Anisotropic Microgels: Microrobots, Building Blocks, Drug Delivery Vehicles, and More

Recent progress in polymer chemistry and microfluidic fabrication has enabled the synthesis of soft hydrogel microparticles with precisely controlled anisotropic shapes, moving beyond simple spheres to complex architectures like ribbons, rods, bowls, and others. This morphological control is not merely aesthetic; achieving a specific particle shape directly unlocks new functional applications by dictating the particle mechanics, interactions, and responses to external stimuli. For instance, ribbon-shaped microgels can undergo a cyclic twisting and untwisting motion when subjected to external fields such as temperature changes or magnetic fields, allowing them to operate as synthetic microswimmers in low Reynolds number environments. In another example, rod-shaped microgels, particularly those integrating magnetic nanoparticles, can be aligned within an injectable hydrogel matrix to create anisotropic scaffolds. This alignment provides critical contact guidance, effectively directing the growth of the nerve tissue for regenerative medicine. Finally, bowl-shaped microgels introduce a unique concavity that transforms them into effective microcontainers capable of stably encapsulating therapeutic cargo and enabling targeted, site-specific drug delivery. This review highlights recent advances in the synthesis, properties, and applications of hydrogel microparticles of various nonspherical shapes.