Nanorobots remain in the realm of science fiction, though research efforts related to small-scale robotics are beginning to approach these dimensions. Nanorobots are robots that are nanoscale in size or large robots capable of manipulating objects that have dimensions in the nanoscale range with nanometer resolution. Nanorobotic manipulation is an enabling technology for NanoElectroMechanical Systems or NEMS. NEMS with novel nanoscale materials and structures will enable many new nanosensors and nanoactuators.
Microrobots are intelligent machines that operate at micron scales. Professor Brad Nelson and his colleagues at The Institute of Robotics and Intelligent Systems have recently demonstrated three distinct types of microrobots of progressively smaller size that are wirelessly powered and controlled by magnetic fields1. These micron sized robots were fabricated and assmebled by tools and processes developed by IRIS researchers. Many of these systems are used for robotic exploration within biological domains, such as in the investigation of molecular structures, cellular systems, and complex organism behavior.
Microrobot next to a fruit fly
For larger scale microrobots, from 2mm to 500 µm, IRIS researchers microassemble three dimensional devices from ferromagnetic material. These microrobots precisely respond to torques and forces generated by magnetic fields and field gradients2.
In the 500 µm to 200 µm range, IRIS researchers have developed a process for microfabricating robots that harvest magnetic energy from weak oscillating fields (1-6mT, 2-5kHz) using a resonance technique3.
At even smaller scales, down to micron dimensions, IRIS researchers have developed microrobots they referred to as Artificial Bacterial Flagella (ABF) that are of a similar size and shape as natural bacterial flagella, and that swim using a similar low Reynolds number helical swimming strategy. ABF are made from a thin-film self-scrolling process and also use a weak magnetic field (1-6mT), but one that rotates rather than oscillates4,5.
The novelty of these three "microrobots" is that they are all tiny devices that can be precisely controlled with as many as six degrees of freedom. Because the distance from which these structures can be controlled is relatively large, the structures can not only be used as tools for manipulating other micro and nanoscale structures such as cells and molecules, similar to particle trapping techniques, but can also serve as vehicles for targeted delivery to locations deep within the human body. The micro and nanorobots are all non-spherical. Therefore, both their position and orientation can be precisely controlled, removing a current limitation of particle trapping.
Microrobot on a U.S. penny
While the potential applications of these devices are exciting, many challenges remain to be addressed. To functionalize these devices and to improve their performance capabilities, fundamental issues in the role surface forces play must be addressed; biocompatibility must be ensured; loading and diffusion of biomolecules must be investigated; and interactions with and manipulation of tissue and macromolecules must be considered, to name but a few of the remaining challenges.
There is a lot yet to do.
1. J. J. Abbott, K. E. Peyer, M. C. Lagomarsino, L. Zhang, L. X. Dong, I. K. Kaliakatsos, B. J. Nelson, "How Should Microrobots Swim?" International Journal of Robotics Research, July 2009.
2. K. B. Yesin, K. Vollmers and B.J. Nelson, "Modeling and control of untethered biomicrorobots in a fluidic environment using electromagnetic fields," International Journal of Robotics Research, vol. 25, pp. 527-536, 2006.
3. K. Vollmers, D. R. Frutiger, B. E. Kratochvil, B. J. Nelson, "Wireless resonant magnetic microactuator for untethered mobile microrobots", Applied Physics Letters, Vol. 92, No. 14, 2008.
4. L. Zhang, J.J. Abbott, L.X. Dong, B.E. Kratochvil, D.J. Bell, D.J. and B.J. Nelson, "Artificial bacterial flagella: Fabrication and magnetic control," Applied Physics Letters, vol. 94, February 2009.
5. L. Zhang, J. J. Abbott, L. X. Dong, K. E. Peyer, B. E. Kratochvil, H. X. Zhang, C. Bergeles, B. J. Nelson, "Characterizing the Swimming Properties of Artificial Bacterial Flagella", Nano Letters, Vol. 9, No. 10, October 2009, pp. 3663-3667.
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