Robust Autonomous Control of a Magnetic Millirobot in In Vitro Cardiac Flow

2026-04-01

AI Summary

Achieving reliable autonomous control of magnetically driven microrobots in pulsatile cardiac blood flow remains highly challenging. This work proposes a vision-guided closed-loop control framework that, for the first time, integrates a multi-coil electromagnetic actuation system with a sliding mode controller augmented by a disturbance observer (SMC-DOB). The approach further incorporates real-time microrobot localization via a UNet architecture and A* path planning, while employing steady-state computational fluid dynamics (CFD) to estimate hydrodynamic drag for feedforward compensation. Experimental results under physiologically relevant pulsatile flow conditions demonstrate significantly enhanced tracking robustness: the root-mean-square error (RMSE) in static fluid is 0.49 mm, and under high-pulsatility, low-viscosity conditions, the RMSE consistently remains below 2 mm—representing a 37% reduction compared to conventional PID control and a 2.4-fold decrease in peak error.

Abstract

Untethered magnetic millirobots offer significant potential for minimally invasive cardiac therapies; however, achieving reliable autonomous control in pulsatile cardiac flow remains challenging. This work presents a vision-guided control framework enabling precise autonomous navigation of a magnetic millirobot in an in vitro heart phantom under physiologically relevant flow conditions. The system integrates UNet-based localization, A* path planning, and a sliding mode controller with a disturbance observer (SMC-DOB) designed for multi-coil electromagnetic actuation. Although drag forces are estimated using steady-state CFD simulations, the controller compensates for transient pulsatile disturbances during closed-loop operation. In static fluid, the SMC-DOB achieved sub-millimeter accuracy (root-mean-square error, RMSE = 0.49 mm), outperforming PID and MPC baselines. Under moderate pulsatile flow (7 cm/s peak, 20 cP), it reduced RMSE by 37% and peak error by 2.4$\times$ compared to PID. It further maintained RMSE below 2 mm (0.27 body lengths) under elevated pulsatile flow (10 cm/s peak, 20 cP) and under low-viscosity conditions (4.3 cP, 7 cm/s peak), where baseline controllers exhibited unstable or failed tracking. These results demonstrate robust closed-loop magnetic control under time-varying cardiac flow disturbances and support the feasibility of autonomous millirobot navigation for targeted drug delivery.

Problem

• magnetic millirobot
• autonomous control
• cardiac flow
• pulsatile flow
• minimally invasive therapy

Innovation

• magnetic millirobot
• sliding mode control with disturbance observer
• vision-guided autonomous navigation
• pulsatile flow compensation
• in vitro cardiac phantom