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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Polymer Science and Engineering

Year Degree Awarded

2017

Month Degree Awarded

May

First Advisor

Murugappan Muthukumar

Subject Categories

Biochemical and Biomolecular Engineering | Biophysics | Physical Chemistry

Abstract

The transparent vitreous, which fills the posterior cavity of the eye, is incredibly engineered. The charged polyelectrolyte hyaluronic acid (HA) network swells to maintain the pressure in the eye, while stiff collagen type II bundles help absorb any external mechanical shock. Our investigations have contributed to a few key developments related to the physical properties of the vitreous:

(1) The stiff collagen network that supports the soft gel network is self-assembled from single triple-helix collagen proteins. Electrostatic interactions drive this assembly, such that the size and concentration are optimized at physiological salt concentrations. The width of the assemblies remarkably changes from 60 nm to 800 nm with only a 50 mM change in the salt concentration.

(2) A soft (~ 2 - 200 Pa) negative polyelectrolyte network swells to support the microscopic and tough collagen bundles. The equilibrium swelling behavior and the response to external manipulation is driven by the charged components of the gel. We have developed a way to determine the thermodynamic quantities responsible for this phenomenon, such as the chemical miss-match parameter of the backbone, the ionizability of the network, and the Poisson ratio. We show that these parameters are enough to predict the equilibrium linear-elastic elasticity of polyelectrolyte gels for a range of strand lengths and salt concentrations.

(3) Finally, using these principles, in collaboration with Dr. Paul Hamilton, and Dr. Nathan Ravi at Washington University, we have developed a new synthetic injectable vitreous substitute for use as a novel double-network therapeutic material.

The vitreous can phase-separate and detach from the retina. This disease is poorly studied and has few treatment options. By studying biomimetic models of the vitreous in vitro, we hope to understand vision-related diseases, the mechanism for collagen fiber formation, intrinsic soft tissue properties, and to formulate therapeutic materials.

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