Photo-magnetically actuated variable-pitch soft propeller robot based on PNIPAM/MWCNTs composite hydrogel

A PNIPAM/MWCNTs composite hydrogel-based photo-magnetic variable-pitch soft propeller robot is fabricated. • Bis/PNIPAM ratio balances mechanics and thermo-swelling, 90° bending in 1.35 s. • 140° directional hydrogel deformation via rigid layer regulation and 55 °C pre-dehydration. • Three-bladed robot achieves full ink mixing in 23 s. We developed a photo-magnetically actuated soft propeller robot with variable-pitch capabilities specifically for microfluidic manipulation. The device is constructed from a PNIPAM/MWCNT composite hydrogel integrated with magnetic components. Its ternary structure successfully decouples magnetic rotational drive from photothermal pitch adjustments. Material optimization using 20% to 30% ethanol volume, 0.3 mm thickness, and a balanced crosslinker ratio ensured robust mechanical strength and thermo-responsive swelling. Leveraging rapid photothermal conversion, the hydrogel achieved a 90° bend in 1.35 s, and up to 140° of directional deformation when constrained by a pre-dehydrated rigid layer. Hydrodynamic evaluations showed that a three-bladed design surpassed a two-bladed alternative in both ascending efficiency and fluid flow stability. The robot achieved complete microfluidic mixing in just 23 s, outperforming conventional single-mode hydrogel propellers by 1.2 to 2.0 times. Ultimately, this comprehensive study provides a robust theoretical and experimental framework for successfully deploying photo-magnetically coupled soft robots in complex microenvironments.