Malonic Acid Diazoesters for C−H Insertion Crosslinking (CHic) Reactions: A Versatile Method for the Generation of Tailor-Made Surfaces

Brush-Like Interface on Surface-Attached Hydrogels Repels Proteins and Bacteria

Interfacing artificial materials with biological tissues remains a challenge. The direct contact of their surface with the biological milieu results in multiscale interactions, in which biomacromolecules adsorb and act as transducers mediating the interactions with cells and tissues. So far, only antifouling polymer brushes have been able to conceal the surface of synthetic materials. However, their complex synthesis has precluded their translation to applications. Here, we show that ultra-thin surface-attached hydrogel coatings of N-(2-hydroxypropyl) methacrylamide (HPMA) and carboxybetaine methacrylamide (CBMAA) provided the same level of protection as brushes. In spite of being readily applicable, these coatings prevented the fouling from whole blood plasma and provided a barrier to the adhesion of Gram positive and negative bacteria. The analysis of the components of the surface free energy and nanoindentation experiments revealed that the excellent antifouling properties stem from the strong surface hydrophilicity and the presence of a brush-like structure at the water interface. Moreover, these coatings could be functionalized to achieve antimicrobial activity while remaining stealth and non-cytotoxic to eukaryotic cells. Such level of performance was previously only achieved with brushes. Thus, we anticipate that this readily applicable strategy is a promising route to enhance the biocompatibility of real biomedical devices. This article is protected by copyright. All rights reserved.

Smooth and Transparent Films Showing Paradoxical Surface Properties: The Lower the Static Contact Angle, the Better the Water Sliding Performance

Smooth and transparent hydrophilic films showing excellent water sliding properties were prepared by using a sol-gel solution of 2-[methoxy (ethyleneoxy)₁₀ propyl]trimethoxysilane and tetraethoxysilane. The resulting hybrid films were statically hydrophilic (static water contact angles (CAs) were in the range of 30-45°), but water droplets (50 μL) could move smoothly on an inclined surface (minimum sliding angle was 6°) without pinning or tailing because of low CA hysteresis (5 ± 1°). Thanks to this hybrid film formation on aluminum (Al) substrate, drainage performance during condensation and frosting/defrosting markedly improved compared to that on hydrophilic, bare Al, or hydrophobic monolayer-covered Al substrates.

Extending the Lotus Effect: Repairing Superhydrophobic Surfaces after Contamination or Damage by CHic Chemistry

Superhydrophobic surfaces have gained a reputation to show a self-cleaning behavior ("Lotus effect") as drops rolling off the surface take along loosely adhering dust particles. However, this self-cleaning process reaches its limits when such surfaces are brought in contact with sticky contaminants such as oils and smaller particles. Once intimate contact is established between the surface and a small particle, it will be almost impossible to remove it because of strong surface interactions. Such contaminations, however, lead to contact line pinning and destroy the superhydrophobic effect. Because the fragility of the micro- and nanostructures prohibits any mechanical cleaning, the sample is usually doomed. Here, we report a universal method for restoring superhydrophobicity: by simple dip-coating, a conformal ultrathin layer (≈10 nm) of a highly hydrophobic and photoreactive fluoropolymer is deposited. Through short UV irradiation (5 min), this thin layer is cross-linked and chemically attached to the underlying surface by C,H-insertion cross-linking, thus covering the contaminant like a thin veil. We use this "cover-up" strategy of masking the contaminants to restore superhydrophobicity. We demonstrate this principle by deliberately soiling the surface with various model contaminants, such as oily substances and particles, and study the repair process.

"Nickel Nanoflowers" with Surface-Attached Fluoropolymer Networks by C,H Insertion for the Generation of Metallic Superhydrophobic Surfaces

Metallic superhydrophobic surfaces (SHSs) combine the attractive properties of metals, such as ductility, hardness, and conductivity, with the favorable wetting properties of nanostructured surfaces. Moreover, they promise additional benefits with respect to corrosion protection. For the modification of the intrinsically polar and hydrophilic surfaces of metals, a new method has been developed to deposit a long-term stable, highly hydrophobic coating, using nanostructured Ni surfaces as an example. Such substrates were chosen because the deposition of a thin Ni layer is a common choice for enhancing corrosion resistance of other metals. As the hydrophobic coating, we propose a thin film of an extremely hydrophobic fluoropolymer network. To form this network, a thin layer of a fluoropolymer precursor is deposited on the Ni substrate which includes a comonomer that is capable of C,H insertion cross-linking (CHic). Upon UV irradiation or heating, the cross-linker units become activated and the thin glassy film of the precursor is transformed into a polymer network that coats the surface conformally and permanently, as shown by extensive extraction experiments. To achieve an even higher stability, the same precursor film can also be transformed into a chemically surface-attached network by depositing a self-assembled monolayer of an alkane phosphonic acid on the Ni before coating with the precursor. During cross-linking, by the same chemical process, the growing polymer network will simultaneously attach to the alkane phosphonic acid layer at the surface of the metal. This strategy has been used to turn fractal Ni "nanoflower" surfaces grown by anisotropic electroplating into SHSs. The wetting characteristics of the obtained nanostructured metallic surfaces are studied. Additionally, the corrosion protection effect and the significant mechanical durability are demonstrated.