Wolfgang H. Goldmann

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.

Cassie-Baxter superhydrophobic surfaces repel aqueous media by trapping a thin air layer known as plastron. However, current methods to estimate plastron characteristics on such surfaces, either directly through digital still imaging/confocal microscopy or indirectly through contact angle goniometry, are technically challenging and often imprecise. Previously, we demonstrated that the solid-liquid area fraction, which quantifies the fraction of the solid surface that is in direct contact with the surrounding liquid, can be accurately measured by reflectance optical microscopy, provided that the material surface has approximately uniform local reflectivity. To eliminate the complexity associated with optical reflectance measurements, we recently demonstrated that the drop adhesion force correlates linearly with the solid-liquid area fraction. In this study, we advance the drop adhesion force measurements obtained at different environments, compression distances, and during pressurization-hold experiments to reveal whether the plastron sustains external pressure or undergoes gradual collapse. Here, we demonstrate that measuring drop adhesion force is a robust, rapid, and technically simple method for assessing plastron properties under a wide range of environmental and surface conditions. The proposed method provides information on plastron stability within minutes and thus could aid in the design of ultrarepellent surfaces with long-term stability in demanding applications.

Superhydrophobic surfaces have attracted considerable attention due to their remarkable ability to repel aqueous media by trapping an air layer. However, estimating the solid-liquid area fraction is challenging due to the complexity of their intrinsic properties and the limited resolution of methods for assessing contact area. We demonstrated that solid-liquid area fraction can be measured using reflectance optical microscopy, which provides a millimeter field of view with a micrometer lateral resolution. However, this method depends on the surface's optical characteristics. To simplify these measurements, this study examines the drop adhesive force as a means of quantifying solid-liquid area fraction. Utilizing a controlled experimental setup, we investigated the relationship between drop adhesive forces and solid-liquid area fraction. After considering various surface geometries obtained by laser and electrochemical treatments, we engineered 23 surfaces with solid-liquid area fractions ranging from 0.1% to ∼50%. Our results show that the adhesive force exerted by droplets on these surfaces increases linearly with the degree of air entrapment beneath the liquid. This provides a measurable indicator of their Cassie-Baxter superhydrophobicity. This research advances our fundamental understanding of plastron on superhydrophobic surfaces, facilitating the development of highly repellent, ultraslippery surfaces.

This commentary provides a comprehensive and forward‐looking analysis of biofouling and the development of antifouling technologies. It culminates in two innovative, non‐toxic approaches: aerophilic surfaces and liquid‐infused slippery surfaces (LISS/SLIPS).

Anodic titanium dioxide (TiO₂) nanotubes (NTs) are well-established implant coatings owing to their nanoscale tunability, osteogenic support, and long-term biocompatibility. However, reproducible approaches that directly link NT geometry with controlled antibacterial functionality and tunable ion release remain limited. Here, we present a spatially selective, geometry-defined copper (Cu) decoration strategy for morphology-defined spaced NTs with an intertube spacing of 70-214 nm and a diameter of ∼145 nm. These NTs were fabricated via fluoride-containing diethylene glycol-based anodization. Directional sputtering was used to deposit Cu as either conformal wall coatings, the common physical vapor deposition configuration, or as discrete top caps, perpendicular to the sputtering target configuration, thus enabling precise control of the Cu metal localization on/in the spaced NTs. Morphology-composition correlations, confirmed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and focused ion beam scanning electron microscopy (FIB-SEM), revealed a clear depth confinement for the cap-decorated NTs versus an extended distribution in the case of the conformal coatings. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) showed that ∼1 atom % Cu, the antibacterial/cytocompatibility threshold in the literature, generated sustained ion release with early bacterial suppression. Higher loadings accelerated Cu²⁺ release but produced variable long-term inhibition, which can be correlated with the Cu configuration type. This geometry-directed sputtering approach provides a reproducible route for spatially controlled Cu placement, with a link between NT geometry, Cu localization, and antibacterial behavior, thus applicable for designing future multifunctional implant surfaces with controlled therapeutic release. It also provides a reproducible strategy for designing future multifunctional, release-tunable implant surfaces.

Durotaxis, cell migration along stiffness gradients, is linked to embryonic development, tissue repair and disease. Despite solid in vitro evidence, its role in vivo remains largely speculative. Here we demonstrate that durotaxis actively drives disease progression in vivo in mouse models of lung fibrosis and metastatic pancreatic cancer. In lung fibrosis, durotaxis directs fibroblast recruitment to sites of injury, where they undergo mechano-activation into scar-forming myofibroblasts. In pancreatic cancer, stiffening of the tumour microenvironment induces durotaxis of cancer cells, promoting metastatic dissemination. Mechanistically, durotaxis is mediated by focal adhesion kinase (FAK)–paxillin interaction, a mechanosensory module that links stiffness cues to transcriptional programmes via YAP signalling. To probe this genetically, we generated a FAK-FAT^L994E knock-in mouse, which disrupts FAK–paxillin binding, blocks durotaxis and attenuates disease severity. Pharmacological inhibition of FAK–paxillin interaction with the small molecule JP-153 mimics these effects. Our findings establish durotaxis as a disease mechanism in vivo and support anti-durotactic therapy as a potential strategy for treating fibrosis and cancer.

Conventional Ag-decorated TiO₂ coatings suffer from low adsorption capacity and burst release kinetics, limiting long-term antibacterial efficacy and risking cytotoxicity. An entirely different payload release approach can be based on metal-organic frameworks (MOFs), which offer tunable porosity, high surface area, and internal diffusion channels. Here, we report a thermally stabilized Ti-based MOF [NH₂-MIL-125(Ti)] functionalized with Ag⁺ via reactive deposition, enabling high Ag loading (∼14.7 wt %) and sustained release. Annealing at 250 °C enhances aqueous stability, allowing diffusion-governed Ag⁺ delivery over >48 h, with 77% of the Ag still present in the MOF after a 24 h release. The system exhibits dose-dependent antibacterial activity in powders and comparable efficacy in coatings, with a more gradual release profile. This scalable platform is promising for long-acting coatings, wound interfaces, and implantable materials.

Traditional treatment of biofouling with toxic paints or antibiotics has significant limitations and challenges, including negative impacts on surrounding ecosystems and the emergence of resistant microbial strains. Antibiotics often prove ineffective in penetrating the dense and protective structure of biofilms, rendering traditional antimicrobial approaches less effective and leading to chronic infections. Toxic paints, while initially effective in reducing microbial colonization, contribute to long‐term environmental contamination and harm non‐target organisms. In contrast, novel technologies such as aerophilic surfaces, a special type of superhydrophobic surface, and liquid‐infused slippery surfaces offer promising alternatives to conventional biofilm management technologies. While aerophilic surfaces create a physical barrier that inhibits biofilm formation by reducing the direct contact of aqueous media with solid surfaces, liquid‐infused slippery surfaces enhance the anti‐biofouling effect by maintaining a protective lubricating layer that prevents organisms from settling. These nontoxic technologies not only provide a more sustainable and effective means of combating biofilms but also minimize the environmental impact associated with conventional treatments. By leveraging the unique properties of advanced materials, we can increase the durability and effectiveness of surfaces, leading to improved outcomes in various fields, including medical devices and marine applications.

The term "aerophilic surface" is used to describe superhydrophobic surfaces in the Cassie-Baxter wetting state that can trap air underwater. To create aerophilic surfaces, it is essential to achieve a synergy between a low surface energy coating and substrate surface roughness. While a variety of techniques have been established to create surface roughness, the development of rapid, scalable, low-cost, waste-free, efficient, and substrate-geometry-independent processes for depositing low surface energy coatings remains a challenge. This study demonstrates that fluorinated phosphate ester, with a surface tension as low as 15.31 mN m-1, can form a self-assembled monolayer on metal oxide substrates within seconds using a facile wet-chemical approach. X-ray photoelectron spectroscopy was used to analyze the formed self-assembled monolayers. Using nanotubular morphology as a rough substrate, we demonstrate the rapid formation of a superhydrophobic surface with a trapped air layer underwater.