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Title:Modeling interactions between cells and the aqueous environment
Author(s):He, Yichen
Advisor(s):Espinosa-Marzal, Rosa
Department / Program:Civil & Environmental Engineering
Discipline:Environmental Engineering in Civil Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Cell Model
Polyacrylamide hydrogel
Layer by Layer (LBL) method
lipid bilayer
Abstract:When nanoparticles, heavy metals and ions generated from industry are released to the environment, they may react with cells of organisms and can be toxic to them. The primary purpose of this study is to develop a novel cell model that mimics several reveal cell properties including nanomechanical behavior, and to investigate the interactions between them and the aqueous environment. The novel cell model developed in this work has potential applications as a platform to investigate cytotoxicity. In this study, the cell membrane model consists of a hydrogel-supported lipid-bilayer. Hydrogels are cross-linked polymer networks that can absorb large amounts of water without dissolving or loosing their shape. A number of hydrogels are stimuli-sensitive. They can change their structures and properties in response to changes in environment, such as pH, temperature, and ionic strength. These polymer hydrogels have wide applications in various biological and clinical fields, including drug delivery, contact lenses, and artificial implants. Biocompatibility and hydrophilic properties of hydrogels are the basis of these applications. In this study, neutral PAAm hydrogel is used as support for the lipid bilayer. The used hydrogel is a (neutral) polyacrylamide (PAAm) hydrogel. The lipid bilayer used in this study is Eggphosphatidycholine (EggPC). A layer-by-layer method with two polyelectrolytes, poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH), was used to graft the EggPC to the neutral PAAm hydrogel. An electrostatic attraction is the main driving force for the adsorption of the bilayer on the hydrogel-supported polyelectrolyte multilayer (PEM). The developed cell model has been fully characterized in this work by using different surface analytic techniques. On a silica substrate, lipid vesicle ruptures and fuses above a critical vesicle concentration to form a continuous lipid bilayer. QCM-D measurements and AFM imaging were performed to verify the formation of the bilayer on the silica substrate. The adsorption kinetics of the lipids on the hydrogel-supported PEM completely differs from that on the “hard” silica substrate. However, the change in dissipation supported the formation of a lipid bilayer. Further, the adsorbed mass on bovine serum albumin (BSA) verified that the adsorbed lipids on the PAAm hydrogel-PEM complex form a lipid bilayer, but the surface coverage is only partial. Thus, BSA adsorbs on the PEM through the defects of the lipid bilayer. The interactions between cells and the environment happen through the cell membrane, and very often the nanomechanical behavior determines such interactions, and also cell sensing and response. In this work, the nanomechanical properties of PAAm hydrogels, PAAm-supported PEM and lipid bilayers were studied using atomic force microscopy (AFM), including both nano-indentation and the response to shear. A significant difference in the elasticity (and viscoelasticity) between the behavior of the hydrogel-supported PEM and the silica-supported lipid bilayer was concluded from these studies, as well as very different mechanisms for the energy dissipation upon shear. The question that remains to be answered is the behavior of the cell model constituted of the hydrogel-supported PEM and the lipid bilayer, which is the outlook of this work.
Issue Date:2015-07-22
Rights Information:Copyright 2015 Yichen He
Date Available in IDEALS:2015-09-29
Date Deposited:August 201

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