Fabrication of All‐Water‐Based Self‐Repairing Superhydrophobic Coatings Based on UV‐Responsive Microcapsules

Superhydrophobic coatings that are also self‐healing have drawn much attention in recent years for improved durability in practical applications. Typically, the release of the self‐healing agents is triggered by temperature and moisture change. In this study, UV‐responsive microcapsules are successfully synthesized by Pickering emulsion polymerization using titania (TiO₂) and silica (SiO₂) nanoparticles as the Pickering agents to fabricate all‐water‐based self‐repairing, superhydrophobic coatings. These coatings are environmentally friendly and can be readily coated on various substrates. Compared to conventional superhydrophobic coatings, these coatings can regenerate superhydrophobicity and self‐cleaning ability under UV light, mimicking the outdoor environment, after they are mechanically damaged or contaminated with organics. They can maintain the superhydrophobicity after multiple cycles of accelerated weathering tests.     

Versatile Nanocomposite Coatings with Tunable Cell Adhesion and Bactericidity

TiO₂‐Ag nanocomposites are known for their bactericidal effect during exposure to appropriate UV radiation. While involving hazardous radiation, and limited to accessible areas, the bactericidity of these coatings is not persistent in the absence of UV light, which impedes their commercial application. Herein it is shown that TiO₂‐Ag nanocomposites can be made highly bactericidal without the need of irradiation. Beyond this, bactericidity can even be mitigated in the presence of pre‐irradiated coatings. Biocompatibility and cell adhesion are also negligibly small for the as‐processed, non‐irradiated coatings, and become fairly high when the coatings are irradiated prior to testing. This opens the possibility to pattern the coatings into areas with high and low cell adhesion properties. Indeed by irradiating the coating through a mechanical mask it is shown that fibroblast cell adherence is sharply confined to the irradiated area. These properties are achieved using TiO₂‐Ag thin films with high silver loadings of 50 wt%. The films are processed on stainless steel substrates using solution deposition. Microstructural characterization by means of X‐ray diffraction, Raman, and X‐ray photoelectron spectroscopy, high‐resolution scanning electron microscopy, and atomic force microscopy show a highly amorphous TiO₂‐Ag_xO nanocomposite matrix with scattered silver nanoparticles. UV irradiation of the films results in the precipitation of a high density of silver nanoparticles at the film surface. Bactericidal properties of the films are tested on α‐haemolyzing streptococci and in‐vitro biocompatibility is assessed on primary human fibroblast cultures. The results mentioned above as to the tunable bactericidity and biocompatibility of the TiO₂‐Ag coatings developed herein, are amenable to silver ion release, to catalytic effects of silver nanoparticles, and to specific wettabilities of the surfaces.     

Mono‐Bisthienylethene Ring‐Fused versus Multi‐Bisthienylethene Ring‐Fused Photochromic Hybrids

Novel bisthienylethene‐based tetraazaporphyrin and phthalocyanine hybrids (BTE–TAPs) were prepared as photo‐switching molecules. All new compounds were characterized by mass spectrometry (MS), ¹H NMR spectroscopy, elemental analysis, UV‐vis absorption, and luminescence spectroscopy. All BTE–TAP compounds undergo open‐to‐closed and closed‐to‐open ring photoisomerizations in different quantum yields by irradiation with 365 nm or 730 nm light. The near‐IR luminescence of the hybrids can be regulated in a reversible manner by the photoisomerization of the bisthienylethene moiety. These compounds are useful as fluorescent probes and as non‐destructive readouts for erasable memory media. The phosphorescent BTE–TAP–Pt^II complex was also prepared, and its photochromism and changes in phosphorescence in a polycarbonate film were studied. These properties could give rise to other practical uses of BTE–TAP hybrids.     

Mussel Byssus‐Like Reversible Metal‐Chelated Supramolecular Complex Used for Dynamic Cellular Surface Engineering and Imaging

Inspired by the load‐bearing biostructures in nature, a multifunctional shell for encapsulating cell using the polyphenol–metal complexes is fabricated. The artificial shell is formed by cross‐linking of tannic acid and iron ion on cell surface. It can protect cells from unfriendly environments, including UV light irradiation and reactive oxygen damage. With the hybrid property of polyphenol and metal liands, the shell provides a versatile platform for cell surface engineering. The magnetic nanoparticles, DNA molecules, as well as the magnetic resonance imaging agents are easily incorporated into the shell. More interestingly, unlike the traditional passive coatings, here the shell can be controllably disassembled under external stimuli. The dynamic coating is used as a reversible element to regulate cell division and surface modification. The cell viability and protein expression experiments further confirm that the shell formation and degradation processes are biocompatible. This multifunctional coating strategy is applicable to multiple living cell types, including yeast cells, Escherichia coli bacteria, and mammalian cells. Therefore, this platform would be useful for living cell based fundamental research and biological applications.     

DNA/Tannic Acid Hybrid Gel Exhibiting Biodegradability,Extensibility, Tissue Adhesiveness,and Hemostatic Ability

DNA has emerged as a novel material in many areas of materials science due to its programmability. Especially, DNA hydrogels have been studied to incorporate new functions into gels. To date, only a few methods have been developed for fabricating DNA hydrogels, such as the use of complementary sequences or covalent bond. Herein, it is demonstrated that one of the most well‐known plant‐derived polyphenols, tannic acid (TA), can form a DNA hydrogel which is named TNA hydrogel ( T A + D NA ). TA plays a role as a “molecular glue” by a new mode of action reversibly connecting between phosphodiester bonds, which is different from the crosslinking utilizing complementary sequences. TA intrinsically degrades due to ester bonds connecting between pyrogallol groups, causing a degradable DNA hydrogel. Furthermore, TNA gel is multifunctional in that the gel is extensible upon pulling and adhesive to tissues because of the rich polyphenol groups in TA (ten phenols per TA). Unexpectedly, TNA gel exhibits superior in vivo hemostatic ability that can be useful for biomedical applications. This new DNA hydrogel preparation method represents a new technique for fabricating a large amount of DNA‐based hemostatic hydrogel without chemically modifying DNA or requiring the crosslinking by complementary sequences.     

Network Polydiacetylene Films: Preparation,Patterning, and Sensor Applications

The synthesis, characterization, and functionalization of polydiacetylene (PDA) networks on solid substrates is presented. A highly transparent and cross‐linked diacetylene film of DCDDA‐bis‐BA on a solid substrate is prepared first by tailoring the monomers with organoboronic acid moieties as pendant side groups and consequent drop‐casting and dehydration steps. Precisely controlled thermal curing plays a key role to obtain properly aligned diacetylene monomers that are closely packed between the boronic acid derived anhydride structures. A second cross‐linking, which occurs by polymerization of the diacetylene monomers with UV irradiation, induces a transparent to blue color shift. Accordingly, colored image patterns are readily available by polymerization through a photomask. The color change that takes place as a response to various organic solvents can be simply detected by naked eyes. The thermofluorescence change of PDA networks is demonstrated to be an effective method by which to obtain the microscale temperature distribution of thermal systems. The ease of film formation and stress‐induced blue‐to‐red color change with a simultaneous fluorescence generation features of the network structure should find a great utility in a wide range of chemical and thermal sensing platforms.     

Silver Nanoparticle Impregnated Polycarbonate Substrates for Surface Enhanced Raman Spectroscopy

The embedding of nanoscopic metal structures into polymeric matrices represents a convenient way to stabilise a controlled dispersion of protected nanoparticles whilst taking advantage of their physical characteristics. Supercritical carbon dioxide (scCO₂) has been used to produce silver nanoparticles in optically transparent polycarbonate (PC) matrices allowing fine scale dispersions of particles to be produced within a prefabricated polymer component. Characterization of these nanocomposites has been performed using transmission electron microscopy (TEM) and UV‐vis spectroscopy. The substrates give excellent responses in surface‐enhanced Raman spectroscopy (SERS) for both 4‐aminothiophenol and rhodamine 6G target molecules. They offer significant benefits over more conventional SERS substrates in that they are cheap, flexible, mechanically robust and temporally stable. Post‐processing the films via simple etching techniques, provides an additional degree of design control and the potential to fabricate devices with unique excitation and detection geometries for a wide range of applications.     

Vapor‐Based Initiator Coatings for Atom Transfer Radical Polymerization

A novel polymeric initiator coating for surface modification via atom transfer radical polymerization (ATRP) is reported. The synthetic approach involves the chemical vapor deposition of [2.2]paracyclophane‐4‐methyl 2‐bromoisobutyrate and can be applied to a heterogeneous group of substrates including stainless steel, glass, silicon, poly(dimethylsiloxane), poly(methyl methacrylate), poly(tetrafluoroethylene), and polystyrene. Surface analysis using X‐ray photoelectron spectroscopy and Fourier‐transformed infrared spectroscopy confirmed the chemical structure of the reactive initiator coatings to be consistent with poly[(p‐xylylene‐4‐methyl‐2‐bromoisobutyrate)‐co‐(p‐xylylene)]. Appropriate reactivity of the bromoisobutyrate side groups was confirmed by surface initiated atom transfer radical polymerization of a oligo(ethylene glycol) methyl ether methacrylate. After solventless deposition of the CVD‐based initiator coating, hydrogel films as thick as 300 nm could be conveniently prepared within a 24 h timeframe via ATRP. Moreover, the polymerization showed ATRP‐specific reaction kinetics and catalyst concentration dependencies. In addition, spatially controlled deposition of the initiator coatings using vapor‐assisted microstructuring in replica structures resulted in fabrication of spatially confined hydrogel microstructures. Both protein adsorption and cell adhesion was significantly inhibited on areas that were modified by surface‐initiated ATRP, when compared with unmodified PMMA substrates. The herein described initiator coatings provide a convenient access route to controlled radical polymerization on a wide range of different materials. While demonstrated only for a representative group of substrate materials including polymers, metals, and semiconductors, this method can be expected to be generically applicable – thereby eliminating the need for cumbersome modification protocols, which so far had to be established for each substrate material independently.     

Multifunctional Au‐Coated TiO2 Nanotube Arrays as Recyclable SERS Substrates for Multifold Organic Pollutants Detection

A multifunctional Au‐coated TiO₂ nanotube array is made via synthesis of a TiO₂ nanotube array through a ZnO template, followed by deposition of Au particles onto the TiO₂ surface using photocatalytic deposition and a hydrothermal method, respectively. Such arrays exhibit superior detection sensitivity with high reproducibility and stability. In addition, due to possessing stable catalytic properties, the arrays can clean themselves by photocatalytic degradation of target molecules adsorbed to the substrate under irradiation with UV light into inorganic small molecules using surface‐enhanced Raman spectroscopy (SERS) detection, so that recycling can be achieved. Finally, by detection of Rhodamine 6G (R6G) dye, herbicide 4‐chlorophenol (4‐CP), persistent organic pollutant (POP) dichlorophenoxyacetic acid (2,4‐D), and organophosphate pesticide methyl‐parathion (MP), the unique recyclable properties indicate a new route in eliminating the single‐use problem of traditional SERS substrates and show promising applications for detecting other organic pollutants.     

Sample Target Substrates with Reduced Spot Size for MALDI‐TOF Mass Spectrometry Based on Patterned Self‐Assembled Monolayers

The wetting properties of structured self‐assembled monolayers are used to fabricate sample target substrates for MALDI‐TOF mass spectrometry. Combining the advantages of a hydrophobic‐hydrophilic surface pattern and the possibility of obtaining micrometer patterns allows an increase in the sensitivity of MALDI‐TOF mass spectrometry analysis and a reduction in the traceable concentration down to fmol µL^?1. This easy, cheap and fast patterning process provides substrates that allow sensitive, high‐resolution mass spectrometry of dilute solutions.     

Arsonic Acid Self‐Assembled Monolayers Protect Oxide Surfaces from Micronewton Nanomechanical Forces

The development of new surface coatings is critical for combating wear and increasing the device lifetime in microelectromechanical systems (MEMS). Here, a class of arsonic acid self‐assembled monolayers (SAMs) is reported that form readily on oxide substrates including silicon oxide, borosilicate glass, and titanium oxide. Monolayers are easily prepared using a straightforward soaking technique, which is amenable to large‐scale commercial applications. Monolayer formation on borosilicate glass and titanium oxide is characterized using infrared spectroscopy. Monolayers on borosilicate glass, native silicon oxide and titanium oxide are evaluated with contact angle measurements, as well as wear measurements using nanoscratching experiments. On titanium oxide and borosilicate glass, monolayers prepared from hexadecylarsonic acid provide significantly greater surface protection than surfaces reacted under similar conditions with hexadecylphosphonic acid, a common modifying agent for oxide substrates.     

3D π‐Conjugated Oligothiophenes Based on Sterically Twisted Bithiophene Nodes

3D conjugated architectures consisting of short oligothiophene chains attached to a connecting node formed by a sterically twisted bithiophenic system have been synthesized by various combinations of bromination and organometallic couplings. The analysis of the electronic properties of these systems by UV‐vis absorption spectroscopy and cyclic voltammetry shows that the effective conjugation length depends on the twist angle in the central bithiophene node and on the number, length, and composition of the conjugated branches. A first evaluation of the potential of this new class of compounds for the realization of organic solar cells has been carried out. To this end two prototype bulk heterojunctions based on two representative compounds as donors and [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) as acceptor have been realized. A short‐circuit current density of 1.33 mA cm^–2 and a power conversion efficiency of 0.20 % have been measured under AM 1.5 (air‐mass 1.5) simulated solar irradiation.     

Nanoporous Ultra‐Low‐Dielectric‐Constant Fluoropolymer Films via Selective UV Decomposition of Poly(pentafluorostyrene)‐block‐Poly(methyl methacrylate) Copolymers Prepared Using Atom Transfer Radical Polymerization

Block copolymers of poly(pentafluorostyrene) (PFS) and poly(methyl methacrylate) (PMMA) (PFS‐b‐PMMA) have been synthesized using atom transfer radical polymerization (ATRP). Then, nanoporous fluoropolymer films have been prepared via selective UV decomposition of the PMMA blocks in the PFS‐b‐PMMA copolymer films. The chemical composition and structure of the PFS homopolymers and copolymers have been characterized using nuclear magnetic resonance (NMR) spectroscopy, thermogravimetric analysis (TGA), X‐ray photoelectron spectroscopy (XPS), time‐of‐flight secondary‐ion mass spectrometry (ToF‐SIMS), and molecular‐weight measurements. The cross‐sectional and surface morphologies of the PFS‐b‐PMMA copolymer films before and after selective UV decomposition of the PMMA blocks have been studied using field‐emission scanning electron microscopy (FESEM). The nanoporous fluoropolymer films with pore sizes in the range 30–50 nm and porosity in the range 15–40 % have been obtained from the PFS‐b‐PMMA copolymers of different PMMA content. Dielectric constants approaching 1.8 have been achieved in the nanoporous fluoropolymer films which contain almost completely decomposed PMMA blocks.     

A Unique Disintegration–Reassembly Route to Mesoporous Titania Nanocrystalline Hollow Spheres with Enhanced Photocatalytic Activity

A novel disintegration–reassembly route is reported for the synthesis of mesoporous TiO₂ nanocrystalline hollow spheres with controlled crystallinity and enhanced photocatalytic activity. In this unique synthesis strategy, it is demonstrated that sol–gel‐derived mesoporous TiO₂ colloidal spheres can be disintegrated into discrete small nanoparticles that are uniformly embedded in the polymer (polystyrene, PS) matrix by surface‐induced photocatalytic polymerization. Subsequent reassembly of these TiO₂ nanoparticles can be induced by an annealing process after further coating of a resorcinol–formaldehyde (RF) resin, which forms self‐supported hollow spheres of TiO₂ at the PS/RF interface. The abundant phenolic groups on the RF resin serve as anchoring sites for the TiO₂ nanoparticles, thus enable the reassembly of the TiO₂ nanoparticles and prevent their sintering during the thermal crystallization process. This unique disintegration–reassembly process leads to the formation of self‐supported TiO₂ hollow spheres with relatively large surface area, high crystallinity, and superior photocatalytic activity in dye degradation under UV light irradiation.     

Plant‐Inspired Pyrogallol‐Containing Functional Materials

Pyrogallol‐containing molecules are ubiquitous in the plant kingdom. The chemical synthesis of these molecules remains challenging. Thus, they are obtained via purification from heterogeneous mixtures of plant extracts. Previous studies have focused on their biological roles, such as antioxidants. Additionally, the molecules are used as ink colorants and in tanning processes for leather. Recently, many disciplines have paid attention to adhesiveness of pyrogallol‐containing molecules, including the control of interface properties in energy storage/generation and medical devices, as well as the changes in wettability related to membrane technologies. In particular, pyrogallol‐containing molecules act as “molecular glues,” binding to virtually all biomacromolecules, for example, DNA/RNA, soluble proteins, insoluble extracellular matrices, and peptides. Furthermore, the cohesion of pyrogallol by forming pyrogallol‐to‐pyrogallol covalent bonds is useful for the preparation of bulk hydrogels and thin films. The content of this review focuses on interactions with biomacromolecules used as molecular glues, used as modifiers in material‐independent surface chemistry, and applied as chemical moieties to form covalent linkages to fabricate hydrogels and related biomaterials. Future perspectives include the development of new pyrogallol‐containing materials, the understanding of chirality in adhesion, and the improvement of the mechanical stability for applications in various biomedical, energy, and industrial devices.     

Void Engineering in Metal–Organic Frameworks via Synergistic Etching and Surface Functionalization

The rational design and engineering of metal–organic framework (MOF) crystals with hollow features has been used for various applications. Here, a top‐down strategy is established to construct hollow MOFs via synergistic etching and surface functionalization by using phenolic acid. The macrosized cavities are created inside various types of MOFs without destroying the parent crystalline framework, as evidenced by electron microscopy and X‐ray diffraction. The modified MOFs are simultaneously coated by metal–phenolic films. This coating endows the MOFs with the additional functionality of responding to near infrared irradiation to produce heat for potential photothermal therapy applications.     

Tissue Tapes—Phenolic Hyaluronic Acid Hydrogel Patches for Off‐the‐Shelf Therapy

Hydrogels have been applied to improve stem cell therapy and drug delivery, but current hydrogel‐based delivery methods are inefficient in clinical settings due to difficulty in handling and treatment processes, and low off‐the‐shelf availability. To overcome these limitations, an adhesive hyaluronic acid (HA) hydrogel patch is developed that acts as a ready‐to‐use tissue tape for therapeutic application. The HA hydrogel patches functionalized with phenolic moieties (e.g., catechol, pyrogallol) exhibit stronger tissue adhesiveness, greater elastic modulus, and increased off‐the‐shelf availability, compared with their bulk solution gel form. With this strategy, stem cells are efficiently engrafted onto beating ischemic hearts without injection, resulting in enhanced angiogenesis in ischemic regions and improving cardiac functions. HA hydrogel patches facilitate the in vivo engraftment of stem cell–derived organoids. The off‐the‐shelf availability of the hydrogel patch is also demonstrated as a drug‐loaded ready‐made tissue tape for topical drug delivery to promote wound healing. Importantly, the applicability of the cross‐linker‐free HA patch is validated for therapeutic cell and drug delivery. The study suggests that bioinspired phenolic adhesive hydrogel patches can provide an innovative method for simple but highly effective cell and drug delivery, increasing the off‐the‐shelf availability—a critically important component for translation to clinical settings.     

Oligophenylenevinylenes in Spatially Confined Nanochannels: Monitoring Intermolecular Interactions by UV/Vis and Raman Spectroscopy

Perhydrotriphenylene‐based channel‐forming inclusion compounds (ICs) and thin films made of polyphenylenevinylene (PPV)‐type oligomers with terminal alkoxy groups are investigated and compared in a combined experimental and theoretical approach. Interchromophore interactions and host‐guest interactions are elucidated by UV/Vis and Raman spectroscopy. The impact of the local environment of the chromophore on the optical and photophysical properties is discussed in light of quantum‐chemical calculations. In stark contrast to thin films where preferential side‐by‐side orientation leads to quenching of photoluminescence (PL) via non‐emissive traps, the ICs are found to be attractive materials for opto‐electronic applications: they offer high chromophore concentrations, but at the same time behave as quasi‐isolated entities of tightly packed, well‐oriented objects with high PL quantum yields and the possibility of color tuning.     

Inkjet‐Printable Amphiphilic Polydiacetylene Precursor for Hydrochromic Imaging on Paper

Hydrochromic materials find great utility in a wide range of applications including humidity sensing and measuring the water contents of organic solvents, as well as substrates for rewritable paper and human sweat pore mapping. Herein, an inkjet printable diacetylene (DA) is described that can be transformed by UV irradiation to a hydrochromic‐conjugated polymer on conventional paper. Specifically, an amphiphilic DA that contains an ­imidazolium ion head‐group is found to be compatible with a common office inkjet printer. Various computer‐designed images are printed on paper using this substance. UV irradiation of the printed images results in the generation of blue‐colored images associated with formation of a polydiacetylene (PDA). The resolutions of the images are almost identical to those generated using a conventional black ink. Importantly, the printed images undergo a blue‐to‐red color change upon exposure to water and the hydrochromism is found to be temperature dependent. The facile color change that occurs near body ­temperatures enables use of the hydrochromic PDA‐coated paper for rapid and precise mapping of human sweat pores from fingers, palms, and feet.     

Light‐Induced Swelling‐Responsive Conductive,Adhesive, and Stretchable Wireless Film Hydrogel as Electronic Artificial Skin

Light‐induced wireless soft electronic skin hydrogels with excellent mechanical and electronic properties are important for several applications, such as soft robotics and intelligent wearable devices. Precise control of reversible stretchability and capacitive properties depending on intermolecular interaction and surface characteristics remains a challenge. Here, a thin‐film hydrogel is designed based on titanium oxide (TiO₂) polydopamine–perfluorosilica carbon dot‐conjugated chitosan–polyvinyl alcohol‐loaded tannic acid with controllable hydrophobic–hydrophilic transition in the presence of UV–vis light irradiation. The shifting of surface wettability from hydrophobic to hydrophilic by irradiation affects thin‐film water permeability and swelling ratio. This allows the penetration of water into the matrix to change its mechanical strength, electronic properties, and adhesive behavior. Specifically, the hydrogel displays mechanical strain as high as 278% in response to light stimuli and demonstrates the ability to regain its initial state determining the elasticity of the fabricated material. Moreover, the thin‐film hydrogel shows an increase in conductivity to 1.096 × 10^?3 and 1.026 × 10^?3 S cm^?1 when irradiated with UV and visible light, respectively. The hydrogel exhibits capacitive reversibility that follows finger motion which can be identified directly or remotely using wireless connection, indicative of its possible applications as an artificial electronic skin.