Multilayer tubes that constrict, dilate, and curl in response to stimuli†
Tubular structures in nature have the ability to respond to their environment—for example, blood vessels can constrict or dilate, thereby regulating flow velocity and blood pressure. These tubes have multiple concentric layers, with each layer having a distinct composition and properties. Inspired by such natural structures, we have synthesized responsive multilayer tubes in the laboratory without resorting to complex equipment such as a 3-D printer. Each layer of our tubes is a polymer gel formed by free-radical polymerization of water-soluble monomers. We can precisely control the inner diameter of the tube, the number of layers in the tube wall, and the thickness and chemistry of each layer. Tubes synthesized in this manner are robust, flexible, and stretchable. Moreover, our technique allows us to incorporate stimuli-responsive polymers into distinct regions of these tubes, and the resulting tubes can change their shape in response to external stimuli such as pH or temperature. In the case of laterally patterned tubes, the tube can be made to constrict or dilate over a particular segment—a behavior that is reminiscent of blood vessels. In the case of longitudinally patterned tubes, a straight tube can be induced to systematically curl into a coil. The versatility of our technique is further shown by constructing complex tubular architectures, including branched networks. On the whole, the polymeric tubes shown in this paper exhibit remarkable properties that cannot be realized by other techniques. Such tubes could find utility in biomedical engineering to construct anatomically realistic mimics of various tissues.