Mobile micro- and nanorobots are proposed for future biomedical applications, such as diagnostics and targeted delivery. For their translation to clinical practice, biocompatibility and biodegradability of micro- and nanorobots are required aspects. The fabrication of small-scale robots with non-cytotoxic biodegradable soft components will allow for enhanced device assimilation, optimal tissue interaction and minimized immune reactions. The 3D microfabrication of biodegradable soft helical microswimmers via two-photon polymerization of the non-toxic photocrosslinkable hydrogel gelatin methacryloyl (GelMA) is reported. GelMA microswimmers are fabricated with user-defined geometry and rendered magnetically responsive by decorating their surface with magnetic nanoparticles. In contrast to previous rigid helical microrobots, the soft helical microswimmers can corkscrew above the step-out frequency with relatively high values of forward velocity, suggesting an unprecedented self-adaptive behavior. Cytotoxicity assays show the toxicity of GelMA is at least three orders of magnitude lower than that of poly(ethyleneglycol) diacrylates, which are widely used for fabricating hydrogel-based microswimmers. GelMA microswimmers are fully degradable by collagenases. Furthermore, they support cell attachment and growth, and are gradually digested by cell-released enzymes during culture. These non-cytotoxic biodegradable hydrogel microswimmers will greatly expand their applications in medicine by eliminating the concerns of retrieving microrobots after fulfilling tasks in body.
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