Research On Magnetically Responsive Microstructures Fabricated By Femtosecond Laser And Their Multifunctional Droplet Manipulation Applications

In order to adapt to harsh survival environment,organisms have evolved many unique liquid manipulation capabilities.Inspired by these liquid manipulation behaviors,a variety of active droplet manipulation methods based on excitationresponsive materials have been developed by researchers,which have been successfully applied in the fields of fine chemistry and biomedicine.The magnetically responsive microstructure surfaces can be reversibly deformed under the excitation of magnetic field,so as to realize the active manipulation of droplets.However,the existing droplet manipulation methods based on magnetically responsive microstructures are inflexible,and can only achieve droplet manipulation in a single plane.In addition,the preparation methods of magnetically responsive microstructure surfaces are complex,which further limits the practical applications of magnetic excitation-based droplet manipulation.Femtosecond laser micro/nano processing technology,as an emerging means of high precision and high efficiency processing,provides a new idea for the preparation of magnetically responsive microstructures.A variety of magnetically responsive microstructures have been prepared by using femtosecond laser micro/nano processing technology to realize diverse droplet manipulation.The droplet horizontal propulsion speed has been improved and the spatial dimensions of droplet manipulation have been extended.We also demonstrate the application of magnetically responsive droplet manipulation in the fields of microchemical reactions and polymerase chain reactions.The main research contents of this article are summarized as follows:1.An efficient method for the preparation of rectangular pore structure templates with high aspect ratio(～8.73)is proposed by combing femtosecond laser processing technology and polystyrene material.Rapid preparation of magnetically responsive microplates array structures surface is realized based on the polystyrene templates.2.The Janus microplates array structures with different wettability on two sides are prepared by selective laser modification.A large span of reversible tuning of the droplet contact angle on the structure surface from～158°to～40° is achieved by magnetic field control.Through surface color coating and magnetic control bending,the functions of bionic discoloration and camouflage are realized.Finally,a magnetically responsive microplates array structure with a transparent substrate is prepared to demonstrate the application of magnetically controlled optical shutter.3.A superhydrophobic magnetically responsive microplates array structure is proposed.The rapid droplet transportation in the horizontal plane is realized by the excitation of a spatially varying and periodic magnetic field.In addition,the,controllable capture and release of droplet in the vertical plane are achieved based on the localized high adhesion at the top of the microplate and the magnetically controlled bending deformation of the structure.Finally,the applications of magnetically responsive microplates array structure for continuous fluid mixing and liquid metal transport are demonstrated.4.A magnetic Janus film robot(MJF-robot)is designed.Driven by the periodic magnetic field,the MJF-robot enables the spontaneous wrapping and controllable transport of droplet.Based on the directional tumbling behavior and the superhydrophobic characteristic of the outer surface,the MJF-robot can achieve controllable dispensing and release of daughter droplet under the capillary force.The MJF-robot can also be rotated by the rotating magnetic field for rapid mixing of liquids.In addition,by combining the photothermal property of the MJF-robot with its stirring capability,heating and stirring can be achieved simultaneously.Finally,by modifying the surface of the MJF-robot with chitosan,its application in the polymerase chain reaction(PCR)is further expanded.