Imagine if a hard metal implant could be bonded to soft biological tissue without using any adhesive, then easily removed when no longer needed. That and other nifty things could soon be possible, thanks to a new understanding of electroadhesion.
Putting it simply, electroadhesion is a phenomenon in which two objects become electrostatically or chemically bonded to one another after an electric current has passed through them both. They remain bonded even after the current has been removed, but will neatly separate when subjected to a current of opposite polarity.
In recent years, we've seen electroadhesion utilized in everything from wall-climbing robots to soft robotic grippers. And while some of those applications have involved bonding hard materials to pliable ones, few if any have involved bonding unaltered hard materials to truly "soft-and-guishy" ones. In fact, electroadhesion has most often been used to bond soft-to-soft and hard-to-hard.
That's where the new study comes in.
Led by Prof. Srinivasa Raghavan, a team at the University of Maryland has been able to electroadhesively bond hard materials such as tin, lead and graphite to very soft materials such as chunks of fruit, vegetables and raw chicken meat.
In one case, after a 5-volt current had been applied to a cylinder of acrylamide gel and a slab of graphite for about three minutes, the two became so strongly bonded that the gel tore instead of separating when someone tried pulling them apart. When the polarity of the current was reversed, though, the two materials easily and nondestructively separated.
The process can even be utilized for joining and releasing underwater objects. That said, not just any combination of substances works.
It was found that the hard material must be capable of conducting ions, and the soft material has to contain salt ions. The scientists believe that a chemical bond forms when the two materials exchange ions – this hypothesis is supported by the fact that metals with low electrical conductivity (such as titanium) don't work, nor do soft materials with little salt content, such as grapes.
It is hoped that once the process is better understood and developed further, it could be utilized not only in implants but also in applications such as biohybrid robots and better-performing batteries.
A paper on the research was recently published in the journal ACS Central Science.
Source: American Chemical Society