Last year, as we reported in Cosmos, US engineers unveiled a double-sided adhesive that could quickly and firmly stick to wet surfaces such as biological tissues.
Now the team from Massachusetts Institute of Technology has gone what can only be considered an important step further by creating a version that can be taken off again without causing damage.
By applying a liquid solution, it can be peeled away like a slippery gel during surgery or once the tissue has healed. It’s like “a painless Band-Aid for internal organs”, says Xuanhe Zhao, co-author of a new paper in the journal Proceedings of the National Academy of Sciences.
In this case both necessity and initial success were the mothers of invention.
Zhao and colleagues designed their original adhesive out of biocompatible polymers then reinforced them by embedding NHS esters – chemical groups that form stronger and longer-lasting bonds with proteins on a tissue’s surface.
The bonds were so strong, however, that they were difficult to break. “Removing the tape could potentially create more of an inflammatory response in tissue, and prolong healing,” says co-author Hyunwoo Yuk.
Their response was to tweak the adhesive by adding a disulfide linker molecule, which can be placed between covalent bonds with a tissue’s surface proteins. The molecule’s bonds are strong, but they can easily be severed if exposed to the right reducing agent.
The researchers then searched the literature to identify a suitable and biocompatible agent and found that glutathione, an antioxidant naturally found in most cells, can break long-lasting covalent bonds such as disulfide, while sodium bicarbonate – simple baking soda – can deactivate shorter-lasting hydrogen bonds.
Tests on various organ and tissue specimens, including pig heart, lung and intestines, proved successful. In all cases, the researchers say, regardless of how long the tape had been on the tissue, they were able to peel it away within about five minutes of applying the agent.
“That’s about the time it takes for the solution to diffuse through the tape to the surface where the tape meets the tissue,” says co-author Xiaoyu Chen. “At that point, the solution converts this extremely sticky adhesive to just a layer of slippery gel that you can easily peel off.”
The researchers also fabricated a version of the adhesive etched with tiny channels the solution could diffuse through.
This potentially could be used with implants and medical devices, where it is not possible to spray on the reducing agent. Instead, it would be applied to the tape’s edges.
If you’re interested in the basic idea of how sticky tape works, Phil Dooley has the answer here.
Nick Carne is editor of Cosmos digital and editorial manager for The Royal Institution of Australia.
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