Magnetically Actuated Micro- and Nanopropellers

The futuristic vision of nanorobots performing various tasks not easily achieved by macroscopic machines has inspired the development of micron-sized swimmers and propellers that can be navigated with high precision at very small length scales. This thesis focuses on a particular class of such devices, magnetic helical particles, which are propelled using homogeneous rotating magnetic fields. I describe an optimized fabrication process based on the physical vapor deposition technique Glancing Angle Deposition, which allows the production of uniform colloids with complex shapes in very high yields. This process is extended to obtain magnetic helices with diameters below 100 nm. The resulting particles' propulsion behavior was observed experimentally, and compared with theoretical models. Furthermore two different strategies are examined for navigating not only simple Newtonian fluids, but also more complex biological fluids. In the first case, propulsion in hyaluronic acid is achieved by tuning the propellers' diameter to a size on the order of the medium's pore size. For the penetration of gastric mucin gels, a microorganism's propulsion strategy is mimicked, which relies on enzymatically changing the rheological properties of the local environment. These results illustrate the application of biomimetic locomotion tactics to artificial swimmers.