Die Fähigkeit künstlicher Mikroschwimmer, auf äußere Reize zu reagieren und deren mechanistische Ursprünge, gehören zu den umstrittensten Fragen der interdisziplinären Wissenschaft. Die Erzeugung chemischer Gradienten ist dabei eine technische Herausforderung, da sie aufgrund von Diffusion schnell abflachen. Inspiriert von ‘Stop-flow’ Experimenten aus der chemischen Kinetik zeigen wir, dass die Erzeugung eines mikrofluidischen Gradienten durch Kombination mit einer Druckrückkopplungsschleife zur präzisen Kontrolle des Stoppens erfolgen kann. Das ermöglicht es uns, die mechanistischen Details der Chemotaxis von künstlichen katalytischen Janus-Mikromotoren zu untersuchen. Wir stellen fest, dass diese Kupfer-Janus-Partikel eine chemotaktische Bewegung entlang des Konzentrationsgradienten sowohl in positiver als auch in negativer Richtung zeigen, und wir demonstrieren die mechanische Reaktion der Partikel auf unausgewogene Widerstandskräfte, die dieses Verhalten erklären.

<p>Microparticles have been investigated not only as feedstock spherical or amorphous bulk materials used for shape molding, but also as agents that can perform work in the micron scale. The fabrication of microparticles with active properties of self-propulsion, self-assembly, and mobility with enhanced mechanical, thermal, and chemical properties is of particular interest for emerging technologies such as drug delivery, micro-robotics, micro energy generation/harvesting, and MEMS. Conventional fabrication methods can produce several complex particle shapes in one fabrication session or hundreds of spheroid shaped particles per second. Innovative techniques, as flow lithography, have demonstrated control over particle form and composition for continuous fabrication cycles. In recent years predefined shape polymer microparticles have been fabricated as well as ceramic microparticles through suspension processing with these set of techniques. Even though ceramic materials have been fabricated, there is still a strong need to increment the palette of available materials to be processed via flow lithography. We have pioneered the production of shaped ceramic microparticles by Stop-Flow Lithography (SFL) using preceramic polymers, providing control of particle size and shape in the range of 1 – 1000 μm. The principal arranged technique (SFL) combines aspects of PDMS-based microfluidics and photolithography for the continuous cyclable fabrication of microparticles with predefined shapes. The PDMS microchannel devices used were fabricated with vinyl film molds in a laminar hood avoiding the need for a cleanroom, procedure that reduced fabrication costs. After a fabrication session, the preceramic polymer microparticles were collected, washed, and dried before entering an inert atmosphere furnace for pyrolysis. Additionally, by treating the material initially as liquid polymer, special properties can be added by converting it into an emulsion or a suspension. Microparticles were functionalized by introducing porosity and magnetic nanoparticles in the preceramic polymer matrix. The porous characteristic of a particle leads to an increase in surface area, allowing the particle to be infiltrated with a catalyzer or act as a chemical/physical carrier, and the magnetic behavior of the particles allows a controllable trajectory with defined external magnetic fields. These two properties can be used to fabricate bifunctional microparticles to serve as drug carriers through human arteries and veins for drug delivery purposes. We successfully fabricated solid and functional ceramic microparticles in the 10 – 50 μm range with predefined shapes as hexagons, gears, triangles, and ovals. This system is an economical route to fabricate functional defined shape particles that can serve as microrobots to perform tasks in liquid media.</p>