Block copolymers amphiphilic, neutral micelles

As the data from Fig. 10.5 suggests, the PHis-PEG micelles are unstable and can release their contents at neutral pH. In order to deal with this problem, an amphiphilic block copolymer, PLLA-PEG, was added to make mixed micelles, in which the core was expected to contain poly(L-lactic acid) (PLLA) and PHis chains. The PLLA block in the core stabilized the micelles and hence suppressed the drug release at the near neutral pH. The optimum content of PLLA-PEG was found to be about 25 0% (Fig. 10.7). The DOX delivered from such mixed micelles showed low cytotoxicity at pH above 7.0 but high cytotoxicity at pH 6.8 [143]. 

The impact of different surfactants (SDS, DOSS, CTAB and hexadimethrine bromide, bile salts °), nonionic and mixed micelles, and additives (neutral and anionic CDs," " tetraalkylammonium salts, organic solvents in EKC separations has been demonstrated with phenol test mixtures. In addition, phenols have been chosen to introduce the applicability of more exotic EKC secondary phases such as SDS modified by bovine serum albumin, water-soluble calixarene, " starburstdendrimers, " " cationic replaceable polymeric phases, ionenes, amphiphilic block copolymers,polyelectrolye complexes,and liposome-coated capillaries. The separation of phenols of environmental interest as well as the sources and transformations of chlorophenols in the natural environment have been revised. Examples of the investigation of phenols by EKC methodologies in aquatic systems, soil," " and gas phase are compiled in Table 31.3. Figure 31.3 illustrates the electromigration separation of phenols by both CZE and EKC modes. 

Micelles that are pH responsive are the nanoparticles of amphiphilic block copolymers or graft copolymers consisting of pH-responsive blocks. At the neutral pH, the insoluble blocks aggregate to form a core and the soluble blocks form a shell (or corona). The pH-responsive blocks may form pH-responsive cores,shells,or both. Polymeric micelles with polybase cores such as PDEA, poly(2-(diisopropylamino)ethyl methacrylate) (PDPA), ... 

Typical examples of well-defined amphiphilic anionic block copolymers are PS-PAA and PS-PMAA in the neutralized form (PS-PANa and PS-PMANa) which have been studied extensively over the last years by Tuzar [114,136] and by Eisenberg and co-workers [127, 178] who have also recently reviewed this topic of self-assembly of polyelectrolytes. These copolymers with a PAA or PMAA sequence have been examined in a very wide compositional and molar mass range. At high pH, the (meth)acryhc blocks are ionized resulting in stable micelles with extended shell regions, due to the electrostatic repulsion of the shellforming chains. 

Fig. 18 Composite micelles consisting of antisense oligonucleotides and (a) viral capsids or (b) synthetic polymers, (a) Micelles of DNA amphiphiles loaded with either small hydrophobic compounds top left) or with hydrophilic compounds by hybridization top right) were used to template virus capsid formation at neutral pH. TEM images show micelles incorporated into virus capsids with T = 1 or 2 geometry and an empty capsid formed at pH 5.0 as control inset). Scale bars 40 nm. (b) Representation of a blend micelle. Diblock DNA copolymer PPO-h-DNA was mixed with a triblock copolymer Pluronic (PEO-h-PPO-h-PEO) composed of the same hydrophobic block, PPO [21] (figure reproduced with permission of Royal Society of Chemistry)...

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