Date of Award

5-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Chemical and Biomolecular Engineering

Advisor

Guiseppi-Elie, Anthony

Committee Member

Blenner, Mark A

Committee Member

Kitchens, Christopher L.

Committee Member

Lee, Jeong Soo

Committee Member

Roberts, Mark E.

Abstract

Bioresponsive hydrogels are emerging with technological significance in targeted drug delivery, biosensors and regenerative medicine. The design challenge is to effectively link the conferred biospecificity with an engineered response tailored to the needs of a particular application. Moreover, the fundamental phenomena governing the response must support an appropriate dynamic range, limit of detection and the potential for feedback control. The design of these systems is inherently complicated due to the high interdependency of the governing phenomena that guide sensing, transduction and actuation of the hydrogel. The objective of the dissertation is to review the current state of bioresponsive hydrogel technology and introduce a method of extending the technology through integrated control loops; explore fundamental phenomena which affect ion transport within biomimetic hydrogels; and investigate, via in silico studies, the fundamental design parameters for the implementation of a feedback control loop within a bioresponsive hydrogel. In one study, effects of valence number, temperature and polymer swelling on release profiles of monovalent potassium and divalent calcium ions elucidates mechanistic characteristics of polymer interactions with charged species. For comparison, ions were loaded during hydrogel formulation or loaded by partitioning following construct synthesis. Using the Korsmeyer-Peppas release model, the diffusional exponents were found to be Fickian for pre- and post-loaded potassium ions while preloaded calcium ions followed an anomalous behavior and postloaded calcium ions followed Case II behavior. Results indicate divalent cations interact through cation-polyelectrolyte anion complexation while monovalent ions do not interact with the polymer. Temperature dependence of potassium ion release was shown to follow an Arrhenius relation and calcium ion release was temperature independent. In another study, data generated from the previous Chymotrypsin system is used to build and validate a finite element model. The model provides insight into key engineering parameters for the design of an enzymatically actuated, feedback controlled release. A drug delivery platform comprising a biocompatible, bioresponsive hydrogel and possessing a covalently tethered peptide-inhibitor conjugate was engineered to achieve stasis, via a closed control loop, of the external biochemical activity of the actuating enzyme. The FEM model was used to investigate the release of a competitive protease inhibitor, MAG283, via cleavage of Acetyl-Pro-Leu-Gly|Leu-MAG-283 by MMP-9 in order to achieve targeted homeostasis of MMP-9 activity, a goal for the treatment of chronic wound pathophysiology. It was found the key engineering parameters for the delivery device are the radii of the hydrogel microspheres and the concentration of the peptide-inhibitor conjugate loaded into the hydrogel. Homeostatic drug delivery, where the focus turns away from the drug release rate and turns towards achieving targeted control of biochemical activity within a biochemical pathway, is an emerging approach in drug delivery methodologies for which the potential has not yet been fully realized. By understanding mechanistic phenomena and key engineering parameters for design, advancements in bioresponsive hydrogels will continue to produce novel technologies in biomedical applications.

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