Sub-micron Colloidosomes with Tuneable Cargo Release Prepared Using Epoxy-Functional Diblock Copolymer Nanoparticles

HYPOTHESIS:Pickering emulsions stabilized using epoxy-functional block copolymer nanoparticles should enable the formation of sub-micron colloidosomes that are stable with respect to Ostwald ripening and allow tuneable small-molecule cargo release. EXPERIMENTS:Epoxy-functional diblock copolymer nanoparticles of 24 ± 4 nm were prepared via reversible addition-fragmentation chain transfer (RAFT)-mediated dispersion polymerization of methyl methacrylate (MMA) in n-dodecane. Sub-micron water-in-n-dodecane Pickering emulsions were prepared by high-pressure microfluidization. The epoxy groups were then ring-opened using 3-aminopropyltriethoxysilane (APTES) to prepare cross-linked colloidosomes. The colloidosomes survived removal of the aqueous phase using excess solvent. The silica shell thickness could be adjusted from 11 to 23 nm by varying the APTES/GlyMA molar ratio. The long-term stability of the colloidosomes was compared to precursor Pickering emulsions. Finally, the permeability of the colloidosomes was examined by encapsulation and release of a small molecule. FINDINGS:The Pickering emulsion droplet diameter was reduced from 700 to 200 nm by increasing the salt concentration within the aqueous phase. In the absence of salt, emulsion droplets were unstable due to Ostwald ripening. However, emulsions prepared with 0.5 M NaCl are stable for at least one month. The cross-linked colloidosomes demonstrated much more stable than the precursor sub-micron emulsions prepared without salt. The precursor nanoemulsions exhibited complete release (>99 %) of an encapsulated dye, while higher APTES/GlyMA ratios resulted in much lower dye release, yielding nearly impermeable silica capsules that retained around 95 % of the dye.