A team from Harvard School of Engineering and Applied Sciences (SEAS) have managed to create an extremely tough gel that is capable of being stretched to 21 times its length. It is hoped that the gel, known as hydrogel, will be able to be used in replacing damaged cartilage in human joints.
The gel is a hybrid of two weak water-based gels that combine to create the super-strong substance. The gel is not just strong, but it is also exceptionally tough, self-healing, and bio-compatible — all of which means it is ideal for use in medicine and tissue engineering.
“Conventional hydrogels are very weak and brittle—imagine a spoon breaking through jelly,” explains lead author Jeong-Yun Sun, a postdoctoral fellow at the Harvard School of Engineering and Applied Sciences (SEAS). “But because they are water-based and biocompatible, people would like to use them for some very challenging applications like artificial cartilage or spinal disks. For a gel to work in those settings, it has to be able to stretch and expand under compression and tension without breaking.”
The main ingredient in hydrogel is polyacrylamide, which is also used in soft contact lenses and as the electrophoresis gel that separates DNA fragments in biology labs. The other main component is alginate, which is a seaweed extract used to thicken food. These ingredients combine to form a network of molecules that pull apart very slightly over a large area without cracking.
However, through a series of experiments, the research team showed that even with a huge crack, the hybrid gel can still stretch to 17 times its initial length. In one experiment, the researchers used a razor blade to cut a 2-cm notch across the gel and it held without breaking.
The most important feature of hydrogel is that it is able to maintain its elasticity and toughness over multiple stretches.
“The unusually high stretchability and toughness of this gel, along with recovery, are exciting,” says Suo. “Now that we’ve demonstrated that this is possible, we can use it as a model system for studying the mechanics of hydrogels further, and explore various applications.”
Via TG Daily