Chemical and Biomolecular Engineering - Theses
Now showing items 1-12 of 253
Engineering of DNA Micro- and Nanoparticles: Towards Vaccine Delivery
Vaccines are an effective tool for preventing and controlling various diseases by inducing adaptive immunity. Nanomaterials play an important role in vaccine development. Micro- and nanocarriers can be engineered to improve the therapeutic efficacy of vaccines by (i) preventing the degradation and systemic clearance of vaccine antigens and (ii) facilitating the uptake of vaccines in antigen-presenting cells (iii) co-delivering adjuvants and antigens at desired intracellular compartments for optimal immunotherapy. However, it is important to engineer a carrier that is both effective and safe. Micro- and nanoparticles based on DNA have shown great potential for biological applications, owing to the programmable sequences, predictable interactions, versatile modification sites, and high biocompatibility of DNA strands. This thesis aims to develop facile strategies to synthesize DNA particles for vaccine delivery by self-assembly approaches. First, a simple strategy to synthesize DNA microcapsules is reported. The cytosine-phosphate-guanosine oligodeoxynucleotides (CpG) motif is an efficient vaccine adjuvant that can effectively stimulate the immune system to secrete cytokines. By loading and crosslinking Y-shaped DNA building blocks (containing CpG motifs) into sacrificial calcium carbonate templates, monodisperse and spherical DNA capsules were obtained. These DNA microcapsules were internalized into cells efficiently, accumulated in endosomes, and induced immune cells to secrete high-level of cytokines. Next, we developed a template-assisted and versatile approach for synthesizing a new set of multifunctional particles through the supramolecular assembly of tannic acid (TA) and DNA molecules. Uniform and stable DNA-TA particles with different morphologies could be easily synthesized by using different types of DNA strands. Intriguingly, different DNA sequences can be encoded into this DNA-TA particle for applications in immunotherapy or gene delivery. The incorporation of CpG motifs and ovalbumin into the particles allows the intracellular antigen/adjuvant co-delivery to amplify cytokines production in macrophages, through synergistic effects. In addition, green fluorescent protein (GFP)-expressing plasmid DNA could be transfected by using the DNA-TA particles in HEK293T cells. Finally, nanometer-sized particles were engineered by exploiting the one-pot supramolecular assembly of TA, DNA, and PEG for intracellular delivery of CpG motifs. TA-DNA-PEG nanoparticles with different sizes could be fabricated by adding different molecular weight PEG chains. TA-DNA nanoparticles with tunable size were also synthesized by varying the molar ratio of TA and DNA. The obtained nanoparticles can enhance the cellular uptake of CpG oligonucleotides and consequently the production of cytokines in macrophages. Overall, the engineered DNA-based particles have potential for co-delivering nucleic acids and protein antigens in immune cells to enhance the immunological response against infectious diseases and cancer.
Metal–Phenolic Networks: From Simple Composites to Tailored Architectures
Metal–phenolic networks (MPNs), which are made using metal ions and phenolic ligands, have attracted widespread interest owing to their hybrid physicochemical properties and high affinity to diverse substrates. The combination of MPNs with functional materials can lead to MPN composites capable of outperforming the individual components in a wide range of emerging applications. However, the small pore size of MPNs limits the possibilities of loading MPN-based materials with other functional components. In addition, the controlled assembly of MPN composites for functional thin films with tailored structures has been largely unexplored. This thesis focuses on the engineering of the composition and structure of MPN composites for various applications. Firstly, a supramolecular fluorescent labeling strategy was developed using luminescent MPN composites that consist of a MPN and commercially available dyes. To demonstrate the versatility of this strategy, 16 types of particle substrates that are formed from different materials, and have different sizes and surface chemistries, were successfully labeled. This strategy obviated the need to covalently conjugate the dyes or to modify the surface chemistry of the substrates. In addition, customized luminescence regimes (e.g., red, blue, multichromatic, and white light) were readily achieved using common fluorophores. The fluorescent coating is stable in many biological environments, such as in serum and the cytosol, which demonstrates its potential to study the cell association and internalization of particles in real-time. Secondly, a cubosome templating strategy was developed to prepare ordered mesoporous MPN particles with uniformly large pores (around 40 nm). The large mesopores allow various cargos (e.g., biomacromolecules) to diffuse into the particles while the phenolic groups stabilize the cargos. This led to considerably higher loading amounts than those typically achieved when using commercially available SiO2 with 50 nm pores. In addition, meso-MPN particles that are loaded with enzymes acted as highly efficient bioreactors, displaying catalytic activities that exceed those prepared from porous silica particles. Thirdly, cubosome templates were also engineered in the form of monoliths using diffusion-induced self-assembly, and the formation mechanism and precise molecular organization of the monoliths were investigated by both experiments and all-atom molecular dynamics simulations. The large pores of the polymer monoliths were then used to synthesize ordered MPN-based monoliths. These results show the significant potential of using MPN composites in various fields, including chemistry, biology, and materials science.
Engineering Versatile Particles and Films through Metal-Phenolic Chemistry
Metal-phenolic chemistry, owing to its facile and versatile functions to manipulate dynamic interactions (e.g., interfacial adhesion and coordination crosslinking) at the molecular level, has emerged as a powerful tool for the rational design and engineering of hybrid metal-organic materials. In particular, leveraging a myriad of advantages, including a rich choice of building blocks, the combined properties of phenolics and metals, and dynamic coordination bonds, metal-phenolic network (MPN) particles and films have been explored in diverse fields such as drug delivery, functional elastomers, and water treatment. Despite significant progress, the mechanisms related to the kinetics (e.g., assembly process) and thermodynamics of MPNs are poorly understood, resulting in less control over the physicochemical properties of MPN particles and films. This thesis (1) reviews the fundamental insights about metal-phenolic interactions underpinning the dynamic nature of coordination bonds and universal adhesion to surfaces; (2) develops various assembly strategies, including oxidation-mediated assembly, enzyme-mediated assembly, and spray assembly, to endow MPN particles and films with controllable properties (e.g., thickness, pore size, roughness, and wettability) and functionalities (e.g., fluorescence, catalysis, radical scavenging, and UV-shielding), thereby (3) expanding the applications of MPN particles and films, specifically in gas separations, biomineralization, biomolecule conjugation, and oil-water separations; and (4) discusses the underlying mechanism governing the assembly process and resultant coordination states of MPNs by various characterization methods. Some unsolved challenges and perspectives related to MPN chemistry are also highlighted. This thesis provides insightful perspectives into the chemistry of MPN assembly and other metal-organic coordination complexes.
Nanoengineering Antibody Assemblies for Biomedical Applications
The clinical success of monoclonal antibody therapy has inspired research in understanding the fundamental molecular basis of antibody-antigen interactions and the engineering of antibodies with enhanced or novel properties. With the emergence of nanomedicine, antibodies have been widely applied as targeting ligands decorated on the surface of therapeutic nanostructured modalities – including liposomes, protein nanoparticles, and polymeric assemblies – for drug delivery and imaging applications. However, little is known about how antibodies assembled in a cluster or particulate form interact with antigens in a biological system, largely due to the challenge in preparing ‘pure’ antibody assemblies with controlled physicochemical properties. In this thesis, a mesoporous silica template-mediated assembly platform was applied to fabricate well-defined nano-assemblies of therapeutic antibodies, including conventional monoclonal antibodies and antibody-drug conjugates. The antibody nano-assemblies (AbNAs), crosslinked with poly(ethylene glycol)-N-hydroxysuccinimide (PEG-NHS), preserved the selectivity of the monoclonal antibody and induced receptor-mediated internalization of antibodies to achieve enhanced intracellular response, such as growth inhibition. This strategy presents opportunities for intracellular delivery of monoclonal antibodies, as well as a versatile platform for fundamental studies on the interactions between antibody assemblies and cells. Facile engineering of AbNAs can be achieved by leveraging the intrinsic property of the PEG crosslinker, such as chain architecture (PEG arm numbers and arm length), to regulate bio-nano interactions. As a widely recognized stealth material, PEG can prolong blood circulation time to allow the accumulation of nanoparticles in target tissues, however, it could also result in decreased targeting efficacy by blocking the antigen-binding sites. This thesis investigates the influence of PEG crosslinking, specifically the effect of using PEG crosslinkers with different chain architecture on the formation of AbNAs and their bio-interaction with respect to specific binding and uptake by phagocytic cells. PEG crosslinkers with less arms but longer arm length were found to be more beneficial for AbNAs to achieve both minimal phagocytic capture and optimal targeting. Furthermore, the targeting efficacy of AbNAs could be enhanced by substituting conventional monoclonal antibodies with engineered antibody fragments. Nanobodies, also known as single-domain antibodies (sdAb), are the smallest antigen-binding unit (12-15 kDa) that solely bind to the target antigen. The unique structure of nanobodies offers several desirable features, including small size, high stability, strong antigen-binding affinity and low immunogenicity, which makes nanobodies superior for antibody nano-assembly engineering. The nanobody nano-assemblies (NanoNAs), prepared via the template-mediated assembly platform, exhibited significantly enhanced selective association to target cells and reduced phagocytic association in comparison with full-sized AbNAs, owing to the unique structure of nanobodies that allowed a large amount of active binding sites to be presented on the particle surfaces and eliminated crystallisable fragment (Fc) receptor-mediated capture by phagocytic cells. Overall, the versatile antibody nano-assembly systems expanded our understanding of antibody-antigen interactions, and provides a facile platform to engineer antibody assemblies with novel or enhanced properties for biomedical applications.
Design and Synthesis of Antimicrobial Polypeptide Polymers
The goals of this thesis were to explore the impact of architectural design on the potency of antimicrobial polypeptide polymers. To this aim, we firstly investigated the synthesis and kinetics of flexible polymeric macroinitiators obtained via photo reversible addition-fragmentation chain-transfer polymerization (RAFT) for the ring opening polymerization of N-carboxyanhydrides. This study revealed the bottlebrush polymers benefit from a cooperative folding of alpha helices in chlorinated solvent, resulting in fast kinetic rates. Furthermore, free primary amine and trimethylsilylated macroinitiators were shown to offer similar initiation efficiency, kinetics, and polypeptide control, which allowed the selection of appropriate initiators and polymerization conditions for future applications. Based on this synthetic knowledge, amphipathic bottlebrush polypeptide polymers, termed brush Structurally Nanoengineered Antimicrobial Peptide Polymers (brush SNAPPs) were synthesized. Their direct antibacterial activity was evaluated against Gram-positive and Gram-negative pathogens by means of in vitro assays. The outcome of the structure activity investigation revealed the bottlebrush morphology is indeed antibacterial, with short bottlebrushes of backbone degree of polymerization of 16 behaving similarly to star shaped SNAPPs and displaying preference for Gram-positive bacteria. In contrast, a brush SNAPP with longer backbone length of 190 displayed greater efficacy when challenged with Gram-negative Acinetobacter baumannii. These results, combined with the reduced cytotoxicity of the brush SNAPP architecture provide guidance for the treatment of Gram-negative infections. Aiming to further reduce the observed mammalian toxicity of polypeptides, we next focused on PEGylation as a means to improve SNAPP biocompatibility. Three different avenues for the polymerization of brush poly(ethylene glycol) methyl ether acrylate (PEGA) with high chain end fidelity were investigated. Blue LED-activated RAFT polymerization yielded remarkable alpha- and omega- group retention compared to thermal and UV activated RAFT methods. This technique was applied toward the synthesis of discrete polypeptide nanogels comprised of a comb-brush PEGA and bioactive polypeptide corona, aiming to selectively target Gram-positive pathogens. Antibacterial evaluation of the SNAPP nanogel hybrid against Escherichia coli and Staphylococcus aureus demonstrated this architectural design furnishes bacteriostatic and bactericidal properties, with selective targeting of S. aureus whilst also achieving an improved therapeutic profile and antifouling protection. Together, these results have generated important considerations for the future design of antimicrobial polypeptide therapeutic agents of varied architecture.
Lift Induced Particle Migration in Dilute Suspensions
Small particles moving near a wall experience particle-scale inertial lift forces in a direction normal to the wall and hence, migrate away from the wall. In addition, particles in suspensions experience hydrodynamic collision forces and migrate away from or towards the wall. These forces are critical in the biological context as they contribute to the separation between platelets and red blood cells that ensure the repair and integrity of blood vessels. These migration mechanisms have also been utilised to design and optimise micro-scale cell-sorting microfluidics for (e.g.) novel health detection systems and `smarter' industrial shear enhanced membrane filtration devices. Despite these important applications, a comprehensive model that can predict the lift and drag forces acting on a small particle moving near a wall is not available. Models that have previously been developed are limited to specific wall separation distances, fluid shear rates, and particle slip velocities, which do not cover practically relevant parameter ranges. Further, particle-scale lift models have not been previously employed in the context of suspension modelling to predict the averaged motion of many particles, as opposed to the motion of a single particle. Such suspension modelling is necessary to predict the performance of real biological and industrial multiphase flows. Hence, this thesis aims to develop a comprehensive model of particle lift applicable to the parameter ranges found in typical biological and industrial flows and apply this model to predict the behaviour of particle suspensions in these flows. The work is conducted in two parts. Firstly, the hydrodynamic forces acting on a small spherical particle moving with a finite particle Reynolds numbers in single wall-bounded flows are investigated via direct numerical simulation. Based on these results, new lift and drag models are proposed for rigid spherical particles moving in quiescent and simple shear flows, valid for any wall separation distance, and shear and slip particle Reynolds numbers of order 0.1 or less. The models are used to examine the behaviour of single buoyant and neutrally-buoyant particles moving near walls, and the results are validated against existing experimental and numerical data. Secondly, a two-fluid model, which includes the developed wall-bounded forces, is implemented to predict particle migration in mono-disperse, dilute suspensions at low particle Reynolds numbers. Different implementation methods related to solid phase velocity boundary conditions, the force application phase, and secondary wall effects are discussed. Using this model, the transient solid concentration profiles in Taylor-Couette flows are examined and compared against available experimental results.
Developing methods for assessing concept maps of process safety
Process Safety is a key element of engineering that ensures the rapid human advancements can occur safely. It is important for the people who are already working in the process industries, and for those who will join them in the future. Process Safety education is a mandatory component and should be in the chemical engineering syllabus in every university around the world. A concept map is a graphical representation of information that shows the relationships between concepts. Since its development, it has been used to represent ideas and concepts in a simple and holistic manner. This study investigates whether concept maps may be used to assess learning by individual students and by cohorts of students of the Process Safety domain. To achieve that objective, a method of assessing concept maps through a categorical scoring system is proposed by developing appropriate categorisations for the concepts, links and propositions. The concept categories for the Process Safety domain were developed and validated via a novel process to remove human subjectivity. The process involved defining ten categories into which each of the concepts could be assigned. Several sets of concept maps were analysed independently by three assessors, requiring the assessors to assign every concept into one of the proposed categories. Analysis of the assessors’ responses was aided by presenting their responses in a three-way table. The use of the novel table allowed the assessors’ responses to be compared effectively. This comparison tool enabled identification of problematic categories for further refining. The analysis of the distribution of the concepts, with the help of the proposed Link Quality Index, revealed more information about students’ understanding of the topic. This study analysed different types of connections between concepts to obtain more context and understanding of the concept maps, which represents students’ grasp of the Process Safety knowledge. The students generally appreciated the non-physical preventative measures, such as procedures and maintenance, but they did not recognise the importance of the education, training and values, such as responsibility towards Process Safety. This information is useful in helping to redesign the curriculum. This study also proposes a method that may be applied beyond Process Safety domain; the classification of propositions into one of three proposed attributes, Professional Practice, Values, or Technical Knowledge. The application of this method to engineering students’ concept maps revealed that students show high awareness towards Technical Knowledge. Students also demonstrate the ability to use higher order thinking in explaining the relationship of the behaviour of the Professional Practices and Values. Upon applying this method to nursing students’ concept maps, on the topic of Oxygenation, it is found that nursing students had similar patterns in their awareness of technical attribute. However, nursing students generally were more oriented towards using lower order thinking in explaining relationship between concepts. Overall, this study found that concept maps are a useful method to be applied in Process Safety domain; however, students need to be aware of the importance of having complete and clear propositions which are essential in indicating their understanding.
Nanofabrication of patterned surface structures by controlling surface-initiated and crosslinked ultra-thin polymeric films
This thesis reports the successful development and use of surface-initiated polymer films via ring-opening metathesis polymerization (ROMP) and solid-state continuous assembly of polymers reactions as capable bottom-up processes for nanofabrication of organic and inorganic materials. Chapter 1 presents an overview of existing bottom-up nanofabrication methods. Chapter 1 also highlights the drawbacks of current top-down fabrication methods and the opportunities to expand bottom-up methods to nanofabrication, of which are the focus of this thesis. In Chapter 2, the development of a protocol for solid-state continuous assembly of polymers via ring-opening metathesis polymerization (ssCAPROMP) from silanized substrates is presented. This method expands upon previously reported protocols by utilizing an olefinic silane to form highly crosslinked and tailorable polymer thin films which are covalently attached to surfaces. Polymer films constructed using the new anchoring layer showed similar growth characteristics and film thicknesses when compared with previous studies on CAP film growth, but overcome the high degree of steric hindrance and typical minimal macro-cross linker attachment encountered when previously working with silanized silicon surfaces and CAP processes. Films were also successfully reinitiated multiple times, a key property of the CAP process. Optimization of the protocol was carried out via thorough testing of reaction conditions, offering insight into the reactivity of the SI-ROMP process at play. The protocol was further developed to work on the organic material SU-8, a negative photoresist commonly used in microfluidic devices and bio-microelectromechanical systems (bioMEMS) and could be patterned using two methods: masking of the silanization step and subsequent lift-off prior to initiation and film growth, or through selective surface functionalization via the use of polymeric stamps and micro-contact printing procedures. The study presented in Chapter 2 translates the significant advantages of the solid-state CAPROMP protocol when forming polymer films into a method that can be integrated into the fabrication of robust sensors, bioMEMS or microfluidic devices which require tailorable yet stable polymer thin films. In Chapter 3, the ssCAPROMP protocol developed in Chapter 2 was used as a reactive ink system for a micro/nano 3D printing platform to access spatially defined, crosslinked polymer features. The printing platform used was a modified atomic force microscope whereby a hollow cantilever and an aperture at the tip was used to deliver material from a reservoir through a nanofluidics channel to the substrate. Material delivery was controlled by applying pressure to the reservoir. Utilizing the control over polymer properties offered by CAP, a reactive polymer crosslinker was created that encompassed a number of critical parameters in order to be printed successfully; the ink must undergo rapid crosslinking, it must have a low glass-transition temperature to be printed, and the crosslinking must be of a living nature to enable the printing of multiple layers continuously. The reactive ink could be used without solvent and was delivered through the aperture of the tip onto an initiated surface where it was found to crosslink almost immediately, even in ambient conditions and without requiring an inert atmosphere. This rapid crosslinking enabled the delivery of several layers of which each crosslinked, allowing the build-up of various line heights. A comparison of line heights after washing and drying found that when printing with both the 4 micrometer aperture and the 300 nm aperture, repeated depositions in the same location resulted in an almost quantitative addition of material based on the number of depositions. Overlapping lines were also printed and showed that the height at the overlapped location was the sum of the heights of both lines, highlighting the ability to print on top of existing lines. Experiments showed that by waiting a short period of time between overlapping lines, line heights could be increased as the feature could “cure” before the next deposition. Print directionality was shown to affect line widths based on the contact between the deflected tip and the direction it moves. Structures with three distinct layers were also created, showing that this method of delivering reactive ink and crosslinking in-situ could create three-dimensional patterns. By combining this printing platform with the versatility in ink and polymer chemistry offered by CAP, a robust platform for creating three dimensional structures with a layer resolution of down to 2 nm and a minimum line width down to 450 nm was demonstrated. In Chapter 4, the surface-initiated ring-opening metathesis polymerization of norbornene was used to direct the bottom-up construction of TiO2 and ZnO via atomic layer deposition (ALD). Norbornene monomers were used in the vapor phase to avoid excessive polymerization and cross-metathesis side reactions that occur when using solution-based SI-ROMP. This process afforded surface-bound polymer films in an extremely rapid fashion, with 100 nm films achievable in less than one minute of vapor exposure. The polymer films were exposed to TiO2 and ZnO thermal ALD processes and then analyzed via XPS to observe any inorganic material growth. It was found that 100 nm of surface-initiated polynorbornene could resist ALD of at least 1200 cycles, challenging a current paradigm of using small molecules to prevent ALD deposition. Several norbornene-based monomers were synthesized as surface-binding initiators that were selective for copper and copper oxide over silicon oxide. These initiators were used in conjunction with coplanar and topographical copper features on silicon oxide wafers in order to selectively attach initiator to the patterned features. Once coated, the functionalized features were used to grow polymer in an area-selective fashion and these substrates were subjected to ALD to test the ability of the polymers to perform area selective deposition (ASD). ASD of ZnO was achieved using a hydroxamic acid-based initiator, enabling the deposition equivalent of 38 nm of ZnO before any nucleation was observed on the polymer surface. This was also tested on large areas, where a large Sierpinski’s triangle 300 micrometers across was created on a substrate using e-beam lithography to demonstrate that large scale ASD could be performed. Polymers grown on the copper surfaces showed inhibition of ALD for up to 675 cycles of ZnO. These results show that SI-ROMP is not only an excellent tool for the bottom-up construction of organic materials as is shown in Chapters 2, 3 and 4, but that long macromolecules can be used to drive the patterned bottom-up construction of inorganic films relevant to semiconductor and device fabrication to great effect. Finally, in Chapter 5 we propose several pathways where expansion upon the work contained in this thesis may lead to further advances in the bottom-up construction of organic and inorganic materials for nanofabrication.
Near-net shaping of dense ceramics via freeze-casting
At present, producing dense complex-shaped ceramic parts require time-consuming and labour intensive processes, that are unsuitable for large-scale mass production. This results in prohibitively expensive part costs, in turn limiting the range of practical applications for complex-shaped dense ceramic materials. With process modifications, the freeze-casting process has potential as a suitable near-net shaping process for this application. In freeze-casting, a well-dispersed suspension of particles, such as a dispersion of ceramic powder in a carrier solvent, is frozen in a mould to produce a solid part. The frozen solvent can then be removed by sublimation in a freeze dryer, to produce a ceramic green body. Sintering this part enables us to produce a dense ceramic part retaining the shape of the mould. Current research in the field of freeze-casting elsewhere is primarily focused on tailoring the freezing process, to create solvent-crystals of various morphologies, for use as pore-forming templates in the production of highly porous components. In this thesis, freeze-casting was performed with highly loaded non-aqueous alumina ceramic suspensions, primarily with submicron alumina in cyclohexane carrier solvent, with the end-goal of producing dense ceramic components. Previous progress in this research area has been hindered by the samples exhibiting severe internal cracking. In this thesis the mechanisms and key factors responsible were identified for crack formation within samples, and applied this new understanding to explore selected avenues for mitigating the formation of cracks through changes to the process and to the suspension composition. In this work, the role of each of the primary freeze-casting process steps (freezing, freeze-drying and pressureless sintering) were systematically explored relating to both microstructure development and crack formation. A range of techniques were used to examine internal sample microstructures, including micro computed-tomography (micro-CT) and SEM imaging, with specific attention being given to the effects of freeze-drying conditions on samples. The key conclusions are as follows. By performing dense freeze-casting with highly loaded suspension, and by maximising the freezing rate (using pre-chilled moulds to minimise the templated pore size), it was demonstrated that dense and complex-shaped objects can be formed via this process. The formation of undesirable internal cracks in this process was identified and proven to occur during the freeze-drying step, with cracks being absent in the frozen state, and present prior to sintering. It was found that the rate of sublimation drying influences both the distribution and configuration of the crack network, with fast drying rates (rapid sublimation under vacuum) resulting in both external radial ‘spoke’ cracking and internal discontinuous cracking, while slow drying rates (self-sublimation of samples in a freezer at ambient pressure) resulted in ‘onion-like’ concentric ring cracks. While cracks occur during drying, it was identified that the development of cracks occurs towards the start of drying, and significantly, that crack development occurs independently to the progress of drying and solvent removal. Addition of an acrylic binder to the suspension was shown to significantly increase the mechanical green body strength, and this reduced but did not eliminate cracks. With regards to crack mitigation, the combination of both using slow drying rates, and adding an acrylic binder to the suspension, was demonstrated to successfully mitigate crack formation. Finally, the use of cyclooctane as an alternative carrier solvent also resulted in reduced cracking, confirming that the solvent selection is integral to the effectiveness of the dense freeze-casting process. In this way, the viability of a dense freeze-casting process for rapid production of complex shaped ceramic components was critically evaluated, and potential limitations of this process were identified and considered.
The structural-functional relationship of polymer-surfactant complexes relevant to personal care product
Polymer-surfactant (PS) mixtures are widely used to control both solution and surface properties. The link between the molecular structure of polymers and surfactants and their associative behaviours is of great interest and it is not very well understood. The examination using several different methods in the colloidal systems is to link the function of PS complexes to their microstructure from different aspects. My thesis aims to investigate how oppositely charged PS complexes can affect the interaction and the adhesive force of drops to surfaces and link these attributes to the target functions of a formulation, including shelf life stability and drop deposition or adhesion of an emulsion formulated chemical products, for example, personal care products. This was achieved by using both novel microscopic methods to quantify adhesion interactions and probe the adsorption and microstructure of PS complexes coated on drops and model surfaces as well as correlating these data to macroscopic methods for bulk solution properties. In this work, cellulose based cationic polymer and anionic surfactants, sodium lauryl (or dodecyl) sulphate surfactants were used based on current key ingredients in personal care product formulation. We have studied when drops will stick to surfaces in the presence of PS complexes by systematically varying the components of PS complexes (e.g. polymer type, surfactant concentration and type, and electrolyte concentration) and correlating the observed drop adhesion to hydrophobic surfaces with the phase diagrams of PS complexes. This observed that polydispersity in anionic surfactant headgroup can drive different drop adhesion, which motivated studies on surfactants in the absence of polymer to see how polydispersity of head group affects the micellization of the surfactant by measuring their critical micelle concentration (cmc) as a function of polydispersity degree and added electrolyte as well as the shape and dimension of the micelle using small angle neutron scattering (SANS). These measurements demonstrated that by controlling the degree of polydispersity in surfactant headgroup, the micelle character and their interaction with polymer can be possibility predicted. The measurements of drop adhesion were then compared to the adsorption of the PS complexes in order to explain how the structure of PS complexes on different surfaces can affect drop adhesion. The adsorption of PS complexes onto model surfaces that have more complexity, relevant to skin, hair or textiles were studied by measuring the adsorbed PS layer thickness using AFM imaging as well as force measurements in combination with measures of the adsorbed amount using QCM-D. By combing the observation of the layer thickness and adsorbed mass of PS complexes upon surfactant and electrolyte dilutions, and the effect from surface character, more insights of the mechanism of the structure change of PS complexes is understood.
The electrochemical regeneration of granular activated carbons in situ of permeable reactive barriers
Permeable reactive barriers have proven to be an effective and cost efficient remediation technique for the clean-up of petroleum hydrocarbon contaminated sites in extreme regions such as the Antarctic. The materials within these barriers, namely granular activated carbon, decontaminate migrating groundwaters via adsorption processes and prevent further spread of pollutants into the environment. However, with long operational periods, the activated carbon becomes saturated and is no longer effective at capturing contaminants. In an effort to prevent this, this thesis investigated the possibility of using in situ electrochemical treatments as a means of regenerating the activated carbon in these barriers such that the continuous replacement of saturated material is not necessary. Aqueous phase studies were first conducted to assess which electrochemical reactions aid in the degradation of solubilized petroleum hydrocarbons. Due to the natural presence of chloride and iron at the contaminated sites in the Antarctic and sub-Antarctic, the active chlorine and electro-Fenton pathways were chosen. Similarly, naphthalene, a high priority pollutant for removal in these regions, was chosen as a model compound to investigate the efficacy of the selected reactions. Upon application of an electric current in a near-saturated naphthalene solution, both reaction pathways achieved full contaminant removal within 3 hours of treatment. Further analysis showed that the naphthalene was electrochemically transformed into species of lesser toxicity with minimal energy usage that is appropriate for use in remote regions. Varying operational conditions were assessed to determine the underlying mechanism for which naphthalene was removed, and a dynamic kinetic model was developed for each reaction that could accurately predict treatment outcomes over a range of reagent concentrations, treatment timeframes, and applied electric currents. Due to the success for which the active chlorine and electro-Fenton pathways degraded naphthalene in the aqueous phase, the reactions were applied to naphthalene loaded granular activated carbon to determine the extent of regeneration that could be achieved. Regardless of the reaction applied, only 30 % regeneration could be achieved under any of the regenerative trials conducted, indicating that only the exterior surface of the porous granular activated carbon was likely being regenerated. As the micropores within the activated carbon were essentially unaffected by electrochemical treatments, macroporous or non-porous materials may be better suited for achieving high regeneration efficiencies. Although complete regeneration of the activated carbon was not reached, the developed technology can still prolong the longevity for which granular activated carbon can perform within permeable reactive barriers; over four cycles of treatment, the exterior surface was continually restored and freed up adsorptive sites for further adsorption processes. Thus, an ideal method for applying electrochemical treatments in situ of existing permeable reactive barriers is recommended.
Protein–Polyphenol Networks: From Fundamentals to Biomedical Applications
Naturally occurring building blocks have attracted scientific interest for the assembly of functional materials due to their intrinsic biocompatibility and biodegradability. Proteins are a particularly crucial class of functional biomacromolecules involved in most fundamental processes of living organisms that can be assembled into nanomaterials for various biomedical applications. Another ubiquitous class of biomacromolecules are polyphenols, which have traditionally been referred to as “vegetable tannins”, have recently been employed in engineering advanced materials, owing to their available physicochemical and biological properties and capability of assembly through diverse interactions. This thesis aims to introduce protein–polyphenol networks (PPNs), namely interconnected networks of proteins and polyphenols that can be deposited on a wide array of substrates. The polyphenol-mediated protein assembly of materials such as films, capsules, or nanoparticles (NPs) are introduced in this thesis because self-assembly approaches allow for the rapid generation of tailorable materials under mild conditions. This thesis also focuses on exploring the fundamentals of the interactions between proteins and polyphenols, which helps in understanding the assembly mechanism of PPNs. The binding affinity between polypeptides and polyphenols is studied by analytical chemistry techniques, focusing on the interactions between side chains of proteins and polyphenols, which is crucial for the controllable design of protein-based materials. Then, a straightforward and versatile strategy through interfacial polyphenol-mediated protein assembly is introduced to create a library of functional PPN materials, including bioactive surface coatings and functional capsules. Moreover, the PPN capsules not only can be used to clarify the governing interaction(s) between different proteins and polyphenols, but also can be employed in various applications (e.g., enzymatic catalysis, fluorescence imaging, and cell targeting). Next, a template-mediated supramolecular assembly method is developed to synthesize PPN NPs capable of endosomal escape and subsequent protein release in the cytosol. The versatility of this strategy in terms of NP size and protein type makes this a promising platform for potential applications in protein therapeutics. Finally, the protein–polyphenol interactions related to actual biological environments are investigated by the studying protein corona formed around different polyphenol-modified gold NPs (AuNPs). Protein corona compositional analysis demonstrates the binding preference of serum proteins with various polyphenols, and cellular uptake behaviors of polyphenol–AuNPs can elucidate the role of polyphenols in bio–nano interactions, which can act as reference works for the future implementation of polyphenols in biomedical applications.