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The design of autonomous, dynamically selfassembled robots that perform collective motion at the microscale can help in advancing the fundamental principles of self-assembly and coordinated behavior of complex structures. Here, we discuss the dissipative collective dynamics of soft colloidal micro-rotators driven by magnetic rotating fields with different orientation. The micro-rotators were polydimethylsiloxane microbeads with internally aligned magnetic nanoparticle chains, which respond to the torque created by rotating magnetic fields. The dynamic assembly patterns and their collective motion when actuated by in-plane and by transversal rotating fields were characterized. In all cases, we observed a rich variety of new modes of collective dynamics of the micro-rotor ensembles. We categorized these dynamics into three different types including caterpillar motion and cartwheel motion in case of a transverse-plane rotating field and gear-like motion in case of an in-plane field. The influence of field parameters such as rotational speed was studied. These fascinating dynamic patterns and motility modes could find application in future microrobots operating in complex biological fluids. 

The long-ranged interactions induced by magnetic fields and capillary forces in multiphasic fluid–particle systems facilitate the assembly of a rich variety of colloidal structures and materials. We review here the diverse structures assembled from isotropic and anisotropic particles by independently or jointly using magnetic and capillary interactions. The use of magnetic fields is one of the most efficient means of assembling and manipulating paramagnetic particles. By tuning the field strength and configuration or by changing the particle characteristics, the magnetic interactions, dynamics, and responsiveness of the assemblies can be precisely controlled. Concurrently, the capillary forces originating at the fluid–fluid interfaces can serve as means of reconfigurable binding in soft matter systems, such as Pickering emulsions, novel responsive capillary gels, and composites for 3D printing. We further discuss how magnetic forces can be used as an auxiliary parameter along with the capillary forces to assemble particles at fluid interfaces or in the bulk. Finally, we present examples how these interactions can be used jointly in magnetically responsive foams, gels, and pastes for 3D printing. The multiphasic particle gels for 3D printing open new opportunities for making of magnetically reconfigurable and “active” structures.