liposome

Liposomes are microscopic spherical vesicles composed of one or more phospholipid bilayers that enclose an aqueous core. They form spontaneously when amphiphilic phospholipids are dispersed in water and can be unilamellar or multilamellar. The bilayer provides a flexible, semi-permeable barrier that helps determine stability and drug release.

Hydrophilic drugs can be encapsulated in the aqueous interior, while hydrophobic drugs reside within the lipid membrane. This versatility allows liposomes to modify pharmacokinetics, improve solubility, and reduce systemic toxicity. Typical vesicle sizes for systemic administration range from about 50 to 200 nanometers, though larger or multilamellar formulations exist. Surface charge and composition influence biodistribution and stability.

Surface modification, such as polyethylene glycol (PEG) grafting, reduces opsonization and extends circulation time. Targeting ligands on the liposome surface can enhance delivery to specific tissues or cells. Common preparation methods include thin-film hydration, reverse-phase evaporation, ethanol injection, and microfluidic assembly. Liposome formulations can be sterilized by aseptic processing or filtration and are usually stored refrigerated or frozen; some are lyophilized to improve stability.

Applications and examples: liposomes are used as drug delivery systems for anticancer drugs (for example, liposomal doxorubicin and liposomal daunorubicin) and antifungal agents (liposomal amphotericin B). They are also explored for vaccines and gene delivery, and have influenced broader lipid-based nanoparticle approaches in modern therapeutics.

Advantages include improved drug solubility, altered tissue distribution, and reduced peak toxicity. Limitations involve physical and chemical instability, potential payload leakage, clearance challenges for non-stealth formulations, and higher manufacturing costs. Liposome science began with the work of Alec Bangham in the 1960s and has since advanced toward extensive clinical translation.