Programmable Spatiotemporal Magnetic Fields for Selective Multimodal Actuation and Deterministic Decoupling of Heterogeneous Magnetic Robots.

Abstract

Magnetic milli/microrobots hold strong potential for biomedical applications, but their deployment as multi-robot systems is limited by short-range magnetic coupling, which prevents independent control in confined environments. Here, we present an expanded field-free region (FFR)-based control framework for spatially selective actuation of multiple magnetic torque-driven robots in confined environments. A generalized selective-control criterion incorporating the minimum rotating magnetic field required for robot actuation enables the framework to accommodate robots with different magnetic responses and operating conditions. Through programmable displacement and oscillation of the FFR, the framework extends conventional selective locomotion to include velocity regulation under a constant rotating magnetic field and oscillation-induced stick-slip locomotion. For strongly interacting permanent-magnet robots, a dedicated decoupling field reorients their magnetic moments to transition the inter-robot interaction from attraction to repulsion, enabling subsequent deterministic separation, whereas weakly interacting low-remanence robots can be separated using conventional FFR-based selective locomotion without dedicated decoupling. The framework is validated across different fluid viscosities and robots with distinct magnetic properties and is further integrated with robot redistribution and FFR-selective magnetic heating to achieve spatially regulated thermal responses. Finally, proof-of-concept demonstrations show clot-removal and targeted-delivery emulation and selective robot navigation in a 3-dimensional cerebrovascular phantom. These results establish an expanded FFR-based framework for sequential selective control of magnetic robots in confined environments and support its potential use in imaging-compatible robotic platforms for biomedical interventions.