Interfacial click chemistry for improving both dextran shell density and stability of biocompatible nanocapsules

• Click reaction occurred at oil/water interface in an emulsion-evaporation process.
• Azide functions of dextran-based stabilizer reacted with α-alkyne polylactide.
• Click Cu(I)-catalyzed azide-alkyne cycloaddition reaction was optimized.
• Dextran-covered oily-core/polylactide-shell nanocapsules were characterized.
• Increase of dextran coverage density and thickness was observed for clicked objects.

Dextran-covered nanocapsules (NCs) have been obtained by emulsion-evaporation method coupled with an in situ click Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction occurring at liquid/liquid interface. To assure biocompatibility and biodegradability of NCs, α-alkyne PLA was chosen as inner shell and Miglyol 810 (M810) as oily core. NCs were covered by a hydrophilic superficial layer of dextran modified by azide-terminated 6-carbon aliphatic side chains, so-called DexN3. DexN3 was dissolved in the aqueous phase, but during emulsion process it migrated at the interface to act both as stabilizer and as reactant. Click reaction occurred at the oil-in-water interface between azide functions from DexN3 and alkyne groups of PLA present in the organic phase. Influence of different parameters, such as catalyst system or sonication conditions, has been studied on CuAAC reaction efficiency. CuSO4/AAsc was proven to be the most efficient catalyst. NCs characteristics in terms of particle size distribution, dextran coverage, colloidal stability in presence of salt and of SDS (competitive surfactant) as well as their morphology have been investigated. Core–shell NCs were obtained with various M810 content. Covalent linkages between PLA shell and dextran coverage improved colloidal stability of NCs, even in presence of SDS but also increased dextran density and thickness, in comparison to non-clicked NCs.

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