Date of Award

Summer 2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Materials and Infrastructure Systems

First Advisor

Donald T. Haynie

Abstract

Three major concerns in the science of materials today are control over structure and function at the molecular level, biodegradability, and scalability of production. Polymeric materials, notably polyelectrolyte multilayer films, have shown considerable promise in all these areas, and for rational development of multifunctionality. Polypeptides constitute an especially interesting class of polyelectrolyte, given their inherent biodegradability, means of control over structure, methods of large-scale synthesis, and ability to encode biological information. Relatively little is known, however, about polypeptide multilayer films, despite recent advances in the general area.

In this dissertation, ten heteropolypeptides were designed and synthesized by Fmoc chemistry. These peptides and homopolypeptides available from a commercial source have been used to carry out a systematic study of the physical basis of polypeptide multilayer film assembly, structure, and stability, in order to gain a greater grasp of the roles of different kinds of non-covalent interaction, degree of polymerization, and polydispersity. The data show that amino acid composition, sequence, and specific combination of anionic and cationic polypeptides together determine film growth behavior, secondary structure content, overall density, surface morphology, and susceptibility to environmental perturbations. The peptides are largely unstructured in solution but tend to form β sheets in a multilayer film at neutral pH. Electrostatic interactions dominate polypeptide adsorption and film stability, but hydrophobic interactions and hydrogen bonding have a significant influence on internal structure and surface morphology, decreasing film density and increasing film thickness and roughness. Experimental results of polypeptide multilayer films correlate well with molecular dynamics (MD) simulation results of interpolyelectrolyte complexes (IPECs) of the same polypeptide designs. Microcrystals of pyrene, a hydrophobic model drug, have been encapsulated by the polypeptides used in film study. The drug release kinetics have been found to depend on precoating material, polypeptide structure, and microcapsule architecture.

The results of this dissertation will inform materials science, studies of polyelectrolyte multilayer films and micro/nanocapsules, and protein folding. In particular, this work will help to provide a foundation for the engineering of novel peptide-based biomaterials for a variety of purposes, such as enantiomeric separations, antimicrobial films, artificial skin grafts, cell and tissue culture, biodegradable implant coatings, artificial cells and drug delivery systems.

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