Molecular Exchange in Lipid Nanoparticles via Time-Resolved Small Angle Neutron Scattering

The nano-scale dynamics of lipid nanoparticles (LNPs) for drug delivery play a large role in their function. Limited molecular motion is important for avoiding degradation prior to entering cells. Intracellularly, enhanced molecular motion is then vital for effective endosomal escape. We experimentally quantify such nano-scale dynamics through time-resolved small-angle neutron scattering (TR-SANS). This technique, previously leveraged only for simpler self-assembled systems, provides unprecedented insight to molecular behavior of LNPs. We find using TR-SANS in combination with traditional SANS and small-angle x-ray scattering (SAXS) that as pH drops below the pKa of the ionizable lipid, internal structure becomes more disordered and molecular exchange of cholesterol between LNPs occurs at a much faster rate. The results give insight into the behavior enabling delivery and provide a quantifiable metric by which to compare formulations. Successful analysis of this multi-component system also expands the opportunities for using TR-SANS to characterize other complex biomaterials.