Research On Magnetic Microrobots Fabricated By Femtosecond Laser And Their Biomedical Applications

There are a variety of natural organisms at the micro scale and each of them derives unique ways of locomotion to adapt to the ever-changing living environment.Inspired by these microbial locomotions,researchers gradually became interested in artificial micro/nano robots and began to conduct related researches.Compared with traditional robots,microrobots show the advantages of small size and light weight,therefore,they are expected to become a new generation of technical tools for targeted drug delivery,non-invasive surgery,and cells transplantation.Femtosecond laser two-photon polymerization technology can realize true three-dimensional microstructure processing.It can break through the optical difraction limit to obtain sub-micron processing resolution,so it is very suitable for preparing micro/nano robots with controllable morphology.However,the traditional femtosecond laser direct writing(DLW)technology always prints the microstructures through point-by-point scaning so that it brings low processing efficiency,which obstructs mass manufacturing.In addition,limited by current non-intelligent materials,micro/nano robots still do not have the shape-morphing capabilities to adapt to more complex application requirements.Based on the spatial light modulation technology,a method is proposed for efficiently fabricating micro/nano robots with modulated vortex beams,and wireless magnetic fields are used to achieve precise motion control of the microrobot.Besides,based on synthetic stimulus-response materials,reversible shape morphing of microrobots has been realized,and finally they are applied to biomedical fields such as cell transportation and targeted drug therapy.The details are as follows:1.The working principle of the phase-type spatial light modulator is introduced and the method of generating the holographic phase of the vortex beam is illustrated.Moreover,its propagation characteristics in space and focusing properities at high numerical aperture are simulated.In addition,the two magnetic field driving principles of magnetic torque and gradient force are clarified respectively.Furthermore,the magnetic field intensity distribution generated by electromagnetic coil is calculated and simulated,and a three-dimensional Helmholtz coil driving system is built to provide magnetic torque to realize micro/robot actuation.2.The modulated vortex beam is used to fabricate the magnetic-actuated microhelix robot,which greatly improves the processing efficiency.An asymmetrical conical microhelix robot is developed,which exhibits more excellent swimming performance under the magnetic torque.Thanks to the hollow inner cavity and the functional surface,the conical microhelix robot is used to realize the loading,transportation and release of nanoparticles and neural stem cells.3.A new type of photopolymer material that can respond to pH stimulation has been developed.By adopting asymmetric scanning point spacing,microrobots with programmable anisotropic shape-morphing are realized.Under the control of the dynamic magnetic field,the developed magnetic microcrab realizes the complicated operation of the microparticle by claws morphing.In addition,taking adcantage of the shape switching in the physiological environment,the developed magnetic microfish completes the encapsulation and controllable release of therapeutic drugs by mouth morphing.By combining these two functions,the precise treatment of local Hela cells in the complex artificial network is realized.4.The vortex beam processing system is optimized and rapid fabrication of a shape-morphing conical tubular microrobot is realized by single exposure within 0.1 s.This kind of microrobot is used to realize the dynamic switching of the microsphere lens imaging.In addition,the magnetically guided microrobot is used to complete the active loading,transportation and release of particles.Based on environmentally adaptive shape-morphing,the traversal of the complex narrow network is completed by microrobot.In the end,the application prospect of group cooperative motion is proposed on the basis of the interaction among large quantities of microrobots.