**4. Conclusions and Outlook**

WPI hydrogels containing two types of TA have been produced, which withstand autoclaving. The greatest influence on the swelling change is exerted by the amount of TAs contained in the WPI hydrogels. An increase of the TA/WPI ratio in the hydrogels to 0.30 (for ALSOK 02 and ALSOK 04 both) leads to a significant decrease in MI compared with the control hydrogel without TA in neutral conditions (pH 7). The pH lowering leads to a MI decrease and an increase in the amount of released TAs by 1.5–2 times compared with incubation at neutral pH (pH 7) for all WPI hydrogels with and without TAs. The maximum TAs release was observed for hydrogels with the TA/WPI ratio 0.0375 (for ALSOK 02 and ALSOK 04 both) in alkaline pH (pH 9) and amounted to almost 80% 48 h after the incubation start. According to the swelling data, at this time point, the hydrogels begin to destruct, since their MI have negative values at 48 h. Future work will investigate the possible simultaneous release of hydrogel material. Also, measurements of the pH and zeta potential of the hydrogel dependence on pH gelification will be investigated in our future work. All obtained hydrogels containing TAs have cytotoxic properties against the human laryngeal cell carcinoma (Hep-2) Hep-2 cell line. An increase in the concentration of TAs in hydrogels leads to an increase in the cytotoxic effect. Thus, a WPI hydrogels can be used as anti-cancer scaffolds with a prolonged release profile of TAs.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/1996-194 4/14/4/749/s1, Figure S1: Linearity using ALSOK 02 demonstrating the line equation and the linear correlation coefficient (R2), Figure S2: Linearity using ALSOK 04 demonstrating the line equation and the linear correlation coefficient (R2), Table S1: *p*-Values for two-way analysis of variance (ANOVA) statistics for the WPI-TA hydrogel's swelling data (TA/WPI ratio–0.0375/0.075/0.15/0.3) at pH 7 compared to the swelling data of the WPI hydrogel without TA, Table S2: *p*-Values for two-way analysis of variance (ANOVA) statistics for the WPI-TA hydrogel's swelling data (TA/WPI ratio– 0.0375/0.075/0.15/0.3) at pH 5 compared to the swelling data of the WPI hydrogel without TA, Table S3: *p*-Values for two-way analysis of variance (ANOVA) statistics for the WPI-TA hydrogel's swelling data (TA/WPI ratio–0.0375/0.075/0.15/0.3) at pH 9 compared to the swelling data of the WPI hydrogel without TA, Table S4: *p*-Values for two-way analysis of variance (ANOVA) statistics for the cell viability data of WPI-TA hydrogels (TA/WPI ratio–0.0375/0.075/0.15/0.3) compared to the WPI hydrogel without TA.

**Author Contributions:** Conceptualization, design, planning, O.A.M.; methodology, O.A.M., B.C.N.J.; and R.A.V.; inves-tigation, O.A.M., B.C.N.J.; and R.A.V., and V.O.P.; data curation, O.A.M. and R.A.V.; writing—original draft preparation, O.A.M. and R.A.V.; writing—review and editing, T.E.L.D. and V.O.P.; supervision, O.A.S. and T.E.L.D.; project administration, T.E.L.D.; funding acquisition, O.A.S. and T.E.L.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** These researches on the hydrogel formation, the drug release and anticancer activity of hydrogels was funded by RUSSIAN SCIENCE FOUNDATION (grant number 19-75-10043). T.E.L.D. acknowledges THE BRITISH COUNCIL for their support in the framework of the Researcher Links Russia grant "Patient-tailored biomaterials for tissue regeneration, combating microbial contamination and drug delivery".

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

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The data that support the findings of this study are contained within the article.

**Acknowledgments:** The authors thank Patrick Ricquier (Omnichem NV, Belgium) for providing the tannic acids.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
