Date of Award

Winter 1-1-2010

Document Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical & Biochemical Engineering

First Advisor

Kristi S. Anseth

Second Advisor

Christopher N. Bowman

Third Advisor

Hang (Hubert) Yin

Abstract

Poly(ethylene glycol) (PEG)-based hydrogels represent a class of biomaterials with a growing interest for their application in numerous fields, such as drug delivery and regenerative medicine. PEG is commonly used in these applications due to its hydrophilic and bioinert properties. Additionally, peptides have been successfully incorporated within PEG hydrogels to serve as biological functionalities within a synthetic polymer platform. Peptide-functionalized PEG hydrogels have been shown to act as extracellular matrix (ECM)-mimics capable of enhancing cell survival, function, and differentiation. Alternatively, peptides can be designed to degrade in recognition of highly specific, cell-secreted proteases. This phenomenon has been exploited for the fabrication of peptide-functionalized "smart" hydrogels, capable of undergoing macroscopic property changes in response to cellular events. The goal of this thesis work was to design functional peptide sequences and control their presentation within PEG hydrogels for various biological applications.

Specifically, two unique therapeutic delivery platforms containing covalently incorporated human neutrophil elastase (HNE) sensitive peptides were designed. First, substrates were engineered with amino acid point mutations ultimately resulting in enzymatically-controlled degradation kinetics of varying rates. These peptides were photopolymerized within PEG hydrogels as pendant functionalities, and their subsequent release was only observed in the presence of enzyme. The rate of release was ultimately dictated by environmental factors (e.g., [enzyme]) and substrate design (e.g., kcat). Next, HNE-sensitive peptides were incorporated as functional crosslinks within PEG-based hydrogels using thiol-ene photopolymerization. Protein therapeutics were included in the pre-cursor solution and physically entrapped upon gel formation. The peptide crosslinks render the gel degradable and allow for protein release upon exposure to HNE. The rate of gel degradation and subsequent protein release was influenced by gel formulation, enzyme concentration, and substrate design.

Finally, cyclic, multivalent peptides were designed and synthesized using sequential thiol-ene/thiol-yne chemistries, exploiting the versatility of these radical-mediated photoreactions. Results demonstrate that these novel synthetic routes provide a robust and efficient method to form complex peptide architectures that better mimic protein structure. Collectively, this thesis provides insight related to peptide design and subsequent use within synthetic hydrogels for various biological applications, especially those related to drug delivery and regenerative medicine.

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