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Characterizing Liposome Formation, Structure, and Stability

24 October 2018 No Comment

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Liposomes have been attractive delivery systems for decades due to their composition of natural biological lipids and structural resemblance to cell membranes suggesting metabolic compatibility, low toxicity, biocompatibility and lack of a strong immune response1.  They are comprised of spherical vesicles with an aqueous core enclosed by one or more phospholipid bilayers or lamellae and are frequently classified based on their size, polydispersity, and number of bilayers2. Control over these parameters has remained a challenge with most preparation methods and is further accentuated when moving from a laboratory to industrial scale. The desirable size for drug delivery [systems] ranges between 50 and 200nm3. They are often used in studies of model biological membranes, phase transition and spacing, targeted drug delivery to specific areas of a human body, etc4.  The extent of liposome instability in various biological fluids such as plasma depends on the relative concentrations, size and lamellarity, lipid composition and incubation temperatures1.

Biophysical characterization of these systems and their payloads is critical to understanding and optimizing their fabrication and function. looks at optimal conditions for extruding liposomes as well as their stability under different conditions. We highlight the limit of detection for fluorescently labeled liposomes. Malvern Panalytical provides a cost-effective suite of characterization tools to measure critical parameters of these products. Nanoparticle Tracking Analysis (NTA) from our NanoSight product line measures size, concentration and fluorescence. Dynamic (DLS) and Electrophoretic (ELS) Light Scattering from Malvern Panalytical’s Zetasizer Ultra measures size, zeta potential, and payload stability. Small- and Wide-Angle X-ray scattering (SAXS/WAXS) on the Malvern Panalytical Empyrean Nano system enable determination of the lamellarity, structure and dimensions of the lipid bilayers.

Complementary experimental techniques for the characterization of liposomes include:

Benefits:

  • Measurements can be done in situ and at different composition of lipid and buffer.
  • Only minimal sample preparation is required.
  • Only several minutes measurement time are often sufficient.
  • Liposomes were characterized with respect to their size, zeta potential, fluorescence, concentration, stability and morphology.

Here is a summary of what you can understand about liposomes based on the technique used:

Technique  

 

Deduced information 

 

Relates to

 

DLS z-avg. size and size distribution Liposome-cell interaction
ELS Zeta potential, surface charge Stability against aggregation. Interaction with other molecules
NTA Number-avg. size and size distribution
Particle concentration, fluorescence
Liposome-cell interaction, labeling efficiency
SAXS Lamellarity, repeat distances and order; single bilayer structure Membrane rigidity. Stability. Drug release profile
WAXS Alkyl chain packing, thermal phase transitions Membrane rigidity. Stability. Drug release profile
DSC Thermal behavior
Drug-liposome interaction
Membrane rigidity. Stability. Drug release profile

 

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References:

  1. Woodle, M. C. (1995). Sterically stabilized liposome therapeutics. Advanced Drug Delivery Reviews, 16(2–3), 249–265. https://doi.org/10.1016/0169-409x(95)00028-6
  2. Patil, Y. P., & Jadhav, S. (2014). Novel methods for liposome preparation. Chemistry and Physics of Lipids, 177, 8–18. https://doi.org/10.1016/j.chemphyslip.2013.10.011
  3. Harashima, H., Sakata, K., Funato, K., & Kiwada, H. (1994). Pharmaceutical Research, 11(3), 402–406. https://doi.org/10.1023/a:1018965121222
  4. Chibowski, E., & Szcześ, A. (2016). Zeta potential and surface charge of DPPC and DOPC liposomes in the presence of PLC enzyme. Adsorption, 22(4–6), 755–765. https://doi.org/10.1007/s10450-016-9767-z