Low Molecular Weight Micelles

I.F. Uchegbu et al. (eds.), Fundamentals of Pharmaceutical Nanoscience, DOI 10.1007/978-1-4614-9164-4_2, © Springer Science+Business Media New York 2013 Abstract Low molecular weight amphiphile micelles are formed from the selfassembly of comparatively hydrophilic amphiphiles (molecular weight <1,500 Da). These structures may be spherical or present as nanofi bres in the case of peptide amphiphiles; the latter with one axis in the 5–20 nm size range. Micelles are formed from amphiphiles in aqueous media and micelle formation is driven by the need to reduce the energetically unfavourable interactions between the hydrophobic regions of the amphiphilic molecule and the bulk water molecules. Micelles are used for the delivery of hydrophobic drugs and are usually used in intravenous formulations. Hydrophobic drugs may be encapsulated within the hydrophobic micelle core, increasing the level of hydrophobic drug that may be incorporated within aqueous media by over 1,000-fold in some cases. The characterisation of micelles for pharmaceutical use involves a determination of: the critical micellar concentration (the concentration at which micellisation starts), the colloidal stability of the dispersion, micelle particle size, micelle morphology and the drug encapsulation or drug solubilisation capacity of the micellar dispersion. Micelles formed from low molecular weight amphiphiles are dynamic structures and there is continuous exchange of material between the micellar aggregate and the bulk medium; this dynamic exchange has a negative effect on the stability and biocompatibility of micellar formulations.