Facile Preparation of Eco-Friendly, Flexible Starch-Based Materials with Ionic Conductivity and Strain-Responsiveness

This work demonstrates a facile and "green"method to prepare eco-friendly, flexible, transparent, and ionically conductive starch-based materials, which have great potential for personal health-monitoring applications such as disposable electrodes. This method relies on the use of the CaCl2 solution and enables both the efficient disorganization and amorphization of high-amylose starch granules with low energy consumption and the reinforcement of the starch chain network by starch-metal cation complexation. Specifically, the method involves a simple mixing of a high-amylose starch with the CaCl2 solution followed by heating the mixture at 80 °C for 5 min. The whole process is completely environmentally benign, without any waste liquid or bioproducts generated. These resulting materials displayed tunable mechanical strength (500-1300 kPa), elongation at break (15-32%), Young's modulus (4-9 MPa), toughness (0.05-0.26 MJ/m3), and suitable electrical resistivity (3.7-9.2 ω·m). Moreover, the developed materials were responsive to external stimuli such as strain and liquids, satisfying the requirements for wearable sensor applications. Besides, composed of only starch, CaCl2, and water, the materials are much cheaper and eco-friendly (can be consumed by fish) compared with other polymer-based conductive hydrogels.