MOLECULAR AND PROCESS DETERMINANTS OF SELF-ASSEMBLIES FROM AMPHIPHILIC MACROMOLECULAR BRUSHES
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Date
2016-08-25
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Johns Hopkins University
Abstract
The self-assembly of amphiphilic block copolymers is widely studied as an approach to engineer nano-objects. In aqueous medium, the hydrophobic blocks collapse to form the micelle core while the hydrophilic parts serve as the stabilizing corona. Polymeric micelles are emerging as promising carriers for the delivery of hydrophobic drugs, wherein the poorly water-soluble agents could be solubilized in the micelle core, allowing for their transport at concentrations considerably higher than their intrinsic solubility in water. A variety of different morphologies, including spherical micelles, cylindrical or worm-like micelles, toroids and vesicles result from the self-assembly of linear amphiphilic block copolymers by manipulating the ratio of dissimilar blocks, solvent quality, coronal interactions, and processing parameters.
Macromolecular brushes are graft polymers with densely grafted side chains. Crowded grafting results in a uniquely extended backbone conformation and influences their physicochemical properties. In this dissertation, the self-assembly behavior of amphiphilic macromolecular brushes with poly(glycidyl methacrylate) (PGMA) as backbone bearing poly(ethylene glycol) and poly(D,L-lactide) side chains, was studied. We systematically investigated how variation in the molecular characteristics of amphiphilic brushes, and processing parameters, influenced their aggregate structure.
Amphiphilic macromolecular brushes were further used as hydrophobic solute stabilizers, successfully generating solute nanoparticles by a rapid change in solvent quality. Nanoparticle morphology was found to strongly depend on the physicochemical characteristics of the solute, on occasions resulting in unusual shapes. Anisotropic morphologies observed are attributed to the mobility of hydrophobic core, and it may potentially assist the shape control of nonspherical aggregate morphologies.
Through a judicious choice of side-chain and backbone length, unimolecular nanoparticles can be readily achieved from amphiphilic macromolecular brushes. These are promising for drug delivery purposes, particularly upon dilution in the blood stream. Harnessing their potential as drug carriers warrants a detailed study regarding their ability to stabilize hydrophobic solutes. We found that a particular type of copolymer adopts a unimolecular structure in the presence of hydrophobic solutes, driven by hydrophobic interactions between the solute and the brush amphiphile. The stability of loaded particles was examined by interactions with human serum albumin. Finally, the release profile of loaded nanoparticles was investigated.
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Keywords
macromolecular brush, bottlebrush polymer, molecular brush, solution self-assembly, solute stabilization, unimolecular micelle, single-chain nanoparticle