Exosome-functionalized carbonate apatite nanoparticles as potential immunomodulatory mucosal vaccine adjuvant: physicochemical characterization and cytocompatibility on macrophages and buccal epithelial cells

Abstract

Mucosal vaccines offer a promising strategy for inducing site-specific immunity, but their effectiveness depends heavily on safe and efficient delivery systems. This study aims to study exosome-functionalized carbonate apatite (CHA-EXO) nanoparticles as a novel immunomodulatory adjuvant for oral mucosal vaccination. The CHA nanoparticles were synthesized and functionalized with mesenchymal stem cell-derived exosomes with physical adsorption. Their physicochemical properties, including functional groups, morphology, size distribution, and surface charge, were characterized. Loading efficiency and stability were observed with Bradford assays. Cytocompatibility was assessed in RAW264.7 and TR146 cells using the MTT assay. Comparative analysis was performed against aluminum hydroxide as a conventional adjuvant. The synthesized CHA-EXO nanoparticles exhibited a nanoscale diameter of approximately 100-120 nm, with a moderate increase in size following exosome functionalization in a concentration-dependent manner. They maintained a stable dispersion, showing surface charges of -31.63 to -37.48 mV in water and around -26 mV in artificial saliva. The nanoparticles demonstrated high cytocompatibility in both TR146 and RAW264.7 cells (> 75% viability), performing better than aluminum hydroxide at comparable moderate doses. Furthermore, the functionalized nanoparticles formed stable complexes with high loading efficiency, reaching 93.89% at elevated exosome concentrations, and released only 19.40% of the cargo within 24 h. These findings indicate exosome immobilization and enhanced potential for increased cellular interaction. The CHA-EXO nanoparticles show promise as a stable and biocompatible oral mucosal adjuvant, offering both physicochemical stability and favorable cell interactions.