Researchers examine the application and usefulness of nanoparticle tracking analysis and dynamic light scattering techniques in the characterization of liposomes used as drug delivery vehicles.
Liposomes are fast becoming a preferred vehicle for delivering therapeutic drug molecules to target sites – meaning techniques to measure the size, concentration and zeta potential of the preparation are growing in importance For a drug delivery vehicle to be successful, it will ideally localise and target the therapeutic agent to the site of interest and enable a measurable drug interaction with the affected tissue. Used increasingly for this purpose are liposomes, whose applications now include both systemic and topical drug delivery. With the capacity for formulation as liquids, solids or semi-solids, liposomes are being used in treatments ranging from targeting fungal infections to hepatitis A and acute lymphoblastic leukaemia.
The physical characterisation of liposomes plays an important role in supporting the development of appropriate formulations. Here, we examine the contribution made by the complementary techniques of Nanoparticle Tracking Analysis (NTA) for size analysis and light scattering (dynamic and electrophoretic) for size and zeta potential measurement. ‘Go-To’ Vehicles Liposomes are artificially prepared spherical vesicles that are composed of a lipid bilayer. They were originally used as model systems to study membrane properties such as permeability. Given their ability to incorporate water-soluble materials in their aqueous volume or oil-soluble materials in the lipid bilayer, recent applications for liposomes have focused on their suitability for use as drug delivery vehicles. By controlling the lipid composition and/or through surface modification, liposomes can be designed for specific applications. They may be single-or multi-layered, are biodegradable and essentially non-toxic, and can be produced in different sizes. Their ability to carry both hydrophilic and hydrophobic payloads makes them very versatile. Furthermore, surface modification with the addition of antibodies or peptides, for instance, enables targeting of drugs at specific biological sites or can enhance the longevity of the drug delivery system in vivo. These properties are helping liposomes become the drug delivery system of choice for many developers. Many pharmaceutical uses of liposomes have been described for, among other applications, protecting therapeutic agents against the gastrointestinal environment and facilitating gastrointestinal transport of compounds; targeting and restricting a drug to a particular site; enhancing solubilisation; and improving drug intracellular uptake (1). Topical applications of liposome preparations are also attracting considerable interest both for pharmaceutical and cosmetic use. The mechanisms through which liposomes can deliver drug molecules to target sites include diffusion and, more commonly, direct cell fusion. In the latter process, the lipid bilayer of the liposome will fuse with other bilayers – the cell membrane, for example – thereby transporting the contents of the liposome into the target cell. Click here to see the full article
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