Researchers from GKSS Research Center Geesthacht GmbH in Teltow, Germany, RWTH Aachen and mnemoScience GmbH, both in Aachen, Germany, and Massachusetts Institute of Technology in Cambridge have developed shape-memory polymers that react to the application of ultraviolet radiation of different wavelengths. Described in the April 14 issue of Nature, the materials may have use in medical applications such as stents or self-tying sutures.Similar to previously reported thermoresponsive shape-memory polymers, the photoresponsive materials incorporate molecular switches that form physical cross-links to fix the materials into a deformed shape and that release the cross-links to enable the materials to return to their original shape. In the new polymers, this is achieved using cinnamic groups that react differently to irradiation shorter or longer than 260 nm.The researchers examined the performance of two photoresponsive shape-memory polymers at room temperature and found that they have a comparable strain recovery rate to thermoresponsive materials, but a much lower strain fixity rate. They note, however, that the suitability for remote activation and the insensitivity to local temperature make the photoresponsive materials superior for medical applications.