Simultaneous coupling of metal removal and visual detection by nature-inspired polyphenol-amine surface chemistry.

The interplay between polyphenols, amines, and metals has broad implications for surface chemistry, biomaterials, energy storage, and environmental science. Traditionally, polyphenol-amine combinations have been recognized for their ability to form adhesive, material-independent thin layers that offer a diverse range of surface functionalities. Herein, we demonstrate that a coating of tannic acid (TA) and polyethyleneimine (PEI) provides an efficient platform for capturing and monitoring metal ions in water. A unique feature of our PEI/TA-coated microbeads is the 'Detection-Capture' (Detec-Ture) mechanism. The galloyl groups in TA coordinate with Fe(III) ions (capture), initiating their oxidation to gallol-quinone. These oxidized groups subsequently react with PEI amines, leading to the formation of an Fe(II/III)-gallol-PEI network that produces a vivid purple color, thereby enabling visual detection. This mechanism couples metal capture directly with detection, distinguishing our approach from existing studies, which have either solely focused on metal removal or metal detection. The metal capturing capacity of our materials stands at 0.55 mg g-1, comparable to that of established materials like alginate and wollastonite. The detection sensitivity reaches down to 0.5 ppm. Our findings introduce a novel approach to the utility of metal-polyphenol-amine networks, presenting a new class of materials suited for simultaneous metal ion detection and capture in environmental applications.

Silk Fibroin Enhances Cytocompatibilty and Dimensional Stability of Alginate Hydrogels for Light-Based Three-Dimensional Bioprinting.

Three-dimensional (3D) bioprinting is a technology under active study for use in tissue engineering and regenerative medicine. Bioink comprises cells and polymers and is the essential material for 3D bioprinting. The characteristics of the bioink affect its printability, gelation behavior, and cell compatibility. In this study, alginate derivatives were synthesized to induce rapid gelation, and a bioink was prepared by mixing these alginate derivatives with silk fibroin to enhance cell compatibility. A low-concentration (3 wt %) alginate/silk fibroin (Alg/SF) bioink was pregelated by the ionic cross-linking of Alg to increase the viscosity for 3D printing. The rheological and mechanical properties were analyzed using a rheometer and a texture meter, respectively. Analysis of cell viability and proliferation using fibroblasts (NIH-3T3) in the bioinks showed that the Alg/SF bioink has improved cytocompatibility compared to that of conventional Alg bioinks, making it a promising material for tissue engineering.

Temperature- and pH-induced dual-crosslinked methylcellulose/chitosan-gallol conjugate composite hydrogels with improved mechanical, tissue adhesive, and hemostatic properties.

Gauze or bandages are commonly used to effectively control bleeding during trauma and surgery. However, conventional treatment methods can sometimes lead to secondary damages. In recent years, there has been increased interest in developing adhesive hemostatic hydrogels as a safer alternative for achieving hemostasis. Methylcellulose (MC) is a well-known thermo-sensitive polymer with excellent biocompatibility that is capable of forming a hydrogel through physical crosslinking owing to its inherent thermo-reversible properties. However, the poor mechanical properties of the MC hydrogel comprising a single crosslinked network (SN) limit its application as a hemostatic material. To address this issue, we incorporated a chitosan-gallol (CS-GA) conjugate, which has the ability to form chemical crosslinks through self-crosslinking reactions under specific pH conditions, into the MC hydrogel to reinforce the MC hydrogel network. The resulting MC/CS-GA hydrogel with a dual-crosslinked network (DN), involving both physical and chemical crosslinks, exhibited synergistic effects of the two types of crosslinks. Thus, compared with those of the SN hydrogel, the composite DN hydrogel exhibited significantly enhanced mechanical strength and tissue adhesive properties. Moreover, the DN hydrogel presented excellent biological activity in vitro. Additionally, in rat hepatic hemorrhage models, the DN hydrogel exhibited high hemostatic efficiency, showcasing its multifunctional capabilities.

Low-Viscous, Dilute Phase Adhesive from Dense Polyphenolic Coacervates of Poly(vinyl alcohol) and Tannic acid.

This study explores a polyphenolic coacervate, named VATA, formed by poly(vinyl alcohol) (PVA) and tannic acid (TA). Distinct from conventional studies that have focused on the bottom, dense phase of coacervates, this research emphasizes the top, dilute phase, low-viscous coacervate liquid termed liquid-VATA (l-VATA). Due to TA's capability of intermolecular association as well as adhesiveness, phenomena not typically observed in the upper dilute phase of standard polyelectrolyte-based coacervates are revealed. At first glance, the dilute phase l-VATA coacervate resembles a water-like, low-viscous mixture solution of PVA, TA, and PVA/TA complexes. However, analysis shows that nearly all of the TA molecules associate with PVA chains, forming PVA/TA complexes. Furthermore, supraparticular association was observed between PVA/TA complex nanoparticles upon applying external shear force. A broad survey of shear rate and strain showed that the solution exhibited sequential shear-thickening, followed by shear-thinning behavior. The water-like, low viscosity of l-VATA unexpectedly reveals robust adhesiveness and thus able to lift an entire mouse using just a single human hair strand. Even in cases of failure, no interfacial failure was detected between mouse and human hair. In addition to enabling hair-to-hair bonding, our study also showcases the efficacy of l-VATA in facilitating hair-to-skin adhesion. The results illustrate how the lower viscosity of l-VATA can be exploited for a wide range of industrial and cosmetic applications, allowing the formulation of thin, uniform adhesive layers, something unachievable with the dense, viscous VATA glue. Thus, this study highlights the importance of investigating the top dilute phase of coacervates, shedding light on an area often underestimated compared to the bottom dense phase reported in prevalent coacervate studies.

Eco-friendly silk fibroin/tannic acid coacervates for humid and underwater wood adhesives.

Bioadhesives derived from biomass are steadily gaining spotlight as substitutes for formaldehyde-based resins in the adhesive industry. However, there is a need to develop novel water-resistant bioadhesives with high adhesive and cohesive strengths because the currently available biomaterial-based adhesives have low mechanical strength. In this study, a complex coacervate was prepared easily by mixing silk fibroin and tannic acid to produce a bioadhesive with high adhesive and cohesive strengths as well as water resistance. The silk fibroin-tannic acid coacervate adhered well to various substrates, and its adhesive strength according to the type of substrate and water contact angle were evaluated comparatively. In particular, the adhesive strength of this adhesive on a wood substrate was systematically analyzed by varying different experimental parameters (relative humidity, surface roughness of the substrate, water stability, and pH). This cost-effective coacervate is applicable as an eco-friendly wood adhesive.

Dual crosslinked alginate hydrogels by riboflavin as photoinitiator.

Photodegradation behavior of riboflavin (RF) as photoinitiator and photosensitizer was investigated. When the visible light was irradiated to RF, the radical activation and decomposition of RF was induced by reactive oxygen species (ROS) that has formed by dissolved oxygen. One of its photoproducts, lumichrome (LC), was a reduced form of RF, which lost its color when photodegraded. Photodegradation mechanisms of RF and its photoproducts by light irradiation were investigated using structural quantitative analysis derived from UV-Vis spectra. It was found that RF provided photocrosslinking reaction to make alginate-based hydrogels. For this investigation, alginate derivative with tyramine moiety was prepared by EDC/NHS chemistry and it used to induce photocrosslinking, which might serve to reinforce the unstable ionic crosslinking in the physiological environment of alginate hydrogel. The structural stability of single-crosslinked (ionically or covalently crosslinked) or dual-crosslinked (ionically and covalently crosslinked) alginate-based hydrogels were compared using rheometer, texture analyzer and SEM.