Abstract: Fog collection offers a promising route to mitigating global water scarcity, particularly in arid and coastal regions, yet its practical efficiency is often limited by sluggish droplet capture and transport. Developing surfaces that enable rapid, directional droplet motion while retaining long-term stability and self-cleaning capability remains a critical challenge. Here, inspired by cactus spines and spider silk, we report a Superhydrophilic Gradient Surfaces (SHLGS) fabricated via a simple and scalable combination of 3D printing and spray coating. The wave-like spindle architecture extends the three-phase contact line, enhancing droplet capture and retention, while the superhydrophilic gradient drives spontaneous, directional droplet transport. Energy released during droplet coalescence and deformation further accelerates droplet motion, continuously refreshes the surface, and markedly improves collection efficiency. Consequently, the SHLGS achieves a fog collection rate of up to 18 g cm-2 h-1, together with excellent structural stability and robust self-cleaning performance under prolonged operation. This work establishes a scalable, bio-inspired surface design strategy for efficient fog harvesting and directional liquid transport, with broad implications for water-harvesting and functional surface engineering.

Key words: Biomimetic surface')">Biomimetic surface, 3D printing, Superhydrophilic gradient surface, Efficient fog collection, Directional transport