Date of Award

2015

Degree Type

Thesis

Department

Chemical and Biomedical Engineering

First Advisor

Holland, Nolan

Subject Headings

Chemical Engineering Elastin-like polypeptides phase transition rheology protein based polymer multiphase system

Abstract

Elastin-like polypeptides (ELPs) are environmentally responsive biopolymers. These protein based polymers are specific in that they exhibit phase separation in response to a number of stimuli. Some of these stimuli include temperature, light, and pH. There are a large number of factors to consider when designing ELP constructs that allow for control of the transitioning behavior, some of which include amino acid sequences, protein concentration, salt concentration, and the polymer chain length. Elastin-like polypeptides are soluble in water at low temperatures, however, upon an increase in temperature, the proteins become insoluble in water and phase separate. This point of temperature triggered phase transitioning shows lower critical solution temperature (LCST) behavior and is referred to as the inverse transition temperature (Tt). The transition is completely reversible and the ELPs will return back into solution upon decreasing temperature below the Tt.The linear elastin-like polypeptide (GVGVP)40 and the trimerized (GVGVP)40-foldon were expressed in a bacterial system using Escherichia coli (E. coli). Exploiting ELP temperature triggered transitioning to an insoluble state, highly concentrated protein solutions were formed for each sample. In this study, various rheometric experiments were conducted on (GVGVP)40 and (GVGVP)40-foldon. The storage, G', and loss, G", dynamic moduli were determined to characterize the viscoelastic behavior of highly concentrated ELP solutions. Shear viscosities as functions of time, temperature, and concentration were determined. As well, various other rheological properties were determined and used to help better understand and characterize these highly concentrated ELP solutions. The ELPs studied showed shear thinning characteristics along with more viscous compared to elastic behaviors at all angular frequencies. A power law model was fit to relate the viscosity of the solutions to the protein concentration. Starting at high concentrations then diluting stepwise th

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