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Recent Submissions
Effect of substrate topography on human vascular smooth muscle cell proliferation and phenotype change
(University of Waterloo, 2025-01-22) David, Dency
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.
Efficacy of Vision Screenings in Waterloo Region
(University of Waterloo, 2025-01-22) McKinney, Marisa
Purpose: In 2018, the province of Ontario (Ontario) mandated a universal vision screening program for all senior kindergarten (SK) children (age 4-6 years). The purpose of the vision screening program is to detect children with risk factors for amblyopia, strabismus, and/or high refractive errors. The overarching aim of this thesis is to evaluate the effectiveness of Ontario’s universal vision screening program for SK children and how accurate the program is in identifying vision problems. These objectives are explored through two studies: parental adherence to vision screening recommendations survey, and investigation of the ability of Ontario’s vision screening program in identifying a SK child with a vision problem combined with determination of overall referral rates.
Methods: All parents/guardians (parents) of SK students who participated in Ontario’s vision screening program in the Region of Waterloo (ROW) from October 2022 to December 2023 were invited to participate in the initial study to evaluate parental compliance to vision screening recommendations and barriers to seeking vision care. Following the first study, parents who reported taking their child to an optometrist following the vision screening were invited to participate in a follow-up study, evaluating the program sensitivity and specificity and overall screening accuracy. For the second study, the vision screening results were compared to the eye exam results, and all vision screening data (visual acuity, stereoacuity and autorefraction) for children who participated in the 2022-23 vision screening program were analyzed to determine the screening program’s overall referral rate and for all three screening tools.
Results: 108 parents from 67 schools in the ROW responded to the survey to evaluate parental compliance in seeking vision services following the screening. The results of the survey found that over half (58/108, 54%) of the children screened were already under the care of an optometrist prior to the screening and less than half (48/108, 44%) of parents were prompted to obtain eye care, including 25% (27/108) who had already had a previous optometric examination. For the follow-up study that examined vision screening accuracy, 65 individuals participated. The vision screening program demonstrated a sensitivity of 0.935 and specificity of 0.406, producing a high rate of false positives (30%). Paired t-tests revealed significant differences in the accuracy of the vision screening tools compared with eye exam findings, particularly for refraction – sphere (OD: p = 0.005, OS: p < 0.001), cylinder (OD: p = < 0.001, OS: p < 0.001), and spherical equivalent (OD: p = 0.016, OS: p = 0.004). The retrospective review of the screening data included a total of 4837 vision screening results from 135 schools in ROW. The screening had an overall referral rate of 54% (2606/4837) and children were most commonly referred for autorefraction (43%; 2099) results followed by stereoacuity (31%; 1510).
Conclusion: This analysis of Ontario's vision screening program for SK children in the ROW highlighted key findings. The program was effective at encouraging parents that received a refer to go to the optometrist (64%), though 31% of all parents misreported screening results, suggesting a need for clearer communication. The program showed high sensitivity (0.935) but low specificity (0.406), with a 54% referral rate and 30% false positives which may contribute to lack of public trust over time. Adjusting referral criteria based on evidence could reduce false positives.
Modeling Ablation in Al/CuO Nanothermite Pellet Combustion
(University of Waterloo, 2025-01-22) Mondegari, Mohsen
Nanothermites are reactive materials composed of metal and metal oxide nanoparticles, engineered to produce rapid exothermic reactions with high energy density. Aluminum and copper oxide (Al/CuO) are widely used due to their strong reactivity and ability to achieve efficient combustion, making them ideal for applications in energetic materials.
This thesis investigates the combustion of Al/CuO nanothermite pellets, with a particular focus on ablation—mass loss due to thermal degradation and chemical reactions. A numerical model is developed to capture key combustion characteristics, including flame speed, pressure distribution, and temperature response, while accounting for both thermal and mechanical effects across varying packing densities. Leveraging the Porous-material Analysis Toolbox based on OpenFOAM (PATO), this model simulates complex reactions, heat flux, and ablation dynamics, thereby addressing existing gaps in understanding ablation effects on nanothermite combustion and enhancing predictive capabilities for these materials.
In its simulation methodology, this study adapts PATO to model multiphase reactive materials, formulating governing equations for mass, momentum, and energy conservation. A two-dimensional axisymmetric model was selected to represent the cylindrical pellet structure. Key parameters, including material porosity, permeability, specific heat, and thermal conductivity, were tailored to the properties of nanothermite materials, while distinct boundary conditions were applied to simulate ignition and ablation phases. Simulations were conducted across various packing densities, with some models incorporating ablation-specific boundary conditions to capture changes in flame speed, peak pressure, and pellet stability under different conditions.
Results indicate that ablation intensity significantly influences the combustion dynamics, with higher intensities leading to reduced flame speeds and peak pressures. The study's findings highlight the potential for controlled nanothermite combustion by optimizing pellet packing density and ablation characteristics, offering applications in propulsion and micro-energetics.
Engineering of Electrode-Electrolyte Interphase for High Performance Aqueous Rechargeable Batteries
(University of Waterloo, 2025-01-22) Liu, Zhongyi
The development of advanced aqueous rechargeable batteries is critical for the realization of sustainable, safe, and cost-effective energy storage systems to support renewable energy technologies. However, challenges such as narrow electrochemical stability windows and material degradation limit their practical application potential. To address these issues, this thesis systematically introduces electrode-electrolyte interphases for aqueous lithium-ion, aqueous sodium-ion and aqueous zinc-ion batteries to enhance their electrochemical performance.
In the first study, a novel hybrid electrolyte system comprising lithium methanesulfonate-trimethyl phosphate (LiMS-TMP-H2O) was developed to address key limitations of aqueous batteries, including the narrow electrochemical stability window (ESW) and low output voltage. The in-situ formation of lithium phosphate interphases (Li3PO4), derived from TMP, significantly enhances the ESW to approximately 4.5 V, enabling compatibility with a wide range of electrode pair materials. These include LiMn2O4(LMO)/LiTi2(PO4)3 (LTP), LMO/TiO2, LMO/Li4Ti5O12(LTO), LMO/Zn2Nb34O87(ZnNbO), LiCoO2(LCO)/LTO, LiN0.33Co0.33Mn0.33O2(NCM111)/LTO, and LiNi0.5Co0.2Mn0.3O2(NCM523)/LTO. These configurations exhibit high output voltages (up to 2.5 V) and excellent cycling stability, with performance maintained over 1,000 cycles. Notably, this electrolyte design offers an exceptionally low bill of materials (BOM) cost, accounting for only 0.4% of the cost of a 21 m water-in-salt (WIS) electrolyte and approaching the cost of dilute aqueous sulfate electrolytes. These attributes highlight the potential of this electrolyte as a universal and cost-effective solution for the development of high-voltage, long-lifespan aqueous batteries.
The second study elucidates the phase transformation mechanism of NaMnO2 and introduces TMP as a multifunctional electrolyte co-solvent for aqueous sodium-ion batteries. TMP not only enhances sodium-ion intercalation/de-intercalation on the cathode side but meanwhile in-situ forms a stable, robust and uniform solid electrolyte interphase on the anode side. These functions lead to batteries with enhanced performance with a high specific capacity of 198.21 mAh/g, an operation time of over 1440h and an energy density of 121.935 Wh/kg and in addition, this co-solvent expands the electrochemical stability window of the electrolyte to around 3.0V and imparts excellent low-temperature performance to the batteries (82.91mAh/g at -20℃), advancing ASIBs as a safe and environmentally friendly energy storage solution.
In the third study, the challenges of cathode degradation in Zn/MnO2 batteries are addressed through the development of an artificial Kaolinite-based Cathode-Electrolyte Interphase (K-CEI). This interphase effectively mitigates Mn2+ dissolution and suppresses the formation of Zn-vernadite nanoplates, ensuring stable cathode morphology and improved cyclic stability. The batteries with K-CEI achieve a reversible specific capacity of 380.89 mAh/g over 1,000 cycles and maintain superior performance across various MnO2 phases, providing insights into the design of next-generation long-lifespan aqueous Zn/MnO2 batteries.
Linear Acceleration Perception on a Moving VR Environment
(University of Waterloo, 2025-01-22) Zhou, Justin
Understanding how people perceive linear acceleration is crucial for creating more realistic and immersive virtual environments. This thesis investigates how people perceive
linear acceleration on a moving platform while in virtual reality (VR). The objective is the
identify the Just Noticeable Difference (JND), which represents the smallest detectable
change in stimuli that users can perceive. The study integrates a physically moving platform with a VR environment, employing a staircase method to determine upper and lower
perception bounds. By focusing on human sensitivity to acceleration, the research aims
to bridge the gap between physical and virtual motion experiences, a key motivator for
enhancing VR realism.
The results demonstrate that at low accelerations, there is an distinguishable upper
and lower bound of acceleration perception. These findings, validated through statistical
methods including t-tests, offer insights into how people perceive changes in acceleration.
However, unexpected trends, such as increased variability at lower accelerations, suggest
further investigation is needed to confirm the applicability of Weber’s Law in this context.
The research also highlights practical applications, such as space conservation in VR
motion systems, by leveraging the lower acceleration JND to shorten track distances without compromising perceived realism. Limitations, including sample size and equipment
constraints, are acknowledged, and future work is proposed to explore higher speeds, angular acceleration, and alternative experimental conditions. By advancing our understanding of linear acceleration perception, this study provides a foundation for improving VR
systems used in training, entertainment, and rehabilitation, ensuring they balance realism,
comfort, and practicality.