# Dual Stimuli-Responsive Polysaccharide Hydrogels Manufactured by Radiation Technique
## 3 Results
### Stimuli-Responsive Swelling
The current examples in Figure 9a,c show the pH-driven changes in the DS of CMC gels formed with 2.5% crosslinker by irradiation with 25 kGy. The DS of 2.5, 5, and 10% CMC gels decreases, respectively, from ca. 52, 120, and 150 g/g of 67, 83, and 87% upon lowering the pH to below 2. Thus, as one might have expected, the pH responsivity of CMC hydrogels is large, and dependent on the CMC concentration. Additionally, the increase in the amount of crosslinker to 5% reduced the EDS to ca. 28 g/g (Figure 9d), but did not change the pH response compared to the aforementioned 2.5% CMC gels, which is unapparent in the view of the following findings. Accordingly, the effect of PEGDA crosslinker on 5% CMC hydrogels formed with 50 kGy is significant, as shown in Figure 10a,b. The DS changes from the initial EDS of ca. 207 and 52 g/g of ca. 78 and 67%, respectively, for 2.5 and 5% PEGDA. This is obviously due to the higher crosslinking density and lower initial EDS at pH 7. Additionally, despite the same amount of CMC in the starting mixture before irradiation, the number of carboxyl moieties in the gel might slightly differ as some uncrosslinked or degraded fragments of chains were extracted beforehand. As demonstrated above, in the double polysaccharide gels, the EDS greatly depends on the HPC content, and the data in Figure 11 show that the HPC also influences the pH responsivity. For hydrogels of 5/5 CMC/PEGDA formed with 25 kGy, the initial EDS is ca. 63, 69, and 84 g/g, and the DS change is of approximately 76, 72, and 62%, dependently on the HPC concentration, and 0, 5, and 10% HPC, respectively. As the second polysaccharide concentration rises, in addition to the network being looser, the molar number of the carboxyl moieties is lower, and consequently, the pH responsivity is reduced. The general observation is that the gels collapsed at a low pH return approximately return to their initial EDS after several days at a neutral pH. Figure 8: Temperature-depending swelling of 5% HPC hydrogels, containing CMC and the crosslinker; CMC%/PEGDA% composition and dose: (**a**) 5/2.5, 50 kGy; (**b**) 2.5/5, 25 kGy; (**c**) 2.5/5, 50 kGy. Figure 10: pH-dependent swelling of CMC%/HPC% 5/5 formed with 50 kGy; with PEGDA of (**a**) 2.5% and (**b**) 5%. Figure 9: pH-dependent swelling of CMC hydrogels formed with 25 kGy in the presence of PEGDA; CMC%/PEGDA% content: (**a**) 2.5/2.5, (**b**) 5/2.5, (**c**) 10/2.5, and (**d**) 2.5/5. The summary of swelling variation as a function of either temperature or pH of HPC/CMC gels is presented in Table 2. Typically, the EDS at room temperature and in the neutral pH depends on the composition, foremost on the crosslinker content, and the absorbed dose. The hydrogels comprising the anionic CMC, formed with or without the crosslinking agent, significantly reduce their volume/mass upon the decrease in the pH of the swelling medium. The presence of HPC as a co-component somewhat alters the pH-responsive character of the gels, but renders the material temperature sensitive. Therefore, the hydrogels display double-stimuli responsive characteristics. Analogous systems were chemically synthesized using CMC and a synthetic polymer of PNIPAAm as interpenetrating polymer networks to be used for drug delivery [43]. Those gels responded to the temperature by 20-50% with the peak transition characteristic to PNIPAAm at 34-37 \({}^{\circ}\)C or at lower temperature that depended on the gel composition and the pH of the medium. In current studies, deswelling in response to decreasing pH is greater than that in response to the increasing temperature, assuming a similar molar content of side groups, carboxyl and 2-hydroxypypyl, which provide the polysaccharide with an ionic and amphiphilic character. For instance, for the gel of 10/2.5/5 HPC/CMC/PEGDA (Table 2) formed with 25 kGy, the DS change is ca. 32% and 51% as a response to the temperature and pH change, respectively.