## 4 Passive Anti-Biofouling Nanoc Coatings
### Fouling Release Strategies
#### 4.2.2 Biomimetic Hierarchical Micro- and Nanostructured Superhydrophobic Surfaces
The surface below the droplet is completely wetted by the liquid. the assembly, and heat and pressure were applied. As a consequence, the nanoporous polycarbonate membrane adopted the dome-shaped microtopography of the aluminium mold, while the nanopores were filled up with the molten polypropylene. By this imprinting process, the hierarchical topographical features of the microdome patterned aluminum mold-nanoporous polycarbonate membrane template assembly were copied on the polypropylene film as an inverse replica. After demolding and etching of the polycarbonate membrane, hierarchically structured polypropylene films resembling the Lotus leaves surface topography comprising microdomes having diameters in the range from about 5 to about 400 \(\upmu\)m, heights in the range from about 2.5 to about 500 \(\upmu\)m, and pillars covering the domes with diameters in the range from about 20 nm to about 5 \(\upmu\)m and aspect ratios (height: diameter ratios) in the range from 2 to about 50 were prepared [142; 145]. Medical devices coated with such films displayed antifouling properties [145]. [PERSON] et al. [146] developed a new bottom-up approach to the fabrication of superhydrophobic surfaces by casting a solution of an elastomer, styrene-\(b\)-(ethylene-\(co\)-butylene)-\(b\)-styrene (SEBS), on different substrates (glass, polymer, metal) followed by evaporation of the solvent. Unlike most polymers used to fabricate superhydrophobic surfaces by casting methods, which are crystalline or plastic at room temperature, elastomers are amorphous and soft, comparatively presenting a much looser packing and consequently increased mobility of the polymer chains. Hence, the micro- and nanostructures formed during solvent evaporation are not stable and collapse. The novelty of the fabrication method proposed by the authors consists of the utilisation of a mixture of a polymer solvent and a polymer nonsolvent in an appropriate ratio to prepare the casting solution. More specifically, they used decanol and \(p\)-xylene as a nonsolvent, and respectively, as a solvent for the said SEBS elastomer. Since the nonsolvent has a higher boiling point (233 \({}^{\circ}\)C) than that of the solvent (137 \({}^{\circ}\)C), it tends to remain in the gel-like body of the elastomer during evaporation of the solvent. Therefore, it can act as a soft liquid template inducing aggregation and stabilising the SEBS micro- and nanostructures newly formed during the evaporation of the solvent. After eventual drying under vacuum, a solid superhydrophobic film having a porous, rough surface morphology was left on the substrate. The distribution and the size of the pores could be tuned by varying the solvent/nonsolvent ratio. The SEBS coatings cast from a 50:50 (\(v\)/\(v\)) mixture of \(p\)-xylene and decanol exhibited a contact angle of 156\({}^{\circ}\). For comparison, the pristine commercial SEBS elastomer with 29 wt.% styrene has a contact angle of only 96\({}^{\circ}\). Moreover, while the original elastomer had no significant antibiofouling properties, the superhydrophobic SEBS surfaces manufactured by this method completely inhibited the adhesion of both \(E\). _coli_ cells and platelets, as proved by SEM imaging [146]. Furthermore, the superhydrophobic SEBS coatings exhibited improved anticoagulant properties. The blood clotting time indexes (BCIs) on these surfaces had increased up to four times as compared to the corresponding BCIs on the pristine SEBS elastomer. They also showed good biocompatibility, the hemolysis ratio on the SEBS superhydrophobic coatings being up to eight-fold lower than that on the surface of the commercial SEBS elastomer [146]. However, the structured superhydrophobic surfaces in the Cassie-Baxter regime are prone to loss of their antibiofouling properties, especially under submerged conditions when an irreversible transition to the Wenzel state can easily occur.