The concept might be understood by thinking of a fried potato chip. Consider a flat slice of potato. As we fry the slice, different regions shrink by different amounts and the original “flat” grid becomes curved.
What the team did is to program the final metric of the polymer by changing the spatial concentration of N-isopropylacrylamide, a molecule that undergoes a dramatic, reversible volume reduction at 33°C. Above the transition temperature, the flat gel discs fold into controllable three-dimensional shapes. The initial state of the polymer before bending was gel-like disks and the form into which the polymer was bent was prescribed during the setup of the polymer.
After the discs were gently warmed they curved into domes, saddles and even sombrero-shaped structures. Such diverse reversible shape control in a soft material could have applications ranging from optics to biomedicine.
When the density varies across the disc, the sheet buckles to relieve the pressure of uneven shrinkage. The researchers worked out what shrinkage patterns would produce the structures they wanted and then used an automated mixing system to produce “cocktails” of gels with the right properties.
The ability to create pre-planned, spontaneously formed objects, say the researchers, can have far-reaching consequences for various manufacturing processes as well as for creating structures that have to meet specific climatic conditions.
Dr. Sharon explained the potential of the research by saying: “Our work enables the creation of highly complex structures, which sometimes would be difficult to manufacture through regular industrial means”. Additionally, such research provides greater understanding of the ways in which complex structures, such as flowers, develop in nature.
TFOT recently covered a different research into shape memory polymers developed by the Ohio based company Cornerstone Research Group (CRG).
More information about the project can be found at the Hebrew University website and Science Magazine.
