Gallol-Rich Hyaluronic Acid Hydrogels: Shear-Thinning, Protein Accumulation against Concentration Gradients, and Degradation-Resistant Properties

We report the multifunctionality of a small adhesive functional group called gallol (three hydroxyls attached to benzene), which is the ubiquitous moiety found in many vegetables and fruits. First, the chemical tethering of gallols to a polysaccharide backbone and the addition of another gallol-rich compound, oligo-epigallocatechin gallate, result in the spontaneous gelation of the hyaluronic acid-gallol, and the cross-linking is due to the extensive level of hydrogen bond formations from both gallol-to-gallol and gallol-to-hyaluronic acid. Second, we found that the gallol-involved cross-linking is reversible, resulting in a shear-thinning effect of the hyaluronic acid-gallol hydrogels, allowing this hydrogel system to be injectable. Third, due to gallol’s superior ability to bind proteins via noncovalent interactions, the hyaluronic acid-gallol hydrogels exhibit spontaneous loading of proteins from a buffer solution to the hydrogel inside against the concentration gradient (i.e., active entrapment phenomenon). By simply dipping the gels into a protein-containing solution (270 μg/mL), approximately 93% of the total proteins is actively entrapped into the gels. Furthermore, the protein affinity of the gallols is useful for physically immobilizing the degradation enzyme, hyaluronidase, to prevent the rapid, uncontrolled degradation of the gallol-rich hyaluronic acid gels

Fabrication of a Micro-omnifluidic Device by Omniphilic/Omniphobic Patterning on Nanostructured Surfaces

We integrate the adhesive properties of marine mussels, the lubricating properties of pitcher plants, and the nonfouling properties of diatoms into nanostructured surfaces to develop a device called a micro-omnifluidic (μ-OF) system to solve the existing challenges in microfluidic systems. Unlike conventional poly(dimethylsiloxane)-based fluidic systems that are incompatible with most organic solvents, the μ-OF system utilizes a variety of solvents such as water, ethanol, dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, <i>n</i>-hexane, 1,2-dichloroethane, acetic acid, 2-propanol, acetone, toluene, diesel oil, dioxane, gasoline oil, hexadecane, and xylene. The μ-OF system is based on a phenomenon called microchannel induction that spontaneously occurs when virtually all droplets of solvents are applied on omniphilically micropatterned regions of a slippery liquid-infused porous surface. Any solvents with surface tension greater than that of the lubricant (17.1 mN/m, Fluorinert FC-70) are able to repel the infused lubricant located on top of the omniphilic microlines, triggering controlled movement of the droplet by gravity along the microlines. We also demonstrated that the μ-OF system is reusable by the nonadsorption properties of the silicified layer. Due to the organic solvent compatibility, we were able to perform organic reactions with high portability and energy efficiency in operation

Phenolic Pyrogallol Fluorogen for Red Fluorescence Development in a PAS Domain Protein

Phenolic Pyrogallol Fluorogen for Red Fluorescence Development in a PAS Domain Protei

Role of Dopamine Chemistry in the Formation of Mechanically Strong Mandibles of Grasshoppers

Role of Dopamine Chemistry in the Formation of Mechanically Strong Mandibles of Grasshopper

Wisdom from the Human Eye: A Synthetic Melanin Radical Scavenger for Improved Cycle Life of Li–O₂ Battery

Li–O₂ batteries are attractive systems because they can deliver much higher energy densities than those of conventional lithium-ion batteries by engaging light gas-phase oxygen as a cathode active material. However, the inevitable generation of residual superoxide radicals gives rise to irreversible side reactions and consequently causes severe capacity degradation over cycling. To address this chronic issue, herein, we have taken a lesson from the human eye. Analogous to Li–O₂ batteries, the human eye is liable to attack by reactive oxygen species (ROS), from its lifetime exposure to sunlight. However, it protects itself from the ROS attack by using melanin as a radical scavenger. To mimic such a defense mechanism against radical attack, we included polydopamine (pD), which is one of the most common synthetic melanins, in the ether-based electrolyte. As an outcome of the superoxide radical scavenging by the pD additive, the irreversible side reaction products were alleviated significantly, resulting in superior cycling performance. The present investigation provides a message that simple treatments inspired by the human body or nature could be effective solutions to the problems in various energy devices

Bioinspired Templating Synthesis of Metal–Polymer Hybrid Nanostructures within 3D Electrospun Nanofibers

Novel metal nanostructures immobilized within three-dimensional (3D) porous polymeric scaffolds have been utilized for catalysts and biosensors. However, efficient, robust immobilization of the nanostructures both outside and inside of the 3D scaffolds is a challenging task. To address the challenge, we synthesized a redox-active polymer, catechol-grafted poly­(vinyl alcohol), PVA-<i>g</i>-ct. The grafted catechol is inspired by the adhesion mechanism of marine mussels, which facilitates binding and reduction of noble metal ions. Electrospinning the PVA-<i>g</i>-ct polymer results in highly open porous, 3D nanostructures, on which catechol mediates the spontaneous reduction of silver ions to solid silver nanocubes at an ambient temperature. Yet, gold and platinum ions are partially reduced and complexed with the nanofiber template, requiring an additional thermal treatment for complete reduction into solid metal nanostructures. Furthermore, silver–gold and silver–platinum hybrid nanostructures are generated by sequential treatments with metal ion precursor solutions of each. This study suggests that catechol-grafted polymer nanofibers are an attractive reactive template for the facile synthesis and immobilization of noble metal nanostructures within a 3D porous matrix for the potential applications to sensors, catalysis, and tissue engineering

Tannic Acid as a Degradable Mucoadhesive Compound

To achieve site-specific delivery of pharmaceuticals, the development of effective mucoadhesive polymers is essential. Thus far, only a few polymers, such as thiolated ones and related variants, have been studied. However, their mucoadhesiveness varies depending on the type of polymer and the degree of chemical functionalization. Furthermore, the chemistry of tethering often requires harsh reaction conditions. Recently, pyrogallol-containing molecules have emerged as good tissue and hemostatic adhesives, but their in vivo mucoadhesive properties have not been demonstrated. Herein, we found that pyrogallol-rich tannic acid (TA) formulated with poly­(ethylene glycol) (PEG), named TAPE, exhibits superior mucoadhesive properties. TAPE is prepared by a simple physical mixture of TA and PEG. It remained on esophageal mucus layers for at least several hours (<8 h) after oral feeding. The mucoadhesion originated from intermolecular interaction between the polyphenols of TA and mucin, exhibiting pH dependency. TAPE adhered strongly to mucin in neutral conditions but bound weakly in acidic conditions due to different hydrolysis rates of the ester linkages in TA. Thus, TAPE might be useful as a long-lasting esophageal mucoadhesive composite

Mussel- and Diatom-Inspired Silica Coating on Separators Yields Improved Power and Safety in Li-Ion Batteries

In this study, we developed an integrative bioinspired approach that improves the power and safety of Li-ion batteries (LIBs) by the surface modification of polyethylene (PE) separators. The approach involves the synthesis of a diatom-inspired silica layer on the surface of the PE separator, and the adhesion of the silica layer was inspired by mussels. The mussel- and diatom-inspired silica coating increased the electrolyte wettability of the separator, resulting in enhanced power and improved thermal shrinkage, resulting safer LIBs. Furthermore, the overall processes are environmentally friendly and cost-effective. The process described herein is the first example of the use of diatom-inspired silica in practically important energy storage applications. The improved wetting and thermal properties are critical, particularly for large-scale battery applications

Vanadyl–Catecholamine Hydrogels Inspired by Ascidians and Mussels

In general, mechanical properties and gelation kinetics exhibit a positive correlation with the amount of gelation reagents used. Similarly, for catechol-containing hydrogels, which have attracted significant attention, because of their unique dual properties of cohesion and adhesion, increased amounts of cross-linking agents, such as organic oxidants and/or transition metals (Fe³⁺), result in enhanced mechanical strength and more rapid gelation kinetics. Here, we report a new metal–ligand cross-linking chemistry, inspired by mussels and ascidians, that defies the aforementioned conventional stoichiometric concept. When a small amount of vanadium is present in the catechol-functionalized polymer solution (i.e., [V] ≪ [catechol]), organic radicals are rapidly generated that trigger the gelation reaction. However, when a large amount of the ion is added to the same solution (i.e., [V] ≫ [catechol]), the catechol remains chemically intact by coordination that inhibits gelation. Thus, a large amount of cross-linking agent is not necessary to prepare mechanically strong, biocompatible hydrogels using this system. This new chemistry may provide insight into the biological roles of vanadium and its interaction with catechol-containing molecules (i.e., determination of the liquid state versus the solid state). Excess amounts of vanadium ([V] ≫ [catechol]) coordinate with catechol, which may result in a liquid state for ascidian blood, whereas excess amounts of catechol ([V] ≪ [catechol]) generate an organic radical-mediated chemical reaction, which may result in solid-state conversion of the mussel byssal threads

Leaf Vein-Inspired Electrospraying System by Grafting Origami

Stable, long-term divisions of a water stream into two or more under electric fields (often for electrospray) have not been achieved owing to water’s high surface tension (72 dyn/cm), even though it seems to be a simple technical problem. In nature, leaf veins evenly distribute water to cells, despite the numerous bifurcating divisions of veins. The main reason is the extensive interconnections among veins. Herein, we discuss a stably operating multichannel water electrospray system. The system is called a “<u>L</u>eaf vein-inspired <u>E</u>lectrospraying system by <u>G</u>rafting <u>O</u>rigami (LEsGO)” and was inspired by leaf vein structures. LEsGO is a hierarchical electrospraying system prepared with cellulose paper; multiple channels can be constructed through the simple grafting of a two-channel paper unit. We demonstrate a 600% increase in water-spraying performance in an eight-channel LEsGO compared with conventional single-nozzle systems. LEsGO may potentially contribute to devices such as mass analyzers, microencapsulators, and dust removers