Droplet manipulation on smart slippery surface: From fabrication to applications

Droplet manipulation has attracted considerable interest due to its significant potential in various fields, such as microfluidics, biomedical detection, and energy harvesting. In particular, bio-inspired slippery surfaces integrated with smart materials have advanced intelligent droplet manipulation. They offer enhanced driving forces, low surface adhesion, and programmable multifunctionality. This review focuses on recent progress in droplet manipulation based on these smart slippery surfaces. This review first introduces the key concepts, fundamental design principles, and essential criteria for constructing slippery surfaces. It proceeds to discuss current fabrication strategies for porous substrates, as well as the selection criteria and properties of various lubricants. Subsequently, we systematically illustrate how smart slippery surfaces, under different external stimuli, can generate a wide variety of controllable driving forces. These driving forces enable sophisticated droplet manipulation behaviors, including directional transport, splitting, rotation, and bouncing. Additionally, we exemplify the emerging applications of droplet manipulation on smart slippery surfaces, including microreactors, water collection, triboelectric nanogenerators (TENGs) and digital microfluidics (DMF). Finally, we discuss the remaining scientific and technological challenges, and outline potential research directions for future developments. We hope this review will serve as a valuable reference to stimulate further research in the rapidly evolving field of smart slippery surface development and precise droplet control.