Nanogel

The core of reversed micelles can be transformed to a highly viscous domain (nanogel) by entrapping appropriate species, such as viscous solvents and hydrophilic macromolecules, or by performing in situ appropriate polymerization reactions or intramolecular cross-linking of water-soluble polymer chains [232-234]. 

Solutions of surfactant-stabilized nanogels share both the advantage of gels (drastic reduction of molecular diffusion and of internal dynamics of solubilizates entrapped in the micellar aggregates) and of nonviscous liquids (nanogel-containing reversed micelles diffuse and are dispersed in a macroscopicaUy nonviscous medium). Effects on the lifetime of excited species and on the catalytic activity and stability of immobilized enzymes can be expected. 

Nanogels made up of various intramolecularly cross-linked macromolecules have been prepared simply by performing the polymerization of hydrophilic monomers solubilized in the micellar core of reversed micelles, and they represent distinct macromolecular species from those obtained in bulk [191,240]. 

Tamura A, Oishi M, Nagasaki Y (2009) Enhanced cytoplasmic delivery of siRNA using a stabilized polyion complex based on PEGylated nanogels with a cross-linked polyamine structure. Biomacromolecules 10 1818-1827... 

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... 

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. 

Nanogels are nanometer-sized hydrogel nanoparticles (less than about 100 nm) with three-dimensional networks of physically crosslinked polymer chains. They have attracted growing interest over the last decade because of their potential for applications in biomedical fields, such as DDS and bioimaging [246-249]. 

Nanogel-lipasc complex (Stabilization oftipasc complexed with nanogel)... 

Fig. 13 (a) CHP nanogel and (b) the interaction between CHP nanogel and lipase. Reprinted from [257] with permission... 

Usual PLAs have two enatiomeric forms, PLLA and poly(D-lactide) (PDLA), which are synthesized from LLA and the D,D-isomer of lactide (DLA), respectively. It is well known that 1 1 mixture of PLLA and PDLA can form a stable stereocomplex (SC), which has a higher Tm and higher mechanical strength than either of homopolymers [261], We reported on the utility of SC formation to enhance the stability of nanogels. Monodisperse SC nanogels were obtained through the self-assembly of an equimolar mixture of Dex-g-OLLA and Dex-g-ODLA in a dilute aqueous solution. 

The SC nanogels had 70 nm mean diameter with narrow size distribution, significantly lower critical aggregation concentration (CAC), and stronger thermodynamic stability compared with those of the corresponding l- or D-isomer nanogels [163]. 

Tamura M, Ichinohe S, Tamura A, Ikeda Y, Nagasaki Y (2011) In vivo and in vitro characteristics of core-shell-type nanogel particles optimization of core cross-linking density and surface PEG density in PEGylated nanogels. Acta Biomaterialia. doi 10.1016/j. actbio.2011.05.027... 

Oishi M, Nagasaki Y (2010) Stimuli-responsive smart nanogels for cancer diagnostics and therapy. Nanomedicine (Lond) 5 451 -68... 

Figure 8.14 Schematic diagram of the interconversion between diblock copolymer and star-like nanogel throngh the radical crossover reaction of alkoxyamine units [44],...

Table 8.4 Correlation between compositions, molecular weights of diblock copolymer 57, and core sizes and number of arms of star-like nanogels...

Amamoto, Y Higaki, Y Matsuda, Y Otuska, H. Takahara, A. Programmed formation of nanogels via a radical crossover reaction of complementarily reactive diblock copolymers. Chem. Lett. 2007, 36, 1098-1099. 

Particle of gel of any shape with an equivalent diameter of approximately 0.1 to 100 pm. Modified from [2]. The definition proposed here is recommended for its precision and because it distinguishes between a microgel and a nanogel. 

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