*3.1. Characterization of the Synthesized HAMA Hydrogel*

First, the swelling capacities of the synthesized HAMA hydrogels were evaluated using a gravimetrical approach. The weights of both the fully swollen and thermally dried hydrogel samples were separately determined. The results obtained are presented in Figure S2, where it can be observed that the average weight before swelling was ~8.17 mg. Once the dried samples had absorbed a sufficient amount of water to reach the equilibrium state of swelling (refer to Figure S3), the average weight dramatically increased to ~1526.23 mg, giving an average swelling ratio of 18,581%. This massive extent of swelling could be due to the superhydrophilic property of the HA. Thereafter, the morphology of the microscopic structure established inside the hydrogel layer was inspected using SEM. Figure 3a depicts the SEM image to illustrate the cross-sectional view of the synthesized HAMA hydrogel. It can be observed that a highly porous structure with an interconnected backbone was formed, in which most pores had either an oval or elongated bubble shape and their size varied from 20 to 200 μm in diameter. Such a high density of the porous structure also proved the considerable swelling capacity exhibited by the HAMA hydrogels.

**Figure 3.** (**a**) Cross-sectional SEM image and (**b**) FTIR spectrum of the synthesized HAMA hydrogel. The numbers in (**b**) denote the prominent peaks detected by the FTIR analysis.

The functional groups associated with the synthesized HAMA hydrogels were identified by FTIR analysis. The FTIR spectrum acquired is presented in Figure 3b, in which numbers (1 to 6) are used to denote the prominent peaks detected. Among all the peaks, peak 1 situated at 3436.34 cm−<sup>1</sup> was much broader than the others, which could be due to the O-H or N-H stretching, considering that both stretching vibrations occurred at an overlapped frequency band between 3200 and 3600 cm−<sup>1</sup> [35]. Peak 2 situated at 1628.07 cm−<sup>1</sup> was likely contributed by the carbonyl (C=O) stretching rather than the N-H bending of the secondary amide group. This is because, for most secondary amides, the weak N-H bending adsorption often appears at the frequency band between 1500 to 1560 cm−<sup>1</sup> [36]. Peak 3 situated at 1410.64 cm−<sup>1</sup> corresponded to the vibration of the O-C=O group [37]. Peaks 4 and 5 situated at 1153.41 and 1046.36 cm−<sup>1</sup> were related to the C-O and C-O-C stretching, respectively. Peak 6 situated at 650.68 cm−<sup>1</sup> was a fingerprint peak of HA [37], which could have been caused by a combinational manner of bending vibrations.
