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 FeO nanoparticles. Solvent-casted polyvinyl alcohol/sodium carboxymethyl cellulose film is prepared as the substrate, and Fe ions are introduced to coordinate with carboxylate groups by surface treatment. Two processes, photo-reduction of Fe to Fe ions and the hydrolytic reaction of the two ions, are sequentially combined to in situ generate magnetic FeO particles. Spatiotemporal control of UV light irradiation determines the Fe/Fe ratio and, therefore the amount of generated FeO 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 Al-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.