Adsorption and Spreading of Sponge-Phase Lipid Nanoparticles on SiO₂ and TiO₂ Surfaces: Ion-Specific Effects and...

Among different lipid nanoparticle systems, sponge-phase nanoparticles (SPNPs) have recently attracted interest due to their ability to encapsulate large macromolecules along with demonstrated high interfacial activity. The potential application of SPNPs calls for investigations into how buffer conditions affect SPNP structure and interfacial activity. Herein, we systematically investigated how different buffer conditions affect SPNP preparation by characterizing solution-phase colloidal properties and interfacial adsorption behavior on oxide surfaces. Dynamic light scattering, electrophoretic mobility, and small-angle X-ray scattering (SAXS) measurements showed that SPNPs prepared by the same dispersion method had similar size, charge, and internal structure largely independent of the buffer condition. Interestingly, however, the interfacial activity of the different SPNP samples depended strongly on the buffer condition used for nanoparticle preparation. Quartz crystal microbalance-dissipation (QCM-D) experiments revealed that certain buffer preparation conditions increased attractive SPNP-SiO₂ surface interactions, which resulted in more favorable adsorption and structural rearrangements to form thin lipid layers. Some SPNP samples adsorbed and underwent structural rearrangements to form thin lipid layers on less energetically favorable TiO₂ surfaces as well. These findings support that SPNPs have high interfacial activity and dynamic responsiveness that are affected by ion-specific buffer conditions and the physicochemical nature of the surface. The study also provides insight into how to formulate SPNPs to control their affinity to interfaces of relevance for biomedical applications.