Scientists have created “smart” plastics that are capable of being moulded into new shapes when illuminated by ultraviolet light and will have significant medical and industrial applications.

The achievement will have potential applications in a variety of fields, said the researchers at Massachusetts Institute of Technology (MIT) and the German GKSS research centre.



“This is really a new family of materials that can change from one shape to another by having light shone on them,” said Robert Langer, professor at MIT and co-author of the paper.



The plastics can be deformed and temporarily fixed in a new shape. Key to the process is the so-called “molecular switches,” or photosensitive groups, that are grafted onto a permanent polymer network.



The resulting photosensitive polymer film is then stretched with an external stress, and illuminated with ultraviolet light of a certain wavelength. This prompts the molecular switches to crosslink, or bind one to another.



When the light is switched off and the external stress released, the crosslinks remain, maintaining an elongated structure.



Exposure to light of another wavelength cleaves the new bonds, allowing the material to spring back to its original shape.



A variety of other temporary shapes can be produced in addition to elongated films, said the researcher.



“While the deformation is well-fixed for (the irradiated) layer, the other keeps its elasticity. As a result, one contracts much more than the other when the external stress is released, forming an arch or corkscrew spiral shape,” said the authors.



The researchers said the temporary shapes were very stable for long times even when heated to 50 degrees Celsius. Currently, they are developing medical and industrial applications using photosensitivity of the plastics.



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