Superhydrophobic surfaces as bio-interfaces: linking Cassie-Baxter wetting and plastron stability to antibacterial and antibiofouling performance

Superhydrophobic surfaces, defined by water contact angles greater than 150°, exhibit extreme water repellency through a multifaceted mechanism involving low-surface-energy chemistry and hierarchical micro-nano structuring. This intricate design traps air beneath liquid droplets, thus producing strong water repellency. The Cassie-Baxter theory explains this behavior by modeling the interface as a composite of solid and air, which reduces liquid-solid contact and enables low adhesion, high drop mobility, and self-cleaning effects. In biofouling applications, plastron functions as an effective barrier layer, reducing contact between the solid surface and the aqueous medium that contains aggressive ions and microorganisms. A central challenge has been accurately measuring the solid-liquid area fraction. Recent advances have introduced simple, reliable, accessible, and rapid methods based on optical microscopy and drop adhesion force measurements. These approaches improve our ability to assess plastron stability, a key determinant of long-term performance, on short time scales. Despite substantial progress, long-term stability, particularly during immersion, remains a critical limitation, because performance depends on maintaining a stable plastron layer. Current research focuses on developing durable surface architectures, implementing scalable fabrication methods, and using environmentally sustainable materials. Overall, the field is moving toward multifunctional coatings that integrate fundamental theory with practical, real-world applications.