Polymeric micelles actions

Scheme 4 Drug action mechanisms of thermoresponsive polymeric micelles.

Carriers, including polymeric micelles, are required to have multi-functionality in order to overcome these barriers and exert their biological action. 

Fig. 8.6 Mechanism of action of tribologically active additives in nanoparticle form (a) adsorption step for molecular and nanoparticulate species (b) destruction of the surface-modifying layer and (c) several nanoparticles in a polymeric micelle [57]...

The ultimate goal for intelligent polymeric micelles might be conjectured from the recent collaboration between the National Aeronautics and Space Administration (NASA) and the National Cancer Institute (NCI) (71). NASA and NCI are trying to construct a biodevice that, for prolonged periods of time, can patrol in the body, sense abnormalities like the presence of tumors, diagnose them, and take suitable action to alleviate the problem. Such a device would, in turn, incorporate a process for the integration of all the successful achievements of novel carriers at present. 

The passive targeting of polymeric micelles to solid tumors can be achieved by the enhanced permeability and retention effect (EPR effect). Maeda and his coworkers presented this new drug targeting strategy in 1986 (31,32). As illustrated in Fig. 3, the vascular permeability of tumor tissues is enhanced by the actions of secreted factors such as kinin. As a result of this increased vascular permeability, macromolecules selectively increase their transport from blood vessels to tumor tissues. Furthermore, the lymphatic drainage system does not operate effectively in tumor tissues. 

The effects of emulsifiers in emulsion polymerization systems may be enumerated as follows (l stabilization of the monomer in emulsion, (2) solubilization of monomer in micelles, (3) stabilization of polymer latex particles, (4) solubilization of polymer, (5) catalysis of the initiation reaction, and (6) action as transfer agents or retarders which leads to diemical binding of emulsifier residues in the polymer obtained. 

As explained before, when surfactant, water, and monomer(s) are mixed, the colloidal system obtained consists of monomer-swollen micelles (if the surfactant concentration exceeds its CMC) and monomer droplets dispersed in an aqueous phase that contains dissolved molecules of surfactant and a small amount of the sparingly water-soluble monomer(s). When free radicals are generated in the aqueous phase by action of an initiator system, then the emulsion polymerization takes place. Its evolution is such that the colloidal entities initially present tend to disappear and new colloidal entities (polymer latex particles) are bom by a process called nucleation. For convenience, we first focus on the particle nucleation mechanisms, a very important aspect of emulsion polymerization. 

It is clear that the formation of liquid crystalline suspensions of poly(tetrafluoroethylene) whiskers is dominated by the action of the surfactant and by the tendency of crystallizable macromolecules to polymerize in extended chain form when synthesized far below their melting or dissolution temperature (25). Strong indications exists that the presence of surfactant in the polymerization at a level above its critical concentration for rod-like micelle formation is a necessary requirement for the production of the liquid crystalline suspensions. 

Surfactant—polymer systems have additional technological significance since surfactants are normally used in the emulsion polymerization of many materials, often involving the solubilization of monomer in micelles prior to polymerization and particle formation. Surfactants have also been shown to increase the solubility of some polymers in aqueous solution. The combined actions of the surfactant as a locus for latex particle formation (the micelle) in some cases, particle stabilization by adsorbed surfactant, and as a solubilizer for monomer permit us to expect quite complex relationships between the nature of the surfactant and that of the resulting latex. 

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