Triple-Stimuli Responsive Soft Robots with Photo-Programmable Ferriferous Oxide Particle Patterns.

Magneto-driven soft robots featuring remote and highly permeable controllability are considered promising, especially in biomedical and engineering applications. However, there is still lack of a high-precision method to regulate the distribution of magnetic fillers in polymer substrates, which severely limits the improvement of the actuating functionality. This work provides a photo-regulatable method to develop soft robots with locally distributed magnetic Fe₃O₄ nanoparticles. Solvent-casted polyvinyl alcohol/sodium carboxymethyl cellulose film is prepared as the substrate, and Fe³⁺ ions are introduced to coordinate with carboxylate groups by surface treatment. Two processes, photo-reduction of Fe³⁺ to Fe²⁺ ions and the hydrolytic reaction of the two ions, are sequentially combined to in situ generate magnetic Fe₃O₄ particles. Spatiotemporal control of UV light irradiation determines the Fe³⁺/Fe²⁺ ratio and, therefore the amount of generated Fe₃O₄ nanoparticles that decide magnetic field, NIR light, and moisture responsive actuating functionalities. Moreover, the external geometry of the composite can be tuned by inducing the formation of Al³⁺-carboxylate coordinates for strain retention, which enables shape programming of the composite to exhibit complex 3D-3D actuating behaviors. The proposed method enables the design and preparation of soft robots with spatially tunable magnetism and more advanced actuating behaviors.