Formation of supported lipid bilayers on silica hollow nanospheres: Surface passivation and controlled release of hydrophilic payloads

Electrostatics governs the formation of supported lipid bilayers on silica hollow nanospheres • Lipid coating passivates the particle surface and enables non-adsorptive encapsulation of hydrophilic cargo • The mesoporous silica shell acts as a secondary diffusion barrier, exhibiting hydrated-ionic-radius-dependent salt release Hollow silica nanospheres (SHNs) coated with a supported lipid bilayer (SLB) combine the high loading capacity of a hollow interior with the biocompatibility and tunable surface properties of a lipid membrane, making them promising for controlled delivery applications. Here, we systematically investigate the formation of SLBs on SHNs of varying diameters using neutral, positively charged, and negatively charged liposomes. We demonstrate that SLB formation requires sufficient ionic strength to overcome electrostatic repulsion between the negatively charged silica surface and liposomes of like charge. In contrast, positively charged liposomes form SLBs irrespective of salt concentration due to electrostatic attraction. Using an aggregation-based titration method, we quantify surface coverage and reveal that smaller SHNs are slightly more favorable for surface bilayer assembly. Notably, the lipid coating effectively passivates the silica surface, imparting exceptional colloidal stability. Beyond surface functionalization, we explore the encapsulation and release properties using alkali metal chlorides as non-adsorbing model cargos. The hollow cavity is readily accessible for loading, and the mesoporous silica shell acts as a secondary diffusion barrier, leading to release kinetics that scale with the hydrated radius of the cation. These findings establish design principles for lipid-coated SHNs as tunable carriers for hydrophilic substances with controlled release capabilities. Download: Download high-res image (142KB) Download: Download full-size image