Scientists at the University of Cambridge have developed a new type of soft material with an ability to endure monumental forces. Described as "super jelly," the novel hydrogel uses a unique internal structure likened to molecular handcuffs to respond to compression by entering a glass-like state, enabling it to be run over by a car without being crushed.
Hydrogels are of much interest to materials scientists. Their high water content makes them suitable for use in the human body, and affords them stretchy and self-healing properties that can be put to use in robotics, advanced contact lenses, artificial tissues and wound healing. The authors of this new study sought to expand on these capabilities by tweaking the underlying molecular structure.
“In order to make materials with the mechanical properties we want, we use crosslinkers, where two molecules are joined through a chemical bond,” says Dr Zehuan Huang, the study’s first author. “We use reversible crosslinkers to make soft and stretchy hydrogels, but making a hard and compressible hydrogel is difficult and designing a material with these properties is completely counterintuitive.”
To achieve this, the scientists turned to barrel-shaped molecules called cucurbiturils, which "handcuff" pairs of other molecules together inside its cavity. They then used molecules designed especially to remain inside this cavity for longer than usual, which has the effect of keeping the network tightly linked and enabling it to vary from a rubber-like state to one resembling ultra-hard, shatterproof glass.
According to the team, this enables the "super jelly" to withstand forces equivalent to an elephant standing on top of it without being crushed. With no elephants on hand, the team put the material to the test by running over it in a car instead, demonstrating how it could revert to its original shape.
“At 80 percent water content, you’d think it would burst apart like a water balloon, but it doesn’t: it stays intact and withstands huge compressive forces,” says Professor Oren A. Scherman, who led the research. “The properties of the hydrogel are seemingly at odds with each other.”
The scientists also used the novel material to make a pressure sensor for human motions, such as standing, walking and jumping. They are now continuing to develop the material with a view to adapting it for biomedical applications, such as cartilage replacement, and potentially soft robotics.
“To the best of our knowledge, this is the first time that glass-like hydrogels have been made," says Huang. "We’re not just writing something new into the textbooks, which is really exciting, but we’re opening a new chapter in the area of high-performance soft materials."
The research was published in the journal Nature Materials, while you can see the super jelly get run over in the video below.
Source: University of Cambridge
