A Glue That’s Sticky Even Under Water

A team of Korean researchers have developed adhesives that allow for reversible binding when wet.

AsianScientist (Jan. 31, 2018) – A research group at the Ulsan National Institute of Science and Technology has invented a strong adhesive that retains its stickiness when wet and can even be used underwater. They published their findings in ACS Macro Letters.

Wet adhesives are protein-based substances that are applied to the joining surfaces in a fluid state. Mussels and clams produce such adhesives to stick to ship hulls. Stable adhesion between surfaces under wet conditions is highly desirable for many practical applications, particularly in the bioengineering and medical fields, where most surfaces are wet.

However, complicated surface treatment and expensive protocols restrain the extensive use of these natural protein adhesives. Furthermore, they are typically permanent adhesives, limiting their applications where reversible binding may be necessary.

In the present study, a team of scientists led by Professor Jeong Hoon-Eui developed hydrogels that are stickier than natural biological glues. The microhooks of the adhesive hydrogels were designed to exhibit a unique structural configuration with protruding heads.

Under wet conditions, the adhesion between the interlocked microhook arrays is greatly enhanced because of the hydration-triggered shape reconfiguration of the hydrogel microstructures. Furthermore, this water-responsive shape change was reversible—the microstructure can recover its original shape and size upon drying.

“These adhesives take the form of thin flexible films with bioinspired mushroom-shaped micropillars uniformly spread on the surface of microstructure,” said Mr. Park Hyun-Ha at UNIST, who is the first author of the study. “When the interlocked arrays are exposed to water, a shape transformation of the hydrogel microhooks occurred due to the swelling of the hydrogel, resulting in significantly increased wet adhesion, both in the shear and normal directions.”

The research team noted that in contrast to other wet binding systems, the current interlocking mechanism does not involve any complicated surface treatment or chemical moieties. This allows for a simple yet efficient method of strong and reversible wet adhesion that is also cost-effective. Moreover, their adhesive does not soften or dissolve in water, thus enabling it to retain its bond strength over long durations.

“This wet-responsive and reversible hydrogel interlocking adhesive can serve as a robust and versatile wet adhesive for a broad range of applications which require stable and strong adhesion under diverse wet conditions,” Jeong concluded.

The article can be found at: Park et al. (2017) Flexible and Shape-Reconfigurable Hydrogel Interlocking Adhesives for High Adhesion in Wet Environments Based on Anisotropic Swelling of Hydrogel Microstructures.


Source: Ulsan National Institute of Science and Technology; Photo: Shutterstock.
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