Self-Assembled Polymer Nanoparticles

Parameters Affecting Self-Assembly and Functionalization When amphiphilic block copolymers are exposed to a solution that solvates only one of the blocks, the polymers self-assemble into micelles [126]. For applications in which bioactive polymers compose the micelle, particle size determines the maximum drug loading, blood-serum half-life, and bio distribution [127,128]. Block copolymer chain length and composition, as well as the method of self-assembly, were found to influence the final size of these particles [80, 129-131]. By varying these parameters, the size of the polymer aggregates could be controlled in the range from 30 nm to 1 pm [129,130]. 

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Zhong X, Yuan R, Chai Y, Liu Y, Dai J, Tang D (2005) Glucose biosensor based on self-assembled gold nanoparticles and double-layer 2d-network (3-mercaptopropyl)-trimethoxy-silane polymer onto gold substrate. Sensor Actuator B 104 191-198... 

Recently, many studies have focused on self-assembled biodegradable nanoparticles for biomedical and pharmaceutical applications. Nanoparticles fabricated by the self-assembly of amphiphilic block copolymers or hydrophobically modified polymers have been explored as drug carrier systems. In general, these amphiphilic copolymers consisting of hydrophilic and hydrophobic segments are capable of forming polymeric structures in aqueous solutions via hydrophobic interactions. These self-assembled nanoparticles are composed of an inner core of hydrophobic moieties and an outer shell of hydrophilic groups [35, 36]. 

Diez I, Hahn H, Ikkala O, Bomer HG, Ras RHA (2010) Controlled growth of silver nanoparticle arrays guided by a self-assembled polymer-peptide conjugate. Soft Matter 6 3160-3162... 

Self-Assembly of Nanoparticles Mediated by Polymers on the Planar Substrates... 

Polymer-mediated self-assembly of nanoparticles provides a versatile and effective approach for the fabrication of new materials. This bottom-up strategy builds up nanocomposite materials from diverse nanosized building blocks by incorporation of molecular-level recognition sites. The flexibility and reversibUity of self-assembly processes imparted by specific molecular interactions facilitates the formation of defect-free superstmctures, and it can be further explored in fields ranging from electronics to molecular biology. 

Figure 6.1 General schematic representation of polymer-mediated assembly of nanoparticles (a) functionalization of nanoparticles through place-exchange method, (b) incorporation of complementary functional group to polymers, and (c) self-assembly of nanoparticles through electrostatic or hydrogen bonding interactions.

The hydrogen-bond mediated self-assembly of nanoparticles and polymers provides a versatile and effective method to control interparticle distances, assembly shapes, sizes, and anisotropic ordering of the resultant nanocomposites. This approach presents the bottom-up strategy to fabricate nanomaterials from molecular building blocks, which have great potential for assembling and integrating nanoscale materials and particles into advanced structures, systems, and devices. 

Akiyoshi K., Nishikawa T., Kobayashi S.-I., Sunamoto J. Self-assembled hydrogel nanoparticles complexation and stabilization of soluble proteins. In Yalpani M., ed. Biomedical Function and Biotechnology of Natural and Artificial Polymers. ATL Press 1996 115-125. 

The recent progress in polymer synthesis and nanotechnology is stimulating the development of adhesives with improved performance. A few percent of nanometer-scale additives can be added to formulations in order to achieve significant changes in property profiles. Molecular nanoparticles and nanometer-scale, highly branched polymers can be dispersed in order to facilitate energy dissipation at the crack tip by means of multiple plastic deformation. The self assembly of nanoparticles forms skeleton-like superstructures which account for... 

Fig. 10.7 Immobilized Pd nanoparticles by bottom-up self-assembled polymers.

Self-assembly of nanoparticles with polymers is providing access in order to stabilize metal and semiconductor nanocomposites for fabrication of new materials. Characteristics of the individual building blocks mainly include the following (Skaff et al., 2008) ... 

Nanocomposite materials fabricated using polymer-mediated self-assembly of nanoparticles is a versatile and effective tool for the advancement of nanotechnology. The ability to control properties of the polymer and the nanoparticle core and shell at the molecular level provides access to a wide variety of materials with tunable properties. Nanoparticles in polymers would provide a powerful platform for device fabrication. 

Figure 4. Experimental design based on the new concept of self organization to obtain a hierarchic dot or stripe pattern composed of metal nanoparticles. Here polymer is used for constructing the super-layer structure with the wavelength X that is chosen by dewetting instability. The patterned polymer islands simultaneously provide the initial and boundary conditions of sub-layer, i.e., the conditions for self-assembly of nanoparticles.

A typical example of dissipative structure-assisted self-assembly of nanoparticles is shown in Figure S. The dark dots and lines are aggregates of organopassivated Cu nanoparticles, and the light surroundings are polystyrene matrices. The dewetting process determines first the wavelength of spatial pattern (frozen dissipative structure) of polymer matrices that are isolated one... 

Finally, nanoscale features can be also obtained by using nanoparticles. For instance, hierarchical hybrid nanoparticle-polymer porous assemblies have been obtained by self-assembly of nanoparticles at the polymer solution-water droplet interface. The first example was reported by Russell et al. [75] who prepared honeycomb structured interfaces by casting a chloroform solution of PS using TOPO-stabilized CdSe nanoparticles. As a result of the breath figures mechanism. 

Polymer micelles in aqueous medium are typically obtained with hydrophobic-hydrophiKc, so-called amphiphilic, block and graft copolymers. Analogous to conventional low-molecular surfactants, and in a selective solvent of one of the blocks, such polymeric surfactants self-assemble into nanoparticles with well-defined sizes and structures. 

In the next part, we will focus our attention on nanosecond processes that occur in shells of self-assembled polymer micelle-like nanoparticles in aqueous media [56, 57]. Fluorescent probes that strongly bind to the nanoparticles have usually been employed to obtain information on the shell or on the immediate vicinity of nanoparticles. Suitable probes include amphiphilic fluorophores, i.e., fluorescent surfactants, such as prodan, laurdan, or patman (see chapter Huorescence Studies of Polymer Containing Systems , Fig. 2). They contain a fairly polar fluorescent head-group and a nonpolar aliphatic tail, which secures the favorable hydrophobic interaction and sorption on polymer nanoparticles. They bind to micelles [55, 56] and their localization depends on the polarity of the head-group and on the length of the tail. In the case of patman, the strongly polar head is usually located in the peripheric part of the solvated shell and the nonpolar tail is oriented towards the... 

A number of assembly methods employ self-assembly of nanoparticles at the air-water interface. Monolayers (and subsequent multilayers) can be formed at the interface due particle interaction and transferred to a solid substrate by controlled dip-coating and vertical deposition methods similar to Langmuir-Blodgett film deposition [81-86]. Regular monolayers of polymer colloids can also be assembled via an electrohydrodynamic route, whereby electrophoretically deposited particles between two electrodes can be manipulated to cluster in the presence of an electric field. On application of an AC or DC field, contrary to electrostatic norms, the like-charged particles are observed to coalesce producing large close-packed 2D crystalline domains [87]. 

Koizumi, S and Hashimoto, T, (2009) Time-resolved SAXS studies of selfassembling process of palladium nanoparticles in templates of polystyrene-block-polyisoprene melt effects of reaction fields on the self-assembly. Polymer, 50, 2696-2705. 

Drug delivery is an application that has been investigated using amphiphilic phosphazene polymeric materials. An example of this was provided using polyphosphazenes substituted with N,N-diisopropylethylenediamine, an amine functionalized MW2000 poly[ethylene glycol] (AMPEG), and 4-ethyl-aminobenzoate These polymers were found to self-assemble into nanoparticles and were seen to be effective in the delivery of doxorubicin. 

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