Controlled servoing of micro- and nanostructures is of great interest in disciplines such as bioscience or biomedical engineering. Applications in molecular biology include single cell manipulation for fundamental studies and investigations of forces and motion associated with biological molecules. Wireless control of micro/nanostructures in fluids over large distances is also a tremendous need in medicine, especially in cancer therapy. Targeted drug delivery aims at the enhancement of the drug uptake of the cancerous tissue, and the minimization of the required drug dose. A significant challenge of untethered control of micro/nanostructures is providing them with power for mobility. One approach is wireless magnetic control.
We present a magnetic manipulation system for control of an untethered micro- or nanostructure with 5 degrees of freedom (3 for position and 2 for pointing orientation). The system, called the MiniMag, consists of 8 stationary electromagnets with soft magnetic cores arranged in a single hemisphere. Arbitrary fields and gradients up to 50 mT and 5 T/m at frequencies up to 2 kHz can be achieved for a workspace of 1 ccm. The resolution is limited solely by the imaging method. This is accomplished through the superposition of the magnetic fields of the individual coils and capitalizes on a linear representation of the coupled field contributions.
The system can be incorporated with an inverted or a non-inverted microscope, and various control strategies can be explored. Examples include gradient-based motion, cork-screw-like motion of helical structures by rotating magnetic fields, and stick-slip actuation on surfaces induced by oscillating magnetic fields. This allows for the experimental exploration of fluid dynamics at low Reynolds regimes and fundamental studies of the principles of motion of nanostructures. In-vitro studies include fluid dynamic investigations of e.g. nickel nanowires (NWs) that are pulled with magnetic gradients at different NW orientations. Moreover, the system has been applied to manipulate single cells and measure internal cellular forces. Microbeads functionalized with anti-E.coli antibodies were successfully positioned in close proximity of macrophages using closed-loop servoing along a user-defined path. We show that this method can be used to study the mechanobiology involved during bead phagocytosis. In another application we demonstrate the feasibility of delivering signals to predefined locations of 3D engineered micro tissues.
Simone Schürle was born in Ulm, Germany, in 1985 and studied Industrial Engineering and Management at the University of Karlsruhe. During her studies she focused in Micro- and Nanosystems Technologies. In 2005 she completed a research stay at the University of Canterbury, New Zealand, in the field of Bio Mechanical Engineering. She gained further practical experience during internships in R&D and marketing in Nano Imprint Lithography at SUSS MicroTec in Munich, Germany. Subsequently, in 2008, she was invited to perform research on the assembly and electrical characterization of carbon nanotubes at the University of Kyoto, Japan. After 4 months of traveling around the world she joined the Institute of Robotics and Intelligent Systems at the Swiss Federal State of Technology, Switzerland, as a PhD candidate in 2009. Her main research interests are now in magnetic manipulation of micro and nanostructures for applications in life sciences, such as single cell manipulation and targeted drug delivery.