Coil Formation of a Silicone String Using UV–Ozone Treatment

[Image: see text] Microcoils are used in various mechanical devices. However, existing methods for producing microcoils from polymers often require expensive equipment. In this study, microcoils were prepared using a cost-effective and simple method. The material used was silicone, which is a biocompatible polymeric material. Silicone was solidified inside glass capillaries to form thin, straight strings with a diameter of 140 μm. The string was then transformed to a coil shape by oxidation using UV–ozone treatment while it was prestretched and pretwisted. The resilience force from the prestretching and pretwisting forces caused the string to bend and twist, respectively. As a result of the combination of these deformation modes, a coil was formed. As an application of the coils, an actuator was prepared, which repeatedly transforms between straight and coiled shapes. The actuation was caused by the swelling/deswelling of silicone with hexane. A large strain of 54% was obtained.