Hydrogel microrobots for water purification: A bio-inspired review of functional components and mechanisms

This article introduces and explains the functional components of hydrogel microrobots by using metaphorical approaches. Hydrogel microrobots represent a new generation of microscale robotic systems that utilize the unique properties of stimulus-responsive hydrogels to exhibit diverse capabilities, including targeted movement, sensing, adsorption, and degradation of pollutants, as well as the transport and release of beneficial ions and disinfectants. Comparing the functional parts of these microrobots with the organs of living organisms provides insight into their complex mechanisms of operation and can inspire innovative design. Hydrogel-based microrobots, which combine material intelligence, nanotechnology, and environmental engineering, offer a cutting-edge approach to water pollution management. This review examines locomotion mechanisms, stimulus-responsive designs, and advanced applications of hydrogel microrobots for removing emerging pollutants. Reported performances include MXene-based hydrogel microrobots adsorbing over 60% of dye contaminants within 2 min and ultimately achieving >90% removal, thermosensitive magnetic microrobots removing >94% of Pb (II) and arsenic, hierarchically structured hydrogel actuators capturing 94.63% of microplastics, and photoresponsive hydrogel microrobots degrading >90% of antibiotics or organic dyes. Despite persistent challenges in scalability, robustness in complex matrices, and real-world deployment, these quantitative achievements underscore the transformative potential of hydrogel microrobots as active platforms for water purification and environmental remediation.