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Mussels stick under water by using their own ions to combat the salt around them [Also see Report by Maier et al. ] When visiting a beach, we can see that mussels, oysters, and barnacles attach themselves to rocks even while being pounded by waves. These organisms remain affixed by secreting adhesives. Human efforts to make such wet-setting glues are often foiled by the presence of water. Instructions on tubes of adhesives remind us that the surfaces must be clean and dry, given that our materials interact better with water than with the pieces of a broken dish. On page 628 of this issue, Maier et al. ( 1 ) have divulged a potentially key part of the underwater adhesion story. Mussels appear to gain surface access for glues by using their own protein-based ions to outcompete the ions in their saltwater environment.

Catechol-containing polymers inspired by marine mussels have gained significant interest in recent years, leading to applications in several fields. Among these polymer systems, poly(vinylcatechol-styrene) (PVCS) has become a popular option due to its exceptional underwater adhesion strength, with readily available monomers and diverse synthetic routes being available. However, the translation of any novel adhesive chemistry from academic research to real-world applications can be challenging. Acrylates, epoxies, and urethanes were introduced to markets over half a century ago and remain dominant. However, bonding in wet environments remains lacking. The work presented here addresses this gap by focusing on the formulation of PVCS-based adhesives for conditions outside of the research lab. An emphasis was placed on handling properties when working underwater. A collection of different substrates were bonded together and several commercial glues provided benchmarks. Environmental conditions were studied to broaden the potential applications of PVCS adhesives in underwater settings. By optimizing formulations, we present an adhesive system that retains the superior underwater bonding of PVCS while also offering enhanced workability. This approach may help open the door to utilization of a new adhesive chemistry for underwater applications.

Nearly all adhesives 1 , 2 are derived from petroleum, create permanent bonds 3 , frustrate materials separation for recycling 4 , 5 and prevent degradation in landfills. When trying to shift from petroleum feedstocks to a sustainable materials ecosystem, available options suffer from low performance, high cost or lack of availability at the required scales. Here we present a sustainably sourced adhesive system, made from epoxidized soy oil, malic acid and tannic acid, with performance comparable to that of current industrial products. Joints can be cured under conditions ranging from use of a hair dryer for 5 min to an oven at 180 °C for 24 h. Adhesion between metal substrates up to around 18 MPa is achieved, and, in the best cases, performance exceeds that of a classic epoxy, the strongest modern adhesive. All components are biomass derived, low cost and already available in large quantities. Manufacturing at scale can be a simple matter of mixing and heating, suggesting that this new adhesive may contribute towards the sustainable bonding of materials. We present a sustainably sourced adhesive system, with performance comparable to that of current industrial products, made from epoxidized soy oil, malic acid and tannic acid, all biomass derived, low cost and readily available.

In this review, we survey recent literature (2009–2013) on hydrogels that are mechanically tough and adhesive. The impact of published work and trends in the field are examined. We focus on design concepts, new materials, structures related to mechanical performance and adhesion properties. Besides hydrogels made of individual polymers, concepts developed to toughen hydrogels include interpenetrating and double networks, slide ring polymer gels, topological hydrogels, ionically cross-linked copolymer gels, nanocomposite polymer hydrogels, self-assembled microcomposite hydrogels, and combinations thereof. Hydrogels that are adhesive in addition to tough are also discussed. Adhesive properties, especially wet adhesion of hydrogels, are rare but needed for a variety of general technologies. Some of the most promising industrial applications are found in the areas of sensor and actuator technology, microfluidics, drug delivery and biomedical devices. The most recent accomplishments and creative approaches to making tough and sticky hydrogels are highlighted. This review concludes with perspectives for future directions, challenges and opportunities in a continuously changing world.

Rubber sheets that reversibly bind and release substrates have been made by copying a subtlety in the shape of octopus suckers. The findings reveal how macro-scale biological structures can influence function. See Letter p.396 Octopus-inspired sticky patch Adhesives fall broadly into two categories, working either through chemical bonding or attraction at the interface, or through mechanical interlocking to ensure that surfaces stick together. Finding an adhesive in either of these categories that works under dry conditions and when immersed in liquids, and isn't readily contaminated, is an ongoing challenge. Changhyun Pang and colleagues have taken inspiration from the shape of octopus suckers to develop and fabricate a textured polymer patch that adheres through mechanical deformation. The patch displays good adhesive properties in various media, yet is resistant to chemical contamination.

Marine mussels produce an impressive adhesive material for affixing themselves to rocks in the turbulent marine environment. This glue is generated by application of proteins to the surface followed by extensive cross-linking to yield the final matrix. Prior studies have shown that simple oxidation or reactivity brought about by metal ions may be key to this protein cross-linking process. Here we have explored protein cross-linking reactivity in which combinations of metals and oxidants may display synergistic effects with respect to adhesive curing. Extracted adhesive proteins were mixed with a series of metals, oxidants, and combinations thereof. In some cases, synergistic curing was observed. For example, we found that iron(II) ions with hydrogen peroxide brought about a greater degree of protein cross-linking than the sum of the individual components. These studies were performed as part of our efforts to provide perspectives on the connections between biology, chemistry, and functional materials.

Mussels generate adhesives for staying in place when faced with waves and turbulence of the intertidal zone. Their byssal attachment assembly consists of adhesive plaques connected to the animal by threads. We have noticed that, every now and then, the animals tug on their plaque and threads. This observation had us wondering if the mussels temper or otherwise control catechol chemistry within the byssus in order to manage mechanical properties of the materials. Here, we carried out a study in which the adhesion properties of mussel plaques were compared when left attached to the animals versus detached and exposed only to an aquarium environment. For the most part, detachment from the animal had almost no influence on the mechanical properties on low-energy surfaces. There was a slight, yet significant difference observed with attached versus detached adhesive properties on high energy surfaces. There were significant differences in the area of adhesive deposited by the mussels on a low- versus a high-energy surface. Mussel adhesive plaques appear to be unlike, for example, spider silk, for which pulling on the material is needed for assembly of proteinaceous fibers to manage properties.