Collective climbing of colloidal swarms on the vertical wall.

Self-assembled colloidal swarms capable of climbing vertical walls, navigating complex geometries, and operating in confined spaces hold immense promise for emerging biomedical applications. However, harnessing this potential remains challenging as the fundamental mechanisms governing collective behaviors on vertical planes are not yet fully understood. Here, we report the self-assembly of magnetic colloidal particles into swarms that can climb vertical walls. The collective climbing behavior arises from the density-dependent velocity of the particles and their specific magnetic interactions on vertical surfaces. The resulting self-assembled wall-climbing swarm exhibits fingering instabilities at its leading edge and demonstrates both passive deformability in response to environmental constraints and active controllability. Our findings advance the understanding of collective behavior in active matter systems and nonequilibrium self-assembly in complex geometries, offering insights relevant to targeted drug delivery and the design of intelligent, soft materials.