Polyethylenimine-CO2 adduct-stabilized vaterite hydrocolloidal particles

Abstract

We explore CaCO3 mineralization via the addition of a Ca(OH)2 solution to branched polyethylenimine–CO2 (PEI-CO2) adduct solutions. The alkylammonium carbamate zwitterions (i.e., CO2-adducted linkages) in PEI-CO2 adducts can hydrolyze to release bicarbonate ions to form CaCO3in situ; meanwhile, the zwitterions themselves transform into the polyamine structure of polyethylenimine (PEI). The PEI-CO2 polymer serves as both the CO2 source and template for vaterite CaCO3 nucleation and growth. A relatively low dosage of the Ca(OH)2 solution (e.g., at 9.2–37% stoichiometry) preserves enough CO2-adducted linkages in the templating PEI-based chains, allowing them to firmly adsorb onto the growing vaterite nanocrystallites, providing long-term vaterite phase and colloidal stability. The high molecular weight of the used PEIs (e.g., 10 k–25 k Da) strengthens the adsorption as well. The mesoporous structure, the dissolution in a weakly acidic environment (pH 6.5), the low cytotoxicity, the ease of endocytosis, and the presence of reactive PEI amino groups all make the obtained vaterite nanoparticles a versatile candidate for effective and acid-responsive drug delivery. This work highlights the multifunctionality of PEI-CO2 adducts for CaCO3 mineralization, serving as a CO2 source and vaterite template and providing the vaterite phase and colloid stability, as well as reactivity for further modification.