Waxy rice amylopectin towards stretchable elastic conductive hydrogel for human motion detection

Neat waxy rice amylopectin (WRA) is inexpensive, non-toxic, and non-irritating. However, it alone does not give rise to a robust hydrogel. We thus took the dynamic hydrogen-bonding interaction to bring the WRA element into a polyacrylamide (PAAm) network to elicit a stretchable elastic composite hydrogel through the co-crosslinking reaction. We investigated dynamic interactions between the pre-crosslinked waxy rice amylopectin (PWRA) and PAAm, as well as PWRA themselves, by a series of quantitative reaction models, which revealed the hydrogen-bonding interactions as mainly being built from –OH and –NH2 groups. The optimal hydrogen-bonding interaction required an optimal weight ratio of PWRA to PAAm at 0.7, in which the composite hydrogel demonstrates the best mechanical elasticity and strength. For example, it is elastically elongated to 520%, and can be repeatedly stretched 100 times without apparent mechanical fatigue in its elasticity. Sodium ions were introduced into the composite network to elicit the hydrogel conductivity (0.18 S m−1). As a pressure of ≥10 kPa was applied to its surface, it could respond to the pressure by generation of a resistance signal in 0.16 s, showing a rapid pressure-responsive capability. This responsive process can reversibly proceed for 100 cycles, while keeping its sensitivity. It is included in a sensing device that can detect pressure from movements of the finger, elbow, and knee. In another application, it is capable of recording the variation of the walking pace and revealing the physical conditions of people during running or walking, providing a new direction for the application of starch-hybridized hydrogels.