Researchers at ye olde Massachusetts Institute of Technology have developed a high strength hydrogel adhesive that forms bonds as strong as those between human cartilage, tendons, and bones. The adhesive is composed of roughly 90 percent water and, the MIT team notes, is stronger than any other hydrogel, elastomer, tissue adhesive, or nanoparticle gel ever created.
Invincible Wafer Bonding
In its current iteration, the adhesive hydrogel can bond to glass, silicon, titanium, aluminum, and ceramic materials. (Presumably, further development will allow it to stick effectively to other surfaces, as well.) Using standard industrial peeling tests, MIT researchers found that one kilojoule of force per square meter (0.88 BTU/ft2) is needed to separate the hydrogel from a surface.
To demonstrate this toughness in a way that’s a bit easier to understand, researchers applied the hydrogel to a silicon wafer like those used in semiconductors and state-of-the-art electronic devices. The wafer was then struck multiple times with a hammer. Though the glass-like composite shattered into countless pieces, the hydrogel adhesive proved its wafer bonding bona fides, as every single one of those pieces remained firmly in place.
By adding salt to the hydrogel recipe, researchers can make the hydrogel electrically conductive. Within a closed circuit, the material enables the flow of salt ions across the electrical loop. As a demonstration, the hydrogel was used as a connection between two metal plates wired to an LED light. Even when stretched to over four times its original size, the connection remained secure enough to keep the light lit continuously.
The stretchiness, toughness, and dielectric properties of the new aerogel could allow semiconductors to continue working if damaged. The material could be used in flexible solid batteries. And, as it is also biocompatible, it could be useful for implantable medical devices like sensors and catheters.
“Chemical Anchorage” is Not A City in Chemical Alaska
To create its mighty bonding power, the hydrogel adhesive dissipates the energy used to stretch it while maintaining its chemical anchorage to the surface. “Chemical anchorage plus bulk dissipation leads to tough bonding,” said lead researcher Xaunhe Zhao. “Tendons and cartilage harness [this concept], so we’re learning this principle from nature.”
With that comparison in mind, the MIT team is conducting further research to determine if the hydrogel adhesive could be used as synthetic “tendons” or “cartilage” in robots. “Hydrogels can act as actuators,” Zhao said. “Instead of conventional hinges, you can use this soft material with strong bonding to rigid materials [to] give a robot many more degrees of freedom.”
The future is very sticky, transparent, and 90 percent water. And the future is now!