(318c) How Well Can You Tailor the Charge of Lipid Vesicles?

Artificial biomembrane assemblies, such as vesicles or liposomes, are indispensable tools for studying fundamental lipid-lipid or lipid-protein interactions, and for applications in drug delivery. Their modular construction enables control over critical attributes like particle size, composition, and surface charge towards tuning colloidal stability, toxicity, interactions with cells/tissues and drug loading efficiency. In this work, we investigated the surface charge tunability of two-component liposomes (anionic DMPS/DMPG and zwitterionic DMPC) by varying membrane composition and the solution environment. Both indirect measurements of charge using zeta potential and direct measurement of electrostatic forces using the surface force apparatus (SFA) were used – a first direct comparison of the two techniques. A near-linear increase in charge was observed at very low charged lipid loading beyond which charge saturation was observed both in physiological (high) salt and low salt conditions. Agreement with theoretical predictions from the Gouy-Chapman-Grahame-Stern model at high salt and Manning condensation at low salt can describe the interplay between membrane composition, lipid headgroup ionization (pKa), electrolyte concentration, and solution pH. The theoretical frameworks used here can provide guidelines to understand this interplay and establish a range of achievable potentials for a specific system and predict the response to triggers like pH and salt concentration changes.