Fig. 1. Maintenance of swarm integrity at targeted junctions.

(A) Schematics illustrating the use of magnetic particle swarms to block the junctions inside a targeted region. (B) Schematic analysis of the forces exerted on tip-particles. The brown circles indicate magnetic particles. The black dashed circles denote the tip-particles. The magnetic interaction forces and their resultant interaction force are indicated by thin blue arrows and a thick blue arrow, respectively. The fluidic drag force and the reaction force are indicated by thick red arrows. γ is the branching angle of the junction. θ is the angle between the magnetic interaction force and the x axis. The configurations of particles at junctions with different branching angles are demonstrated in the green boxes. Purple regions represent the walls of junctions.