Stimuli responsive self-folding using thin polymer films

The ability to manipulate the curvature of thin films in response to a specific stimulus such as light, heat, pH, electric fields or chemicals can be utilized to create a variety of smart three dimensional (3D) materials. Because of the high structural and chemical variability of polymers that can be created by synthetic approaches, thin films composed of polymers are especially useful in creating a wide range of stimuli-responsive structures. Moreover, since polymer thin films can be patterned by a number of planar techniques such as photolithography, molding, or imprinting, a variety of precisely patterned 2D precursors can be used to fold-up functional structures such as tubular, spherical and polyhedral capsules, biomimetic actuators and even microsurgical tools. This article reviews recent advances and highlights future challenges.

► Self-folding provides a means to enable stimuli responsive materials.
► Layering and spatial patterning of thin polymer films can cause them to curve or bend.
► Materials and devices fold and unfold when exposed to stimuli including biochemicals.
► Self-folding enables untethered actuation at small size scales.
► Differential crosslinking and swelling can enable biomimetic actuators.