Intelligent behaviors of hydrogel and liquid crystalline polymer aggregations and collectives: a mini-review

Responsive materials exhibit intelligence through their intrinsic ability to autonomously sense and respond to external stimuli. These materials have the potential to form robotic swarms characterized by high flexibility, robust scalability, and fault tolerance. Among various responsive materials, hydrogels and liquid crystalline polymers (LCPs) are particularly advantageous due to their capability for reversible morphological transformations in response to external stimuli, including light, heat, electric field, and magnetic field. While numerous reviews have summarized magnetic swarm robotics, a comprehensive analysis of swarm aggregation behaviors in hydrogel- and liquid crystal-based polymer systems remains lacking. This review addresses this gap by examining (sub)millimeter-scale swarm robots, the fundamental mechanical properties of hydrogels and LCPs following aggregation and assembly, and the respective advantages and limitations of these materials in swarm robotics. Additionally, future research directions in this emerging field are discussed.