From Hydrophilic to Superhydrophobic: Tuning Surface Wettability through Salvinia-Inspired Topographies.

The development of superhydrophobic surfaces traditionally relies on combining surface roughness with low-surface-energy coatings. In contrast, this work demonstrates the use of two-photon polymerization to induce superhydrophobicity on hydrophilic substrates solely through structural design. A comprehensive set of Salvinia-inspired microstructures was fabricated with precise control over geometrical features such as the number of arms, arm diameter, fill configuration, spacing, and height. Static contact angle measurements revealed that surface architecture plays a pivotal role in modulating wettability, with optimized structures achieving contact angles above 160° without any chemical modification. The study further investigates how morphological fidelity, governed by two-photon polymerization (TPP) printing parameters─specifically slicing distance and hatching distance─influences surface quality, roughness, and droplet behavior. Power spectral density analysis and 3D surface topography confirm that fabrication resolution critically impacts the performance of designed features. Finally, fabrication efficiency was evaluated in terms of areal fabrication rate, highlighting trade-offs among design complexity, printing resolution, and throughput. The results establish a set of design principles for achieving superhydrophobicity on hydrophilic materials and provide a scalable framework for future applications in microfluidics, biomimetics, and surface engineering where chemical-free wettability control is desired.