Encapsulation of Nanoparticles in Block Copolymer Micellar Aggregates by Directed Supramolecular Assembly

Abstract

Incorporation of inorganic nanoparticles (NPs) into selfassembled block copolymers offers a powerful route for the formation of hybrid materials with desired optical, electronic, and magnetic properties through the choice of NPs and their distribution in polymer assemblies. Nanostructured block copolymer domains act as a scaffold that directs not only the position of the NPs but also their orientation. NPs/polymer hybrid materials have been prepared in solution by incorporating one or multiple hydrophobic NPs into a hydrophobic core of spherical amphiphilic block copolymer micelles. Careful control of micellization conditions will allow other hydrophobic ingredients to co-assemble with the amphiphilic polymers, resulting in micelles that encapsulate therapeutic molecules and NPs for imaging and targeting. Cylindrical or wormlike micelles show particular interest in drug delivery because of their large core volume (per carrier) and elongated structures, which offer additional opportunities to control biodistribution and release profiles of therapeutic agents. The “precipitation method”, which is a practical way to incorporate NPs into micelles, does not easily allow the growth of extended wormlike micelles with NPs encapsulated in the core. Several groups have reported the successful incorporation of NPs into hydrophilic portions of wormlike micelles through electrostatic interaction of corona-forming blocks with NPs. Recently, we reported the encapsulation of iron oxide NPs within wormlike micelle cores through interfacial instabilities of emulsion droplets containing amphiphilic polymers. However, it is hard to achieve high loading and uniform dispersion of NPs in wormlike micelle cores. So far, precise control over NPs position in wormlike micelle cores with homogeneous distribution remains a challenge. Herein we introduce a simple, yet versatile approach for the encapsulation of NPs within wormlike micelle cores through directed supramolecular assembly. The concept for preparation of the hybrid nano-objects is illustrated in Figure 1a. Typically, polystyrene–poly(4-vinylpyridine) (PS20k–P4VP17k, volume fraction of PS fPS= 56%) and pentadecylphenol (PDP) were dissolved in chloroform to form PS–P4VP(PDP)x (x represents the ratio of PDP to 4VP