Bioinspired Cross-Linked Anionic Hydrogel Microparticles as Potential Adjuvants for Safe Vaccines: Colloidal-Chemical Characteristics, Morphology and Biological Properties.

Novel anionic cross-linked hydrogel-based microparticles with controlled size, functionality, porosity, and morphology were synthesized via tailored precipitation polymerization of hydrophobic and hydrophilic monomers in the presence of dimethacrylate as a cross-linking agent. The resulting hydrogel microparticles (HG5), with a size of 250 ± 50 nm and a polydispersity index of 0.079, were readily dispersible in water and formed stable suspensions at physiological pH (7.2-7.4). Their physicochemical properties were comprehensively characterized using FT-IR, NMR, DLS, SAXS, TEM, and turbidimetry. HG5 efficiently incorporated albumin as a model antigen with a loading efficiency of 95%, forming stable hydrogel-protein complexes that maintained their hydrodynamic size and colloidal stability over one month of storage. Biological evaluation demonstrated low toxicity toward pseudonormal cell lines, with cell viability remaining above 50% at concentrations up to 5 mg/mL and no detectable apoptotic effects in HEK293 cells. Human peripheral blood mononuclear cells (PBMCs) were sensitive to HG5 exposure, exhibiting an IC50 of 0.52 mg/mL, while showing good hemocompatibility with hemolysis below 5%. HG5 significantly enhanced immunogenicity, increasing BSA-specific antibody levels by 1.9-fold compared to the immunization without adjuvant (p < 0.05). These findings demonstrate the potential of HG5 as a versatile platform for protein delivery and vaccine adjuvant development.