Liposomes

Low amphiphile concentration

Molecules dispersed randomly without any ordering

Higher amphiphile concentration

Molecules will spontaneously assemble into micelles

Micelles

Hide hydrophobic tail inside micelle core

Expose hydrophilic head to aqueous solution

CMC

Critical micelle concentration

Minimum concentration of surfactant at which micelle formation takes place

High amphiphile concentration

Assemblies will become ordered

Hexangular columnar phase

Amphiphiles form long cylinders that arrange in a hexagonal lattice

Middle soap phase

Lamellar phase

Highest concentration

Neat soap phase

Extended sheets of amphiphiles separated by thin layers of water

Liposomes

Vesicular structure of 1 or more lipid bilayers encapsulating an aqueous core

2 layers of molecules arranged in 2 concentric circles

Multilamellar

Multitude of concentrically orientated bilayer around core

Unilamellar

1 bilayer surrounding an aqueous core

Formed by sonication of multilamellar liposome

Membrane entrapped drugs

Liposome carry strongly lipophilic drugs fully buried in lipid bilayer

Entrapped/encapsulated drugs

Liposomes carry strongly hydrophilic drugs isolated in aqueous interior

Membrane associated drugs

Liposomes carry drugs with intermediate logP partition between lipid and aqueous phase

PC, Phosphatidylethanolamine

Natural phospholipid

Major lipid component used in the preparation of pharmaceutical liposomes

What factors create a rigid bilayer

Long alkyl chain length

Saturated carbons

Presence of cholesterol

Rigid bilayer

More stable

Retain entrapped drug for longer

Fluid bilayers

Rapid release delivery

Liposome stability

Lipid composition

Storage conditions

Stabilisers

Advantages of liposomes as drug carriers

Lipid composition - biodegradable

Natural phospholipids - biologically inert/low toxicity

Biodistribution to whole body - target specific receptors

Liposome classification

Conventional

Sterically stabilised

Immunoliposomes

Cationic

Conventional liposomes

Neutral/negative charge

Used for passive targeting to cells of the MPS

Sterically stabilised liposomes

Carry hydrophilic coatings

Obtain prolonged circulation times

Covalently attach Hydrophilic polymer, PEG to liposome bilayers to enhance binding

Immunoliposomes

Antibody targeted

Used for active targeting purposes

Antibody coupled to liposomal surface

Cationic liposomes

Positively charged

Deliver genetic material