Date of Award

Spring 2022

Project Type

Dissertation

Program or Major

Chemical Engineering

Degree Name

Doctor of Philosophy

First Advisor

Young Jo Kim

Abstract

In this dissertation I investigated the structural properties of melanin biopigment from different sources as an antibacterial and endotoxin bonding agent. I extracted melanin from Equus ferus hair with acid hydrolysis (termed EquusMel) and characterized it by microscopic and spectroscopic techniques. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that EquusMel is mainly elliptical in shape with a mesoporous and layered structure within the individual particles. Wide-angle (WAXS) and small-angle (SAXS) X-ray scattering measurements demonstrated a semicrystalline multilayered structure with order spacing of 45.2 Å. Pore size distribution determined by the Barrett–Joyner–Halenda (BJH) method showed primary pores within the range of 30–50 Å. Nitrogen adsorption–desorption isotherms exhibited a Brunaur–Emmett–Teller (BET) surface area of 3 m2/g. Raman, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) spectra revealed similar chemical signature between EquusMel and synthetic melanin (SynMel). I investigated the antibacterial effect and its mechanism of action for EquusMel. I found that EquusMel has distinct antibacterial activity due to its potential to generate reactive oxygen species (ROS). ROS generated via oxidation of catechols is considered the main mechanism of antibacterial activity. The simplicity of EquusMel extraction and its antibacterial property allows this biomaterial to be applicable to a variety of areas. Zinc cations (Zn2+) were loaded on melanin structure (Mel-Zn) for rapid and selective separation of gram-negative bacteria and lipopolysaccharide (LPS) from blood. Mel-Zn was characterized by XPS and Raman which revealed the successful Zn2+ loading. I identified that Mel-Zn rapidly captures approximately 90% of Escherichia coli in whole blood and 100% of LPS in PBS, which can reduce bacteremia loads and mitigate the spread of these infectious agents to other tissues and organs. Additionally, simultaneous binding to bacteria and LPS could enhance the efficacy of antibiotic therapy. Adsorption of protein from individual protein model solutions, as well as LPS-spiked protein solutions, was found to be minimal. Hemolysis and coagulation assays demonstrate the blood biocompatibility of Mel-Zn, which could be adapted for clinical use in an extracorporeal membrane to remove pathogens and LPS in acute sepsis patients.

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