| Chemical catalytic synthetic micro and nano motor is a kind of artificial micro and nano devices which can transform environmental chemical energy into kinetic energy by chemical catalysis. In nature, kinesin, myosin and other molecular motor can transform the energy from catalytic decomposition of adenosine triphosphate(i.e., ATP) into movement. Gain enlightenment from these, in the past decade, it is committed to design and synthesize of artificial micro and nanomotor, in order to achieve application in the field of targeted drug delivery, separation, biosensors, and other micro/nano devices.Based on this, this paper inspired by the protein molecular motor which could hydrolyze ATP for energy realize movement, use LBL self-assembly method to prepare a series Janus hollow polyelectrolyte microcapsules. By modified catalyst on one side of the microcapsules, catalytic decomposition of hydrogen peroxide to produce oxygen for drive the microcapsule motors motion, and investigate motor behavior and mechanism in-depth study and discussion.Firstly, we used layer-by-layer self-assembly method to prepare polyelectrolyte hollow microcapsules. By using laser scanning confocal microscopy, scanning electron microscopy and transmission electron microscopy to get the structure and morphology of the microcapsules. The loading capacity, thermal stability and other properties of microcapsule were studied in detail. The results showed that the prepared hollow polyelectrolyte microcapsules were 8 μm in diameter, with uniform morphology, structural stability and good monodispersity. By adding absolute ethanol in an aqueous solution to regulate the microcapsule shell permeability, we established a method to achieve the effective loading of the microcapsules by changing the solvent. Thermal stability of microcapsules were further studied by a focused laser beam of 650 nm to achieve a fast fusion of gold nanoparticles modified polyelectrolyte microcapsules. The dynamic fusion process of the microcapsules was followed by optical microscopy, the changes in membrane structure, the photothermal effect of gold nanoparticles, the effect of Au NP density in the capsule shells on the fusion process were also investigated, and the thermal model photothermal effect was established. By these studies of microcapsules basic performance, laid a good foundation for the follow-up preparation of Janus microcapsule motor.We chose platinum as the catalyst because it has a relatively high stability and catalytic activity, using layer by layer self-assembly method combined with the micro-contact printing method, firstly designed and fabricated a dendritic platinum nanoparticles functionalized Janus multilayer microcapsule motor. Scanning electron microscopy and transmission electron microscopy showed that dendritic Pt nanoparticles with diameter of 200 nm successfully modified on one side of the microcapsules, and the capsule structure retain completely. Detailed study of the movement of the motor in the hydrogen peroxide solution, showed motor movement have two typical kinds of moving trajectories, in a 30% H2O2 solution at a speed of about 1 mm/s. The speed of the movement depends on the concentration of hydrogen peroxide.We used the layer-by-layer self-assembly method combined with vacuum sputtering method to design and prepare a platinum coated Janus half shell coated polyelectrolyte multilayer capsule motor. Scanning electron microscopy characterization showed that a 20 nm Pt layer was sputtered on one side of microcapsules, with the asymmetric distribution of this catalyst, it is possible to enhance the driving force then effectively increase the movement speed of the motor. Further we studied the movement of Pt catalytic Janus motor in low concentration of hydrogen peroxide, and the results showed that in 5% hydrogen peroxide solution the average rate of motor can reach 140 μm/s, and about more than 80% motor particles can carry self-propelled movement. In the low concentration of 0.1% hydrogen peroxide, the motor can’t achieve self-drive movement, the "on / off" behavior of movement can be achieved by laser stimulation method.In order to improve the catalytic rate and biocompatibility of artificial motors, we use a vacuum sputtering combined with EDC crosslinking method to synthesize catalase based biological hybrid motor. Compared with platinum-catalyzed motor, the speed of this enzymatic biocompatibility motor has been further improved. Catalase catalyzed motor permeability test results show that the structure of the motor is not damaged and retains the advantages of the microcapsules of loading, and to determine the motor can be efficiently loaded microcapsules molecular weight of 10 k Da. To statistical analysis the motor velocity, the results show that in the same hydrogen peroxide concentration the enzyme-catalyzed motor velocity is much higher than the motor platinum catalyst, in 5% hydrogen peroxide at a speed of 140 μm/s. Further studies showed that enzymatic motor velocity and temperature of the solution have a great relationship. At 37oC physiological temperature, micromotors can move at lower concentrations of hydrogen peroxide solution, in 0.1% hydrogen peroxide can still move at a speed of 5 μm/s. The vacuum sputtered gold shell surface in polyelectrolyte microcapsules can be used for firmly fixed catalyst of catalase by covalent cross-linking. Then the Janus structure produced, and the gold shell also can act as a response to the near-infrared photothermal therapy agents. In vitro experiments, the target magnetic motor motion control to cancer cells achieved successfully, and by near-infrared laser stimulation drug package realized remote controlled release.The driving force of the above mentioned Janus microcapsules motor comes from the hydrogen peroxide decomposition of redox reactions, so the micromotor can only work in an aqueous solution of hydrogen peroxide. But the future of micro and nano motor working environment, especially the human environment, without the presence of hydrogen peroxide, design and preparation of no fuel based engine is critical to the future of transport in vivo biomedical applications and drug transport. Based on these ideas, this paper designed and fabricated a Janus light driven motor. This motor using water as the "fuel" and can translate light energy into heat energy then translate into mechanical energy to achieve movement. So the motor get rid of the dependence on the common "fuel" hydrogen peroxide. Further systematic theoretical study carried out miniature optothermal driven mechanism. The self-developed drive control and microscopic observation system was used for analysis different power laser driven movement. Under the focused laser irradiation(at power of 100 m W), the light driven motor can produce instant high temperature by photothermal effect, and can be achieved independent movement in the seconds. The speed can reach 55 μm/s, and the velocity increases with increasing laser intensity. Under 110 m W unfocused laser power irradiation, the microcapsule motor of 1μm in diameter can move at speed up to about 30 μm/s. Motor speed is directly effect by the laser intensity, and is inversely proportional to the motor diameter. By analyzing the effects of the optothermal motor, the establishment of a optothermal driven thermal model for the application of light and heat micro drive motor provides a theoretical basis. Based on the dynamic simulation, a further research was done on the targeted and photothermal cancer therapy application of the light-driven micromotor. This light-driven micromotor could be used in bio-medical application.In summary, we believe the Janus microcapsule motors prepared in this paper will widely be used in the field of micro-drive and micro-positioning, and have a very good application prospect, because of their unique properties and advantages. |
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