Motion Control Of Micro/nanomotors And Construction Of Cell-based Micromotors

Micro/nanomotors are the tiny machines that can convert surrounding energy to their propulsive force and effective movement.The autonomous movement of Micro/nanomotors facilitates their broad applications in environmental remediation,energy generation,biosensing and targeted drug delivery.However,most of the current applications of micro/nanomotors remain in the proof-of-concept stage,and they still face some obstacles in practical applications,such as the motion control and biocompatibility of these microsystems.Motion control is prerequisite for completing complex tasks in dynamic environments.The biocompatibility of these active platforms determines their application prospects in biomedical fields.Based on the above understanding,we have designed two types of hybrid-powered micromotors to realize the motion control,including acceleration,brake and direction reversal.On the other hand,we also present two cell-based micromotors to improve the biocompatibility of the motor itself and the propulsive fuel and enable the protection of cell robots from the damage from surroundings.The detailed contents include the following four aspects:1.The new hybrid micromotors are designed by combining photocatalytic TiO2 and catalytic Pt surfaces into a Janus microparticle.The chemical reactions on the different surfaces of the Janus particle hybrid micromotor can be tailored by using chemical or light stimuli that generate counteracting propulsion forces on the catalytic Pt and photocatalytic TiO2 sides.Such modulation of the surface chemistry on a single micromotor leads to switchable propulsion modes and reversal of the direction of motion that reflect the tuning of the local ion concentration and hence the dominant propulsion force.An intermediate Au layer(under the Pt surface)plays an important role in determining the propulsion mechanism and operation of the hybrid motor.The built-in optical braking system allows "on-the-fly" control of the chemical propulsion through a photocatalytic reaction on the TiO2 side to counterbalance the chemical propulsion force generated on the Pt side.The adaptive dual operation of these chemical/light hybrid micromotors,associated with such control of the surface chemistry,holds considerable promise for designing smart nanomachines that autonomously reconfigure their propulsion mode for various on-demand operations.2.Hybrid light/acoustic-powered microbowl motors,composed of Au and TiO2 with a structure-dependent optical modulation of both their movement and collective behavior are reported by reversing the inner and outer positions of Au and TiO2.A microbowl composed of interior TiO2(Au)and exterior Au(TiO2)surfaces is named TiO2-Au(Au-TiO2)microbowl.The microbowl propels in an acoustic field toward its exterior side independent to their compositions.UV light activates the photochemical reaction on the TiO2 surface in the presence of hydrogen peroxide and the Au/TiO2 system moves toward its TiO2 side by self-electrophoresis.Controlling the light intensity allows switching of the dominant propulsion mode and provides braking or reversal of motion direction when TiO2 is on the interior,or accelerated motion when the TiO2 is on its exterior.Theoretical simulations offer an understanding of the acoustic streaming flow and self-electrophoretic fluid flow induced by the asymmetric distribution of ions around the microbowl.The light-modulation behavior along with the tunable structure also leads to the control of the swarm behaviors under the acoustic field,including expansion or compaction of ensembles of microbowls with interior and exterior TiO2,respectively.Such structure-dependent motion control thus paves the way for a variety of complex microscale operations,ranging from cargo transport to drug delivery in biomedical and environmental applications.3.An endogenous enzyme-powered Janus platelet micromotor(JPL-motor)system is designed by immobilizing urease asymmetrically onto the surface of natural platelet cells.This Janus distribution of urease on platelet cells enables uneven decomposition of urea in biofluids to generate enhanced chemophoretic motion.The cell surface engineering with urease has negligible impact on the functional surface proteins of platelets,and hence,the resulting JPL-motors preserve the intrinsic biofunctionalities of platelets,including effective targeting of cancer cells and bacteria.The efficient propulsion of JPL-motors in the presence of the urea fuel greatly enhances their binding efficiency with these biological targets and improves their therapeutic efficacy when loaded with model anticancer or antibiotic drugs.Overall,asymmetric enzyme immobilization on the platelet surface leads to a biogenic microrobotic system capable of autonomous movement using biological fuel.The ability to impart self-propulsion onto biological cells,such as platelets,and to load these cellular robots with a variety of functional components holds considerable promise for developing multifunctional cell-based micromotors for a variety of biomedical applications.4.A versatile bacterial microswimmer system with cytoprotective MOF exoskeletons is developed,capable of protecting bioengines from enzyme attackers.Zeolitic imidazolate framework-8(ZIF-8)nanoparticles(NPs)are fully coated on the surface of motile bacteria through tannic acid(TA)complexation.The ZIF-8 wrapping is demonstrated with negligible influence on bacterial motility under optimized conditions.Moreover,ZIF-8@E.coli microswimmers still maintain their shapes and motion performance in the presence of lysozyme,verifying the effective preservation of formed ZIF-8 exoskeletons on the bacterial surface.Coupling with the drug loading capacity of ZIF-8,Doxorubicin(DOX)-loaded ZIF-8@E.coli microsystem shows comparable ability to pass through Transwell membrane both in the condition of with and without lysozyme,leading to enhanced anticancer efficacy compared with passive drugs.Encapsulating bacteria with MOF layer generate multifunctional biohybrid microswimmers,enabling active drug delivery under biological threats in surroundings.Such design facilitates the development of biohybrid microswimmers to apply in harsh environments and meets rigorous requirements in practical biomedical applications.