Magnetic-field-driven ultra-small 3D hydrogel microstructures: Preparation of gel photoresist and two-photon polymerization microfabrication

摘要

In the biomedical micro-electromechanical systems (MEMS) field, the fabrication of three-dimensional (3D) magnetic hydrogel microdevices and microactuators with sizes smaller than 100 μm is difficult. In this paper, magnetic-field-driven 3D hydrogel microstructures were fabricated through four steps: the synthesis of surface-modified Fe3O4nanoparticles (Fe3O4NPs), the preparation of a magnetic gel photoresist, two-photon polymerization microfabrication, and a solvent-exchange process. For the preparation of a stable magnetic gel photoresist, surface-modified Fe3O4NPs with an average size of 7.8 nm were synthetized and well dispersed in gel photoresist. The magnetic gel photoresist exhibited a good UV photopolymerization effect, and a magnetic-field-driven macroscopic hydrogel was prepared. The two-photon polymerization properties of gel photoresists with various Fe3O4NP contents were investigated in detail, and the minimum width of fabricated lines reached 106 nm for the photoresist with 0.32 wt% Fe3O4NPs. Three hydrogel microstructures—the Qingdao University logo, a magnetically actuated micro-rod, and a magnetically actuated micro-nail—were successfully fabricated using a gel photoresist with 0.96 wt% Fe3O4NPs. Importantly, obvious and reversible external-magnetic-field-driven bending behavior of the 3D hydrogel micro-nail with a size of 10 μm was observed.