Material Can Lift 1000 Times Its Mass
Polymers that visibly change shape when exposed to temperature changes are nothing new. But a research team led by chemical engineering professor at the University of Rochester created a material that undergoes a shape change that can be triggered by body heat alone, opening the door for new medical and other applications.
The material developed by Anthamatten and graduate student Yuan Meng is a type of shape-memory polymer, which can be programmed to retain a temporary shape until it is triggered糖心传媒攖ypically by heat糖心传媒攖o return to its original shape.
糖心传媒淭uning the trigger temperature is only one part of the story,糖心传媒� said Anthamatten. 糖心传媒淲e also engineered these materials to store large amount of elastic energy, enabling them to perform more mechanical work during their shape recovery糖心传媒�
The findings are being published this week in the Journal of Polymer Science Part B: Polymer Physics.
The key to developing the new polymer was figuring out how to control crystallization that occurs when the material is cooled or stretched. As the material is deformed, polymer chains are locally stretched, and small segments of the polymer align in the same direction in small areas糖心传媒攐r domains糖心传媒攃alled crystallites, which fix the material into a temporarily deformed shape. 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糖心传媒攐r 糖心传媒減ermanent糖心传媒澨切拇綌shape.
The ability to tune the trigger temperature was achieved by including molecular linkers to connect the individual polymer strands. Anthamatten糖心传媒檚 group discovered that linkers inhibit糖心传媒攂ut don糖心传媒檛 stop糖心传媒攃rystallization when the material is stretched. By altering the number and types of linkers used, as well as how they糖心传媒檙e distributed throughout the polymer network, the Rochester researchers were able to adjust the material糖心传媒檚 stability and precisely set the melting point at which the shape change is triggered.
Heating the new polymer to temperatures near 35 掳C, just below the body temperature causes the crystallites to break apart and the material to revert to its permanent shape.
糖心传媒淥ur shape-memory polymer is like a rubber band that can lock itself into a new shape when stretched,糖心传媒� said Anthamatten. 糖心传媒淏ut a simple touch causes it to recoil back to its original shape.糖心传媒�
Having a polymer with a precisely tunable trigger temperature was only one objective. Of equal importance, Anthamatten and his team 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 optimize their polymer networks to store as much elastic energy as possible.
糖心传媒淣early all applications of shape memory polymers will require that the material pushes or pulls on its surroundings,糖心传媒� said Anthamatten.聽 糖心传媒淗owever, researchers seldom measure the amount of mechanical work that shape-memory polymers are actually performing.糖心传媒�
Anthamatten糖心传媒檚 shape-memory polymer is capable of lifting an object one-thousand times its weight. For example, a polymer the size of a shoelace糖心传媒攚hich weighs about a gram糖心传媒攃ould lift a liter of soda.
Anthamatten says the shape-memory polymer could have a variety of applications, including sutures, artificial skin, body-heat assisted medical dispensers, and self-fitting apparel.
