Evaporation-assembled magnetic microrobots with stable geometry and polymer-tunable function

Magnetic microrobots require anisotropic geometries to achieve controlled locomotion and adaptable material compositions to incorporate functions such as stimuli-responsive cargo release. However, existing fabrication strategies rarely combine stable, well-defined anisotropic structures with broad material versatility. Here, we introduce a bottom-up assembly approach that converts magnetic polymer nanoparticles into solid conical microrobots while retaining compatibility with multiple polymer systems. Using the same fabrication protocol, we assemble microrobots from different biocompatible or biodegradable polymers, including poly(methyl methacrylate), poly(l-lactic acid), and poly(lactic-co-glycolic acid), yielding structures with tunable size, robust mechanical stability, and well-defined anisotropic shapes. These solid assemblies remain intact during actuation and exhibit controlled magnetic locomotion under both magnetic-field gradients and rotating magnetic fields. Beyond locomotion, polymer selection enables functional integration without changing the fabrication strategy. In particular, poly(lactic-co-glycolic acid)-based microrobots exhibit pH-triggered cargo release, with enhanced degradation under acidic conditions. This work establishes polymer nanoparticle assembly as a versatile platform that decouples microrobot geometry for locomotion from polymer composition for material-dependent functionality.