Bruce Lee (left) and Saleh Akram Bhuiyan (right) use a thin platinum wire to deliver a jolt of electricity to a catechol-containing adhesive on a titanium sphere. Photo: Sarah Bird/Michigan Tech.
Bruce Lee (left) and Saleh Akram Bhuiyan (right) use a thin platinum wire to deliver a jolt of electricity to a catechol-containing adhesive on a titanium sphere. Photo: Sarah Bird/Michigan Tech.

With a small zap of electricity, researchers at Michigan Technological University can turn an underwater smart glue prototype from sticky to not in seven seconds.

Turning adhesion on and off is what makes a glue smart. It's one thing to do this in the open air, however, and quite another to do it underwater. So, inspired by nature, researchers led by Bruce Lee, associate professor of biomedical engineering at Michigan Tech, turned to catechols. These are synthetic compounds that mimic the wet-but-still-sticky proteins secreted by mussels and which offer promise for smart adhesives that work in water.

Lee and his team have now shown that the adhesion of a catechol-containing material can be turned off with an electrical current. This technology could find use in underwater glue, wound dressings, prosthetic attachments and car parts. The team reports its work in a paper in the Journal of the American Chemical Society, including the stickiest part of the process – creating a repeatable contact mechanics test that can measure adhesion before and after a jolt of electricity.

"A lot of people have been using catechol to mimic mussels and their adhesive proteins, but applying electricity to deactivate it is new," Lee said. "It's more convenient than using pH like what we were using before and it should be easier to integrate with electronic devices, which means detaching could be automated and could be as simple as pushing a button."

One day, catechol adhesives may help attach equipment to the hulls of submarines, but testing prototypes in scuba gear isn't how new tech gets created. Instead, Lee and doctoral researcher Saleh Akram Bhuiyan needed to control a suite of variables in a small lab space. Simple as it sounds, running a current through a material and checking its stickiness is actually quite difficult to do over and over again.

The method they came up with involves coating the adhesive on a titanium sphere, which is immersed in salty water, and then using a platinum wire electrode to apply electrical stimulation to the adhesive. This set-up makes it easy to control the voltage applied through the wire, glue and sphere, as well as how salty the water is around them. The amount of time the current runs is also important. With more time, voltage and salt, the more the catechol adhesives are oxidized and the less adhesive they become. With strong enough voltage, the glue detaches in only seven seconds.

"The novelty is application of the electricity and the short amount of time it takes to detach," Bhuiyan said. "What I find most unusual about the experiment is the color change. It starts white and when I apply the electricity and the material is deactivated, it oxidizes and turns a red color – and we really like to see that red color."

The next step in the research will be trying to turn the red color back into white. The hallmark of a smart glue is not only deactivating adhesion, but turning it back on. In an earlier study, Lee and doctoral graduate Ameya Narkar were able to accomplish this feat by playing with the pH, and Bhuiyan hopes to apply the lessons from that research to electrical current.

This story is adapted from material from Michigan Technological University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.