**4. Conclusions**

In this work, a dynamic mussel-inspired hydrogel was designed and fabricated by incorporating Fe3<sup>+</sup> ions and TA-ChNFs into a starch-based network. TA-ChNFs play the role of nanofillers and dynamic cross-linkers, thus imparting a SELF ability and high strength to the hydrogel. The hydrogel shows a high SELF ability, mechanical strength, and electro-conductivity. According to our results, the hydrogel reached the highest toughness and notch insensitivity after loading 1 wt.% TA-ChNFs into the hydrogel. Moreover, the hydrogel reinforced by 2 wt.% TA-ChNFs showed the highest self-healing efficiency (98.5%) after 40 min. Additionally, the hydrogel showed repeatable self-adhesive properties, with the ability to attach to almost any surface because of the existence of pyrogallol/catechol groups in TA. The hydrogel is also able to monitor and distinguish motions, showing a good capability as a soft wearable strain sensor. Thus far, there has not been any available research on using TA-ChNFs and starch as potential candidates for fabricating such hydrogels. We anticipate that the hydrogel will be ideally suited for use in self-wearable flexible strain sensors because of its excellent self-healing ability—without needing any external stimuli—and reliable mechanical, electrical, and self-adhesive properties.

*Polymers* **2020**, *12*, 1416

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2073-4360/12/6/1416/s1,. Video S1: 0.5 wt.% TA-ChNF-reinforced hydrogel. Video S2: 0.1 wt.% TA-ChNF-reinforced hydrogel. Video S3: Visual self-healing inspection of a cylindrical-shaped 1 wt.%. TA-ChNF-reinforced hydrogel. Video S4: Merging glass-plastic slides by a 1 wt.%.TA-ChNF-reinforced hydrogel. Video S5: 1 wt.%.TA-ChNF-reinforced hydrogel adhered to rubbery gloves while being stretched without adding any additional adhesive tapes. Video S6: Darkening and lightening of 1 wt.%.TA-ChNF-reinforced hydrogel after applying and releasing the stress using an LED bulb indicator. Video S7: Electrical self-healing ability of the hydrogel reinforced by 1 wt.%.TA-ChNF.

**Author Contributions:** Conceptualization, methodology, acquisition of data, analysis and interpretation of data, drafting of the manuscript, P.H.; project administration, supervision, resources, review and editing, A.Z.K.; supervision, discussions, analysis and interpretation of data, review and editing, A.K.; review and editing, A.Z.; review and resources, H.Y. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
