Enable active mobility of untethered miniature robots in high-resistance multiphase medium

Conventional robotic systems exhibit limited mobility in media characterized by substantial resistance, e.g., solid-liquid mixture (SLM) and solid granular medium (SGM). This challenge is particularly pronounced for untethered miniature robots, as they often lack the capacities to generate sufficient force outputs or to implement strategies that reduce resistance from the surrounding medium. Here, we propose an impact-driven magnetic untethered miniature robot (RoboIMP) capable of delivering repeatable high-force outputs of up to 3 N, surpassing the theoretical force limits of conventional magnetic robots at the same characteristic length. RoboIMP uses reciprocal oscillation to fluidize the surrounding medium, thereby reducing the resistance from the medium by up to 13-fold. This enables effective locomotion of an untethered miniature robot in both SLM and SGM. By integrating functional modules, the proposed system demonstrates various applications, including pipeline cleaning, cargo delivery and retrieval, and navigation in the presence of chyme. © 2026 The Authors