Comparison of post-processing methods for liposomal preparations using different techniques

   Background. Liposome size and polydispersity index are key factors determining the subsequent use of nanoparticles. Traditional synthesis methods do not allow the creation of liposomes of the required size and homogeneity; therefore, post-processing is performed using ultrasound or extrusion.

   Objective. To compare two methods of liposome post-processing: ultrasound and extrusion. To compare the efficiency of two different extruders: Liposofast LF-50 and a proprietary extruder. To compare the efficiency of three membranes made of different materials: polycarbonate, polyethersulfone, and porous anodic alumina, using the extrusion post-processing method.

   Materials and Methods. Commercially available reagents were used for liposome synthesis: phospholipids, cholesterol, and vitamin E (all from Sigma Aldrich, Germany). The physicochemical properties of liposomes were studied using a Zetasizer Ultra (Malvern Instruments, UK). Ultrasonic post-processing was performed using a UZG13-0.1/22 disperser (Russia), extrusion processing was carried out using one of two extruders: Liposofast LF-50 (Avestin, Canada) and an extruder of our own design (Nanotechnologies). The following membranes were used: polycarbonate (PC) 200 nm (Nuclepore, Whatman), polyethersulfone (PES) 200 nm (FMPES-0.20, Vladisart), and experimental membrane samples based on porous anodic aluminum oxide (PAO). To determine differences in membrane morphology, they were examined using a Quanta Inspect scanning electron microscope (FEI, USA).

   Results. PC-based membranes are the most uniform, while PES is the least uniform. All membranes have a declared pore diameter of 200 nm, but only for PAOA is this parameter close to the actual value. PAOA membranes have the highest porosity, while polycarbonate membranes have the lowest. Differentpressures are required for the liposomal colloidal solution to pass through the membranes: 1.5–2 atm is sufficient for PES membranes, 5 atm for PC membranes, and 4–6 atm for PAOA membranes, which significantly affects the extrusion rate.

   Conclusion. A comparison of existing liposome homogenization methods demonstrated the advantage of extrusion. The extruder developed by the authors is comparable to a commercial version. The effectiveness of PAOA membranes compared to commercial analogues is demonstrated.

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