Self-assembled liposomes from electrosprayed polymer-based microparticles

Composite poly(N-isopropylacrylamide) (PNIPAAm)/phosphatidylcholine (PC) microparticles were prepared by electrospraying. PC-based liposomes were subsequently generated upon the addition of water. The microparticles have an average diameter of ca. 1 μm, while the liposomes produced were found to have much smaller diameters of ca. 225–280 nm. The liposomes had zeta potentials of ?44 to ?50 mV, consistent with the formation of a stable suspension. Upon heat treatment, the liposomes exhibit phase transitions due to the influence of PNIPAAm. The liposomes containing 33 % PC have a phase transition temperature of approximately 36 °C, close to physiological conditions. The model drug ketoprofen could be loaded into electrosprayed microparticles and subsequently incorporated into self-assembled liposomes, with an entrapment efficiency for the latter process of ca. 75 %. Sustained drug release regulated by temperature was observed from these drug-loaded materials. At 25 °C, only 45 % of the total drug loading was released after 110 hours, while at 37 °C drug release approached 90 % over the same time period. The self-assembled liposomes reported here, therefore, have great potential as drug delivery devices.