Coordination-Crosslinked Carboxymethyl Chitosan-Mn2+ Hydrogel: Structure–Activity Relationship for In Vitro cGAS-STING Immune Stimulation

Both carboxymethyl chitosan (CMCS) and Mn2+ can stimulate the cGAS-STING pathway to promote the production of immune factors such as type I interferons (I IFNs), thereby regulating the body’s immune response. In this study, a sustained-release Mn2+-loaded CMCS-Mn hydrogel was designed, and the synergistic effects of CMCS and Mn2+ on innate immunity, as well as factors influencing the immune response, were investigated. The optimal gel formulation was obtained with a CMCS concentration of 1 mg/mL and a MnCl2 concentration of 0.02 mol/L, yielding a gel with a particle size of 472.16 nm, a polydispersity index of 0.35, a Mn2+ content of 1.488 mg/g, and a specific surface area of 4.74 m2/g. The hydrogel forms mainly via coordination interactions between Mn2+ and the amino and carboxyl groups on CMCS molecular chains and exhibits pH-dependent Mn2+ release behavior. Cellular assays demonstrated that the combination of 600 μg/mL CMCS-Mn2+ hydrogel and 5 μg/mL free Mn2+ produced the strongest IFN-β induction. The hydrogel exhibits synergistic immunomodulatory effects of both CMCS and Mn2+; while the amino groups are critical for the immunological activity of CMCS, Mn2+ plays a more prominent role. Partial substitution of Mn2+ by Ca2+ can loosen the cross-linked network and further modulate Mn2+ dissociation from the hydrogel.