Hybrid Cerasomes Composed of Phosphatidylcholines and Silica Networks for the Construction of Vesicular Materials with Functionalized Shells

A phosphatidylcholine-based cerasome (PC-cerasome) was prepared by a combination of a copper-catalyzed azide alkyne cyclo-addition (CuAAC) reaction and a sol–gel condensation process. In a 2 wt % urea aqueous solution, azide precursors containing a triethoxysilane group (TEOS) were coupled with an alkyne lysolipid (AL) through a CuAAC reaction to generate triethoxysilane triazole-phosphatidylcholine (TEOSTPC) molecules. TEOSTPC self-assembled into liposomes immediately after formation. Incubation of the liposomes at 50 °C led to a gradual hydrolysis and decomposition of urea, which caused a mildly basic condition. Simultaneously, a base-catalyzed sol–gel condensation of TEOS groups occurred and drove formation of a silica network in the bilayer membranes of the TEOSTPC-liposomes, resulting in cerasomes with an organic/inorganic hybrid shell composed of PC and an SO2 network. Because of the presence of the SO2 network in the bilayer membrane, the cerasomes exhibited good structural stability in the aqueous phase and maintained the vesicular structure even when dispersed in water-miscible organic solvents. Coexistence of the bilayer membrane and SiO2 was verified, which is indicative of an intramembrane sol–gel condensation. The formation process of an SiO2 network in the bilayer membrane was verified using spiropyran-containing triazole-phosphatidylcholine (SPTPC) as a molecular probe. The SPTPC was embedded in TEOSTPC-liposomes, and subsequent sol–gel condensation anchored the SPTPCs in the SiO2 network. During sol–gel condensation, SP isomerized to merocyanine (MC), indicating that the polarity of the microenvironment in the bilayer membrane increased due to formation of the SiO2 network. Moreover, the rigidity of the SiO2 network prohibited MC-to-SP recovery, resulting in a cerasome with a MC-functionalized shell. Based on the structural stability of the PC-cerasome and the convenient preparation method combining CuAAC and sol–gel condensation, we anticipate that these PC-cerasomes will find broad utility in the construction of vesicular materials with functionalized shells.