Engineers have developed an adhesive that could quickly and firmly stick to wet surfaces to seal up rips and tears in lungs and intestines within seconds or to affix implants and other medical devices to the surfaces of organs such as the heart. The adhesive has been developed further so that it can be detached from the underlying tissue without causing any damage. By applying a liquid solution, the new version can be peeled away like a slippery gel in case it needs to be adjusted during surgery, for example, or removed once the tissue has healed.
In considering designs for the original adhesive, the researchers found that it is extremely difficult for tape to stick to wet surfaces, as the thin layer of water lubricates and prevents most adhesives from taking hold. The original adhesive was made out of biocompatible polymers including polyacrylic acid — a highly absorbent material commonly used in diapers and pharmaceuticals — that soaks up water, then quickly forms weak hydrogen bonds with the tissue’s surface. To reinforce these bonds, the researchers embedded the material with NHS esters, chemical groups that form stronger, longer-lasting bonds with proteins on a tissue’s surface.
While these chemical bonds gave the tape its ultrastrong grip, they were also difficult to break and detaching the tape from tissue was a potentially harmful task. To make the adhesive detachable, the team added a new disulfide linker molecule that can be placed between covalent bonds with a tissue’s surface proteins. The team synthesized this particular molecule because its bonds, while strong, can be easily severed if exposed to a particular reducing agent.
They identified glutathione — an antioxidant naturally found in most cells — as a suitable reducing agent that was both biocompatible and able to sever the necessary bonds within the adhesive. It was able to break long-lasting covalent bonds such as disulfide, while sodium bicarbonate (baking soda) could deactivate the adhesive’s shorter-lasting hydrogen bonds.
Concentrations of glutathione and sodium bicarbonate were mixed in a saline solution that was sprayed over samples of adhesive placed over various organ and tissue specimens. In all their tests, regardless of how long the adhesive had been applied to the tissue, the researchers found that once they sprayed the triggering solution onto the tape, they were able to peel the tape away from the tissue within about five minutes without causing tissue damage.
The researchers also fabricated a version of the adhesive etched with tiny channels the solution can also diffuse through. This design should be particularly useful if the tape were used to attach implants and other medical devices. In this case, spraying solution on the tape’s surface would not be an option. Instead, a surgeon could apply the solution around the tape’s edges, where it could diffuse through the adhesive’s channels.