Micelles
A micelle (pronounced /maɪˈsɛl/or /maɪˈsiːl/, plural micelles, micella, or micellae) is an aggregate of surfactant molecules dispersed in a liquid colloid. A typical micelle in aqueous solution forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic single tail regions in the micelle centre. This phase is caused by the insufficient packing issues of single tailed lipids in a bilayer. The difficulty filling all the volume of the interior of a bilayer, while accommodating the area per head group forced on the molecule by the hydration of the lipid head group leads to the formation of the micelle. This type of micelle is known as a normal phase micelle (oil-in-water micelle). Inverse micelles have the headgroups at the centre with the tails extending out (water-in-oil micelle). Micelles are approximately spherical in shape. Other phases, including shapes such as ellipsoids, cylinders, and bilayers are also possible. The shape and size of a micelle is a function of the molecular geometry of its surfactant molecules and solution conditions such as surfactant concentration, temperature, pH, and ionic strength. The process of forming micellae is known as micellization and forms part of the phase behavior of many lipids according to their polymorphism.
Recent US Patents
2/1/2011
7,879,317
Polymeric micelle compositions with improved stability and methods of making thereof
Seo et al of Samyang, South Korea, developed polymeric compositions capable of forming stable micelles in an aqueous solution consisting of an amphiphilic block copolymer of a hydrophilic block and a hydrophobic block, and a polylactic acid derivative wherein one end of the polylactic acid is covalently bound to at least one carboxyl group. The carboxyl group of the polylactic acid derivative may be fixed with a di- or tri-valent metal ion, obtained by adding the di- or tri-valent metal ion to the polymeric composition. (RDC 8/17/2011)
Recent Journal Articles
Effect of block compositions of amphiphilic block copolymers on the physicochemical properties of polymeric micelles
(3783-3790) Polymer 52 #17 (2011)
Li et al of the Tokyo Women’s Medical University, Japan, prepared amphiphilic block copolymers with various chain lengths of poly(n-butyl methacrylate) blocks (PBMA) and poly(N-acryloylmorpholine) blocks (PAM) by RAFT polymerization. Packing parameter of block polymers in water (β < 0.2) indicated the formation of core-corona structures, which was further confirmed from a difference between core- and corona-forming chain surface areas. Hydrodynamic micellar size was related with the numbers of BMA (NBMA) and AM (NAM), and their ratios (NBMA/NAM). With increasing NBMA/NAM value, the polymer aggregation numbers and inner core sizes increased, while the critical micelle concentrations, the corona thickness, and the second virial coefficient of block copolymer micelles decreased. These properties changed with increasing NBMA/NAM value resulted in a linear increase in corona chain unit density (ρAM) that limited chain mobility. Both micellar properties and biocompatible effect can be regulated by tailoring the block compositions of amphiphilic polymers. (RDC 8/4/2011)