Self-assembly of dextran-solanesol block copolymers into spherical micelles for photostabilization of quercetin

Compared with cyclodextrins (CD), carbohydrate-based block copolymers offer enhanced tunability regarding guest encapsulation properties by forming micellar assemblies with adjustable carbohydrate segment lengths. This study investigated the self-assembly of fully bio-based dextran-solanesol block copolymers (Dexₙ-b-Sol, where n represents the average degree of polymerization) and their potential to stabilize water-insoluble bioactive quercetin (QC), a UV-absorbing flavonoid with potential sunscreen applications. Transmission electron microscopy, multi-angle dynamic light scattering, and small-angle X-ray scattering confirmed that Dex₉- and Dex₁₈-b-Sol formed spherical micellar structures, whereas Dex₂₅-b-Sol exhibited a mixed core-shell ellipsoid morphology. In the absence of UV exposure, QC remained most stable in organic solvent, followed by coexistence with β-CD, Dex₂₅-b-Sol, γ-CD, Dex₁₈-b-Sol, and Dex₉-b-Sol, suggesting that both hydrophobicity and structural confinement contribute to its stability. To assess photostability, UV-C irradiation at 254 nm was used as a high-energy model to simulate photodegradation stress. Under UV-C irradiation, bare QC degraded rapidly in organic solvent, showing an exponential decay pattern with a half-life of 4.1 h. Encapsulation with Dex₁₈-b-Sol provided the most effective protection, prolonging the half-life of QC to 10.4 h with no detectable major degradation products. These findings underscore dextran length's role in micellar block copolymer design for natural sunscreens and advanced biomaterials.