Tunable phenolic-modified alginate–chitosan semi-IPNs as multifunctional platforms for localized antimicrobial and antioxidant therapy

• Fully bio-based semi-IPN hydrogels based on alginate and chitosan functionalized with phenolic acids. • Metal-free approach with mild functionalization ensures high biocompatibility and sustainability. • Tunable physical states: injectable liquids, thermo-gels, and freeze-dried porous scaffolds. • Controlled release of lomefloxacin with enhanced antibacterial activity against Staphylococcus aureus. • Improved antioxidant performance supports local therapies for infection-prone tissues. Biopolymer-based hydrogels offer a versatile platform for drug delivery thanks to their biocompatibility, use of natural polymers, and tunable properties. In this study, we developed semi-interpenetrating polymer network (semi-IPN) hydrogels composed of alginate (ALG) and chitosan (CS), chemically modified with caffeic acid (CA) and gallic acid (GA), to enhance both antimicrobial and antioxidant activity. The resulting hydrogels showed tunable physical states, high porosity, and good thermal stability, transitioning from liquid dispersions to solid forms under different conditions. Lomefloxacin was loaded to test local delivery performance. Drug release profiles revealed that the modification influenced release: the ALG-CS_CA hydrogel released about 61 % of Lomefloxacin, while the ALG-CS_GA hydrogel released ∼ 43 %, in line with their swelling behavior. Incorporation of phenolic acids significantly boosted antioxidant capacity, with the GA-modified hydrogel reaching over 80 % scavenging activity. Tests against Staphylococcus aureus confirmed improved antimicrobial activity compared to unmodified ALG-CS matrices. Overall, these fully bio-based, metal-free semi-IPNs combine biocompatibility, antimicrobial and antioxidant functions, and tunable release properties. This sustainable system, based only on natural polymers and mild chemical functionalization, shows strong potential for safe, scalable biomedical applications in localized therapies for infection-prone or inflamed tissues. This green design offers practical advantages for future scale-up and sustainable production.