Few studies aiming to develop a glue with an underwater reusable adhesive property have been reported because combining the two properties of reusable adhesion and underwater adhesion into a single glue formulation is a challenging issue. Herein, preparation of a simple mixture of poly(vinyl alcohol) (PVA) and a well-known phenolic compound, namely, tannic acid (TA), results in an underwater glue exhibiting reusable adhesion. We named the adhesive VATA (PVA + TA). Using VATA, two stainless steel objects (0.77 kg each) are able to be instantly attached. In addition to the high adhesive strength, surface-applied VATA in water retains its adhesive capability even after 24 h. In contrast, cyanoacrylate applied under the same water condition rapidly loses its adhesive power. Another advantage is that VATA's adhesion is reusable. Bonded objects can be forcibly detached, and then the detached ones can be reattached by the residual VATA. VATA maintains nearly 100% of its initial adhesive force, even after 10 repetitions of attach−detach cycles. VATA bonds various materials ranging from metals and polymers to ceramics. Particularly, we first attempt to test the toxicity of the underwater adhesives using an invertebrate nematode, Caenorhabditis elegans and gold fish (vertebrate) due to potential release to the environment.
polymers, but they are water-insoluble, organic-solvent basis glues. [10,11] Despite recent novel approaches in adhesives using nanoparticles, [12] stretchable gels, [13] and numerous bioadhesive studies summarized in reviews, [3,4] bioinspired waterborne and biocompatible adhesives showing superglue-like adhesion strength have not been reported. Phenol-amine synergy is also found in insect exoskeletons in which aminerich polymer backbones are cross-linked by phenolic compounds by N-acetyldopamine, N-β-alanyl-dopamine, and dopamine. [14,15] The key biochemistry in sclerotization (i.e., hardening) processes is crosslinking of amine-rich polymers via phenol-quinone involved oxidative reactions. Being different from mechanically weak adhesive materials inspired by marine organisms mentioned above, Young's moduli of exoskeletons are extremely high exhibiting 1-20 GPa, [16] which is similar to ones of common plastics including nylon (2-4 GPa), poly(ethylene terephthalate) (PET) (2-2.7 GPa), and polystyrene (3-3.5 GPa). So far, no studies attempting uses of insect sclerotization process as a new curing strategy in adhesives are reported. We hypothesized that combining: 1) adhesive properties originated from phenols and 2) insect exoskeleton-like hard material properties inspired by phenol-amine phenolamine crosslinking would result in biomimetic superglues. To achieve this goal, the Exoskeletons of insects formed by sclerotization processes exhibit superstrong properties in moduli. Here, it is demonstrated that mimicking the sclerotization process using phenol and polyamine molecules unexpectedly results in a 100% ecofriendly, biocompatible waterborne superglue. Oxygen presented in air and dissolved in water acts as an initiator producing phenolic radical/quinone for superglue curing. Despite synthesis-free uses of water, phenol, and polyamine, its adhesion strength is comparable to commercial epoxy glue showing >6 MPa in lap shear strength. The phenol-amine superglue bonds to various substrates including ceramics, woods, fabrics, plastics, metals, and importantly biological tissues. Due to strong adhesion, the superglue effectively seals wounds within a few seconds, and, due to its waterborne nature, no harmful respiratory effect is observed because of any release of volatile organic compounds. The easy, cost-effective preparation of the phenol-amine superglue can revolutionize varieties of industrial, biomedical, daily life processes. Phenol-amine synergy found in marine mussels or tunicates inspires researchers to develop material-independent surface chemistry and medical soft adhesives. [1] Examples include polydopamine coatings in surface chemistry [2] and catechol-and gallol-tethered soft adhesives. [3-9] Adhesion forces observed from bioinspired adhesive polymers are generally weak in the range of kPa: hyaluronic acid-catechol (0.8 kPa), [5] poly(glutamic acid)-catechol (26.1-58.2 kPa), [6] poly(methacrylamide)-catechol (10-300 kPa), [7] and chitin-gallol (215 kPa). [8] A few studies reported adhesion in MPa ord...
Polyphenol materials have rapidly emerged as bioadhesives. However, nearly all exhibit low adhesion strength compared to commercial glues. In article number 2002118, Seung‐Woo Cho, Haeshin Lee, and co‐workers show that phenolamine can exhibit adhesive strength >6 MPa, comparable to commercial epoxy glues. The advantage of the phenolamine bioglue is its 100% water basis. It effectively seals various substrates including ceramics, wood, fabrics, plastics, metals, and even wounded skin without any harmful effects. Therefore, these findings are promising in both industrial and biomedical applications.
Liquid–liquid phase separation in an aqueous polymer solution is a unique physicochemical phenomenon, and the material present in the dense bottom layer is called a coacervate. A partial degree of water exclusion during coacervate formation often results in adhesive properties. The high viscosity makes coacervates incompatible with electrospinning processes. Coacervates can be electrospinnable only when the viscosity level of coacervates is adjusted. Electrospinning of coacervates results in a liquid-to-solid phase transition, addressing a long-term stability issue of coacervates. The preserved electrospun membranes can always be reconverted to a coacervate state by dissolution. Herein, we fabricate a spinnable coacervate solution using cosolvents. For neutral, hydrogen bond-dominated coacervates, such as those composed of poly(vinyl alcohol) (PVA) and phenolic tannic acid (TA), the use of a polar cosolvent system such as methanol–water results in an electrospinnable coacervate solution. The spun PVA–TA porous mats are a physicochemically stable solid, and the materials are converted back to an adhesive state upon wetting with body fluid. Considering the emerging studies related to coacervate adhesives, this study suggests that electrospinning a coacervate solution can be a strategy to dramatically increase the material stability and functionality.
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