| Micromachine, which has typical size or manipulation range in microns range, was proposed in the 1960s for the first time. Till 1980s, the first electrostatic micromotor was successfully fabricated, micromachines got their rapid development. Up to now, the products are widely applied in biomedical research, environmental monitoring, traffic and transportation, automatic control, aeronautics and astronautics and national defense etc. Generally, the fabrication and drive of micromachines mainly depended on MEMS technology heavily. With the development of MEMS technology, micro-and nano-micromachines appeared gradually. However, the size decrease of micromachines results in more complex driving instruments, and the traditional driving mechanisms become disabled. Therefore, it is necessary to develop novel fabrication and drive approaches of micromachines. In recent years, the raising of polymer micro fabrication technology made the fabrication of polymer-micromachines more easily. In this dissertation, by using femtosecond laser micro/nanofabrication as a powerful 3D microfabrication platform, micromachines were designed, and fabricated in a controlled manner. Two novel driving mechanisms named magnetically remote driving (MRD) and solvents response driving (SRD) were developed for micromachine manipulation.1. Magnetically remote drivingMagnetically remote drive is a noncontact driving manner which transmits force and moment by using magnet field. This drive mechanism shows great prospects in the biomedical use due to its advantages of its noncontacting and biocompatibility. However, magnetic materials (such as Fe3O4 nanoparticles) are difficult to dope into polymer homogeneously due to their poor compatibility. So, magnetic drive technology has not yet been applied to polymer micromachines. In this dissertation, we represent a fabrication of magnetic polymer micromachines by femtosecond laser processing of ferrofluid photoresists. Subsequently, the micromachines were remotely manuplated in magnetic field.Experimentally, well dispersived Fe3O4 magnetic nanoparticles with uniform diameter of?6 nm were prepared by thermal-decomposition method. After surface modification, PO3-TMPTA was modified on the surface of nanoparticles, and then the surface property of nanoparticles was changed. Experimental results showed that the surface modified nanoparticles could be dispersed in polar solvents (such as MA) uniformly and steadily for a long time.Magnetic photoresists were achieved by dispersing the Fe3O4 nanoparticles into the conventional photoresists which consisted of butyl methacrylate as monomer, PO3-TMPTA as crosslinker, TPO and Irgacure 819 as photoinitiators. In order to obtain high fabricative precision, surface quality of micromachines was significantly improved by using optimizated Fe3O4 nanoparticles as doping agents. Compared with the microstructure containing coprecipitation-synthesized nanoparticles whose surface roughness was 27.5nm, the surface roughness of this optimizated microstructure was only 4.9nm.As a typical illustration, microsprings were fabricated by femtosecond laser two-photon photopolymerization (TPP) of the magnetic photoresists. Experimental results showed that the microsprings could respond sensitively to external magnetic fields. When the intensity of magnetic field was 3000Gs, the deformation of microsprings could reach 81?m, which was 2.25 times of their original lengths. Obviously, the driving effect was significant.Subsequently, a more complex and functional microturbine was designed and fabricated through the same method. In our work we also studied their movements in magnetic field. Experimental results showed that compared with the microturbines containing coprecipitation Fe3O4 nanoparticles, the surfaces of microturbines containing thermal-decomposition Fe3O4 nanoparticles were much smoother. Moreover, the stability and speed of their rotation were better than those containing coprecipitation Fe3O4 nanoparticles due to the much little friction in surface. The maximum rotating speed of the microturbines containing thermal-decomposition Fe3O4 nanoparticles was as high as 400r/min.Through femtosecond laser invert fabrication technology, the microturbines were prepared in microfluidic channel successfully. As effectively active mixing devices, they could be used to solve the problems of solvents mixing in micro scales.2. Solvents response drivingThe responsive features of stimuli-responsive polymer provide the possibility of driving polymer micromachines in a controlled fashion. However, the stimuli-responsive polymers are usually not compatible with microfabrication technology. Although the conventional photoresists could be fabricated with high precision, there are no obvious responsive features of them. In the conflict of device fabrication and responsive properties, we propose a solvents response driving mechanism for conventional photopolymer micromachine by adjusting the experimental parameters.It is well known that cross-linked polymer materials can swell and shrink in organic solvents. Based on this phenomenon, the swelling and shrinking behaviors of bulk materials, microstructured photopolymers, and PDMS were carefully studied. We found that the solvents response behaviors of polymer microstructures fabricated by femtosecond laser were much more obvious due to the relatively large interfacial surface area.For example, methacrylate-based photoresists swelled in solvents whose solubility parameters were similar, and shrunk in solvents whose solubility parameters were different. We first fabricate microwire structures by TPP. And then a reliability test of solvents response of microwires was applied. Experimental results showed that after swelled and shrunk for 50 times, the deformation degree of microwires remained at 17%. It was similar with the initial deformation degree, showing a great reliability, which fully met the high standard of micromachines drive.As a display of solvents response manuplation, slipping-block structures based on microwires shrinking were designed and fabricated. The devices could slip along a rail by the stimulation of n-hexane. The polymer density of the formed networks was controlled effectively by adjusting the laser scanning step length so as to tune the sensitivity of the structures to solvents. In this part, the dependence of the block moving distance and the diameters of microwires on the scanning step length of the laser was also analyzed quantitatively. Experimental results showed that the block moving distance increased with step length, and the diameters of microwires decreased with step length.On this basis, through the flexible and designable TPP fabrication, the bilayer polymer structures with different polymer density were designed and fabricated. Although the structures were consisted with the same material, the microstructure showed directional curving property, due to the different responsive degreen. When they were immersed in n-hexane, the structures could bend directionally. When they were immersed in acetone the structures restored quickly. This bending/restoring action could act repeatedly under the condition of constant external stimulation.Using this bilayer structure as a basic unit, the micromanipulators which can grip in n-hexane and open in acetone were designed and fabricated. The micromanipulators were fabricated on the cladding of fibber by inverting fabrication method. The large-scale three-dimensional precise position was achieved via the operation of fiber in three-dimensions. Finally, as the basic functions of a "microhand", a series of actions, such as capturing, transporting and releasing of microspheres were carried out.The magnetically remote polymer micromachines were fabricated successfully in this dissertation. The key technical problem of the poor compatibility between magnetic nanoparticles and photoresists was solved by successful preparation of ferrofluid photoresist containing surface modified Fe3O4 nanoparticles, which improved fabrication precision greatly. At the same time, improved reliability and stability of magnetic micromechines were obtained for subsequent manipulation. On the other hand, the solvents responsive micromachines were designed based on swelling and shrinking phenomenon of polymer networks for the first time. Controllable micromanipulation of these solvent responsive micromachines was achieved by solvents stimulation. The innovative researches in fabrication and manipulation of micromachines would promote their further developments and applications... |
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