Filter-extruded liposomes revisited: a study into size distributions and morphologies in relation to lipid-composition and process parameters

Abstract

Filter-extrusion is a widely used technique for down-sizing of phospholipid vesicles. In order to gain a detailed insight into size and size distributions of filter-extruded vesicles composed of egg phosphatidyl-choline (with varying fractions of cholesterol)--in relation to extrusion-parameters (pore-size, number of filter passages, and flow-rate), flow field-flow fractionation in conjunction with multi-angle laser light scattering (AF4-MALLS, Wyatt Technology Corp., Santa Barbara, CA) was employed. Liposome size-distributions determined by AF4-MALLS were compared with those of dynamic light scattering and correlated with cryo-transmission electron microscopy and (31)P-NMR-analysis of lamellarity. Both the mean size of liposome and the width of size distribution were found to decrease with sequential extrusion through smaller pore size filters, starting at a size range of ≈70-415 nm upon repeated extrusion through 400 nm pore-filters, eventually ending with a size range from ≈30 to 85 nm upon extrusion through 30 nm pore size filters. While for small pores sizes (50 nm), increased flow rates resulted in smaller vesicles, no significant influence of flow rate on mean vesicle size was seen with larger pores. Cholesterol at increasing mol fractions up to 0.45 yielded bigger vesicles (at identical process conditions). For a cholesterol mol fraction of 0.5 in combination with small filter pore size, a bimodal size distribution was seen indicating cholesterol micro-crystallites. Finally, a protocol is suggested to prepare large (∼ 300 nm) liposomes with rather narrow size distribution, based on the filter extrusion at defined flow-rates in combination with freeze-/thaw-cycling and bench-top centrifugation.

Dexamethasone Loaded Liposomes by Thin-Film Hydration and Microfluidic Procedures: Formulation Challenges

“…After extrusion, the liposomal diameter of the preparations was in the range of 144.1 ± 13.8-162.7 ± 17.0 nm and the poly dispersity index (PDI) was in the range of 0.08-0.39. The higher liposome size with respect to the filter pore size is due to the reversible elastic deformation of the vesicles as reported in the literature [18].…”

Interfacing with Neural Activity via Femtosecond Laser Stimulation of Drug-Encapsulating Liposomal Nanostructures

“…Immediately afterward, uniformly sized liposomes were obtained by extrusion of the suspension through a 400 nm polycarbonate membrane at a temperature above the transition temperature of the lipids. Based on a study of filter-extruded liposomes by Hinna et al (2016), we expect that most of the liposomes are unilamellar with a minority of bilamellar (multiwalled) ones in the mix. The suspension of tether-ready liposomes was then placed in a sample vial (15–20 ml capacity).…”

Liposomes containing lipids from Sulfolobus islandicus withstand intestinal bile salts: An approach for oral drug delivery?

“…Liposomes were prepared by conventional thin-film hydration method followed by sequential filter-extrusion (for details see Hinna et al, 2015). Three formulations were prepared: (A) pure egg lecithin (egg PC), (B) egg PC: cholesterol (ratio 80:20, mol%) and (C) egg PC:TLE:cholesterol (70:18:12, mol%) (Parmentier et al, 2011b).…”