Nanoparticles amphiphilic block copolymers

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]. 

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]. 

Fig. 30 Types of nanocarriers for drug delivery, (a) Polymeric nanoparticles polymeric nanoparticles in which drugs are conjugated to or encapsulated in polymers, (b) Polymeric micelles amphiphilic block copolymers that form nanosized core-shell structures in aqueous solution. The hydrophobic core region serves as a reservoir for hydrophobic drugs, whereas hydrophilic shell region stabilizes the hydrophobic core and renders the polymer water-soluble.

Application of amphiphilic block copolymers for nanoparticle formation has been developed by several research groups. R. Schrock et al. prepared nanoparticles in segregated block copolymers in the sohd state [39] A. Eisenberg et al. used ionomer block copolymers and prepared semiconductor particles (PdS, CdS) [40] M. Moller et al. studied gold colloidals in thin films of block copolymers [41]. M. Antonietti et al. studied noble metal nanoparticle stabilized in block copolymer micelles for the purpose of catalysis [36]. Initial studies were focused on the use of poly(styrene)-folock-poly(4-vinylpyridine) (PS-b-P4VP) copolymers prepared by anionic polymerization and its application for noble metal colloid formation and stabilization in solvents such as toluene, THF or cyclohexane (Fig. 6.4) [42]. 

Alexandridis P (2004) Nanoparticle Synthesis and Colloidal Stabilization using Amphiphilic Block Copolymer Solutions. Abstracts, 32nd Northeast Regional Meeting of the American Chemical Society, Rochester, NY, USA, October 31-November 3, GEN-119... 

Alexandridis P, Sakai T (2004) Amphiphilic block copolymer solutions as media for the facile synthesis and colloidal stabilization of metal nanoparticles. Abstracts of Papers, 228th ACS National Meeting, Philadelphia, PA, USA, August 22-26, 2004,... 

Alexandridis P, Sakai T (2005) Amphiphilic block copolymer-templated nanoparticle synthesis and stabilization. Abstracts of Papers, 229th ACS National Meeting, San Diego, CA, USA, March 13-17, 2005, COLL-474... 

Amphiphilic block copolymers have attracted a great deal of attention in terms of their ability to form nanoparticles. As normally one type of segment, is hy-... 

Title Amphiphilic Block Copolymers and Nanoparticles Comprising the Same... 

Fig. 10.2 Nanoparticles formed via polymer micelles by self-assembly of amphiphilic block copolymers...

In the second approach, metal-ion/complex was first attached to one of the polymer blocks. A thin film of the resulting polymer metal complex was then obtained by spin coating/solution casting. Alternatively, the polymer metal complex may also be dissolved in a suitable solvent system that selectively dissolves one of the blocks. Micelles or nanosized aggregates formed in this case. The micellization of amphiphilic block copolymers and their use in the formation of metal nanoparticles has been discussed previously.44 A monolayer of micelles was introduced on a substrate surface by dipping or electrostatic attraction. The substrate was then subjected to further chemical or physical treatments as mentioned earlier. The third approach involves the formation of micelles from the metal-free block copolymer in a suitable solvent system. The micelle solution was then added with metal ion, which was selectively coordinated to one of the blocks. These micelle-metal complexes can also be processed by a procedures similar to the second approach. 

Amphiphilic block copolymers self-organize in aqueous mixtures to form polymeric micelles having a core of the hydrophobic block and a shell of the hydrophilic block. The cores can absorb additional hydrophobic low molecular weight compounds. The shells can be cross-linked to form capsules that are much more physically robust than the original micelles, as shown in Figure 11.10 (15). The uncross-linked inner phase can be dissolved by a good solvent to produce hollow capsules or serve as a site for trapping metal nanoparticles as catalysts. 

Watanabe S, Fujiwara R, Hada M, Okazaki Y, lyoda T. 2007. Site specific recogni tion of nanophase separated surfaces of amphiphilic block copolymers by hydro philic and hydrophobic gold nanoparticles. Angew Chem Int Ed Engl 46 1120 1123. 

Rahme, K., Vicendo, P, et al. A Simple Protocol to Stabilize Gold Nanoparticles using Amphiphilic Block Copolymers Stability Studies and Viable Cellular Uptake. Chemistry - A European Journal, 5(42), 11151-11159 (2009). 

It is usually difficult to add functionalities (i.e., to insert other amphiphilic molecules into a bilayer membrane) to self-assemble a bilayer nanoparticle after its self-assembly in solvents because the assembled bilayer membrane is a thermodynamically stable. If one can controlled the self-assemble phenomena, more complexed nanostrucutres can be achieved, and it will open a new stage of drug/gene delivery system. Bui et al. prepared a bilayer membrane nanoparticle via two-step self-assemblies using a solubility of amphiphilic block copolymer (Fig. 2.1.8) [108], The nanoparticles were composed of a positively charged complex core (siRNA and polyethyleneimine [PEI]) and a capsid-like (bilayer) shell. The preparation processes were divided into two steps (1) an electrostatic... 

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