A research group led by Associate Professor Hiroya Abe of the Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, has developed a detachable underwater adhesive that adheres firmly at temperatures above the body temperature and detaches easily at temperatures below the body temperature. This was achieved by endowing temperature responsiveness to an underwater adhesive inspired by the underwater adhesive properties of mussel 'beards' (byssus). Underwater adhesives, whose adhesion capabilities can be controlled by temperature, can be used to safely attach biomedical devices to the human body and minimize damage to the skin when removing them, making them promising candidates for practical use. The results were published online in NPG Asia Materials.
Mussels have the ability to strongly adhere to various surfaces in the sea by means of adhesive proteins present in their byssus. The byssus of a mussel contains many catechol groups, which allows the mussel to adhere in water. Mussels can also adhere strongly to inorganic surfaces such as bedrock and quickly detach from the surface when under external stimuli.
The research group designed an underwater adhesive hydrogel inspired by mussels and further developed a temperature-responsive detachable underwater adhesive. This underwater adhesive has the ability to switch its adhesive properties at the body temperature, providing strong adhesion above the body temperature and showing easy detachability at lower temperatures. The prepared hydrogel is composed of dopamine with catechol groups and a temperature-responsive polymer. It is prepared using an air-oxidation polymerization and cross-linking reaction and has a two-sided structure (Janus structure) consisting of a densely cross-linked tough gel layer on one side and a loosely cross-linked adhesive layer on the other side. This property allows the material to have two characteristics: operability and strong adhesion. The adhesion strength between the underwater adhesive hydrogel and solid substrates (e.g., glass, titanium, and aluminum) is >100 kPa at temperatures above the body temperature. Meanwhile, at temperatures below the body temperature, the adhesion strength drops significantly to approximately 0.1 kPa and the material can be easily detached.
Results demonstrate that a difference in the adhesion strength of >1000 times can be controlled by temperature. The change in the adhesion strength due to temperature was also confirmed in experiments using pig skin. When monitoring bioelectrical signals in water, commercial hydrogels quickly swell and peel off from the skin, making continuous monitoring impossible. However, the developed underwater adhesive hydrogel with embedded electrodes can be attached to the human skin at temperatures above the body temperature, enabling continuous monitoring of electrical signals for 10 minutes. After that, the adhesive can be immediately detached from the skin by cooling it to room temperature.
The developed adhesive shows a difference in the adhesion strength of >1000 times depending on temperature, which not only enables stable bonding between a device and biological tissue but also enables gentle peeling. Therefore, this technology is expected to contribute to medical applications such as monitoring bioelectrical signals and wound healing with minimal invasion.
Journal Information
Publication: NPG Asia Materials
Title: Mussel-inspired thermo-switchable underwater adhesive based on a Janus hydrogel
DOI: 10.1038/s41427-024-00569-1
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