Structurally preserved TEMPO-oxidized succinoglycan enables dual pH/temperature-responsive hydrogels with intrinsic antioxidant function.

A multifunctional hydrogel system with dual responsiveness to temperature and pH was developed by incorporating TEMPO-oxidized succinoglycan (TEMPO-SG) into a poly(N-isopropylacrylamide) (pNIPAM) matrix. Succinoglycan, a microbial exopolysaccharide, was selectively oxidized under mildly acidic conditions (pH ~6.8) using TEMPO/NaClO/NaClO2, introducing carboxyl groups while preserving its molecular structure, native substituents, and rheological integrity. This preservation enables TEMPO-SG to function as a structurally stable, intrinsically antioxidant hydrogel matrix without the need for external antioxidant additives. The degree of oxidation was quantified by acid-base titration and confirmed by FTIR and NMR analyses. TEMPO-SG was copolymerized with pNIPAM at various concentrations (0-2.0 wt%) to fabricate hydrogels with tunable mechanical properties. Rheological and swelling analyses showed that increasing TEMPO-SG content improved storage modulus, swelling behavior, and overall gel strength. The hydrogels maintained the thermo-responsive properties of pNIPAM and gained additional pH sensitivity through the carboxyl-rich TEMPO-SG. In vitro drug release using 5-fluorouracil confirmed dual-stimuli responsiveness governed by both temperature and pH. This study presents a novel platform using mildly oxidized microbial polysaccharides to engineer antioxidant, stimuli-responsive hydrogels. The structurally preserved and bioactive TEMPO-SG matrix offers promising applications in controlled drug delivery, wound healing, and antioxidant biomaterials, where sustained functionality, molecular integrity, and biocompatibility are essential.