**Dynamic Mussel-Inspired Chitin Nanocomposite Hydrogels for Wearable Strain Sensors**

#### **Pejman Heidarian 1, Abbas Z. Kouzani 1,\*, Akif Kaynak 1, Ali Zolfagharian 1 and Hossein Yousefi 2**


**\*** Correspondence: kouzani@deakin.edu.au

Received: 9 June 2020; Accepted: 23 June 2020; Published: 24 June 2020

**Abstract:**It is an ongoing challenge to fabricate an electroconductive and tough hydrogel with autonomous self-healing and self-recovery (SELF) for wearable strain sensors. Current electroconductive hydrogels often show a trade-off between static crosslinks for mechanical strength and dynamic crosslinks for SELF properties. In this work, a facile procedure was developed to synthesize a dynamic electroconductive hydrogel with excellent SELF and mechanical properties from starch/polyacrylic acid (St/PAA) by simply loading ferric ions (Fe<sup>3</sup>+) and tannic acid-coated chitin nanofibers (TA-ChNFs) into the hydrogel network. Based on our findings, the highest toughness was observed for the 1 wt.% TA-ChNF-reinforced hydrogel (1.43 MJ/m3), which is 10.5-fold higher than the unreinforced counterpart. Moreover, the 1 wt.% TA-ChNF-reinforced hydrogel showed the highest resistance against crack propagation and a 96.5% healing efficiency after 40 min. Therefore, it was chosen as the optimized hydrogel to pursue the remaining experiments. Due to its unique SELF performance, network stability, superior mechanical, and self-adhesiveness properties, this hydrogel demonstrates potential for applications in self-wearable strain sensors.

**Keywords:** dynamic hydrogels; tannic acid; chitin nanofibers; starch; self-healing; self-recovery
