Biodegradable Nanogel Formation of Polylactide-Grafted Dextran Copolymer in Dilute Aqueous Solution and Enhancement of Its Stability by Stereocomplexation

Monodisperse stereocomplex nanogels were obtained through the self-assembly of an equimolar mixture of dextran-graft-poly(l-lactide) (Dex-g-PLLA) and dextran-graft-poly(d-lactide) (Dex-g-PDLA) amphiphilic copolymers with well-defined composition in a dilute aqueous solution. The stereocomplex nanogel possessed partially crystallized cores of hydrophobic polylactide (PLA) and the hydrophilic dextran skeleton by intra- and/or intermolecular self-assembly between PLLA and PDLA chains. The stereocomplex nanogels exhibited significantly lower critical aggregation concentration (CAC) value as well as stronger thermodynamic stability compared with those of the corresponding l- or d-isomer nanogels. The mean diameter of the stereocomplex nanogels was 70 nm with narrow size distribution, implying they were well-defined and presumably nanogels. Furthermore, stereocomplex nanogel exhibited strong kinetic stability. The tunable degradation properties of Dex-g-PLA nanogels were achieved by varying the number of grafted PLA chains as well as applying stereocomplexation. This study demonstrates the advantage of stereocomplexation in the design of biodegradable nanogels with enhanced stability.