Functionalization of polymer–lipid hybrid materials using supramolecular assembly and π-conjugation chemistry

Go, Yoo Kyung

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https://hdl.handle.net/2142/121251 Copy

Description

Title

Functionalization of polymer–lipid hybrid materials using supramolecular assembly and π-conjugation chemistry

Author(s)

Go, Yoo Kyung

Issue Date

2023-07-12

Director of Research (if dissertation) or Advisor (if thesis)

Leal, Cecília

Doctoral Committee Chair(s)

Leal, Cecília

Committee Member(s)

• Schroeder, Charles M.
• Evans, Christopher M.
• Espinosa Marzal, Rosa M.

Department of Study

Materials Science & Engineerng

Discipline

Materials Science & Engr

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Self-assembly
• Lipids
• Polymers
• Hybridization
• Crystallinity
• π-Conjugation

Abstract

The remarkable complexity and functionality observed in nature are attributed to the diverse building blocks it utilizes, such as lipids, peptides, saccharides, and nucleic acids. These natural components play vital roles in the formation of complex biomembranes and the execution of essential biological functions. Motivated by this form-function of biological membranes, the focus of my research is to replicate and mimic the intriguing properties of biomembranes by combining synthetic and biological materials in a hybrid approach. The fundamental organization and behavior of synthetic or biological soft materials rely heavily on hierarchical self-assembly. Lipids are prime examples, naturally or artificially forming various meso/nanostructures. Synthetic block copolymers mimic the structural and functional characteristics of lipids and proteins. Lipids possess biocompatibility, while polymers with high molecular weight offer mechanical strength and chemical versatility. To develop novel materials for applications such as controlled delivery of drugs/genes, biosensors, and artificial cells, combining lipids and polymers becomes inspiring. The resulting “polymer–lipid hybrid membrane”, a composite material, exhibits synergistic properties that surpass those of individual components. This dissertation comprehensively explores a wide range of polymer-lipid hybrid systems — from vesicles and supported films to π-conjugated assembly — aiming to elucidate their form and function. Polymer crystallinity plays a crucial role in determining various material properties, including heat and mass transport, mechanical responses, and optical properties. However, hybrid systems combining crystalline polymers and lipids are barely explored. To bridge the field of polymer-lipid hybrid materials and polymer physics harnessing crystalline polymer, my research focused on the co-assembly of crystalline polymers and lipids in two different supramolecular systems and applications. The first approach highlighted the fundamental study of mechanically robust crystalline-polymer lipid hybrid vesicles. Mediated by secondary bonding, co-assembly of crystalline polymers and lipid bilayers in water formed hybrid vesicles that possess both the mechanical strength of the polymers and the dynamic organization of lipids. This work successfully shed light on the crystalline polymer-lipid hybrid vesicles for drug delivery. The second study explored the influence of small amounts of lipid additives on the polymer crystal orientation and its impact on heat transport properties. By combining solid-like lipid molecules with a crystalline polymer in a confined film, we discovered a novel method to modulate the self-assembled structure and orientation of polymer crystallites. Remarkably, the lipid additives formed solid-like pillar structures composed of lamellar stacks between the polymer blocks. This nano-confinement effect induced a change in the polymer crystal orientation, leading to a substantial decrease in thermal conductivity of the material. Furthermore, my research traversed π-conjugated lipid membranes that exhibit enhanced fluorescence emission for bioimaging applications. Conjugated polymers have the ability to display fluorescence thus been widely utilized for bioimaging and sensors. However, stabilization of the conjugated polymers into cell cargo remains challenging due to their hydrophobic nature. Inspired by lipids having amphiphilic nature and the ability to assemble into nanoparticles for cell internalization, my research introduced polymerizable lipids that can form π-conjugation bonds across the membranes. Furthermore, we engineered the π-conjugated lipids assembly in 3D bicontinuous cubic phase with the addition of conical lipids and in response to divalent salts. Surprisingly, the π-conjugated backbone of the cross-linked lipid membranes showed enhanced fluorescence in the 3D bicontinuous cubic phase compared to one in a flat lamellar phase. We hypothesize that the negative membrane curvature of the cubic phase induced a distortion of the backbone, resulting in enhanced fluorescence. Temperature-dependent measurement of the fluorescence emission of the networks further revealed the mechanism as aggregation-induced-emission (AIE). Due to the highly ordered 3D porous cubic structure, our approach provides biocompatible materials made of π-conjugated lipids with promising applications in drug delivery, sensing, and bioimaging. Overall, this thesis encompasses three distinct parts, each focusing on a different aspect of hybrid lipid-polymer systems. From mechanically robust vesicles to the influence of lipid additives on heat transport, and the development of π-conjugated lipid membranes for enhanced fluorescence, this research work aimed to contribute to the fundamental understanding and application of lipid-polymer hybrids in various fields. To achieve the goals, this dissertation introduces a characterization platform combining a multitude of X-ray scattering, spectroscopic, and imaging techniques. My works included in this thesis pave the way for the exploration of hybrid polymer-lipid materials and their potential impact across diverse fields. Furthermore, the findings can contribute to a deeper understanding of self-assembling soft materials and facilitate the design of innovative supramolecular systems and applications.

Graduation Semester

2023-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Yoo Kyung Go

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