For the increasing demand of soft materials with wide ranges of applications, hydrogels have been developed exhibiting variety of functions (e.g., stretchable, self-healing, stimuli-responsive, and etc.). So far, add-in components such as inorganic nanoparticles, carbon materials, clays, and many others to main polymers have been used to achieve various unique functions of hydrogels. The multicomponent hydrogel systems often exhibit batch-dependent inconsistent results and problems in multicomponent mixings, require labors during preparations, and accompany unpredictable cross-talk between the added components. Here, we developed 'single polymeric component', alginate-boronic acid (alginate-BA) hydrogel to overcome the aforementioned problems. It exhibits unprecedented multifunctionalities simultaneously, such as high stretchability, self-healing, shear-thinning, pH- and glucose-sensitivities, adhesive properties, and reshaping properties. Multifunctionalities of alginate-BA hydrogel is resulted from the reversible inter- and intramolecular interactions by dynamic equilibrium of boronic acid-diol complexation and dissociation, which was proved by single molecule level Atomic Force Microscopy (AFM) pulling experiments. We also found that the alginate-BA gel showed enhanced in vivo retentions along gastrointestinal (GI) tract. Our findings suggest that rational polymer designs can result in minimizing the number of a participating component for multifunctional hydrogels, instead of increasing complexity by adding various additional components.

A new insect-cuticle- and fruit-browning-mimetic film exhibiting simultaneous self-healing and self-sealing properties only by ambient oxygen without external stimuli is developed. The film is formed at the liquid/air interface via crosslinking of phenolic compounds and poly(amine) chains. The film can be self-healed over a hundred times under ambient air at room temperature without exogenous materials and stimuli.

Since the first report of underwater adhesive proteins of marine mussels in 1981, numerous studies have reported mussel-inspired synthetic adhesive polymers. However, none of them have developed up to human-level translational studies. Here, we report a sticky polysaccharide that effectively promotes hemostasis from animal bleeding models to first-in-human hepatectomy. We found that the hemostatic material instantly generates a barrier layer that seals hemorrhaging sites. The barrier is created within a few seconds by in situ interactions with abundant plasma proteins. Therefore, as long as patient blood contains proper levels of plasma proteins, hemostasis should always occur even in coagulopathic conditions. To date, insufficient tools have been developed to arrest coagulopathic bleedings originated from genetic disorders, chronic diseases, or surgical settings such as organ transplantations. Mussel-inspired adhesion chemistry described here provides a useful alternative to the use of fibrin glues up to a human-level biomedical application.

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.

Mussel-inspired adhesive coatings on biomedical devices have attracted significant interest due to their unique properties such as substrate independency and high efficiency. The key molecules for mussel-inspired adhesive coatings are catechol and amine groups. Along with the understanding of catechol chemistry, chitosan-catechol has also been developed as a representative mussel-inpired adhesive polymer that contains catechol and amine groups for adhesiveness. Herein, we demonstrated the direct writability of chitosan-catechol as a bioink for 3D printing, one of the additive techniques. The use of chitosan-catechol bioink results in the formation of 3D constructs in normal culture media via rapid complexation of this bioink with serum proteins; in addition, the metal/catechol combination containing tiny amounts of vanadyl ions, in which the ratio of metal to catechol is 0.0005, dramatically enhances the mechanical strength and printability of the cell-encapsulated inks, showing a cell viability of approximately 90%. These findings for mussel-inspired bioinks will be a promising way to design a biocompatible 3D bioink cross-linked without any external stimuli.