Chemical Engineering

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This is the collection for the University of Waterloo's Department of Chemical Engineering.

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Influence of Indium Contamination from E-waste on Cell Behaviour
(University of Waterloo, 2025-05-27) Eskandari, Ali
Recent trends show a massive increase in the production of electronic waste (e-waste) worldwide. These e-waste materials often contain heavy metals whose biological impact on human health and the environment is unknown. One of these contaminants is indium, which can be found in many e-waste materials such as solar panels and liquid-crystal displays (LCDs). This thesis investigates how indium affects the functionality, behaviour, morphology, and viability of live mammalian cells. Two types of cells are used in this work: human dermal fibroblast cells (GM5565) and Vero cells (CCL81) isolated from C. aethiops kidney of an African green monkey (Cercopithecus aethiops). Cell adhesion is an essential biological function for division, migration, signalling, and tissue development. Although it has been demonstrated that this cell function can be modified by using nanometer-scale surface topographic structures, it remains unknown how contaminants such as indium (III) ions might influence this specific cell behaviour. Different tissues and organs, such as skin, muscle, and cornea, consist of cells organized in specific patterns that support their function. It is, therefore, important to understand how external cues, such as engineered surfaces or chemical contaminants, can influence the organization and morphology of cells. Two different indium compounds that are commonly seen in both extracting and recycling indium are indium sulfate (In2(SO4)3) and indium chloride (InCl3). These are two of the main sources of indium that humans are regularly exposed to, and can result in potential long-term harmful effects on human health. This thesis investigates the effect of indium on mammalian cells by exposing cells to different concentrations of each of these indium compounds and measuring an array of cell function indicators such as viability, production of Reactive Oxygen Species (ROS), cell alignment, cell morphology, and focal adhesion protein expression. In this thesis, first, the influence of indium chloride on cell adhesion characteristics is investigated, and the morphology of the adherent cells and their mitochondrial reticulum is characterized on cell culture dishes and nanopatterned surfaces using fluorescence confocal microscopy and scanning electron microscopy. Results showed that exposure to indium chloride decreased cell viability, affected cell alignment, had detrimental effects on the behaviour of human fibroblasts, and adversely impacted their mitochondrial morphology. Next, the impact of indium sulfate on cell viability, production of ROS, morphology, and alignment behaviour on tantalum/silicon oxide parallel line/trench surface structures is studied. Cell morphology and orientation on the engineered surfaces are characterized using fluorescence confocal and scanning electron microscopy. Results again confirmed that average cell viability decreased, the concentration of cellular ROS increased, and cell alignment and mitochondrial morphology were adversely affected. Finally, a study on the impact of indium chloride and indium sulfate on Vero cells is presented to investigate the effect of these contaminants on cell viability, ROS production, morphology, and alignment on tantalum/silicon oxide parallel line/trench surface structures. Results showed that when Vero cells were cultured in media containing indium chloride, the cell viability decreased by ∼35% on average, ROS concentration increased, and the cell geometry and alignment were again affected. The impact of indium chloride and indium sulfate on focal adhesion proteins was also studied using the Western blotting technique. The results showed that focal adhesion kinase (FAK) expression increased with increased concentration of indium in the media, and paxillin phosphorylates, while α−actinin stayed unchanged. All of these results confirm that indium has a negative effect on both human dermal fibroblast cells (GM5565) and Vero cells (CCL81) functionality. Their viability dropped to about 65%, and the ROS production increased. The morphology of cells changed to a more compact and circular shape. The alignment of GM5565 cells on the parallel patterns decreased with an increase in indium concentration, while Vero cells’ alignment on patterns in sizes of less than 1 μm increased. It also revealed that indium solutions alter the signalling pathway in Vero cells that are involved in forming focal adhesions.
Development of Facilitated Transport Membranes with Metal-Chelating and Hydrogel-Like Properties for Efficient Olefin/Paraffin Separation
(University of Waterloo, 2025-05-08) Zhang, Jinxuan
Olefins are essential feedstocks for producing a wide range of polymers and chemicals, and their separation from associated paraffins is crucial to obtaining high-purity olefins (>99.5%). However, due to their similar molecular weights and volatilities, olefin/paraffin separation remains a significant challenge. Distillation, the conventional method for this process, is both capital- and energy-intensive. Therefore, the development of alternative technologies that can be effective, sustainable, and energy-efficient for olefin/paraffin separation is a focus. Facilitated transport membranes (FTMs) offer a promising alternative by employing metal ion carriers, typically Ag⁺, to chemically facilitate olefin transport. This work developed a series of FTMs using polymeric matrices with both metal-chelating and hydrogel-like properties, achieving high olefin permeability, selectivity, and stability for olefin/paraffin separation. The first study focused on FTMs based on chitosan and silver nitrate. A large amount of silver was incorporated into the membrane by simply immersing a pre-formed chitosan membrane into an aqueous silver nitrate solution. Through sorption and diffusion, Ag⁺ ions and water were effectively loaded into the membrane, facilitated by the abundant amine groups in chitosan and their chelating interactions with silver ions. The membrane's high-water uptake created an ideal microenvironment for olefin-silver complexation, as well as the migration of both the complexes and silver ions. This study highlights the crucial role of both Ag⁺ and water loading in achieving optimal facilitated olefin transport. To further enhance water retention and membrane performance, a modification using dilute citric acid treatment was proposed. This approach contributes to preserving a small fraction of protonated amine groups, thereby improving the membrane’s water retention capacity and ultimately enhancing its separation efficiency. Next, a poly(vinyl alcohol) (PVA)/poly(vinyl amine) (PVAm)-based membrane was identified as a promising candidate for facilitated olefin transport. These two linear polymers were interpenetrated into a water-insoluble chitosan framework, forming an interpenetrating network (IPN) that achieves membrane insolubility without conventional crosslinking. This approach maximizes the availability of abundant amine and hydroxyl groups within the IPN, enhancing chelating interactions with Ag⁺ and enabling higher Ag⁺ loading compared to crosslinked membranes. The IPN structure allows for a water uptake of up to 2.32 g/g-polymer while maintaining sufficient mechanical strength for facilitated olefin transport, which involves the migration of complexes and silver ions within the membrane. To further optimize the membrane structure, a PVA/PVAm composite FTM with a gradient structure was developed using vapor-solid interfacial crosslinking. Beneath the highly crosslinked outer surface, abundant hydroxyl and primary amine groups were retained to facilitate chelation-based Ag⁺ loading, while the enhanced polymer chain mobility in the interior provided additional free volume for Ag⁺ and water loading. The ultrathin crosslinked surface, formed through interfacial crosslinking, acted as an effective barrier to paraffin molecules while maintaining permeability for olefins, leading to high perm-selectivity in olefin/paraffin separation. Another potential membrane matrix, derived from natural waste cocoons, was investigated for olefin/paraffin separation. Pristine fibroin FTMs exhibited limited performance due to low silver salt and water uptake, attributed to their rigid structure and low swelling capacity. Moreover, their brittleness and mechanical instability prevented them from withstanding the stress induced by Ag⁺ bonding at high concentrations. To address these limitations, fibroin and sericin were blended with chitosan. Both membranes demonstrated increased Ag⁺ and water loading capacities, better film-forming properties, and enhanced olefin permeability and olefin/paraffin selectivity. The β-sheet structure of fibroin in the chitosan/fibroin-Ag⁺ membrane provided greater structural rigidity, reducing paraffin permeability and mitigating competitive effects during mixed-gas permeation, ultimately leading to higher olefin/paraffin selectivity. To further investigate the gas permeation behavior and transport mechanisms in the water-swollen FTMs, the permeability, solubility, and diffusivity of olefins and paraffins were analyzed in four different FTMs. The study demonstrated that the permeability of the FTMs was significantly influenced by Ag⁺ and water content. Sorption tests showed that olefin solubility increased with pressure, deviating from Henry's law due to the combined effects of Ag⁺ complexation and gas condensability. Diffusivity calculations indicated that paraffins generally had higher diffusivity than olefins, primarily governed by molecular size.
Controlled Degradation of Biodegradable Polymers for Use in Melt-Blown Nonwovens
(University of Waterloo, 2025-05-05) Binley, Gillian
Nonwovens have many applications; however, they are typically made from petroleum-based polymers that are unsustainable and release microplastics upon breakdown that pose a risk to the health of both us and the environment. As such, it is necessary to shift to more environmentally benign materials such as biodegradable polymers. Unfortunately, readily available biodegradable polymers do not have the properties required, namely high melt flow index (MFI), for use in melt blowing, a common method for producing nonwovens. Therefore, this thesis aims to modify biodegradable polymers through aqueous hydrogen peroxide-induced controlled degradation to make them compatible with the melt blowing process. Two different biodegradable polymers are subjected to this treatment: poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT). Both systems demonstrated clear evidence of molecular weight reduction due to random chain scission induced by the peroxide radicals with additional contributions from thermal degradation and hydrolysis. PLA was also shown to begin crosslinking once a critical processing time was reached, while processing time appeared to have little effect on PBAT. The degraded products were then melt-blown to produce nonwoven mats with much finer and more uniform fibers compared to their untreated counterparts. The degraded PBAT from the second study was then blended with untreated PLA to develop a final melt-blown nonwoven with more balanced tensile properties than either material alone. Finally, since PLA and PBAT are immiscible when both are present in large quantities, maleation was used as a compatibilization technique to successfully enhance the quality of the melt-blown blends. Overall, reactive batch mixing with aqueous hydrogen peroxide is demonstrated to be a sustainable method for the molecular weight reduction of low MFI biodegradable polymers, allowing them to be well suited for use in melt-blown nonwovens.
Direct Laser Writing of Laser-Induced Graphene for flexible EMI shielding applications
(University of Waterloo, 2025-05-01) Barjinikhabbaz, Mahsa
As electronic devices become an inseparable part of modern life, the challenge of electromagnetic interference (EMI) continues to grow, driving the demand for next generation shielding materials that are not only lightweight and flexible but also highly efficient in safeguarding future technology. Graphene, a carbon-based material, has attracted significant attention for EMI shielding applications due to its exceptional properties. Various methods exist for producing graphene, such as mechanical exfoliation, chemical vapor deposition, and the reduction of graphene oxide. However, among these, direct laser writing (DLW) has recently gained the most recognition. This method stands out due to its scalability, cost-effectiveness, patternability, and eco-friendliness, making it superior to other graphene production techniques. Additionally, the graphene produced using this approach has demonstrated excellent potential for use in EMI shielding. As a proof-of-concept, we explore the performance of laser-induced graphene (LIG) derived via different DLW techniques, in particular, CO2, fiber, and ultraviolet (UV) laser systems, for EMI shielding. The effects of laser parameters, particularly laser fluence, on graphene microstructure, electrical conductivity, and EMI shielding effectiveness are systematically investigated. Results indicate that CO2 and fiber lasers both produce highly conductive and structurally optimized LIG with a total shielding effectiveness of 28.6 dB and 29.8 dB, respectively, whereas UV laser processing results in lower conductivity and reduced shielding performance. To enhance EMI shielding, a novel LIG- polydimethylsiloxane (PDMS) hybrid shield (LPHS) is developed, integrating multilayer LIG within a PDMS matrix. The LPHS design significantly improves the shielding efficiency up to 40 dB through enhanced absorption and multiple reflection pathways while maintaining flexibility and handleability of the shields. This study provides a comprehensive framework for optimizing LIG synthesis for EMI shielding applications, paving the way for scalable and cost-effective solutions in modern electronic systems.
Enhancing Graphene-Based Supercapacitor with Ionic Liquid/Surfactant Electrolyte by Structural Characterization and Modification
(University of Waterloo, 2025-05-01) Liu, Tianyu
Supercapacitors are advanced energy storage devices designed to deliver frequent, short-duration energy bursts due to their distinct charge storage mechanisms. Significant research efforts have been directed toward enhancing their capacitance and energy density. Preliminary investigations have demonstrated promising outcomes through the incorporation of high-surface-area reduced graphene oxide (rGO) as the active electrode material, combined with ionic liquids (ILs) whose broad electrochemical stability window maximizes the energy density and non-ionic surfactant to bind them together while boosting the double layer capacitance. This mixture of surfactant and IL simultaneously facilitates as the electrolyte and a spacer material, preventing restacking of rGO sheets and maximizing the ion accessible surface area. However, the self-assembling process of this composite is not yet fully studied. It is challenging to characterize the nano-scale structure of the composite specifically at the double-layer. Common characterization techniques at this resolution range, such as atomic force microscopy (AFM) and scanning electron microscopy (SEM), probe only the surface. Hence, this thesis investigates the self-assembled structures of GO, IL, and surfactant through small angle X-ray and neutron scattering (SAXS, SANS). These techniques provide bulk structural information on structures in the range of 1 – 100 nm, enabling precise determination of size, shape, and internal organization. The dispersion of each component and their mixtures was studied progressively, from simple to more complex systems, to understand their individual and collective behavior. The surfactant was found to form stable spherical micelles with a radius of 5.9 nm when the concentration reaches 20 mg/mL. The addition of IL to the surfactant allows the formation of an amphipathic micelle by attaching to the hydrophilic tails of the surfactant while also lowering the minimum micelle formation concentration to 0.8 mg/mL due to the strong ion-dipole interaction. However, at higher concentrations, large aggregates were found in the dispersion. This is not favorable for the self-assembly of proposed lamellar structure with rGO in the composite electrode, as it would result in inhomogeneous distribution of electrolyte. The surfactant flattens GO sheets by attaching its hydrophobic segment, promoting the formation of ordered layered structures. A new model of the complete self-assembled structure is proposed based on contrast-varied SANS profiles. The GO is sandwiched by the hydrophobic layer, then the hydrophilic layer decorated by spherical IL droplets. When compressed to dense solid electrodes, these droplets spread and fill up the rGO interlayer spaces. If the electrolyte is insufficient, voids may form, reducing the ion-accessible surface area and leading to poor performance or long work-in cycles observed in previous studies. In addition to the structural characterization, vertical ion bombardment to suppress the work-in cycles and improve rate performance was found to be selectively damaging the electrolyte rather than perforating rGO, resulting in deteriorating capacitance. However, the performance was able to partially recover from cycling. Since long-term electrochemical performance of the electrolyte along was found to negatively impacts its capacitive behavior, this recovery suggests the replenishing of fresh IL, added while assembling the device, driven by scanning potential.
Bioderived Cyrene For Sustainably 3D Printing Organo/Hydrogels
(University of Waterloo, 2025-04-30) BRAZ RAMIREZ, ALINE
Hydrogels possess unique properties that make them suitable for a wide range of applications. Recent advances in 3D printing techniques, such as stereolithography (SLA), have enabled the precise customization of hydrogel structures with complex geometries and controlled mechanical properties. Further development of advanced hydrogel properties remains a key research focus, with particular attention to improving properties such as mechanical integrity, electrical conductivity, and responsiveness to environmental stimuli. Strategies such as incorporating fillers and nanofillers into hydrogel matrices have been explored to enhance these properties. Additionally, the use of organic solvents instead of water, leading to the formation of organogels, has begun to expand the range of printable materials, addressing some limitations associated with hydrogel-based SLA printing, such as structural disintegration. This thesis investigates the use of Cyrene, a bioderived and environmentally friendly solvent, as an alternative to traditional organic solvents in 3D-printed hydrogel systems. Organogels can be 3D printed, and afterwards a simple solvent exchange with water can convert organogels into the desired hydrogels materials, maintaining the advantage of biocompatibility along with the complex structures produced by SLA 3D printing. This research work started by exploring Cyrene’s role in hydrogel formulation, printability, and mechanical performance, comparing its effectiveness with the synthesis route using Cyrene and conventional solvents such as dimethyl sulfoxide (DMSO). Specifically, this study focuses on Cyrene’s application in mask stereolithography (mSLA) 3D printing of organogels. It demonstrates Cyrene’s excellent performance in enhancing hydrogel stretchability and swelling behavior after solvent exchange. Additionally, structural stability during organogel printing is improved due to the application of a previously developed acrylate salt. The findings reported in this work suggest that Cyrene-based hydrogels have promising applications in biomedical fields and soft robotics. Furthermore, we extend this investigation by examining Cyrene as a dispersion medium for graphene, and its use in hydrogel nanocomposites. The study highlights Cyrene’s ability to stabilize graphene dispersion without the need for chemical surfactants, aiming to produce hydrogels with enhanced mechanical strength, electrical conductivity, and multifunctional properties. These advancements open new investigations for applications in flexible electronics, biosensing, and tissue engineering. The research findings provide a comprehensive understanding of Cyrene’s potential as a sustainable solvent in the synthesis of organogels that can be converted into hydrogels after solvent exchange and used for a wide range of applications. The insights gained from this research contribute to the advancement of high-performance, eco-friendly hydrogel materials by demonstrating how Cyrene can serve as a sustainable alternative to conventional organic solvents. By utilizing a bioderived solvent to create organogels, followed by solvent exchange with water, the mechanical properties, structural stability, and biocompatibility of 3D-printed hydrogels can be enhanced. Additionally, the ability to stabilize graphene dispersion in hydrogels without chemical surfactants opens new opportunities for developing conductive and multifunctional hydrogel-based devices. These findings not only support the ongoing shift toward greener material synthesis but also lay the foundation for future innovations in sustainable material science and additive manufacturing.
Engineering Aerotolerance and Quorum Sensing into Clostridium for Use as a Live Biotherapeutic Product against Solid Tumors
(University of Waterloo, 2025-04-30) Sadr, Sara
Tumor targeting remains a significant challenge in cancer therapy, particularly for solid tumors, which constitute approximately 80% of all cancer types. Hypoxia, a hallmark of solid tumors, plays a crucial role in tumor progression and metastasis. However, hypoxia also serves as a distinguishing feature of tumor cells compared to healthy tissue, presenting an opportunity for targeted therapeutic strategies. One such approach involves the use of anaerobic bacteria, particularly clostridia, which have been known for over 60 years to selectively colonize the hypoxic and necrotic regions of tumors. Studies have demonstrated that infection with wild-type clostridia strains can induce tumor lysis and regression. However, despite their ability to degrade hypoxic tumor regions, tumor regrowth from the viable outer rim often leads to incomplete tumor elimination, limiting the efficacy of clostridia-based tumor therapy. This study aims to address the challenge of tumor regrowth by developing an aerotolerant strain of Clostridium sporogenes that cannot grow in healthy tissue but can proliferate in the viable outer rim of tumors. As a part of this effort, the water-forming NADH oxidase gene (noxA) from Clostridium aminovalericum was cloned downstream of the thl promoter from Clostridium acetobutylicum and introduced into C. sporogenes. Experimental analysis confirmed that the heterologous expression of noxA conferred aerotolerance, allowing C. sporogenes to grow in the presence of oxygen. To couple aerotolerance with tumor colonization, the expression of this gene should be regulated. We chose to employ a quorum sensing (QS) promoter. In parallel, a QS regulatory system was designed to enable density-dependent control of gene expression in C. sporogenes. The well-characterized agr operon from Staphylococcus aureus, a Gram-positive bacterium, was introduced into C. sporogenes. Growth and fluorescence assays were conducted to characterize the behavior of the QS system, demonstrating its potential to function as a switch-like regulatory mechanism in C. sporogenes. Additionally, a mathematical model based on kinetic principles was developed and calibrated using experimental data to describe the dynamic of this synthetic QS. While the final integration of noxA under QS control was not completed within the scope of this study, the successful development of both aerotolerance and a functional QS circuit establishes a strong foundation for future assembly and implementation of a regulated-aerotolerant strain of C. sporogenes.
Design Ionically Crosslinked CNT Hydrogels that Mimic Cardiac Tissue Mechanics and Conductivity
(University of Waterloo, 2025-04-25) Akbarnia, Negar
Myocardial infarction remains a leading cause of mortality worldwide due to the heart's limited regenerative ability, resulting in disrupted electrical signaling and compromised contraction. Injectable hydrogels have emerged as a promising, minimally invasive approach to support myocardial healing and restore function post-MI, especially when designed to mimic key characteristics of native cardiac tissue, such as filamentous nanostructure, conductivity, and essential mechanical properties. Such biomimetic materials could potentially prevent pathological progression and enhance cardiac repair. However, the development of an injectable hydrogel that combines both conductivity and a fibrillar structure to effectively mimic cardiac tissue, promote cell growth, and support organ repair has yet to be achieved.The objective of this thesis is to develop an injectable hydrogel with conductivity and a filamentous architecture that mimics cardiac tissue. The primary hypothesis is that carbon nanotubes (CNTs) can serve as the main building blocks for creating nanocolloidal hydrogels with biomimetic filamentous structures. This structural arrangement is designed to mimic the extracellular matrix (ECM), providing a biomimetic environment that supports mechanical resilience. CNTs have attracted significant interest due to their exceptional conductivity and tunable mechanical properties, making them ideal candidates for reinforcing hydrogels in tissue engineering applications, particularly as artificial ECM scaffolds for myocardial regeneration. To incorporate CNTs as the primary building blocks of the hydrogel, they first stabilized in water, addressing one of the major concerns in their biomedical applications—toxicity. This was achieved through non-covalent functionalization by wrapping CNTs with the anionic polymer polystyrene sulfonate (PSS), which introduces electrostatic repulsion, preventing aggregation and ensuring a stable dispersion. Upon introducing salt (CaCl2), the stabilized CNT-PSS suspension undergoes gelation through electrostatic interactions, forming a hydrogel network. Both SWCNTs and MWCNTs have been explored as building blocks hydrogel development. This study incorporates both to compare their structural, mechanical, and electrical properties, identifying the most suitable option for myocardial tissue engineering. By tuning the ratio of Ca2+ cations to CNT-PSS, the rheological and structural properties of the hydrogel were systematically varied. The resulting hydrogels, formulated with both MWCNTs and SWCNTs, exhibited injectability at low salt concentration and strain-stiffening behavior at 1.9M. Additionally, both hydrogel systems demonstrated electrical conductivity, highlighting their potential for myocardial tissue engineering applications. With the SWCNT based hydrogel showing higher strain stiffening behavior than MWCNT based hydrogel.
Coupling Metabolic and Hydrodynamic Compartmental Models for Bioreactor Simulations
(University of Waterloo, 2025-04-21) Promma, Ittisak
Large-scale bioreactors are widely employed across bioprocessing industries for the production of chemicals, pharmaceuticals, and biofuels. The increasing demand for specialized pharmaceuticals has motivated industries to optimize bioreactor operations. However, the complexity of multiphase interactions and the emergence of concentration gradients and intracellular heterogeneity in bioreactors pose significant challenges in accurately predicting and optimizing the performance of bioreactors. Simulations of numerical models have become invaluable for understanding these systems; however, the high computational cost of detailed models—particularly those involving multiphysics—limits their practicality. The computational cost of these models precludes them from being used for real-time applications or for extensive design optimizations. To address this challenge, this thesis proposes computationally efficient methods to solve coupled metabolic and hydrodynamic compartmental models that describe key process dynamics. The compartmental model (CM) approach is based on steady-state multiphase computational fluid dynamic simulations and is designed to accurately represent hydrodynamic properties such as turbulent dissipation energy, oxygen mass transfer, and flow topology. Conventional compartmentalization methods were found to introduce nonphysical ``short-cutting'' effects, leading to inaccuracies in mixing time predictions. To mitigate this, a refined compartmentalization approach was developed to better capture hydrodynamic mixing patterns. Then, a metabolic model was integrated with the compartmental model to explore the metabolic and hydrodynamic interactions. In terms of the metabolic behavior, two key scenarios were considered: i) the intracellular concentrations were assumed to reach instantaneous equilibrium with their extracellular environments at all times and ii) the intracellular concentrations were not in equilibrium with their extracellular environments. For the first case, where intracellular and extracellular equilibration was assumed, a binary search tree metabolic model (BSTMM) was developed from a dynamic flux balance analysis model and coupled with a CM describing the extracellular environment. This method significantly reduces computational complexity by substituting traditional linear optimization solvers with an online point-location approach. The coupled BSTMM-CM successfully captured diauxic growth dynamics and demonstrated substantial computational efficiency, enabling long-term bioprocess simulations on standard desktop hardware. However, kinetic parameters for metabolic models calibrated in small-scale bioreactors could not be directly applied to large-scale systems without recalibration. This finding suggested that intracellular heterogeneity may play a crucial role in metabolic regulation and must therefore be explicitly accounted for. To address this, the second case considered a finite-rate adaptation mechanism governing equilibration between the extracellular and intracellular environments. A method of moments approach, assuming a truncated normal distribution, was implemented to reconstruct the number density function efficiently. This approach demonstrated that intracellular heterogeneity is most pronounced when the characteristic timescales of microbial adaptation and extracellular advection are comparable. The application of this approach to E. coli fermentation data reported in the literature resulted in improved fitting as compared to a model that ignores intracellular heterogeneity. Furthermore, the impact of population heterogeneity on metabolic regulation was evaluated, revealing distinct variations in growth rate and substrate uptake across different regions of the bioreactor. To further improve computational efficiency of the coupled PBM-CM, an adaptive population compartmental scheme is proposed, which dynamically adjusts the compartmentalization over the course of a simulation to balance accuracy and computational cost. This approach was found to be particularly effective for large-scale bioreactor simulations, especially when advection rates exceed microbial adaptation rates, leading to substantial reductions in simulation time with minimal loss of predictive accuracy. This research significantly advances the modeling of large-scale bioreactors by integrating hydrodynamic and metabolic models into a computationally efficient framework. The developed methods provide more in-depth insights into the influence of concentration gradients and intracellular heterogeneity on microbial behavior, ultimately improving the predictive accuracy and scalability of bioprocess simulations.
Development of carbon-based materials for improved sodium-ion battery anodes
(University of Waterloo, 2025-04-21) Dudding, Casey
Sodium-ion batteries (SIBs) are an important future technology for large-scale grid energy storage due to the abundance and lower cost of sodium compared to lithium. However, there are many challenges that continue to hamper their commercial development, including sluggish reaction kinetics, large volume expansions during cycling, and unstable solid-electrolyte interface (SEI) formation. Additionally, more work needs to be done to understand the storage mechanisms of sodium ions in anode materials and to understand what material properties are important for high performance. This thesis focuses on two areas: the development of a new anode material made of red phosphorus nanoparticles (RPNPs) wrapped in reduced graphene oxide (rGO) sheets and an in-depth investigation into the impact of rGO material characteristics on its performance as a SIB anode. In the first section, the synthesis of an rGO@RPNP composite through a scalable spray drying process provides increased performance when compared to the individual components or when the individual components are simply mixed together. This proof of concept is the starting point for future work on increasing red phosphorus loading within the core-shell structures, improving the reduction process to maximize the conductivity of the composite, and investigating methods to improve the initial coulombic efficiency (ICE) through optimization of material properties. The second section attempts to decouple the effects of rGO chemistry and oxygen content from its surface area to understand the effect of the material characteristics on its electrochemical performance. It is found that a non-exfoliated sample slowly reduced to a low temperature of 400 ℃ provides the best performance in terms of desodiation capacity (216 mAh g-1 at 100 mA g-1), and stability (85% retention over 200 cycles) while reducing the irreversible capacity loss by two to threefold compared to previous literature.
Citric Acid as a Facilitator for the Integration of Okara in Soymilk Gels
(University of Waterloo, 2025-04-07) Fathima, Amaan
This study aims to explore the effects of citric acid (CA) in the development of soymilk okara (MO) gels with improved integration of okara in soymilk protein matrix. A two-step approach was adopted. The first step focused on changes in the preparation of ingredients, soybeans, soymilk (M) and okara (O), and their effects on gel texture. The addition of CA at 0.14%, 1.25% and 2.5% (w/w) to M induced protein coagulation, significantly enhancing the mechanical and viscoelastic properties of thermally prepared soymilk gels. The particle size profile of O was manipulated by drying duration producing uniform MO gels with shorter drying time. The surface morphology of CA-treated okara (OCA), visualized with SEM, indicated that the structure of O loosened in OCA0.14 and degraded in OCA2.5. The second step focused on the preparation of soymilk okara gels with CA at two concentrations, 0.14% and 2.5% (w/w). The role of CA on the structure of okara and the coagulation of soymilk was examined by comparing three different formulations: (i) CA treatment of okara prior to its addition to soymilk (M+OCA), (ii) CA treatment of soymilk prior to okara addition (M+CA+O), and (iii) CA addition to a mixture of soymilk and okara (MO+CA). The CA soymilk okara gels were obtained by heat treatment and their physicochemical and texture attributes were examined. The concentration and order of CA addition had different effects on the gels. FTIR, TGA and SEM analyses of CA-treated O (OCA) revealed structural modification in OCA2.5, including decomposition and release of pectic substances, which were not detected in OCA0.14. The CA0.14 soymilk okara gels exhibited similar failure stress, failure strain and Young’s modulus, while viscoelasticity was influenced by the sequence of CA addition, in comparison to MO. Elasticity (Go’) of M+OCA and MO+CA increased threefold and viscosity (Go”) doubled, whereas M+CA+O exhibited a 4.5-fold increase in Go’ and a 3.5-fold increase in Go”. At CA2.5, the failure stress of the CA soymilk okara gels was similar to MO but with a lower failure strain and higher Young’s Modulus which indicated less cohesive, stiffer gels. The Go’ and Go” of M+OCA increased threefold and twofold, while nearly 4.5-fold in Go’ and 4-fold in Go” increases were observed for M+CA+O and MO+CA. The gel microstructure visualized with CLSM revealed changes in the protein network from strand-like in MO to particulate in the presence of CA, with CA2.5 soymilk okara gels having a denser protein network than CA0.14 soymilk okara gels. However, CLSM provided limited insights on the effect of the sequence of CA addition on gel microstructure. In conclusion, the properties of soymilk okara gels explored in this study indicate that the gel texture can be modulated by altering CA concentration or CA sequence of addition. The CA-modification of O was not essential as similar or superior improvement in texture were achieved by pre-aggregating soymilk proteins with CA in the M+CA+O and MO+CA gel formulations.
Strain engineering and bioprocess development for bio-based production of porphyrins
(University of Waterloo, 2025-04-07) Arab, Bahareh
Bio-based production using microbial cell factories has emerged as a transformative approach to addressing the limitations of petrochemical processes, offering renewable, sustainable, and environmentally friendly alternatives for manufacturing valuable chemical compounds. Among various microbial systems, Escherichia coli (E. coli) has become a popular and versatile host for biomanufacturing due to its rapid growth, genetic tractability, and extensive history of industrial use. Through advances in synthetic biology, genome engineering, and metabolic engineering, E. coli can be tailored to produce a wide array of chemicals, including structurally complex compounds like porphyrins. Porphyrins and their derivatives, such as heme and chlorophyll, are critical for various biological and industrial applications, ranging from pharmaceuticals and diagnostics to renewable energy solutions. Despite their significance, challenges such as pathway bottlenecks, feedback inhibition, and intracellular toxicity of intermediates hinder microbial production of porphyrins. This thesis addresses these challenges by implementing integrated engineering strategies to enhance porphyrin biosynthesis in E. coli and establish a robust framework for scalable production. A foundation of this work was the development of a genome engineering toolkit that integrates CRISPR-Cas9 and transposon-based methods. This system allowed for site-specific insertion of heterologous genes and precise inactivation of endogenous genes, achieving editing efficiencies exceeding 90%. Such flexible manipulation of the E. coli genome facilitated the construction of optimized strains for biomanufacturing. For example, the toolkit enabled the creation of a plasmid-free strain capable of producing polyhydroxyalkanoates, demonstrating its potential for industrial applications and providing the foundation for metabolic engineering efforts targeting porphyrin biosynthesis. For the subsequent part of our thesis, the biosynthesis of uroporphyrin (UP), a key precursor for heme, was enhanced by implementing the Shemin/C4 pathway in E. coli. Strategies to increase intracellular succinyl-CoA availability and express a synthetic operon containing genes such as hemA, hemB, hemC, and hemD led to UP titers of 901.9 mg/L under batch bioreactor conditions. Furthermore, most of the UP produced was secreted extracellularly, simplifying downstream purification and demonstrating the feasibility of large-scale production. These advancements highlight the effectiveness of pathway optimization in overcoming metabolic bottlenecks. We used the information obtained from previous chapter to enhance coproporphyrin (CP) biosynthesis. Dual synthetic operons controlled by strong promoters regulated key pathway genes, including hemA, hemB, hemD, hemE, and hemY. Bioreactor cultivation of the engineered strains using glycerol as the primary carbon source under aerobic conditions led to CP titers of up to 353 mg/L with minimal byproduct formation. To the best of our knowledge this study marked the first targeted bio-based production of CP in E. coli, laying the groundwork for its industrial-scale synthesis and emphasizing the importance of precise gene regulation in pathway optimization. Addressing the complexities of heme biosynthesis required a novel two-step strategy integrating in vivo and in vitro approaches. Engineered E. coli strains expressing the coproporphyrin-dependent (CPD) pathway produced ∼85 mg/L of coproheme and ∼18 mg/L of heme in vivo. However, intracellular heme accumulation posed significant toxicity challenges due to limited secretion into the extracellular medium. These challenges were mitigated by developing an optimized in vitro enzymatic conversion process, achieving a 77.2% reaction yield for the conversion of coproporphyrin III to coproheme and a 45.8% yield for the conversion of coproheme to heme. This integrated approach bypassed intracellular toxicity, enabling controlled and scalable production while addressing key bottlenecks in microbial production systems. In our final study, to further enhance porphyrin biosynthesis, strategies were developed to mitigate reactive oxygen species (ROS)-induced stress and redirect dissimilated carbon flux toward type-III porphyrin biosynthesis. Antioxidant supplementation with ascorbic acid (up to 1 g/L) improved the UP-III/UP-I ratio from 0.62 to 2.57, enhancing the production of type-III porphyrins. Additionally, overexpression of ROS-scavenging genes such as sodA and kat significantly increased porphyrin yields. Notably, overexpression of sodA alone resulted in a 72.9% increase in total porphyrin production, reaching titers of 1.56 g/L, while improving the UP-III/UP-I ratio to 1.94. These findings underscore the importance of addressing oxidative stress to optimize metabolic fluxes and enhance type-III porphyrin biosynthesis in E. coli. The study provides a practical platform for improving bio-based porphyrin production at industrial scales. Taken together, this thesis demonstrates the potential of integrating strain engineering, synthetic biology, and metabolic engineering to enhance porphyrin biosynthesis in E. coli. The innovative strategies developed provide scalable, sustainable, and economically viable solutions for producing porphyrins and their derivatives. These advancements open new avenues for industrial applications in pharmaceuticals, diagnostics, and renewable energy, establishing E. coli as a powerful platform for biomanufacturing complex biomolecules.
Advanced Separator Modifications for Lithium-Sulfur Batteries: Multifunctional Organic Frameworks and Nanostructured Composites to Mitigate the Polysulfide Shuttle Effect
(University of Waterloo, 2025-02-18) Fazaeli, Razieh; Yuning, Li
This thesis explores innovative approaches to addressing critical challenges in lithium-sulfur (Li-S) battery technology through the development of modified separator materials. The escalating concerns surrounding climate change, pollution, and fossil fuel depletion are propelling a global transition toward renewable energy sources like wind, solar, and hydropower. Alongside this shift is an increasing demand for efficient, high-capacity, and cost-effective energy storage systems that support these sustainable energy technologies, especially for applications in electric vehicles. Various rechargeable battery technologies, such as lithium-ion, sodium-ion, potassium-ion, magnesium-ion, zinc-ion, and aluminum-ion batteries, have garnered significant research attention due to their high efficiency, reversibility, light weight, and environmental friendliness. Although lithium-ion batteries have achieved widespread success in portable electronics and electric vehicles, they have limitations when it comes to the growing demand for energy density, long cycle life, and affordability. Consequently, next-generation batteries—particularly those based on sulfur chemistry—are being developed to meet these requirements. This thesis specifically investigates how functional materials for separator modification can address the main issues of polysulfide shuttle and conductivity in Li-S batteries, aiming to make these batteries more feasible for next-generation energy storage applications. The first study in this thesis focuses on designing a series of melamine-based porous organic frameworks (POFs) as efficient polysulfide reservoirs to modify glass fiber (GF) separators in Li-S batteries (LSBs). Despite the promising energy density of Li-S systems, the polysulfide shuttle effect—where lithium polysulfides (LiPSs) dissolve and migrate between electrodes—remains a significant barrier to achieving stable cycling and high capacity retention. To tackle this challenge, we synthesized a series of POF materials (POF-C4, POF-C8, and POF-C12) by reacting melamine with dibromoalkanes of varying chain lengths (C4, C8, and C12). The resulting POFs displayed distinct nanoscale pore sizes and solubility properties, which are critical for effective LiPS trapping and utilization. These POFs were then combined with conductive Super P (SP) and polyvinylpyrrolidone (PVP) binder to create a composite layer (POF-Cn/SP/PVP) that was coated onto GF membranes, forming modified separators that enhance the electrochemical performance of Li-S batteries. The batteries incorporating these modified separators were evaluated through various electrochemical tests, and the POF-C8/SP/PVP-modified separator, in particular, demonstrated outstanding performance. It delivered an initial specific capacity of 1392 mAh g⁻¹ at 0.1C and retained 90% capacity over 300 cycles at 0.5C. This enhanced performance can be attributed to the optimal pore structure of POF-C8 and its high nitrogen content, which work in tandem to capture soluble LiPSs and limit their migration toward the lithium anode. Furthermore, the good solubility of POF-C8 ensures uniform dispersion and strong interactions with LiPSs, enabling efficient redox reactions. This study highlights the potential of functional polymer-based separator modifications to mitigate polysulfide migration, improving the stability and longevity of Li-S batteries. The second study investigates the use of Congo Red (CR), a redox-active organic compound, in conjunction with cetyltrimethylammonium bromide (CTAB), a cationic surfactant, to modify GF separators for improved LSB performance. CR has a unique capability of engaging in redox reactions, which aids in suppressing the polysulfide shuttle by capturing LiPSs at the separator interface. The CR-CTAB/SP/PVP-modified GF separators demonstrated enhanced ion transport properties and higher sulfur utilization, addressing core issues that commonly degrade Li-S battery performance. Electrochemical performance tests revealed that LSBs with these CR-CTAB-modified separators achieved an initial specific capacity of 1161.9 mAh g⁻¹ and maintained 994.1 mAh g⁻¹ after 300 cycles at 0.5C, showing significant improvement over the baseline unmodified GF separators. The CR molecules in the separator modification layer serve as efficient adsorbents for polysulfides, while the CTAB molecules aid in stabilizing the structure and enhancing ion transport across the separator. This work emphasizes the importance of incorporating redox-active molecules into separator designs, showing that such molecules can effectively reduce the shuttle effect, enhance performance, and create more durable energy storage systems. The third study delves into the incorporation of a nanocomposite composed of CR and tin dioxide (SnO₂) nanoparticles for further improvement of polysulfide-trapping capability and redox kinetics in GF separators. The CR-SnO₂/SP/PVP-modified separators were synthesized by combining CR, SnO₂ nanoparticles, conductive SP, and PVP binder. This approach resulted in a composite layer with enhanced surface interactions and improved electron transport pathways. Structural characterization using techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM) confirmed the uniform dispersion of CR and SnO₂, indicating strong cooperative interactions between these components. Electrochemical tests demonstrated that LSBs incorporating the CR-SnO₂-modified separators exhibited exceptional performance, with an initial specific capacity of 1377 mAh g⁻¹ at 0.1C and capacity retention of 91% over 300 cycles at 0.5C. The CR-SnO₂ composite material provides dual benefits: CR molecules effectively capture LiPSs, while SnO₂ nanoparticles act as catalysts, promoting redox reactions and enhancing ion transport. This synergy between CR and SnO₂ in the separator layer contributes to stable cycling performance and mitigates capacity loss due to polysulfide migration, making this composite a promising solution for improving Li-S battery stability. The forth study address the shuttle effect challenge by employing cysteine and layered double hydroxides (LDHs) as 2D materials to create an innovative 2D heterostructure (Cys/FeNi-LDH). This heterostructure serves as a robust support for immobilizing V2O5 nanoparticles (NPs). Incorporating V2O5/Cys/FeNi-LDH (VCFN) into a GF separator ensured stable electron and ion pathways, significantly enhancing long-term cycling capabilities. The use of L-cysteine, a cost-effective and readily available amino acid, played a crucial role in enhancing the Li-S battery performance. The remarkable enhancement in electrochemical performance is attributed to the synergistic effects of VCFN nanoparticles, cysteine, and SP. A Li-S battery featuring the VCFN GF separator demonstrated an impressive initial capacity of 1036.8 mAh g⁻¹ and, after 300 cycles at 0.5C, retained a capacity of 920.1 mAh g⁻¹. This thesis demonstrates that modifying the separator is a highly effective strategy for addressing the primary challenges in Li-S batteries, particularly the polysulfide shuttle effect. By tailoring the physical and chemical properties of the separator layer, significant improvements in capacity retention, cycling stability, and rate performance have been achieved. Each of the materials that used for modification of GF separators demonstrates the potential to enhance battery performance through unique mechanisms. The melamine-based POF-C8-modified separator leverages a nanoscale porous framework to trap polysulfides and improve LiPS utilization. Meanwhile, the CR-CTAB and CR-SnO₂ composites add a redox-active element to the separator, aiding in polysulfide trapping and catalyzing redox reactions at the interface. A novel composite of V₂O₅ nanoparticles on Cys/FeNiLDH sheets (VCFN) was synthesized and used to modify GF separators, enhancing the electrochemical stability of LSBs. This research contributes to the field of LSBs by providing insights into the design of multifunctional separators that simultaneously address multiple performance issues, including polysulfide retention, ion transport, and redox catalysis.
A High-Order, Flow-Alignment-Based Compartmental Modelling Method
(University of Waterloo, 2025-02-11) Alexandru, Vasile; Abukhdeir, Nasser; Budman, Hector
Industrially-relevant chemical engineering processes, such as stirred tank bioreactors in the pharmaceutical sector, inherently operate across multiple scales and involve complex, multiphysics, and multiphase interactions. Modelling of these systems is essential for their design, optimization, control, and operational troubleshooting; these processes are often too intricate for experimental approaches alone, with trial runs proving prohibitively costly or key metrics being difficult or impossible to measure. Traditionally, modelling such systems has relied on simplified design equations or idealized models, such as the continuously stirred tank reactor (CSTR). However, these approaches lack the explanatory power required to capture real-system outcomes, such as concentration gradient formation. With advancements in computational capabilities, computational fluid dynamics (CFD) simulations have become standard for investigating specific questions within these systems. Nonetheless, certain critical applications, such as extended simulations of microorganism growth or real-time predictive control, remain impractical due to their high computational demands. Reduced Order Models (ROMs) offer a middle ground between the simplistic CSTR models and the computationally intensive CFD simulations. ROMs trade off some of the generality and accuracy of CFD simulations in exchange for a substantial reduction in computational cost, often by several orders of magnitude. This work focuses exclusively on a specific type of ROM: Compartmental Models (CMs). They are underpinned by the assumption of one-way coupling between the hydrodynamics and mass transport of reactive species. CMs are constructed through a two-step process. First, the domain is divided into non-overlapping compartments using a set of criteria; next, each compartment is represented by one or more simplified models. This network of models decouples mass transport from hydrodynamics and reduces the number of degrees of freedom on which the conservation of mass of the reactive species needs to be solved. This reduction is particularly important for bioreactors, where hundreds of coupled nonlinear reactions are common. Current compartmental modelling methods exhibit several limitations, such as a disconnect between the criteria used for compartment identification and their subsequent modelling, an assumption that each compartment is well-mixed, a reliance on manual compartmentalization or manual intervention, and a non-prescriptive framework that is challenging to adapt to new geometries. This work introduces a novel compartmental modelling method based on flow alignment. The velocity field is analyzed and split into compartments within which the flow is unidirectional. Each compartment is then modelled as a series of 1D Plug Flow Reactors (PFRs). Benchmarking this method against the state-of-the-art method demonstrates that it yields more accurate results while achieving computational speeds that are orders of magnitude faster than traditional CFD simulations. Further, many current CM approaches simplify three-dimensional geometries by either modelling two-dimensional cross-sections and relying on rotational symmetry or by using a uniform grids of compartments. The developed method is extended to fully three-dimensional two-phase stirred tank systems without using these assumptions. It successfully compartmentalizes the distinct recirculatory regions generated by the impellers, eliminating the manual ad hoc intervention required by past methods. Mixing time and concentration predictions at probe locations are validated against CFD simulations, other CMs, and experimental data. The proposed general method performs as well or better than past CMs which were tailor made for the stirred tank geometry. Further, the model's capability to handle complex spatially varying reactions is demonstrated by simulating oxygen dissolution into the liquid phase, accurately capturing spatial gradients in dissolved oxygen concentration. Lastly, a significant limitation in previous compartmental modelling work is the reliance on a single velocity snapshot or a time-averaged steady-state velocity field. For instance, in the case of vortex shedding from a cylinder in the laminar flow regime, neither time-averaged velocity-based CM nor an ensemble of CMs based on discrete velocity snapshots accurately captures the impact of the inherently non-stationary flow topology. The non-stationary nature of such flow fields is addressed by employing projection mappings to cycle through a series of compartmental models, allowing dynamically updating their shape, number, location, and connections. This approach successfully captures the oscillation period of the flow and demonstrates promise in representing non-stationary flow behaviours accurately. In summary, this work advances the field of compartmental modelling by unlocking their the application to complex, industrially-relevant systems by developing a generalized, alignment-based method. This method extends the capability of CMs to handle both time-varying and fully three-dimensional multiphase flows without requiring manual intervention. The approach is validated through benchmarking against CFD simulations, other CM approaches, and experimental data, demonstrating improvements in computational efficiency and accuracy.
Transition metal doped ceria catalyst prepared by direct precipitation method for thermocatalytic conversion of carbon dioxide via reverse water gas shift
(University of Waterloo, 2025-02-05) Xia, Wenxuan; Simakov, David; Yu, Aiping
Since the beginning of the industrial revolution, mankind has utilized large amounts of fossil fuels to obtain energy, which has led to the emission of large amounts of greenhouse gases such as carbon dioxide. How to reduce CO2 and utilize CO2 to obtain high-value products has become a hot topic in today's research. The thermocatalytic reduction of CO2 by using renewable H2 is expected to be a potential solution to these challenges. In this experiment, the reverse water gas shift (RWGS) reaction of various loaded transition metal doped cerium (MCeO2) catalysts (M = Fe, Co, Ni and Cu) was investigated. The desired catalysts have been synthesized by utilizing the direct precipitation method. The reverse water gas shift reaction has been extensively studied including reaction tests and some characterizations such as X-ray crystallography (XRD), Brunauer Emmett Teller (BET), Temperature Programmed Desorption (TPD), Inductively coupled plasma - optical emission spectrometry (ICP - OES) etc. In reaction tests, the performance of M-CeO2 was evaluated in terms of conversion and selectivity by varying the temperature (400°C - 600°C). The resulting reaction products were monitored using an on-line infrared analyzer to identify the formation of carbon monoxide (CO), methane (CH4), and unconverted CO2. T-test results show that transition metal doping has a significant effect in enhancing the surface CO2 adsorption and reduction. effects, including high loading of Fe with higher than 56% CO2 conversion and 100% selectivity to CO at 600 °C, Cu with 100% selectivity to CO but lower CO2 conversion, and Co and Ni with significant methanation ability, especially at high loading. In addition, the structures of the catalysts before and after the reaction were investigated using XRD. The binding strength of CO2 on the doped CeO2 surface was investigated using the programmed temperature rise desorption (TPD) method. The effect of specific surface on CO2 adsorption was investigated using BET. This experiment explores the effect of different kinds of transition metal-doped cerium catalysts on the reverse water-gas shift (RWGS) reaction, which reduces excess CO2 emissions and also provides an idea for CO2 conversion and utilization.
Techno-Economic Assessment of Carbon Capture for Integrated Steel Mills in Canada
(University of Waterloo, 2025-01-29) Titcombe, Anne Adetola; Croiset, Eric
Globally and within Canada, steel production accounts for 10% and 23% of total industrial CO2-eq emissions, respectively. This is primarily owed to the prevalence of the traditional blast furnace-based integrated steel mill, responsible for 73% of steel production globally. This thesis investigates the techno-economic feasibility of carbon capture methods within a Canadian integrated steel mill, focusing on reducing the direct emission intensity of hot rolled steel slabs till non-emitting steel production methods can be employed. The study emphasizes two post-combustion capture techniques: First, Monoethanolamine (MEA) absorption identified as the primary technology due to its maturity and cost efficiency. Second, hybrid methods combining vacuum pressure swing adsorption with low-temperature purification (VPSA-LTP) are explored for their commercial potential and lower thermal energy penalty relative to the chemical absorption base case. A systematic framework involving performance modelling using Aspen Plus and Aspen Adsorption, and cost assessment evaluates energy consumption, cost implications, and environmental benefits of both carbon capture methods. The opportunity for waste heat recovery for the steel production process was also evaluated. A surrogate-based optimization framework was developed and proven to be a tool for conducting a less-computationally intensive techno-economic assessment of batch separation processes. Key findings highlight that the lowest capture cost of $75 per tonne of CO2 captured ($86 per tonne of CO2 avoided) is achieved using a single-point of capture: the central power station, due to its volume and high CO2 composition. To achieve this minimum cost alongside its’ lowest achievable steel emission intensity, this carbon capture implementation includes MEA absorption with an oxy-combustion boiler and waste heat recovery from flared gas and flue gases to offset energy demand. In the case of natural gas supply constraints and overall reliance on electricity, using a hybrid VPSA-LTP process offers the lowest electricity consumption at a cost of $120 per tonne of CO2 avoided. Overall, carbon capture can be used to reduce the emission intensity to 0.76 tonnes of CO₂ per tonne of hot rolled steel slabs while increasing the production cost by 17% to $741 per tonne of steel. It is recommended that advanced solvents and sorbent be explored to further reduce the energy penalty and increase the productivity of their respective methods. There must also be evaluation of alternative decarbonization schemes for further emission reduction and the potential of heat integration with the existing power station to generate more steam in lieu of electricity. There must also be a multi-disciplinary assessment of the impact of policies on the viability of carbon capture as a decarbonization solution for the steel industry.
Engineering cell-penetrating peptide mediated protein-bound nanoparticles for delivering siRNA and chemotherapeutics
(University of Waterloo, 2025-01-27) Wang, Jun; Chen, Pu
Proteins serve as the “workers” of biochemistry, orchestrating nearly all biological functions. Functional endogenous proteins are often related to the pharmacokinetics and pharmacodynamics of drugs and nanomedicines, particularly in processes such as drug absorption, biodistribution, and metabolism. That means the innate interactions between proteins and drugs/nanoparticles exist, but the discovery and application of these interactions are underappreciated so far. By imitating the protein binding behaviors and interactions, some proteins may hold significant promise in drug and nanoparticle delivery due to their biocompatibility and functionalities. This thesis presents a methodology for engineering biomimetic protein coronas to camouflage cationic peptide/siRNA (P/si) nanocomplexes by utilizing proteins derived from the innate P/si protein corona (P/si-PC), which was also applied to the peptide-based lipid nanoparticles (pLNP). By leveraging these protein corona species, an efficient method for producing protein-bound chemotherapeutic nanoparticles in aqueous phases using microfluidic technology was developed. For cationic nanoparticles, the spontaneous nanoparticle-protein corona formation and aggregation in biofluids can trigger unexpected biological reactions. This thesis presents a biomimetic strategy for camouflaging the P/si with single or dual proteins, which exploits the unique properties of endogenous proteins and stabilizes the cationic P/si for safe and targeted delivery. An in-depth study of P/si-PC formation and protein binding was conducted. The results provided insights into the biochemical and toxicological properties of cationic nanocomplexes and the rationales for engineering biomimetic protein camouflages. Based on this, the human serum albumin (HSA) and apolipoprotein AI (Apo-AI) ranked within the top 20 abundant protein species of P/si-PC were selected to construct biomimetic HSA-dressed P/si (P/si@HSA) and dual protein (HSA and Apo-AI)-dressed P/si (P/si@HSA_AI), given that the dual-protein camouflage plays complementary roles in efficient delivery. A branched cationic cell-penetrating peptide (CPP, b-HKR) was tailored for siRNA delivery, and their nanocomplexes including the cationic P/si and biomimetic protein-dressed P/si were produced by a precise microfluidic technology. The biomimetic anionic protein camouflage greatly enhanced P/si biostability and biocompatibility, which offers a reliable strategy for overcoming the limitation of applying cationic nanoparticles in biofluids and systemic delivery. Currently, commercially applied lipid nanoparticles (LNPs) for RNA delivery, such as in siRNA and mRNA vaccines, utilize similar lipid compositions and ratios, raising the risk of unintentional patent infringement. This research attempted to engineer a novel peptide-based LNP formulation stabilized and functionalized by artificial protein corona that constitutes HSA and lipoprotein (Apo-AI; apolipoprotein E, Apo-E). The cationic peptide (b-HKR) enabled efficient siRNA condensation and reversible protein binding. Combining b-HKR and the artificial protein corona offers an alternative to the commonly used ionizable lipids, PEG-lipids, and excipients (such as sucrose), providing both pH-responsive functionality and storage stability. The in vitro results showed that the dual protein (HSA and Apo-AI) functionalized pLNP (pLNP@HSA_AI) is optimal for enhanced stability and RNAi efficacy. In contrast, single protein-functionalized pLNPs encountered a dilemma: pLNP@HSA improved stability but showed almost no RNAi efficacy, while the pLNP@AI exhibited remarkable RNAi efficacy but aggregated upon the addition of Apo-AI. The dual protein (HSA and Apo-E) functionalized pLNP (pLNP@HSA_E) also showed promise in addressing this dilemma, although the use of Apo-E is less cost-effective than Apo-AI due to its limited availability. The use of endogenous proteins, particularly albumin, for the targeted delivery of chemotherapeutics has proven practical. However, how to effectively produce the protein-bound chemotherapeutics nanoparticles in a complete aqueous phase (without the use of organic solvents) is worth pursuing to eliminate the solvent-related safety risks. In this research, the protein-bound Dox (Dox) nanoparticles were successfully produced through a one-step microfluidic mixing process in aqueous phases, in which the nanoparticle formation was instantaneously mediated by a self-assembled nano-peptide (np). The np-mediated HSA-bound Dox (D-np-HSA) and dual proteins (HSA; Apo-AI)-bound Dox (D-np-HSA-AI) nanoparticles exhibited efficient drug encapsulation and pH-triggered drug releases. In vitro cellular studies showed that the nanoparticles (D-np-HSA and D-np-HSA-AI) exhibited superior efficacy in killing tumor cells (A549 and MCF7) while being less toxic to normal cells (NIH3T3) compared to free Dox. Notably, D-np-HSA-AI was less prone to induce drug resistance, and cell lines that developed resistance to free Dox remained sensitive to D-np-HSA-AI. Besides, the results revealed that drug resistance development of A549 is associated with cellular phenotypic (size, morphology, and dividing speed) changes. Cellular (cytoplasmic and nuclear) proteomics was conducted by comparing the protein species, abundances, and relation networks of normal, Dox-induced, and nanoparticle (D-np4-HSA-AI) induced A549 cells, which aimed to provide potential protein biomarkers associated with drug resistance and druggable protein/gene targets for overcoming the drug resistance.
Rheology of Suspensions and impact of Cellulose Nanocrystal as an additive
(University of Waterloo, 2025-01-23) Pattath, Karthika Prashanth; Pal, Rajinder
Suspensions, as complex fluids, embody a fascinating interplay of solid particles within a liquid medium, presenting a diverse range of viscosity behaviors. Unlike simple Newtonian fluids, suspensions exhibit non-linear responses to applied forces, owing to interactions between dispersed particles and the surrounding solvent. Their viscosity can vary significantly with factors such as shape and size of particle, surface chemistry and concentration. Understanding the rheological properties of suspensions is crucial across industries like pharmaceuticals, cosmetics, paints, and food processing, where their flow behavior dictates product quality and performance. The research examines the consistent rheological characteristics of suspensions containing solid particles thickened by cellulose nanocrystals. Two distinct types and sizes of particles are utilized in preparing the suspensions: TG hollow spheres with a Sauter mean diameter of 69 µm and Solospheres S-32 with a Sauter mean diameter of 14 µm. The concentration of nanocrystals ranges from 0 to 3.5 wt%, while the particle concentration varies from 0 to 57.2 vol%. Additionally, the study investigates the impact of salt (NaCl) concentration upto 2 wt% and pH varying from 3 to 11 on suspension rheology. Generally, the suspensions display shear-thinning behavior, with a more pronounced effect observed in suspensions containing smaller particles. Experimental viscosity data conform well to a power-law model, with variations in flow behavior index and consistency index and under different conditions being thoroughly examined and discussed.
Melt-blowing of polymers for porous and functional air filters
(University of Waterloo, 2025-01-23) Kalani, Sahar; Mekonnen, Tizazu
This thesis develops innovative, high-performance, melt-blown nonwoven materials for air filtration. The first chapter presents a two-step process to create nano-porous, compostable PLA nonwovens with high porosity for particulate capture. First, PLA is melt-blended with polyethylene glycol (PEG) of varying molecular weights to enhance melt flow index (MFI), producing blends with MFI values ranging from 56 g/10 min to 238 g/10 min. These blends are processed into microfibers, with diameters from 1.05 to 2.64 µm, using a twin-screw extruder. The second step involves boiling water etching to remove PEG and form nanopores (50–200 nm), achieving approximately 85% particulate capture efficiency for 0.3 µm NaCl particles. This eco-friendly method shows potential for air and water filtration and battery separators. The second chapter addresses the limitations of conventional face masks, which lack antibacterial or antiviral properties. To improve mask functionality, advanced melt-blown filters are created using polypropylene (PP) and Rose bengal (RB), a photosensitizer. The study investigates the impact of processing temperature on fiber morphology, filtration efficiency, and antibacterial properties. The optimized filters show superior antibacterial performance, particulate filtration efficiency, and breathability, offering significant improvements for personal protective equipment (PPE), with enhanced antimicrobial protection and durability.
Effect of substrate topography on human vascular smooth muscle cell proliferation and phenotype change
(University of Waterloo, 2025-01-22) David, Dency; Yim, Evelyn
Cardiovascular diseases (CVDs) remain the leading cause of mortality worldwide, with vascular occlusion being a primary contributor. Bypass grafting is a common surgical intervention to restore blood flow, traditionally using autologous grafts such as saphenous veins and internal thoracic arteries. However, the limited availability and invasive harvesting process of autologous grafts have prompted the development of synthetic small-diameter vascular grafts (sSDVGs) as alternatives. Despite advancements, the clinical efficacy of sSDVGs remains unsatisfactory due to high rates of thrombotic occlusion, intimal hyperplasia (IH), and restenosis, primarily caused by dysregulated vascular smooth muscle cell (VSMC) behavior. VSMCs play a critical role in the progression of IH through their proliferation, migration, and phenotypic plasticity following vascular injury. While extensive studies have explored the influence of substrate topography on endothelial cell (EC) response, the effects on VSMCs remain underexplored. This study investigates the hypothesis that substrate topographies with varying geometries, isotropy, and sizes can differentially regulate VSMC behavior, potentially mitigating IH and improving the functionality of sSDVGs. To test this hypothesis, a 16-pattern multiarchitecture (MARC) chip was employed to screen various surface patterns for their ability to modulate VSMC phenotype. Five promising patterns were selected and individually fabricated on polydimethylsiloxane (PDMS) substrates for further evaluation. The influence of these topographies on VSMC behavior was assessed under normal and platelet-derived growth factor (PDGF)-stimulated conditions by analyzing protein markers associated with VSMC phenotypic states, including α-smooth muscle actin (α-SMA), phosphorylated myosin light chain kinase (pMLCK), F-actin, desmin, vimentin, phosphorylated focal adhesion kinase (pFAK), and yes associated protein (YAP). Among the tested patterns, the 2μm grating emerged as the most effective in inducing a contractile VSMC phenotype. VSMCs cultured on this pattern exhibited reduced proliferation, an elongated spindle-like morphology, and increased expression of muscle-specific proteins, irrespective of PDGF presence. Conversely, VSMCs on the 1.8μm convex microlens and unpatterned substrates showed higher proliferation rates and a diminished contractile phenotype. Remarkably, the beneficial effects of the 2 μm grating pattern were retained when incorporated into a fucoidan-modified polyvinyl alcohol (PVA) hydrogel, a biomaterial known to support EC adhesion and exhibit low thrombogenicity. The 2μm grating suppressed PDGF-induced proliferation while promoting a contractile phenotype and enhancing directional motility. Mechanistic studies revealed elevated pMLCK expression, increased cytoplasmic localization of YAP, and enhanced focal adhesion maturation on 2μm gratings, supporting contractility and reducing proliferation. In contrast, unpatterned and 1.8μm convex lens substrates induced nuclear YAP localization and reduced pMLCK expression, favoring a proliferative phenotype. This study introduces a promising strategy for regulating VSMC behavior through substrate topography, leveraging biophysical cues to promote a contractile phenotype while suppressing proliferation. By incorporating these insights into the design of biomimetic graft surfaces, this approach holds significant potential to address the limitations of sSDVGs, reduce complications such as IH, and improve long-term graft patency. Furthermore, the integration of topographical and biochemical modifications into PVA-based hydrogels represents an innovative avenue for the development of next-generation vascular grafts that combine mechanical strength with enhanced biological functionality. This work paves the way for advancing sSDVGs toward better clinical outcomes, reduced graft failure, and improved patient prognosis.

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