Micelles nanoemulsions

It is useful, for reasons which are apparent in relation to movement of nanoparticles in vivo, to divide nanosystems into two types, hard and soft, although there are obviously intermediate situations. Hard systems, for example, polymeric nanoparticles and nanocapsules, nanosuspensions or nanocrystals, dendrimers, and carbon nanotubes are neither flexible nor elastic. Hard systems can block capillaries and fenestrae that have dimensions similar to the particles, whereas soft systems can deform and reform to varying degrees. Erythrocytes and many liposomes fall into this category and are thus better able to navigate capillary beds and tissue extracellular spaces. Soft systems include nanoemulsions (microemulsions) and polymeric micelles. 

These are transparent or translucent systems covering the size range from 5 to 50nm. Unlike emulsions and nanoemulsions (which are only kinetically stable), microemulsions are thermodynamically stable as the free energy of their formation is either zero or negative. Microemulsions are better considered as swollen micelles normal micelles can be swollen by some oil in the core of the micelle to form O/W microemulsions. Reverse micelles can be swollen by water in the core to form W/O microemulsions. 

Near the HLB temperature, the interfacial tension reaches a minimum, as illustrated in Figure 14.4. Thus, by preparing the emulsion at a temperature 2-4 °C below the PIT (near the minimum in y), followed by rapid cooling of the system, nanoemulsions may be produced. The minimum in y can be explained in terms of the change in curvature H of the interfacial region, as the system changes from O/W to W/O. For an O/W system and normal micelles, the monolayer curves towards the oil such that H has a positive value. However, for a W/O emulsion and inverse micelles the monolayer will curve towards the water and H will be assigned... 

CDC are defined only by their size (most scientists agree on sizes below 1 pm others set 0.5 pm as the upper limit). CDC are very heterogeneous in all other aspects (e.g., thermodynamic stability, chemical composition, and the physical state, including solid, liquid, or liquid-crystalline dispersions) [ 1 ]. The most prominent examples are nanoparticles, nanoemulsions, nanocapsules, liposomes, nanosuspensions, (mixed) micelles, microemulsions, and cubosomes. Some CDC have reached the commercial market. Probably the best known example is the microemulsion preconcentrate of cyclosporine (Sandimmun-Neoral), which minimized the high variability of pharmacokinetics of the Sandimmun formulation. In addition, intravenous injectable CDC have been on the commercial market for many years. Examples include nanoemulsions of etomidate (Etomidat-Lipuro) and diazepam (Diazepam-Lipuro) [2-4], mixed micelles (Valium-MM, Konakion), and liposomes (AmBisome) [5]. 

Therefore, micelle-forming surfactant molecules (e.g., SDS) will be present in three different forms, namely, on the lipid surface, as micelles, and as monomeric surfactant molecules in solution. Lecithin will form liposomes, which have also been detected in nanoemulsions for parenteral nutrition [77], Mixed micelles have to be considered in glycocholate/lecithin-stabilized and -related systems. Micelles, mixed micelles, and liposomes are known to solubilize drugs, and are therefore attractive alternative drug-incorporation sites (especially with respect to the low incorporation capacity of lipid crystals). 

Molecular inclusion or conjugation complexes, micelles, microemulsions, polymeric particles, and emulsions and nanoemulsions can all be classified as matrix type encapsulation systems. 

Huynh, L., Neale, C., Pomes, R., AUen, C. Computational approaches to the rational design of nanoemulsions, polymeric micelles, and dendrimers for drug delivery. Nanomedicine 2012, 8 (1), 20-36. 

When polymer micelles were modified with folate-PEG lipid, polymer micelles with longer folate-linker PEG length showed high cellular uptake in KB cells, similar to nanoemulsion (Hayama et al. 2008). In these cases, nanoemulsions and polymer micelles are essentially composed of PEG lipid and PEG block copolymers, respectively. The effect of folate-PEG on FR-mediated endocytosis was not clear because of the covering with PEG moieties. Because conventional liposomes can be formed without PEG lipid (Figure 14.1), optimal folate modification could be examined. 

Eigure 1.29 shows the variation of r with time t for 20 80 0/W nanoemulsions at two C12EO4 concentrations prepared by the PIT method. It can be seen from Fig. 1.28 that the emulsion containing the higher surfactant concentration gives a higher rate of Ostwald ripening. This may be due to solubilization of the oil by the surfactant micelles. 

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