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PLA nanofibers were successively produced by thermo-responsive transformation of PLA particles in water. The morphological structure of the nanofibers could be optimized by the heat treatment as well as the incorporation of GO to the fiber surface. PLA/GO fiber demonstrated a more stable morphology and GO provided good compatibility between PLA and starch. Both PLA and PLA/GO fibers incorporated in starch films resulted in increased thermal stability and mechanical properties. However, the most favorable properties were assigned starch films containing high concentration of PLA/GO fibers. These films with completely green components could possibly be utilized in biodegradable packaging applications.

<p>The interaction of boronic acid with diols is reversible and pH-dependent. Boronate groups are able to form complex with 1,2- diol or 1,3-diols at pH values above 9. Therefore, the unique property of boronic esters was employed to exploit controllable self-assembly by three independent mechanisms, each of which is independent of the other two. The three interaction mechanisms are 1) electrostatic attraction between positive polymers and negative surfaces. 2) Polyethylene glycol (PEG)—phenolic polymer complex formation, which is one type of hydrogen bonding. 3) Phenylboronate (PBA) binding to polyols.</p> <p>To exploit these interactions, families of water-soluble and bifunctional copolymers containing pairs of non-interacting groups were prepared and characterized. Characterization includes structure, molecular weight, composition, etc. These bifunctional polymers can specifically interact with two other types of polymers/surfaces. Therefore, it provides a possibility to prepare complex assemblies by using multiple polymer/polymer interactions in one step.</p> <p>The utility of multiple, independent interactions was demonstrated by formation of self-assembled multilayer thin films on both silicon wafers and polystyrene latex particles. Moreover, the formation of well-defined nanoparticle aggregates with three different sizes of polystyrene latex particles was studied to extend the application of controllable self-assembly by multiple interactions. The assembly structures of multilayers and latex aggregates were controllable by adjusting the pH and addition of competitive small molecules.</p> <p>In addition to the study of multilayer self-assembly, a new approach for controllable deposition of latex nanoparticles on surfaces was also exploited. Regenerated cellulose films were chemically modified to fabricate the cellulose films bearing surface phenylboronic acid groups (cellulose-PBA). The poly(glycerol monomethacrylate)- stabilized polystyrene (PGMA-PS) latex particles were used to have reversible, pH-dependent adsorption onto the cellulose-PBA by the interaction of boronic acids and diols. Specific adsorption of PGMA-PS onto cellulose-PBA was observed at pH 10.5, whereas the latex particles were removed at pH 4.</p> / Doctor of Engineering (DEng)

Polysaccharides and polypeptides are two types of biopolymers that are used in biomedical, industrial, and commercial applications. Both families of biopolymers are generally biodegradable, sustainable, and often exhibit low toxicity. Polysaccharides and polypeptides are polymers derived from natural resources and can be modified or synthesized through polymerization of various monomers. Polypeptides, specifically, are typically synthesized by polymerizing monomers such as N-carboxyanhydrides (NCAs) or N-thiocarboxyanhydrides (NTAs) to form homopolymers or random copolymers when using two different NCA/NTA monomers simultaneously. Chapter 1 begins with a background on polysaccharide and polypeptide-based materials with a focus on polysaccharide-block-polypeptide block copolymers. Previous work includes combining these two biopolymers through methods requiring post-polymerization purification. Chapter 1 introduces the field, challenges it faces, and how this work can help pose some solutions to these challenges. In this thesis, we utilized NTAs to synthesize polypeptides (Chapters 2 and 3) and as an H2S donor (Chapter 4). Combining polysaccharides and polypeptides into a block copolymer is useful for drug delivery and blend compatibilization applications. In Chapter 2, we synthesized a dextran-block-poly(benzyl glutamate) block copolymer that is amphiphilic; the differences in hydrophilicity among the two blocks allowed for nanostructures to form in situ in water, which we envision can be used for applications in drug delivery. Because nanostructures are formed in situ, this method negates the need for post-polymerization modification or purification, a requirement of many other nanostructure formation procedures. Coarse-grained molecular dynamics simulations were employed to shed light on interactions found on the molecular level. The interactions studied were then used to explain the nanostructures observed experimentally. In Chapter 3, we similarly formed another polysaccharide-block-polypeptide with the same poly(benzyl glutamate) polypeptide used in Chapter 2 but using ethyl cellulose for the polysaccharide. Poly(benzyl glutamate) is similar in structure to the commercial plastic polyethylene terephthalate (PET), a petroleum-based polymer that is not biodegradable. Therefore, this ethyl cellulose-block-poly(benzyl glutamate) BCP was used as compatibilizer to improve mixing in immiscible ethyl cellulose/PET blends. These blends afforded a more bio-derived alternative to PET/petroleum-based plastics. This chapter focuses on the synthetic efforts, a common challenge with polysaccharides, to produce this block copolymer as well as blend preparation and characterization. Chapter 4 utilizes an NTA as an H2S donor rather than a monomer for polymerization. H2S is an endogenous signaling gas that plays an important role in many organs and systems. In humans, H2S deficiency leads to a range of medical issues including hypertension, preeclampsia, liver diseases, and Alzheimer's disease. NTAs are advantageous for H2S delivery in the biomedical field due to their amino-acid origin and innocuous byproducts. The NTA donor in this work was attached to amylopectin via thiol-ene "click" photochemistry with the amino acid cysteine providing the thiol source on amylopectin. H2S release half-lives were in the range of several hours and depended on polymer molecular weight. Lastly, Chapter 5 summarizes the conclusions formed from these projects as well as potential future extensions from this work. / Doctor of Philosophy / Polysaccharides, long-chain sugars, and polypeptides, long-chain amino acid sequences, are two types of biopolymers that are used in biomedical, industrial, and other commercial applications. Both families of biopolymers are generally biodegradable, sustainable, and often exhibit low toxicity. Chapter 1 begins with a background on polysaccharide and polypeptide-based materials with a focus on polysaccharide-block-polypeptide block copolymers. Chapter 1 introduces the field, challenges it faces, and how this work can help pose some solutions to these challenges. In this thesis, we utilized N-thiocarboxyanhydrides (NTAs) to synthesize polypeptides (Chapters 2 and 3) and as an H2S donor (Chapter 4). In Chapter 2, we synthesized dextran-block-poly(benzyl glutamate), a polysaccharide-block-polypeptide block copolymer, that is both hydrophilic and hydrophobic. The differences in hydrophilicity among the two blocks allowed for nanostructures to form in situ in water, which we envision can be used for applications in drug delivery. Computational modeling was then employed to help explain the nanostructures observed experimentally. In Chapter 3, we similarly formed another type of polysaccharide-block-polypeptide. The polypeptide used is similar in structure to the commercial plastic polyethylene terephthalate (PET), a petroleum-based polyester that is not biodegradable. This block copolymer was then employed to improve mixing between blends of immiscible ethyl cellulose (polysaccharide) and PET. These blends afford a more bio-derived alternative to PET/petroleum-based plastics. This chapter focuses on the synthetic efforts, a common challenge with polysaccharides, to produce this block copolymer as well as blend preparation and characterization. Chapter 4 utilizes an NTA as an H2S donor rather than a monomer for polymerization. H2S is an endogenous signaling gas that plays an important signaling role in many organs and systems. In humans, H2S deficiency leads to a range of medical issues including hypertension, preeclampsia, liver diseases, and Alzheimer's disease. In this work, we synthesized a polymeric polysaccharide H2S donor with tunable release rates, which is beneficial for longer therapeutic time and increased patient compliance. Lastly, Chapter 5 summarizes the conclusions formed from these projects as well as potential future extensions from this work.

The design and discovery of new surface-active polymers that self-assemble on solid substrates to form brush layers will have a major impact on numerous applications. Through recombinant DNA technology, there exists the potential to harness a cell's protein synthesis machinery to produce a brush-forming poly(amino acid) (or PAA) with an exactly specified amino acid sequence, thus controlling the polymer's composition at a level unequaled by conventional organic polymer synthesis. The presented work demonstrates the cloning, expression, purification and characterization of de novo-designed PAA's designed to form brush layers on alumina surfaces. Using conventional recombinant DNA methods, the feasibility of producing a PAA consisting of a poly-glutamate block and a poly-proline block was demonstrated. However, the PAA design was limited by the inherent limitations of conventional cloning techniques. We introduce here the development of a simple and versatile strategy for producing de novo-designed, high molecular weight PAA's using recombinant DNA technology. The basis of this strategy is that small DNA modules encoding for short PAA blocks can be easily inserted directly into a commercially available and unmodified expression vector. The insertions can be made repeatedly until the gene encodes for a polymer of desired molecular weight and composition. Thus, sequential modifications can be made to the PAA without having to re-start the gene assembly process from the beginning, thereby allowing for quick determination of how these changes affect polymer structure and function. The feasibility and simplicity of this method was shown during the production of a PAA, consisting of a long zwitterionic tail block and a short acidic anchor block, designed to form optimal brush layers on alumina surfaces. The success and flexibility of this method indicates that it can be applied for production of de novo-designed polypeptides in general. It is hoped that this method will contribute towards the rapid development of bio-inspired protein-based polymers for a variety of applications. This dissertation also contains research that aimed to use phage display technology to develop a new liposome-based immunoassay against biological toxins. This work was part of a collaboration effort with the U.S. Department of Defense and Luna Innovations. / Ph. D.

This dissertation attempts to address the problem of how to prepare protein-based materials with the same level of order and precision at the molecular level similar to the structures we find in nature. It is divided into two parts focusing on feedstock and processing. Part one is devoted to discussing the use of agricultural proteins as a feedstock for material production. Particularly, it focuses on the effect of hydrogen bonding, or lack thereof, between proteins as mediated by hydration or plasticization. The effect of varying plasticizer (glycerol) levels on mechanical properties of a series of proteins is discussed in the context of primary and secondary structure of these proteins. We have found that the extent to which a protein can be plasticized is dependent on its molecular and higher order structure and not simply molecular weight, as it was often assumed in previous studies. The second part of the dissertation focuses on the study of self-assembly as a way to make useful peptide-based materials. There are major efforts underway to study protein self-assembly for various medical and industrial reasons. Despite huge progress, most studies have focused on nanoscale self-assembly but the crossover to the macroscopic scale remains a challenge. We show that peptide self-assembly into macroscopic fibers is possible in vitro under physiological conditions. We characterize the fibers and propose a mechanism by which they form. The macroscopic fibers self-assemble from a combination of β- and α-peptides and are similar to other naturally-occurring systems in which templated self-assembly is used to create functional peptide materials. Finally, the ability to control macroscopic properties of the fiber by varying the ratio of constituent peptides is demonstrated. Owing to the richness of the amino acid building blocks, peptides are highly versatile structural and functional building blocks. The ability to extend and control peptide self-assembly over multiple length scales is a significant leap toward incorporating peptide materials into dynamic systems of higher complexity and functionality. / Ph. D.

The focus of the following research was to use the self-assembly process to create rotaxanes between several large bisphenylene crown ethers (> 22 atoms) with secondary ammonium salts. Also of great interest was to understand the complexation behavior of the crown ethers with the salts, with emphasis on determining the stoichiometries and association constants of the complexations in solution using NMR spectroscopy. The stoichiometry of the complexes was determined by the mole ratio method and the association constants were calculated graphically. Bis-(m-phenylene)-26-crown-8 did not form a complex in solution with several secondary ammonium salts even though the cavity size is large enough to allow the formation of pseudorotaxanes. However, the larger crown ether, bis-(m-phenylene)-32-crown-10 (BMP32C10), did form a complex. The complex stoichiometry varied between 1:1 (crown:salt) in solution and 1:2 in the solid state as evidenced by NMR and X-ray crystallography, respectively. The solid state complexes were pseudorotaxanes. Also, an interesting "exo" complex was formed in the solid state between BMP32C10 and a secondary diammonium salt. The major binding force for the complexes in the X-ray structures was hydrogen bonding. Weaker secondary stabilization was achieved via aryl-aryl aromatic interactions. The difference between the stoichiometries in the two phases and the observance of an "exo" complex demonstrates that one must be careful in describing the complexes in each phase. Also investigated was the complexation formed between dibenzo-24-crown-8 (DB24C8) and secondary diammonium salts. The association constants for the complexes were found to be relatively higher. Due to the weaker association constants and the different stoichiometries of complexation the meta-susbtituted bisphenylene crown ethers were not recommended for the formation of larger complexes, i.e. polyrotaxanes. However, it is suggested that the DB24C8 moiety be used in components of supramolecular assemblies. The functionalization of poly(propylene imine) dendrimers with two different crown ethers as peripheral moieties was attempted. The 1st, 3rd, and 5th generation poly(propylene imine) dendrimers were functionalized with 1,3-phenylene-16-crown-5 moieties by reacting the surface primary amines with the corresponding succinimide ester of the crown ether. The larger DB24C8 succinimide ester was not as reactive and full functionalization was not achieved. / Ph. D.

Functional amyloids found throughout nature have demonstrated that amyloid fibers are potential industrial biomaterials. This work introduces a new 'template plus adder' cooperative mechanism for the spontaneous self-assembly of micrometer sized amyloid fibers. A short hydrophobic template peptide induces a conformation change within a highly α-helical adder protein to form β-sheets that continue to assemble into micrometer sized amyloid fibers. This study utilizes a variety of proteins that have template or adder characteristics which suggests that this mechanism may be employed throughout nature. Depending on the amino acid composition of the proteins used the mixtures form amyloid fibers of a cylindrical (~10 μm diameter, ~2 GPa Young's modulus) or tape (5-10 μm height, 10-20 μm width and 100-200 MPa Young's modulus) morphology. Processing conditions are altered to manipulate the morphology and structural characteristics of the fibers. Spectroscopy is utilized to identify certain amino acid groups that contribute to the self-assembly process. Aliphatic amino acids (A, I, V and L) are responsible for initiating conformation change of the adder proteins to assemble into amyloid tapes. Additional polyglutamine segments (Q-blocks) within the protein mixtures will form Q hydrogen bonds to reinforce the amyloid structure and form a cylindrical fiber of higher modulus. Atomic force microscopy is utilized to delineate the self-assembly of amyloid tapes and cylindrical fibers from protofibrils (15-30 nm width) to fibers (10-20 μm width) spanning three orders of magnitude. The aliphatic amino acid content of the adder proteins' α-helices is a good predictor of high density β-sheet formation within the protein mixture. Thus, it is possible to predict the propensity of a protein to undergo conformation change into amyloid structures. Finally, Escherichia coli is genetically engineered to express a template protein which self-assembles into large amyloid fibers when combined with extracellular myoglobin, an adder protein. The goal of this thesis is to produce, manipulate and characterize the self-assembly of large amyloid fibers for their potential industrial biomaterial applications. The techniques used throughout this study outline various methods to design and engineer amyloid fibers of a tailored modulus and morphology. Furthermore, the mechanisms described here may offer some insight into naturally occurring amyloid forming systems. / Ph. D.