Fish-diversity–inspired multiple soft millirobot system with morphology-encoded selective control

Marine ecosystems, particularly coral reef communities, reveal how morphological diversification in fish species facilitates specialized locomotion through evolutionary optimization of body-fin coordination and hydrodynamic adaptations. Inspired by these biomechanical principles, we developed a morphology-encoded patterned magnetic millirobot (MPMR), whose anterior-to-posterior (AP) length ratio and body contour are predefined during fabrication to yield distinct hydrodynamic responses under the same uniform magnetic actuation. These MPMRs, with various morphologies, successfully emulated the undulatory swimming patterns of different fish species in a fluidic environment. Morphological differentiation in MPMRs has been shown to directly influence their motion performance, with an optimal AP ratio (approximately 1:1) and streamlined body contour maximizing propulsion efficiency. Furthermore, MPMRs with distinct morphologies display different frequency-dependent responses to magnetic actuation, leading to morphology-specific velocity profiles. By leveraging these morphology-encoded performance variations, we achieved effective selective control and multitarget delivery of multiple MPMRs under uniform magnetic fields, both in vitro and ex vivo (gastrointestinal tissue). These findings provide a foundation for future designs of flexible millirobots in similar environments and serve as a reference for advancing selective control methods for multiple millirobots in uniform magnetic fields.