Zwitterionic surfactant/cyclodextrin hydrogel: microtubes and multiple responses

Abstract

Previously reported polymer-free cyclodextrin (CD) hydrogels usually relied on tailored modification of CDs or careful design and synthesis of guests, which may limit their mass production or application. Herein, we report on a hydrogel system based on a native CD (β-CD) and a commercially available zwitterionic surfactant (tetradecyl dimethylammonium propane sulfonate, TDPS). The TDPS/β-CD hydrogel shows excellent mechanical properties with an elastic modulus >10 × 104 Pa and yield stress >100 Pa. Microstructures in the hydrogel were identified to be well-defined microtubes, featuring a long, flexible, bundling, and entangling nature. The microtubes form an extensive 3D network and then a strong hydrogel. The building unit of the microtubes was determined to be 2TDPS@3β-CD complex, which forms a 3D array with a considerable crystalline nature. The array eventually folds up into the microtubes. In addition, the TDPS/β-CD hydrogel was found to be multi-responsive to temperature, pH, urea, and a competitive guest. It is envisioned that the commercial availability and low cost of β-CD and TDPS may facilitate the mass production and application of the present TDPS/β-CD hydrogel.