A photosensitive hydrogel based on a combination of iron tetraoxide and polydopamine

Anisotropy can be effectively achieved with bilayer hydrogels, but the straightforward fabrication of actuated hydrogels with various stimulus responses is still difficult. This work describes the construction of temperature- and near-infrared light (NIR)-driven photosensitive bilayer hydrogels. In order to ensure that the prepared bilayers are tunable and have consistent mechanical properties, the bilayer hydrogels were prepared layer-by-layer, with poly(N-isopropylacrylamide) (PNIPAm) and poly(vinyl alcohol) (PVA) constructing the temperature-sensitive layer and poly(acrylamide) (PAAm) constructing the support layer. The highly effective photothermal conversion material Fe₃O₄@PDA, which has the best photothermal performance when the mass ratio of the two is 1:4, can be made by wrapping Fe₃O₄ in polydopamine (PDA). It was combined with the temperature-sensitive layer hydrogel to create a photosensitive hydrogel that could bend to 190° in 5 min when exposed to near-infrared light. The issue of the microscopic phase separation between Fe₃O₄ and the hydrogel is resolved by encapsulating Fe₃O₄ with PDA, which can make Fe₃O₄ uniformly disseminated in the hydrogel because it is not well diffused in the hydrogel. The photothermal effect is increased synergistically when the two are combined. Furthermore, it barely affects the hydrogel’s mechanical characteristics, which include a tensile strength of 27.65 kPa and a tensile strain of 253%. When exposed to laser light, the hydrogels demonstrated reversible bending motion. With the help of this creative method, remotely controllable light-responsive actuators may be made, creating new opportunities for applications in bioengineering and soft robotics.

Graphical Abstract