Date of Award

2015

Degree Type

Thesis

Department

Chemical and Biomedical Engineering

First Advisor

Holland, Nolan

Subject Headings

Protein-based surfactants, Polypeptides, Elastin, Surface tension, biomedical engineering, biomedical research, biochemistry, chemical engineering, molecular biology, nanotechnology

Abstract

A three-armed star elastin-like polypeptide (ELP-foldon) has thermoreversible character which exhibits phase separation above a transition temperature (Tt) in physiologic salt concentrations. At lower salt concentration, the ELP-foldon behaves like a thermoresponsive surfactant, exhibiting micelle formation above its Tt. The purpose of this study is characterize the surfactant behavior of the ELP-foldon at air-liquid interface by measuring the surface tension. The surface tension is measured as a function of time for different ELP concentrations from 10 nM to 50 ℗æM and over range of temperatures from 25 to 35 ℗¿ using the axisymmetric drop shape analysis (ADSA). The ADSA is a method which is based on the analysis of the shape and size of drop or bubble profiles to measure surface tension. It has been determined that the surface tension is not different between conditions where there are no micelles and where micelle form. Therefore, a critical micelle concentration (c.m.c.) measurement by surface tension is not meaningful. The surface tension exhibits a time-dependent reduction which can be fit with the Hua-Rosen equation. The meso-equilibrium surface pressure is ̃23 mN/m and does not vary with the bulk concentration or the temperature. The time to reach the meso-equilibrium does vary with the bulk concentration. These times scale with concentration by a power of -1.2 and -1.3, suggesting that the process is not fully diffusion limited

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