“At 80% 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,” said Professor Oren Scherman who led the research. “The properties of the hydrogel are seemingly at odds with each other.”
All that is not water is a network of polymers.
“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,” said chemist Zehuan Huang.
The selected crosslinking molecules are cucurbiturils – unusual barrel-shaped molecules – that in this case hold two designer guest molecules inside their voids “like a molecular handcuff” said Cambridge.
The material has a compressive strengths up to 100MPa with no fracture, even when compressed at 93% strain over 12 cycles of compression and relaxation.
“We’ve revisited traditional polymer physics and created a new class of materials that span the whole range of material properties from rubber-like to glass-like,” said Scherman.
In a demonstrator, the researchers made a hydrogel pressure sensor for real-time monitoring of standing, walking and jumping. Potential applications include soft robotics.
The work is published in Nature Materials as ‘Highly compressible glass-like supramolecular polymer networks‘ (only abstract available without payment).
Watch a video of some being run over (the image is a still from this video)