4D printing of magneto-responsive polymer structures by masked stereolithography for miniaturised actuators

Masked stereolithography printing can be used to produce functionalised magneto-responsive polymer structures. Magnetic filler additivation of the photopolymer enables the production of powerful and fast soft robotics. However, current approaches require high filler concentrations, reducing the mechanical properties and compromising the processability. In this study, FeNi nanoparticles were added to a photopolymer to take advantage of their soft magnetic response and high magnetisation. Field-assisted printing gives rise to magnetic anisotropy by arranging laser-synthesised FeNi nanoparticles into uniaxial magnetic strands of up to 500 μm length. Favoured by the small size and even distribution of the nanoparticles, only 0.02 wt% are needed to detect magnetic responsivity. Thus, the impact on the mechanical property is reduced while facilitating the control over the composite magnetic properties. The practical feasibility of the composites is demonstrated by actuating gripper and impeller structures which offer possibilities in applications like drug delivery and tissue engineering.