Micelles, polymer

Generally, the number of the shell chains in a microsphere ranges from a few hundred to a few thousand. The range of the diameter of the core is from 10-100 nm. Such a core-shell structure is very similar to the (AB)n type star block copolymers, which have many arms and spherical polymer micelles of the block or graft copolymers formed in selective solvents that are good for the corona sequence and bad for the core sequence. In fact, many theoretical investigations of the chain con-... 

Figure 11.8 Formation of ordered nanoparticles of metal from diblock copolymer micelles, (a) Diblock copolymer (b) metal salt partition to centres of the polymer micelles (c) deposition of micelles at a surface (d) micelle removal and reduction of oxide to metal, (e) AFM image of carbon nanotubes and cobalt catalyst nanoparticles after growth (height scale, 5 nm scan size, lxl pm). [Part (e) reproduced from Ref. 47].

Perkin, K.K., Turner, J.L., Wooley, K.L. and Mann, S. (2005) Fabrication of hybrid nanocapsules by calcium phosphate mineralization of shell cross-linked polymer micelles and nanocages. Nano Letters, 5,1457-1461. 

Keywords Aliphatic polyesters Amphiphilic polymers Polymer micelles Self-assembly Smart materials... 

Recently, biodegradable polymers have been used to fabricate macro- and nanometer scale self-assembled systems such as microspheres (MSs), nanospheres (NSs), polymer micelles, nanogels, and polymersomes (Fig. 1). These have attracted growing interest because of their potential utility for drug delivery systems (DDS), tissue engineering, and other applications. To construct these self-assembled systems... 

Fig. 1 Typical examples of nanometer-scale polymeric assemblies polymer micelles, polymersomes,...

Many kinds of nonbiodegradable vinyl-type hydrophilic polymers were also used in combination with aliphatic polyesters to prepare amphiphilic block copolymers. Two typical examples of the vinyl-polymers used are poly(/V-isopropylacrylamide) (PNIPAAm) [149-152] and poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) [153]. PNIPAAm is well known as a temperature-responsive polymer and has been used in biomedicine to provide smart materials. Temperature-responsive nanoparticles or polymer micelles could be prepared using PNIPAAm-6-PLA block copolymers [149-152]. PMPC is also a well-known biocompatible polymer that suppresses protein adsorption and platelet adhesion, and has been used as the hydrophilic outer shell of polymer micelles consisting of a block copolymer of PMPC -co-PLA [153]. Many other vinyl-type polymers used for PLA-based amphiphilic block copolymers were also introduced in a recent review [16]. 

Micro- or nanosized polymer particles are generally called microspheres (MSs) or nanospheres (NSs), respectively, and have been used for DDS. The term nanoparticle is more general and includes polymer micelles and nanogels, which are described in Sects. 4-6. Although polymer micelles and nanogels have sufficient surface hydrated layers for dispersion or solubilizaton in aqueous media, MSs and NSs are basically spherical particles of hydrophobic polymers without enough hydrated layers. 

Polymer micelles are nanometer sized (usually several tens of nanometers) self-assembled particles having a hydrophobic core and hydrophilic outer shell composed of amphiphilic AB- or ABA-type block copolymers, and are utilized as drug delivery vehicles. The first polymer micelle-type drug delivery vehicle was made of PEG-b-poly(aspartic acid) (PEG-b-PAsp), immobilizing the hydro-phobic anticancer drugDXR [188-191]. After this achievement by Kataoka et al., a great amount of research on polymer micelles has been carried out, and there are several reviews available on the subject [192-194]. 

As described above, the most common hydrophilic polymer combined with aliphatic polyesters to prepare polymer micelles is PEG. Although there have been many reports on the polymer micelles of PEG-b-aliphatic polyesters, only few recent examples are introduced in this review. Shin et al. reported the therapeutic potential of PEG-b-PLA micelles entrapping multiple anticancer drugs of poor solubility in... 

Matsumura Y, Kataoka K (2009) Preclinical and clinical studies of anticancer agent-incorporating polymer micelles. Cancer Sci 100 572-579... 

Munk P (1996) Equilibrium and nonequilibrium polymer micelles. In Webber SE, Munk P, Tuzar Z (eds) NATO ASI series, series E Applied sciences, vol 327. Kluwer, Dordrecht... 

Figure 6.4 The preparation of nanostructured materials in solution evolves from (a) the classic examples of suspension, dispersion, or emulsion polymerization, to the methods that include the covalent crosslinking of select domains within supramolecular polymer assemblies (b) core crosslinking of polymer micelles (c) shell crosslinking of polymer micelles (SCKs) (d) nanocages from core-eroded SCKs (e) shaved hollow nanospheres from outer shell/core-eroded vesicles.

Figure 6.5 Illustrations of nanoscale spherical assemblies resulting from block copolymer phase separation in solution are shown, along with the chemical compositions that have been employed to generate each of the nanostructures (a) core crosslinked polymer micelles (b) shell crosslinked polymer micelles (SCKs) with glassy cores (c) SCKs with fluid cores (d) SCKs with crystalline cores (e) nanocages, produced from removal of the core of SCKs (f) SCKs with the crosslinked shell shielded from solution by an additional layer of surface-attached linear polymer chains (g) crosslinked vesicles (h) shaved hollow nanospheres produced from cleavage of the internally and externally attached linear polymer chains from the structure of (g)...

The new connective sites provide the opportunity to destroy or disconnect other regions of the nanostructure without destruction of the entire nanoscale entity. This was demonstrated by the excavation of the core of shell crosslinked polymer micelles, by the removal of the colloid from colloidally templated... 

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