## 2 Results and Discussion
### Assessment of Antioxidant Properties
The dashed horizontal line in the figure indicates the fluorescence intensity of the control cells (untreated with hydrogels). ***\(p\) < 0.0001 versus the control. Figure 6: Effect of tested hydrogels on the intracellular level of ROS in keratinocytes (HaCaT cells). The dashed horizontal line in the figure indicates the fluorescence intensity of the control cells (untreated with hydrogels). ***\(p\) < 0.0001 versus the control. The antioxidant properties of CBD and TER observed in this study confirm numerous scientific studies that assessed these properties [16; 37; 38]. This activity is significant in designing hydrogel carriers and other delivery systems of active substances intended for treating dermatological diseases because the excessive production of free radicals leads to many skin diseases and also significantly affects skin appearance [39]. So far, many of CBD's antioxidant activity mechanisms have been described. One of them assumes that CBD reduces oxidative stress by preventing superoxide radical formation, mainly caused by xanthine oxidase and NADPH oxidases, both NOX1 and NOX4 [40; 41]. As shown by [PERSON] and [PERSON], the antioxidant potential of CBD may be related to the abstraction of electrons and hydrogen [38]. This cannabinoid also affects redox balance by being able to alter the level and activity of both antioxidants and oxidants [16]. CBD also reduces ROS production by chelating transition metal ions involved in the Fenton reaction [42]. The antioxidant activity of this compound is also associated with activating a redox-sensitive transcription factor called nuclear factor erythroid 2 (NRF2), which is responsible for the transcription of antioxidant genes with cytoprotective properties [43]. Studies also show that this compound increases the level of superoxide dismutase (SOD) mRNA and increases the enzymatic activity of Cu-, Zn-, and Mn-SOD, responsible for the metabolism of superoxide radicals [41]. Moreover, it can form adducts with glutathione and cytochrome P450 3A11, thus reducing their biological activity [44]. The antioxidant activity of this compound is also associated with supporting the activity of antioxidant enzymes by preventing the decrease in the level of micronutrients necessary for the proper biological activity of enzymes such as superoxide dismutase or glutathione peroxidase [45]. CBD's antioxidant activity is also associated with scavenging free radicals, breaking their chain reactions, and transforming them into less active forms [16]. A significant effect of the antioxidant activity of CBD is also the reduction in lipid and protein modification [16; 45]. We have shown in this study that the antioxidant properties of TER are significantly weaker than those of CBD and other conventionally used antioxidants, which was also confirmed in scientific articles by other authors [46]. However, the incorporation of both of these compounds into the structure of the hydrogel materials shows a strong antioxidant potential related to the possibility of scavenging ROS, increasing the activity of SOD, and reducing the intracellular level of ROS in skin cells in vitro.