Date of Award

8-2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Bioengineering

Advisor

Metters, Andrew T

Committee Member

Vyavahare , Naren R

Committee Member

Burg , Karen J.L.

Committee Member

Webb , Ken

Abstract

In recent years, there has been immense interest in the utilization of photopolymerized hydrogels as carriers for controlled protein delivery and cell scaffolds for tissue engineering applications. Although poly(ethylene glycol) (PEG)-based hydrogels formed from mild photopolymerization methods have been suggested as biocompatible matrices that allow for safely encapsulating biomolecules including proteins, peptides, DNA, and cells, the adverse effects of photopolymerization reactions on the encapsulated proteins have largely been overlooked. In addition, conventional hydrophilic hydrogels fail to effectively control protein delivery rates due to their high permeability. These two problems are critical since the delivery of protein therapeutics from hydrogel matrices in their active form and in optimal rates usually determine whether a device performs successfully in a given application.
The development of ideal hydrogel matrices requires a thorough understanding of protein-polymer interactions and the mechanisms governing protein-delivery rates from a crosslinked polymer network. The primary foci of this dissertation were to evaluate free radical-mediated protein-polymer conjugation and to develop synthetic affinity hydrogels for systematically controlling single and multiple-protein delivery. These research objectives combine the knowledge of protein chemistry, polymer science and engineering, molecular transport kinetics, and mathematical modeling.
The initial research efforts were to evaluate the factors causing protein inactivation during in situ photopolymerization, with the primary focus on photoinitiator chemistry and concentration (Chapter 3). Next, the undesirable formation of protein-polymer conjugates during in situ photopolymerization and their effects on total protein release were investigated (Chapter 3, 4). Once the adverse effects of protein-polymer conjugates were identified, a pseudo-specific metal-ion chelating ligand was used to enhance protein bioavailability (Chapter 4).
Another challenge of using hydrophilic hydrogels for controlled protein delivery is the networks' high permeability to encapsulated proteins. This limitation was circumvented by synthesizing affinity ligands that bind to target proteins and immobilizing them within otherwise inert hydrogel networks (Chapter 5). This modification provided a unique method for tuning the protein delivery rates. Two protein-binding mechanisms, namely electrostatic interaction and metal-ion chelation, were used separately to evaluate the efficacy of proteinligand binding for controlling protein delivery (Chapter 5, 6). A mathematical model was also developed to predict the release of histidine-tagged protein from metal-chelating ligand imprinted affinity hydrogels (Chapter 5). Finally, these two binding mechanisms were used together in a one-step photopolymerized hydrogel matrix to independently control the delivery rates of two proteins encapsulated simultaneously (Chapter 7).

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