Skin tissue defects represent a major threat to human health. It is of vital importance for researchers to develop novel ideal adhesives with strong adhesion, good biocompatibility, low cost, and simple production approaches. Inspired by the phenomenon of free-radical scavenging by polyphenols, as well as the fact that polyphenols improve the mechanical properties of flour products, a tannic acid–thioctic acid (TATA) supramolecular hydrogel was synthesized via the ring-opening polymerization of thioctic acid and thiyl radical–polyphenol Michael addition. The synthetic procedure was robust, facile, time-saving, and low-cost, and thus in accordance with the rules of green chemistry. Successful intermolecular crosslinking was confirmed using X-ray photoelectron spectroscopy (XPS). The multiple hydrogen bonds formed between the polyphenol residues and carboxyl groups endowed the hydrogel with self-healing and injectable properties. Additionally, the TATA hydrogel was used as an adhesive for skin wound healing, and it exhibited decreased therapeutic time and an enhanced regeneration effect compared with suture treatment. This hydrogel also showed antibacterial activity against Methicillin-resistant Staphylococcus aureus in a burn wound infection model. Based on the above features, the TATA hydrogel exhibits potential as a surgical antibacterial bioadhesive for a broad range of medical applications.

Making a hydrogel-based first-aid bandage with green resources, desirable biocompatibility, universal adhesive properties, low cost and simple production is a long-standing research aspiration. Considering this, three naturally existing organic acids, namely tannic acid, thioctic acid and phytic acid, were used to construct a novel adhesive gel (TATAPA hydrogel) for epidermal tissue bandage applications. This hydrogel could be synthesized under mild conditions with no need for a freeze–thawing shaping procedure, and was transparent, moldable and stretchable with good stability under continuous water immersion. In lap-shear tests, the TATAPA hydrogel could adhere to various hydrophilic and hydrophobic surfaces. Moreover, in the case of skin tissue adhesion, the hydrogel could be easily peeled off from the skin, meeting wearability requirements. Rheological tests showed that the hydrogel possessed thermal sensitive properties derived from multi-supramolecular interactions. The methicillin-resistant Staphylococcus aureus (MRSA)-infected burn wound test demonstrated that the hydrogel had desirable antibacterial activity and was beneficial for wound healing. A femoral artery bleeding assay was also used to reveal that the TATAPA hydrogel could be directly pasted onto the bleeding site for hemostasis. Overall, this hydrogel demonstrates potential as a surgical bioadhesive for a broad range of medical applications.

Developing multifunctional hydrogels with stretchability, self-healing ability, adhesiveness, and conductivity into flexible strain sensors for human motion and health monitoring has attracted great attention and is highly desired. However, the present motion detectors mainly focus on stretching, bending, and twisting of different body parts while the expansion–contraction motion has been rarely investigated. In this study, along with carbon nanotubes (CNTs) as conductive components, sodium alginate (Alg) modified with 3-aminophenylboronic acid (PBA) and dopamine (DA) were synthesized and employed as precursors to prepare a multifunctional Alg-CNT hydrogel. The formed dynamic covalent bonds between PBA and DA endowed the hydrogel with a rapid self-healing property (30 s) while the introduction of CNTs remarkably enhanced the mechanical strength and electrical conductivity of the hydrogel. Moreover, the as-prepared hydrogel displayed a satisfactory stretchability (500%) and self-adhesiveness to various substrates. When used as a strain sensor, the Alg-CNT hydrogel that exhibited a fast response (150 ms) and ultra-durability (over 30 000 cycles) was demonstrated to be capable of monitoring subtle expansion–contraction motions (e.g., human breathing and mouse heart beating) via periodic and repeatable electrical signals. Therefore, this multifunctional hydrogel is highly suitable for monitoring expansion–contraction motions, indicating its potential applications in personal health monitoring.

Tannic acid (TA) based materials have received significant interest owing to their broad spectrum of chemical and biological properties. Herein, a novel tannic acid based hydrogel, TA–PEG hydrogel, was synthesized via Mitsunobu polymerization/polycondensation, in which TA and polyethylene glycol (PEG) were simply crosslinked together by ether linkages. This method was performed in one pot, straightforward, metal free and robust, ignoring the strong ionic/hydrophobic interactions between tannic acid and PEG. Bearing catechol and pyrogallol units from TA, TA–PEG hydrogel did not only reduce the silver and gold precursor, but also served as a capping agent and stabilizer for the in situ formed Au and Ag nanoparticles (NPs). Furthermore, the antioxidant activity of the hydrogel was excellent (94%) in the case of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging. TA–PEG hydrogel also showed antibacterial activity against Staphylococcus aureus and Escherichia coli. This work suggested a new method leading to polyphenol based soft materials rather than a complex coacervated microstructure. The resulting TA–PEG hydrogel has potential application in biomedical materials.

Skin pigmentation typically arises from the excessive secretion and accumulation of melanin, resulting in a darker complexion compared to normal skin. Currently, the local application of chemical drugs is a first-line strategy for pigmentation disorders, but the safety and efficacy of drugs still cannot meet clinical treatment needs. For long-term and safe medication, researchers have paid attention to natural products with higher biocompatibility. This article begins by examining the pathogenesis and treatment approaches of skin pigmentation diseases and summarizes the research progress and mechanism of natural products with lightening or whitening effects that are clinically common or experimentally proven. Moreover, we outline the novel formulations of natural products in treating pigmentation disorders, including liposomes, nanoparticles, microemulsions, microneedles, and tocosomes. Finally, the pharmacodynamic evaluation methods in the study of pigmentation disorder were first systematically analyzed. In brief, this review aims to collect natural products for skin pigmentation treatment and investigate their formulation design and efficacy evaluation to provide insights for the development of new products for this complex skin disease.