New polymer changes shape when exposed to body heat

Scientists have developed a new polymer that changes shape when exposed to body heat and could be used in self-fitting apparel and body-heat assisted medical dispensers.
The material is a type of shape-memory polymer, which can be programmed to retain a temporary shape until it is triggered - typically by heat - to return to its original shape.
"We also engineered these materials to store large amount of elastic energy, enabling them to perform more mechanical work during their shape recovery," said Mitch Anthamatten, professor at University of Rochester.
The researchers were able to adjust the material's stability and precisely set the melting point at which the shape change is triggered.

Heating the new polymer to temperatures near 35 degrees Celsius, just below the body temperature, causes the material to revert to its permanent shape.
"Our shape-memory polymer is like a rubber band that can lock itself into a new shape when stretched. But a simple touch causes it to recoil back to its original shape," said Anthamatten.

Having a polymer with a precisely tunable trigger temperature was only one objective, researchers said.
Of equal importance, researchers wanted the material to be able to deliver a great deal of mechanical work as the shape transforms back to its permanent shape.
Consequently, they set out to optimise their polymer networks to store as much elastic energy as possible.

"Nearly all applications of shape memory polymers will require that the material pushes or pulls on its surroundings," said Anthamatten.
"However, researchers seldom measure the amount of mechanical work that shape-memory polymers are actually performing," said Anthamatten.
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 gramme - could lift a litre of soda.
Anthamatten said the shape-memory polymer could have a variety of applications, including sutures, artificial skin, body-heat assisted medical dispensers, and self-fitting apparel.
The study was published in the Journal of Polymer Science Part B: Polymer Physics.