A new stretchy material has been developed that can lift an object one-thousand times its weight while still maintaining the ability to revert back to its original shape, when heated at body temperature.
Scientists at the University of Rochester believe that because of its flexibility their shape-memory polymer will be used as artificial skin but could also be useful when applying sutures, for body-heat assisted medical dispensers and for use as a wearable self-fitting apparel.
“Our shape-memory polymer is like a rubber band that can lock itself into a new shape when stretched,” said lead researcher, Mitch Anthamatten. “But a simple touch causes it to recoil back to its original shape.”
The shape-memory polymer works by controlling the crystallisation that occurs when the material is cooled or stretched.
As the material is deformed, polymer chains are stretched, and small segments of the polymer align in the same direction in small areas called crystallites.
These crystallites fix the material into a temporarily deformed shape, but as the number of crystallites grows, the polymer shape becomes more and more stable, making it increasingly difficult for the material to revert back to its initial shape.
To avoid the material becoming fixed in a deformed state the research team inserted molecular linkers to connect the individual polymer strands.
Anthamatten’s group discovered that linkers inhibit, but don’t stop, crystallisation when the material is stretched.
By altering the number and types of linkers used, as well as how they’re distributed throughout the polymer network, the university researchers were able to adjust the material’s structure and precisely set the point at which the material’s shape can be reverted.
As well as being able to stretch and revert back to its original shape the new material has been optimised so that it can store as much elastic energy as possible.
As a result, the shape-memory polymer is capable of lifting an object one-thousand times its weight. For example, a polymer the size of a shoelace – which weighs about a gram – could lift a litre of soda.
“Tuning the trigger temperature is only one part of the story,” said Anthamatten. “We also engineered these materials to store large amount of elastic energy, enabling them to perform more mechanical work during their shape recovery”
Full details of the shape-memory polymer can be found in the Journal of Polymer Science Part B: Polymer Physics.