Multi-Modal Droplet Manipulation on Laser-Patterned Stimulus-Responsive Gradient Surfaces: Enabling Anti-Gravity Climbing

This study demonstrated laser-ablated fabrication of multigradient bionic superhydrophobic surfaces (MGBs) on the Fe₃O₄@PDMS membrane, integrating passive structural gradients and active stimuli-responsiveness for droplet manipulation. Inspired by lotus-leaf superhydrophobicity and cactus-spine directional transport, laser-patterned MGBs achieve superhydrophobicity (contact angle ≈ 156°) with wedge-step structures. Silicone-oil-infused MGBs enable surface wettability switching to superslippery states, forming a conformal lubricating film enabling liquid-liquid slippage (superslippery SMGBs) with minimal sliding resistance (sliding angle < 3°). The platform combined passive Laplace pressure gradients with active magnetic/near-infrared responses to achieve multimodal control: static mode wedge wettability gradients enabled autonomous transport (peak velocity of 87.75 mm/s) and magnetic actuation reduced friction resistance caused by contact angle hysteresis (Δθ = 10°) through an asymmetrical wedge design, enabling long-distance transport of droplets. NIR triggered Marangoni flow drove droplets to achieve antigravity climbing on a 43° inclined surface (at a speed of 0.24 mm/s). The platform adapted to curved/irregular surfaces and overcame traditional single-mode limitations by synergizing a bioinspired design with magnetic/photothermal stimulation for self-propelled, gravity-defying microfluidic operations.