Investigations into Building Block Structure and Method of Preparation on the Properties of Nanomaterials

This dissertation research is primarily focused on the preparation of polymer-based nanostructures as potential diagnostic agents and therapeutics delivery vehicles. Various polymers, nanoparticles and conjugation techniques were developed to meet the specific requirements of each application. Shell crosslinked nanoparticles: SCKs) are characterized by their structural integrity and available functionality to attach multiple agents on the shell, such as receptor-recognizing or receptor-specific ligands, .imaging agents, Cell transduction components, etc. In this work, SCKs derived from amphiphilic poly(acrylic acid)-block-polystyrene: PAA-b-PS) have been studied as potential diagnostic and therapeutic agent delivery vehicles: Chapters 2 and 4). SCK nanoparticles bearing a cyclic KCRGDC peptide which specifically binds to avb3 integrin receptor were developed as potential delivery system for treatment of acute vascular injuries. Methods were developed to afford clean nanoparticles with significant binding abilities. Nanoscale contrast agents for magnetic resonance imaging were also developed based on SCKs derived from PAA-b-PS and a Gadolinium-DOTA complex to achieve high relaxivity contrast agents. Our results showed that SCKs may serve well as potential diagnostic and therapeutic agent delivery vehicles Meanwhile, these SCKs were also studied as the template for mineralization of silver nanoparticles, along with a nuleating peptide, AG-P35, as a co-template: Chapter 5). Various morphologies of silver nanoparticles were obtained and it\u27s found that the morphology was highly dependent on polymer and peptide concentrations and incubation time. Micelles from a novel hyperbranched fluoropolymer with small sizes able to pass the blood brain barrier were synthesized: Chapter 3). After conjugation with F3 peptide which targets to nucleolin in most tumor cells, and loaded with doxorubicin as the drug to kill the tumor cells, both in vitro and in vivo studies were performed. It was found that F3-peptide conjugated nanoparticle not only specifically bind to the tumor-associated angiogenic endothelial cells, doxorubicin carried by these nanoparticles also caused apoptotic effects on the targeted tumor cells

Immobilization of polymeric nano-assemblies for antibacterial applications

With conventional antibiotic therapies being increasingly ineffective, bacterial infections with subsequent biofilm formation represent a global threat to human health and therefore,new strategies to fight bacteria colonization need to be found. Coimmobilization of functional, nanosized assemblies broadens the possibility to engineer dually functionalized active surfaces with a nanostructured texture. Surfaces decorated with different nanoassemblies, such as micelles, polymersomes, or nanoparticles are in high demand for various applications ranging from catalysis, biosensing up to antimicrobial surfaces. In this thesis, I present a combination of bio-orthogonal and catalyst-free strain-promoted azide-alkyne click (SPAAC) and thiol-ene reactions to simultaneously coimmobilize various nanoassemblies; polymersome-polymersome and polymersome-micelle assemblies were selected. For the first time, the immobilization method using SPAAC reaction was studied in detail to attach soft, polymeric assemblies on a solid support. Together, the SPAAC and thiol-ene reactions successfully coimmobilized two unique self-assembled structures on the surfaces. Additionally, poly-(dimethylsiloxane) (PDMS)-based polymersomes were used as "ink" for direct immobilization from a PDMS-based microstamp onto a surface creating locally defined patterns. Furthermore, an active and a passive strategy based on polymeric micelles were combined to fight bacterial growth. The passive strategy involved covalent immobilization of polymeric micelles through Michael addition between maleimide exposed micelles and thiol functionalized surfaces. Compared to the bare surface, micelle-decorated surfaces showed reduced adherence and survival of bacteria. To extend this passive defense against bacteria with an active strategy, the immobilized micelles were equipped with the antimicrobial peptide KYE28 (KYEITTIHNLFRKLTHRLFRRNFGYTLR). The peptide interacted nonspecifically with the immobilized micelles where it retained its antimicrobial property. The successful surface decoration with KYE28 was demonstrated by a combination of X-ray photoelectron spectroscopy and quartz crystal microbalance with dissipation monitoring. The initial antimicrobial activity of the nanostructured surfaces against Escherichia coli (E. coli) was found to be increased by the presence of KYE28. Combining immobilization reactions has the advantage to attach any kind of nanoassembly pairs, resulting in surfaces with desired interfacial properties. Different nanoassemblies that encapsulate multiple active compounds coimmobilized on a surface will pave the way for the development of multifunctional surfaces with controlled properties and effciency. Additionally, the combination of our active and a passive strategy represents a straightforward modular approach that can easily be adapted, for example, by exchanging the antimicrobial peptide to optimize potency against challenging bacterial strains, and/or to simultaneously achieve antimicrobial and anti-infection properties

Polymeric Nanovectors Incorporated with Ganciclovir and HSV-tk Encoding Plasmid for Gene-Directed Enzyme Prodrug Therapy

In the area of gene-directed enzyme prodrug therapy (GDEPT), using herpes simplex virus thymidine kinase (HSV-tk) paired with prodrug ganciclovir (GCV) for cancer treatment has been extensively studied. It is a process involved with two steps whereby the gene (HSV-tk) is first delivered to malignant cells. Afterward, non-toxic GCV is administered to that site and activated to cytotoxic ganciclovir triphosphate by HSV-tk enzyme expressed exogenously. In this study, we presented a one-step approach that both gene and prodrug were delivered at the same time by incorporating them with polymeric micellar nanovectors. GCV was employed as an initiator in the ring-opening polymerization of ε-caprolactone (ε-CL) to synthesize hydrophobic GCV-poly(caprolactone) (GCV-PCL), which was furthered grafted with hydrophilic chitosan to obtain amphiphilic polymer (GCV-PCL-chitosan) for the fabrication of self-assembled micellar nanoparticles. The synthesized amphiphilic polymer was characterized using Fourier transform infrared spectroscopy and proton nuclear magnetic resonance. Micellar prodrug nanoparticles were analyzed by dynamic light scattering, zeta potential, critical micelle concentration, and transmission electron microscopy. Polymeric prodrug micelles with optimal features incorporated with HSV-tk encoding plasmids were cultivated with HT29 colorectal cancer cells and anticancer effectiveness was determined. Our results showed that prodrug GCV and HSV-tk cDNA encoded plasmid incorporated in GCV-PCL-chitosan polymeric nanocarriers could be delivered in a one-step manner to HT-29 cells and triggered high cytotoxicity

Self-assembly of di-chain surfactant in carbon dioxide

Carbon dioxide holds considerable potential as an environmentally and chemically benign alternative to the potentially hazardous conventional industrial solvents. In spite of its promise, one of the reasons that CO2 has so far failed to achieve its full potential is that few CO2-philic surfactant molecules are known at present that form stable reversed micelles in carbon dioxide. The aqueous or polymeric cores of these surfactant aggregates provide a medium for solubilizing substances (hydrophiles, polar molecule, proteins) that are otherwise insoluble in CO2. As a step in this direction, molecular dynamics simulation of a dichain (or hy-brid) surfactant + water + carbon dioxide (solvent) ternary system is presented in this work to gain valuable insight into the aggregation behavior of these surfactant molecules. Two different system sizes were investigated using detailed and quite real-istic molecular models for all the three chemical species involved. One of the system sizes investigated mimicked the overall composition studied in a recent experimental (SANS) work, while the other provided valuable insight into the effect of surfactant chemistry and architecture on surfactant aggregation. The simulations for the two system sizes used different solvent conditions (supercritical CO2 and high temperature liquid CO2,/sub\u3e) to provide information into the effect of solvent condition on surfactant aggregation. The surfactant system showed a rapid and spontaneous propensity for aggregation of surfactant and water molecules into aggregates that resemble reversed micellar aggregates i.e. the aggregates consisted of an aqueous core surrounded by a layer of surfactant molecules with their head groups immersed in the core and the tails forming a corona. The aggregation mechanism observed in these simulations was a two-step mechanism involving rapid ion-hydration followed by gradual surfactant aggregation via hydrogen bond formation. The aggregation process was found to be diffusion-controlled i.e. dependent on the size of aggregates and the solvent density. Another factor influencing the aggregation process was the steric resistances offered by the surfactant tails. The structural properties of the aggregates were dependent on the water-to-surfactant molar ratio of the system. The size and shape of the aggregates predicted by these simulations were in reasonably good agreement with prior experimental results

Synthetic Poly(Ethylene Glycol)-Based Hydrogels for Biomedical Applications

Ph.DDOCTOR OF PHILOSOPH

Physicochemical aspects of pharmaceutically‐relevant polymers and nanoparticles in solution

Pharmapolymers, colloids, and self-assembled systems for biomedical purposes have gained significant importance in the last decades. Besides innovative synthesis routes and formulation techniques, the characterization of these multicomponent systems is of great importance to obtain an insight into their physicochemical properties. As presented in this thesis, analytical ultracentrifugation with multi-detection represents a characterization tool with great potential for analyzing macromolecules and polymer-based nanocarriers in solution. Besides analytical ultracentrifugation, asymmetrical flow field‐flow fractionation coupled to a multi‐angle laser light scattering detector can be utilized to determine essential properties such as particle sizes or molar masses of macromolecules. In this thesis, methods of analytical ultracentrifugation were developed to analyze polymeric nanocarriers. The results were compared to well-established orthogonal techniques such as asymmetrical flow field‐flow fractionation coupled to a light scattering detector and standard dynamic light scattering. Thereby, different polymeric multicomponent systems, including nanoparticles, polyplexes, micelles, and bioconjugates were studied. These investigations delivered information such as the colocalization of multiple components, i. e., drug, as well as degradation and drug release studies under various conditions. In particular, studies in human serum and at body temperature are of great importance before in vivo experiments are performed. The presented results will allow to overcome current analytical challenges in the characterization of such multicomponent systems for life science applications and boost the synthetic / formulation improvements due to a deep physicochemical understanding of the systems