## 3 Results and Discussion  
ATR-FTIR spectra of ALG, PPy-ALG, and ALG@PPy hydrogels are shown in Figure 2a, where characteristic bands of alginate and polypyrrole were identified [26], indicating the successful formation of the composite. The thermal stability of ALG, PPy-ALG, and ALG@PPy (Figure 2b) showed a loss of adsorbed water occurring up to 164 \({}^{\circ}\)C for all samples, but the weight loss of the composite hydrogels was smaller when compared to neat ALG. ALG and PPy-ALG showed degradation of the main alginate chains in the range from 164 \({}^{\circ}\)C to 420 \({}^{\circ}\)C, associated to the dehydration of ALG, fracture of glycosidic bonds, decarbonylation, and decarboxylation. The weight loss above 420 \({}^{\circ}\)C may be the result of an additional thermal degradation of previously formed residues [27; 28; 29]. ALG@PPy displayed the first loss of mass event at a lower temperature, possibly due to the higher content of polypyrrole on this sample's surface. It is expected that polypyrrole degrades around 290 \({}^{\circ}\)C and 750 \({}^{\circ}\)C [26]. The SEM images of the beads are in Figure 2c-e and indicate that neat alginate is homogeneous, whereas in the composite hydrogels, dispersed particles are observed. The morphology of the composite included the characteristics of both the neat alginate hydrogel and pure polypyrrole (Supplementary Material--Figure S4a and Figure S4b, respectively). In the PPy-ALG hydrogel, a homogeneous surface and randomly distributed polypyrrole nanoparticles are observed inside the ALG matrix, since the small structures formed inside the hydrogel, as observed in Figure 2d, can be attributed to polypyrrole (see Figure S4c). Conversely, in the ALG@PPy (Figure 2e), a rough surface and a shell of polypyrrole is observed, as expected from the protocol employed. The composite hydrogels were exposed to different pH values. In alkaline conditions (pH 12.0), the material completely loses its physical integrity due to calcium ion displacement and gel network breakdown [30; 31; 32]. Thus, these materials are only applicable in neutral to acidic media (pH 1 up to 6). The swelling index (SI) in all tested media is shown in Figure 3. The samples were evaluated in ultrapure water, HCl 0.1 mol L\({}^{-1}\), pH 1, and NaCl 0.1 mol L\({}^{-1}\), pH 6. The ALG@PPy presented the higher SI in all 3 media, followed by the PPy-ALG and pure ALG. For example, in water, the content of absorbed water of ALG@PPy (68.3 wt%) hydrogel was 1.7 times higher than that of the PPy-ALG (39.3 wt%) hydrogel and 2.1 times that of ALG (32.4 wt%) hydrogel. Water uptake is generally related to the number of hydrophilic groups available in the hydrogel network, such as -OH, -COOH, and -COO\({}^{-}\). The higher SI of the samples containing polypyrrole may indicate that less hydrophilic groups of alginate are available to interact with the media since they are preferably interacting with polypyrrole or committed to intra and intermolecular bonds. Another factor is the crosslinking degree of the alginate matrix, which may be lower in the presence of polypyrrole. Finally, a higher hydrogel porosity facilitates the entrance of water and increases SI. Although the hydrogel porosity was not determined, it is possible to infer that polypyrrole particles, when occupying some sites in the alginate matrix, may contribute to the increase in the  
Figure 2: (**a**) ATR-FTIR spectra of the ALG, PPy-ALG and ALG@PPy hydrogels disks. (**b**) TGA and dTGA curves for ALG, PPy-ALG and ALG@PPy hydrogels. SEM images showing the morphology of (**c**) ALG, (**d**) PPy-ALG and (**e**) ALG@PPy hydrogels. number of voids in the alginate matrix, hindering alginate-alginate interactions responsible for the matrix cohesivity. Considering the effect of media, the SI of all samples increased in the order: water < HCl << NaCl. The results are most probably related to alginate matrix behavior in different media.