Encoded Magnetization for Programmable Soft Miniature Machines by Covalent Assembly of Modularly Coupled Microgels

The bottom-up assembly of premagnetized microgels offers remarkable flexibility in programmability, material selection, and complexity for fabricating programmable magnetic soft machines with discrete 3D magnetization profiles. However, the current microgel bonding encounters challenges due to the utilization of adhesives for attachment, biocompatibility for in vivo applications, and the need for elevated temperature for self-healing materials. Here, an approach is presented that leverages N-hydroxysuccinimide ester-activated sodium alginate (SA-NHS) and chitosan (CS) to form modular gels for on-demand assembly through covalent bonding, yielding a tough and durable interface. Photolithography-based patterning and magnetic maneuverability are imparted by introducing poly(ethylene glycol) diacrylate and ferromagnetic particles into SA-NHS or CS, resulting in the creation of modularized magnetic or nonmagnetic microgels. Different magnetization profiles of the modular microgel can be achieved by magnetizing the ferromagnetic particles inside the microgel. To prove the versatility of the proposed method, several programmable magnetic soft machines are developed for various application scenarios, including heterogeneous cell-laden hydrogel assemblies, multisegmented magnetic soft swimmers, programmable magnetic switches for electric circuits, and magnetically triggered release from drug-encapsulated magnetic capsules. This proposed approach holds great potential to engineer highly intricate and hierarchical architectures, enhancing the functionality, versatility, and adaptability of programmable soft machines. An encoded magnetization approach that leverages N-hydroxysuccinimide ester-activated sodium alginate and chitosan is developed to form modular gels for on-demand assembly through covalent bonding. A tough and durable interface is formed after bonding. Different magnetization profiles are obtained by pre-magnetizing the microgels along different orientations. Several programmable miniature machines are developed through covalent bonding.image