FR-16: On Trajectory Control of Magnetized Spherical Solids Driven by Magnetic Force Through Soft Medium

The application of untethered millimeter-sized devices, referred to as bots, for manipulation inside the human body holds immense potential in the field of medicine1. Many future medical procedures involve operating within soft tissues, where the behavior of bots differs significantly from their motion in fluids2, where magnetically driven transport of untethered devices has been extensively explored3. By contrast, trajectory control of small untethered solid bots in soft media has not been reported in the literature. Soft media environment presents new challenges associated with movement history dependence and non-linear effects absent in most fluids. This work formulates, simulates, and experimentally tests a method of control and manipulation of millimeter-sized magnetized solid spherical bots in soft media environments that mimic soft tissues. Spherical bot shapes offer the flexibility of permitting abrupt changes in motion direction. The primary challenge, however, lies in the nonlinear and history-dependent soft medium reaction forces resulting from irreversible modifications to the medium. This work discusses magnetically actuated motion control method for spherical bots in soft media along elementary trajectories consisting of circular and straight segments, which can be combined to generate more complex paths. The proposed control approach is based on a phenomenological model that captures the response forces exhibited by soft media2 using control method illustrated roughly in Fig. 1. Numerical implementation of the suggested trajectory control for circular paths demonstrates excellent agreement with experimental results as evidenced by the examples in Fig. 2, indicating achievable accuracy at the scale of the bot's radius for trajectories with radii of curvature on the order of 10 times the bot's radius.References: 1 B. J. Nelson, I. K. Kaliakatsos, and J. J. Abbott, Annu. Rev. Biomed. Eng., vol. 12, no. 1, p. 55 (2010) 2 Y. Malkova, S. Ran, G. Friedman, J. Mech. Behav. Biomed. Mater., vol. 126, p.105040 (2022) 3 B. J. Nelson, S. Gervasoni, P. W. Y. Chiu, L. Zhang, and A. Zemmar, Proc. IEEE, p. 1 (2022)