Development of Receptor-Binding Domain (RBD)-Loaded PEG-PCL Nanoparticle Formulations Against SARS-CoV-2.

The COVID-19 pandemic caused by the novel coronavirus SARS-CoV-2 has highlighted the critical need for safe and effective vaccines. In this study, subunit nanovaccine formulations were developed using the receptor-binding domain (RBD) of the SARS-CoV-2 spike (S) protein encapsulated in polymeric nanoparticles composed of poly(ethylene glycol)-block-poly(ε-caprolactone) (PEG-PCL). Two surfactants, poly(vinyl alcohol) (PVA) and sodium cholate (SC), were evaluated during formulation via a modified water-in-oil-in-water (w₁/o/w₂) emulsion-solvent evaporation method. The resulting nanoparticles were characterized for particle size, surface charge, encapsulation efficiency, and morphology. Optimized nanoparticles exhibited sizes below 300 nm, polydispersity indices less than 0.3, surface charges between ±10-20 mV, and encapsulation efficiencies exceeding 80%. SDS-PAGE confirmed structural integrity of the RBD, while in vitro release studies demonstrated sustained antigen release over time. Cellular response was assessed by measuring nitric oxide (NO) levels in dendritic cells, indicating comparable levels of cellular activation for both PVA- and SC-containing formulations. These findings demonstrate the potential of PEG-PCL-based nanovaccine systems for safe and stable delivery of viral antigens, offering a promising strategy for future vaccine development against COVID-19 and related pathogens.