Optimal propulsion: Helping nanorobots swim better

(Nanowerk News) Researchers from three Technion-Israel Institute of Technology departments have completed an interdisciplinary study revealing the optimal configuration for nanoscale robots that can travel within the human body to perform a variety of tasks. The model improves previous nature-inspired models.
Led by Professor Alex Leshansky of the Technion’s Wolfson Department of Chemical Engineering, the research team comprised of members of three different Technion faculties (the others were the Department of Mathematics and the Department of Physics) analyzed the optimal configuration for nanoscale robots that are designed to “swim” through the human body. Their findings were recently published in Science Robotics ("Geometric constraints and optimization in externally driven propulsion").
For the last decade, research groups around the world have been working to develop nanometer- or micrometer-scale robots that can move in a liquid environment. These robots provide diverse opportunities in important biomedical applications, including drug delivery.
The original inspiration for the design of these miniature robots comes from bacteria, which move using slender helical tails called flagella. As the flagellum rotates in the liquid, it creates friction that propels the bacterium. Inspired by this natural mechanism, research groups have developed tiny spirals that are driven by a rotating magnetic field.
Although this method offers a number of advantages (including low power requirements of magnetic field), creating these spirals is complicated. As a result, researchers have suggested using random clusters of magnetic nanoparticles as tiny “swimmers.” Such clusters can be easily fabricated using a simple aggregation process. But in the article published in Science Robotics, the Technion researchers demonstrate that this approach does not yield optimal results.
As part of their study, the Technion researchers developed a theory for calculating the optimal speed of these magnetic swimmers based on their shape and magnetization. As a result, they can now calculate the maximum possible speed of random clusters, and the optimal shape for these tiny swimmers. Contrary to expectations, they found that the thin spiral inspired by nature is not the optimal shape, but rather a thick arc with twisted ends. This optimal propeller was shown to move much faster than the previously developed random clusters.
According to Professor Leshansky, the study’s findings will lead to the development of more efficient microrobots: “Most researchers in the field assume that the biomimetic helical shape for tiny swimming devices is the optimal one. To our surprise, we discovered that the optimal shape is rather different than helix and were able to demonstrate more efficient structure.”
Source: Technion-Israel Institute of Technology