*4.6. Characterization*

Tensile strength of the hydrogels was evaluated by performing tensile tests on an Instron 5967 electronic universal testing machine. The PVA and PVA/SbQ hydrogels were cut into dumbbell-shaped samples with a diameter of 7–9 mm and a thickness of 3–5 mm. Additionally, the compressive tests were carried out on cylindrical hydrogel samples with a diameter of 7–9 mm and a thickness of 3–5 mm by an Instron 5967 electronic universal testing machine at room temperature. The compression rate was fixed at 2 mm/min. Measurements of each sample were repeated at least three times and the acquired data were reported as average value and standard deviation.

To estimate the adhesive strength of hydrogels, the shear adhesive strength tests were performed. The PVA, PVA/CNC, PAM and PVA/SbQ hydrogels were cut into a rectangular spline with a size of 40 mm × 10 mm × 5 mm and then adhered to metal sheets, where the adhesion area on one side was 10 mm × 10 mm and the other side was 10 mm × 20 mm, as shown in Figure 1c. The force response was recorded while keeping one metal sheet fixed and moving another metal sheet at a speed of 20 mm/min using a universal testing machine. In the experiment, 5 samples were tested in each group to obtain the average value and standard deviation. The adhesive strength was calculated by the maximum load divided by the adhesion area.

To test the swelling ratio of hydrogels, the hydrogel samples were immersed in distilled water for 3 days at least at room temperature, until the hydrogel weight did not increase. In the next step, these swollen hydrogels were placed in a 40 ◦C oven to evaporate all of the water in hydrogels. The weight of swollen hydrogel and dried hydrogels were recorded, respectively. The equilibrium swelling ratio was calculated by the following equation

$$\rm{ESR\%} = \rm{W\_s/W\_d} \times 100\tag{1}$$

where W<sup>s</sup> and W<sup>d</sup> are the weight of the swollen hydrogel at room temperature and dried hydrogels, respectively.

**Author Contributions:** Conceptualization, Z.L. and H.B.; methodology, Z.L. and C.Y.; software, H.K. and X.H.; formal analysis, Z.L.; resources, H.B., Q.L. and K.K.; writing—original draft preparation, Z.L. and J.H.; writing—review and editing, J.H.; supervision, J.H. and K.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** The authors acknowledge the support from China Scholarship Council scholarship (Z.L.), and the Canada First Research Excellence Fund (CFREF) for its Global Research Initiative in Sustainable Low Carbon Unconventional Resources (J.H.).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

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