Transparent Light‐Driven Hydrogel Actuator Based on Photothermal Marangoni Effect and Buoyancy Flow for Three‐Dimensional Motion

Marangoni‐effect‐driven actuators (MDAs) have the advantages of direct light‐to‐work conversion and convenient operation, which makes it widely researched in the cutting‐edge fields including robots, micromachines, and intelligent systems. However, the MDA relies on the surface tension difference and it only works on the 2D liquid–air interface. Besides, the MDAs are normally pure black due to the light‐absorption material limitation. Herein, a transparent light‐driven 3D movable actuator (LTMA) and a 3D manipulation strategy are proposed. The LTMA is composed of photothermal nanoparticles‐doped temperature‐responsive hydrogel, whose surface energy changes as the nanoparticles absorb light energy. The 3D manipulation strategy combines Marangoni effect with photothermal buoyancy flow for realizing complex self‐propellant and floating/sinking motions. The LTMA can perform more advanced tasks such as 3D obstacle avoidance and 3D sampling. Benefiting from the porous structure of hydrogel, LTMA can naturally absorb the chemical molecules for remote sampling and automated drug delivery. The light‐driven, transparent, three‐dimensionally movable, and programmable actuator has promising prospects in the field of micromachines and intelligent systems. A transparent light‐driven 3D actuator (LTMA) is prepared using hydrogel and photothermal nanoparticles. The LTMA can not only realize the propulsion movements on the liquid‐air interface based on Marangoni effect but also can realize the floating/sinking motions based on the photo‐thermal buoyancy flow. The LTMA with programmable controllability has promising prospects in the field of micromachines and intelligent systems.