Microrobots (MRs) have attracted growing interest for their potentialities in diagnosis and noninvasive intervention in hard-to-reach body areas. The safe operation of biomedical MRs requires fine control capabilities, which strongly depend on precise and robust feedback about their position over time. Ultrasound acoustic phase analysis (US-APA) may allow for a reliable feedback strategy for MR imaging and tracking in tissue. In this article, we combine task-specific magnetic actuation and related US-APA motion tracking to achieve closed-loop navigation of a magnetic MR, rolling on the boundary of a lumen in a tissue-mimicking phantom. A C-arm system attached to a robotic platform is used to precisely position the magnetic actuation source and US-APA detection unit within the workspace, thus enabling MR visual-servoing. In the first place, the proposed approach allows to perform supervised localization of the MR without anya-prioriknowledge of its position. After localization, a robust real-time tracking enables closed-loop MR teleoperation in the phantom lumina over a travel distance of 80 mm (145 body lengths), both in static and counter flow, thus achieving an average position tracking error of 368 micron (0.67 body lengths). For the first time, our results validate US-APA as a reliable feedback strategy for visual-servoing control of MRs in simulated in-body environment.

Independent control of microrobots is a cardinal challenge for manipulation at micro/nano scale. In this paper, we design and assemble an electromagnetic setup to overcome some of the major obstacles in the independent control of microrobots. The demanding magnetic requirements are met by the presented experimental testbed that is able to produce magnetic fields and gradients of, respectively, 160 mT and 3.6 T/m at the center of the workspace. Through the design process of this testbed, we analyze the importance of design parameters and derive a quantitative analysis of the requirements for the dissipation of the generated heat. Further, we present and develop the model and software infrastructure, capable of running at 25 Hz, necessary for independent control of multiple microrobots. We also introduce two novel techniques for current-minimizing mapping of the desired forces into currents at the electromagnet. Finally, the capabilities of the setup are demonstrated through independent control of two, both identical and nonidentical, soft-magnetic microspheres in three-dimensional space—with average root mean square errors of 102$\mu$m and peak velocities of up to 331$\mu$m/s.