Towards increasingly complex model systems for the study of extracellular vesicle-like interactions with the endosomal membrane.

Extracellular vesicle (EVs) are lipid membrane-bound nanoparticles produced by cells, which measure 10s to 1000s of nm in diameter. Due to their provenance, they are innately biocompatible and have huge potential in therapeutics and diagnostics. While the roles of the proteins and nucleic acid cargoes are well studied in these processes and applications, less is known about the role of the lipids. Two crucial steps in delivery of nanoparticle-encapsulated cargo, such as EV-mediated delivery of nucleic acids, are cell uptake and subsequent endosomal escape. Both of these processes involve traversing a lipid membrane, although the physical and chemical environments vary between these two processes. In this NR experiment, we will study how vesicles mimicking the lipid composition of EVs interact with floating membrane bilayers representing the intracellular endosomal membrane at different stages of maturation, and study the fusion processes observed at a range of physiologically relevant pH. This beamtime represents the third in a series of neutron reflectometry experiments in which we will identify the role that the lipid composition and asymmetric distribution of EVs and their synthetic mimics play in cell uptake and endosomal release. It is a crucial step forward in the field of understanding the biophysical mechanisms behind such biological processes, and paves the way towards identifying new EV-mimicking drug delivery vehicles for nucleic acid therapies.