pH-sensitive hydrogel-based magnetic capsule microrobot swarm with multimodal locomotion for targeted drug delivery

Hydrogel magnetic microrobots are promising for targeted drug delivery, but large drug-loaded microrobots are difficult to manipulate as stable swarms under conventional rotating magnetic fields. Here, shell-core magnetic capsule hydrogel microrobots (CHMs) were fabricated by coaxial microfluidics and actuated using a composite magnetic field system. The CHMs exhibited tunable diameters of 100-600 μm and a saturation magnetization of 5.4 emu g⁻¹. Under rotating magnetic fields, individual CHMs achieved torque-driven rolling with a maximum velocity of 0.76 mm s⁻¹. Under programmable rotating gradient magnetic fields, CHM swarms reached a maximum collective velocity of 0.72 mm s⁻¹ and reversibly transformed among clustered, elongated, chain-like, and dispersed morphologies. Aggregation and dispersion efficiencies reached 94% and 90%, respectively, within 1-8 Hz. The CHM swarm navigated confined channels, crossed obstacles, and achieved targeted locomotion in a simulated gastrointestinal environment. CHMs also exhibited pH-responsive drug release, with cumulative release of 4% at pH 1.2 and 23% at pH 7.6 within 10 h. Unlike conventional magnetic swarms relying on dipole-induced self-assembly, this strategy uses a movable magnetic gradient point to collectively confine and transport CHMs, providing a high-integrity non-assembly swarm control approach for targeted drug delivery.