A new polymer morphs from one pre-programmed shape to two others: as the flattened tube (top) is heated, it opens up (middle); heating it further makes it shrink.
New shape-memory polymers can take on three successive shapes
Source: “Polymeric Triple-Shape Materials”
Ingo Bellin et al.
Proceedings of the National Academy of Sciences 103(48): 18043-18047
Results: Researchers at MIT and the GKSS Research Center in Germany have engineered polymers that can be programmed to sequentially take on three different predefined shapes in response to changes in temperature.
Why it matters: Existing shape-memory polymers can assume only two shapes each. The addition of a third shape could enable, say, an arterial stent that could be inserted into an artery in a collapsed form, induced to open once in place, and later shrunk for removal. The researchers demonstrated such an intelligent tube, along with a structure that could be used in device manufacture to connect difficult-to-access parts.
Methods: Each of the new materials is a polymer network consisting of two different cross-linked segments that respond to temperature differently. The researchers first cast the material into its final shape–such as the shrunken version of the stent–using a standard plastic-molding technique. They then use a precise sequence of heating and cooling steps to “program” the other two shapes, taking advantage of the material’s different responses to different temperatures. Heating the material in two steps makes it revert to its intermediate, and finally to its original, shape.
Next Steps: The researchers must demonstrate that the materials are safe enough to be used in medical applications. They are also developing fastener materials that could be useful in manufacturing.