Magnetic Responsive Hydrogel Beads for Efficient Droplet Manipulation on Superhydrophobic Platforms

Efficient directional fluid transport is widely demanded, such as fog water collection, microfluidics and drug delivery. Externally magnetically responsive droplet drivers are extensively studied, but previous magnetic drivers have faced difficulties in regulation and relatively low efficiency. This work is inspired by the shrimps on lotus leaves. Polyvinyl alcohol (PVA) and sodium alginate (SA) are used to form spheres through crosslinking in calcium ions and incorporated Fe₃O₄ to endowed them with magnetism. A PVA/SA@Fe₃O₄ hydrogel bead actuator is prepared to drive droplets on superhydrophobic interfaces. The hydrogel beads are characterized by SEM, FTIR, XPS, and VSM. The transport speed and volume of droplets driven by the hydrogel beads are tested, showing performance improvements compared to other actuators. The tests reflected its ability to rapidly transport 100 µL droplets (≈200 mm s^-1) and manipulate large volumes (≈1200 µL). Meanwhile, the magnetic hydrogel beads are able to drive in various media, opening up more application possibilities for the magnetic hydrogel bead robots.