Kinetically Stable Bicelles with Dilution Tolerance, Size Tunability, and Thermoresponsiveness for Drug Delivery Applications

Mixtures of a phospholipid (1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine, DPPC) and a sodium-cholate-derived surfactant (SC-C₅ ) at room temperature formed phospholipid bilayer fragments that were edge-stabilized by SC-C₅ : so-called "bicelles". Because the bilayer melting point of DPPC (41 °C) is above room temperature and because SC-C₅ has an exceptionally low critical micelle concentration (<0.5 mm), the bicelles are kinetically frozen at room temperature. Consequently, they exist even when the mixture is diluted to a concentration of 0.04 wt %. In addition, the lateral size of the bicelles can be fine-tuned by altering the molar ratio of DPPC to SC-C₅ . On heating to ≈37 °C, the bicelles transformed into micelles composed of DPPC and SC-C₅ . By taking advantage of the dilution tolerance, size tunability, and thermoresponsiveness, we demonstrated in vitro drug delivery based on use of the bicelles as carriers, which suggests their potential utility in transdermal drug delivery.