To showcase the importance of controlling particle size (a unique feature of our production method), we performed studies on the ability of phytantriol-based cubosomal particles of different sizes to fuse with model cell membranes (giant unilamellar vesicles (GUVs)). We loaded our particles with 40 mM calcein (self-quenched) which, following successful fusion with giant vesicles, would lead to an increase fluorescence upon dilution to a lower concentration. The dye was loaded into the particles via microfluidics as before, purified via SEC, and concentrated to an approximate particle concentration of 5E10 particles/ml (determined using Multi-angle DLS). Two size populations were generated, at 130 nm and 310 nm, and diluted to adjust for any discrepancy in concentration between the two. Separately, giant vesicles composed of DOPC with PE-Rhodamine (0.5 mol%) were generated via electroformation. These were mixed at a 1:1 ratio with each LLC size class separately via gentle pipette aspiration, and transferred to a coverslip for imaging. Confocal images were taken of individual giant vesicles after at least 15 minutes. The green channel (detecting fluorescence between 500 nm and 530 nm) was used to determine whether calcein had been delivered to the aqueous centre of the GUV, without loss of membrane integrity, marked by a significant increase in fluorescence intensity.