An application of the reconfigurable magnetic soft machine as a reprogrammable switch in a LED circuit is demonstrated.