We were a little slow on this one (didn't see it 'till C|Net picked it up), but the April MIT Tech Talk newsletter announced that researchers there have invented plastics which can be shaped by light.
"These programmed materials change shape when struck by light at certain wavelengths and return to their original shapes when exposed to light of specific different wavelengths."..."These programmed materials change shape when struck by light at certain wavelengths and return to their original shapes when exposed to light of specific different wavelengths."
This isn't the first shape-changing polymer they've invented. In 2002, "the researchers introduced thermoplastic, biodegradable shape-memory polymers and demonstrated a nifty medical applicationa smart suture that ties itself into the perfect knot."... "Now instead of heat, we can induce the shape-memory effect in polymers with light."
How it works: "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. The result? 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."
In addition to medical applications, I could see this being useful in space, where structures that spring into shape using nothing but the extremely-plentiful radiation from the sun (with no moving parts or power-supply of their own) would come in very handy.
