[Read the Article]
Shape-memory materials can be deformed and cooled, but will release their internal stresses and recover their original shapes when heated above a transition temperature. Shape-memory polymers are lightweight and can withstand large strain changes, but can only support small recovery stresses. Shape-memory alloys have the advantage of large stress recovery, but are heavier and have low recovery strains. To get the best of both worlds, and create shape-memory materials that are both "smart" and strong, Miaudet et al. formed a composite material with carbon nanotubes that had nearly the stress recovery of shape-memory alloys, but still exhibited large strain capabilities. The return of these composites to their original shapes can be seen by blowing hot air onto a fiber deformed in the shape of a knot (clip 1), and in the retraction of a fiber connected to a metallic bar and electrical power supply (clip 2).