Smart Microdevices Laying “Breadcrumbs” to Find the Way Home: Chemotactic Homing TiO2/Pt Janus Microrobots

Synthetic microrobots or micromotors are known to show “intelligent” behavior such as magnetotaxis, phototaxis, chemotaxis, active detection, and chemical communication. Herein, we present the concept of micromotors laying “breadcrumbs”; that is, these micromachines can move/return to a home position without external guidance after their external energy input is stopped. As a demonstration, TiO₂/Pt Janus micromotors that move forward with UV light can return back following the previous path when the UV light is turned off. Such autonomy of motion opens the door for truly independent applications of micromotors in the “deliver‐and‐return” fashion.     

Hypersonic‐Induced 3D Hydrodynamic Tweezers for Versatile Manipulations of Micro/Nanoscale Objects

Developing microrobots for precisely manipulating micro/nanoscale objects has triggered tremendous research interest for various applications in biology, chemistry, physics, and engineering. Here, a novel hypersonic‐induced hydrodynamic tweezers (HSHTs), which use gigahertz nano‐electromechanical resonator to create localized 3D vortex streaming array for the capture and manipulation of micro‐ and nanoparticles in three orientations: transportation in a plane and self‐rotation in place, are presented. 3D vortex streaming can effectively pick up particles from the flow, whereas the high‐speed rotating vortices are used to drive self‐rotation simultaneously. By tuning flow rate, the captured particles can be delivered, queued, and selectively sorted through the 3D HSHTs. Through numerical simulations and theoretical analysis, the generation of the 3D vortex and the mechanism of the particles manipulation by ultrahigh frequency acoustic wave are demonstrated. Benefitting from the advantages of the acoustic and hydrodynamic method, the developed HSHTs work in a precise, noninvasive, label‐free, and contact‐free manner, enabling wide applications in micro/nanoscale manipulations and biomedical research.     

Biohybrid bacterial microswimmers with metal-organic framework exoskeletons enable cytoprotection and active drug delivery in a harsh environment

The inspiring idea of using motile bacteria as bioengines to create biohybrid microswimmers has been realized by integrating functionalized cargos with bacteria recently. However, existing pernicious factors in ambient conditions, such as enzymes, may attack bacterial microsystems when they are executing tasks. Here, a versatile bacterial microswimmer system with cytoprotective metal-organic framework (MOF) exoskeletons is reported, capable of protecting the bioengine from enzyme degradation. Zeolitic imidazolate framework-8 (ZIF-8) nanoparticles (NPs) are fully coated on the surface of motile bacteria (Escherichia coli MG1655) 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 microsystems retain their effective propulsion after being treated with lysozyme, enabling the accelerated crossing through the Transwell membrane and improving anticancer efficacy compared with passive drugs. The fabricated bacterial microswimmers were also verified with chemotactic motion and prolonged retention time in the mouse bladder, holding great potential to design an active medical platform with improved therapeutic efficacy for targeted disease treatment, such as bladder cancer. Combining bacteria with MOFs generates multifunctional biohybrid microswimmers with capabilities of cytoprotection and active drug delivery. Such design facilitates the development of active biosystems to apply in harsh environments and meets rigorous requirements in clinical biomedical applications.     

Giant Vesicles with Encapsulated Magnetic Nanowires as Versatile Carriers,Transported via Rotating and Nonhomogeneous Magnetic Fields

Two real‐time methods to transport magnetic nanowires confined in giant hybrid vesicles upon the application of different strategies are studied. The microscale carriers are either magnetically guided through the viscous medium by a nonhomogenous field or advected by precisely monitored hydrodynamic flows. The slender geometry of the magnetic component enables the application of large torques, the in situ characterization of the rotational dynamics, as well as the guided propulsion via the continuous thrust of the nanowire tip on the confining bilayer. The flexibility of the vesicles, required to deform along the steering direction during passage through microscale openings, is enhanced via the adsorption of nonionic surfactants on the lipid membrane. The resulting integrated system is an excellent candidate to transport colloidal cargos or fluid amounts of some picoliters in microfluidic platforms, even in physiological environments, since it combines the maneuverability of propelled microscopic systems and the protection conferred by the vesicle.