Browsing by Department "Department of Mechanical Engineering"
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Item 13-moment-equations from nonequilibrium thermodynamics and kinetic theory: Comparison for non-linear one-dimensional flows(Physics of Fluids, 2025) Bell, Luke; Struchtrup, HenningThe GENERIC-13 moment equations (general equation for the non-equilibrium reversible-irreversible coupling) [Struchtrup & Öttinger, Phys. Fluids 34, 017105 (2022)] were developed to have complete thermodynamic structure, in contrast to Grad’s 13-moment equations which are not accompanied by a suitable formulation of the second law of thermodynamics and loose hyperbolicity for larger deviations from equilibrium. With GENERIC-13 constructed to agree with Grad-13 to second order in the Knudsen number, both sets are considered and compared for hyperbolicity and plane heat transfer, and Couette and Poiseuille flows. It is shown that the GENERIC-13 equations are unconditionally hyperbolic. Jump and slip boundary conditions for GENERIC-13 are developed from the second law with coefficients adapted from kinetic theory. Additional asymptotically vanishing boundary conditions are constructed such that solutions of the GENERIC-13 equations reduce to those of Grad-13 to second and of Navier–Stokes–Fourier equations to first order in the Knudsen number.Item 3D bioprinted coaxial testis model using human induced pluripotent stem cells: A step toward bicompartmental cytoarchitecture and functionalization(Advanced Healthcare Materials) Robinson, Meghan A.; Kung, Sonia H.; Youssef, Khaled Y.; Scheck, Kali M.; Bell, Robert H.; Sar, Funda; Haegert, Anne M.; Asmae, M. Mahdi; Cheng, Changfeng; Yeack, Salina V.; Mathur, Bhairvi T.; Jiang, Feng; Collins, Colin C.; Hach, Farach; Willerth, Stephanie M.; Flannigan, Ryan K.Fertility preservation following pediatric cancer therapy programs has become a major avenue of infertility research. In vitro spermatogenesis (IVS) aims to generate sperm from banked prepubertal testicular tissues in a lab setting using specialized culture conditions. While successful using rodent tissues, progress with human tissues is limited by the scarcity of human prepubertal testicular tissues for research. This study posits that human induced pluripotent stem cells (hiPSCs) can model human prepubertal testicular tissue to facilitate the development of human IVS conditions. Testicular cells derived from hiPSCs are characterized for phenotype markers and profiled transcriptionally. HiPSC-derived testicular cells are bioprinted into core�shell constructs representative of testis cytoarchitecture and found to capture functional aspects of prepubertal testicular tissues within 7 days under xeno-free conditions. Moreover, hiPSC-derived Sertoli cells illustrate the capacity to mature under pubertal-like conditions. The utility of the model is tested by comparing 2 methods of supplementing retinoic acid (RA), the vitamin responsible for inducing spermatogenesis. The model reveals a significant gain in activity under microsphere-released RA compared to RA medium supplementation, indicating that the fragility of free RA in vitro may be a contributing factor to the molecular dysfunction observed in human IVS studies to date.Item 3D bioprinted skin co-culture model with air liquid interface (ALI) stratification for investigating microbiome-skin cell interactions.(2026) Díaz González, Giselle Yolanda; Willerth, Stephanie; Tuffs, StephenChronic wounds pose a serious and persistent public health challenge, resulting in devastating patient consequences and imposing a substantial economic strain on healthcare systems. Conventional treatments frequently fail because they target only single characteristics of the wound rather than addressing the complex, interconnected cycle where the microbiome and microenvironment play crucial roles in perpetuating inflammation. To develop effective biotherapies, advanced in vitro models that accurately replicate the complex skin microenvironment are urgently needed. Existing models, such as two-dimensional (2D) cultures and animal models, lack the necessary physiological complexity, are hindered by species-specific differences, and present ethical concerns. Three-dimensional (3D) bioprinting has emerged as a powerful alternative, enabling the creation of in vitro skin models that more closely mimic human in vivo conditions. The primary goal of this work was to investigate the clinical need, design, and verification of a 3D bioprinted stratified skin co-culture model suitable for studying the intricate interactions between the skin microbiome and cutaneous cells. Constructs were generated using extrusion-based bioprinting (EBB) with a high-viscosity, fibrin-based bioink containing co-cultured human keratinocytes (HEKa) and fibroblasts (HDFs), successfully creating a multi-layered structure replicating the epidermis and dermis. Crucially, epidermal stratification was induced through the Air-Liquid Interface (ALI) methodology to replicate the primary air-liquid barrier where bacteria reside and ensure comprehensive host-microbe dynamics. The functional maturity and interactions between the host-microbiome within the model were validated through biochemical signaling detection of cytokines through Human Cytokine/Chemokine Panel A 48-Plex Discovery Assay®, analyzing conditioned media collected pre- and post- inoculation with Staphylococcus epidermidis (S. epidermidis) and Staphylococcus aureus (S. aureus), the results confirmed a colonization model capable of restoring the cutaneous barrier and maintaining a stable homeostatic environment through active molecular communication. Furthermore, achieving comprehensive analysis of this full-thickness, high-viscosity hydrogel construct required optimizing bioprocessing techniques. This process involved utilizing cryoslicing methodology, following specific protocols for cryopreservation infiltration using sucrose and optimal cutting temperature (O.C.T) solution, to preserve scaffold integrity and facilitate accurate microscopic evaluation. Optimized staining procedures, including Hematoxylin & Eosin (H&E) for scaffold stratification development, DAPI immunofluorescence staining for structural morphology, Safranin-O for extracellular matrix (ECM) components, and Gram staining for bacterial characterization, were then employed. This comprehensive framework provides a crucial standardization for creating and analyzing complex 3D skin models, offering a valuable, controllable, reproducible in vitro platform. Ultimately, this research aims to facilitate the efficient development of novel biotherapies that encompass microbiome homeostasis to effectively and efficiently address chronic wounds.Item 3D Bioprinting Human Induced Pluripotent Stem Cell-Derived Neural Tissues Using a Novel Lab-on-a-Printer Technology(Applied Sciences, 2018-11) De la Vega, Laura; Gómez, Diego A. Rosas; Abelseth, Emily; Abelseth, Laila; da Silva, Victor Allisson; Willerth, Stephanie M.Most neurological diseases and disorders lack true cures, including spinal cord injury (SCI). Accordingly, current treatments only alleviate the symptoms of these neurological diseases and disorders. Engineered neural tissues derived from human induced pluripotent stem cells (hiPSCs) can serve as powerful tools to identify drug targets for treating such diseases and disorders. In this work, we demonstrate how hiPSC-derived neural progenitor cells (NPCs) can be bioprinted into defined structures using Aspect Biosystems’ novel RX1 bioprinter in combination with our unique fibrin-based bioink in rapid fashion as it takes under 5 min to print four tissues. This printing process preserves high levels of cell viability (>81%) and their differentiation capacity in comparison to less sophisticated bioprinting methods. These bioprinted neural tissues expressed the neuronal marker, βT-III (45 ± 20.9%), after 15 days of culture and markers associated with spinal cord (SC) motor neurons (MNs), such as Olig2 (68.8 ± 6.9%), and HB9 (99.6 ± 0.4%) as indicated by flow cytometry. The bioprinted neural tissues expressed the mature MN marker, ChaT, after 30 days of culture as indicated by immunocytochemistry. In conclusion, we have presented a novel method for high throughput production of mature hiPSC-derived neural tissues with defined structures that resemble those found in the SC.Item 3D Bioprinting Mesenchymal Stem Cell-Derived Neural Tissues Using a Fibrin-Based Bioink(Biomolecules, 2021) Restan Perez, Milena; Sharma, Ruchi; Zeina Masri, Nadia; Willerth, StephanieCurrent treatments for neurodegenerative diseases aim to alleviate the symptoms experienced by patients; however, these treatments do not cure the disease nor prevent further degeneration. Improvements in current disease-modeling and drug-development practices could accelerate effective treatments for neurological diseases. To that end, 3D bioprinting has gained significant attention for engineering tissues in a rapid and reproducible fashion. Additionally, using patient-derived stem cells, which can be reprogrammed to neural-like cells, could generate personalized neural tissues. Here, adipose tissue-derived mesenchymal stem cells (MSCs) were bioprinted using a fibrin-based bioink and the microfluidic RX1 bioprinter. These tissues were cultured for 12 days in the presence of SB431542 (SB), LDN-193189 (LDN), purmorphamine (puro), fibroblast growth factor 8 (FGF8), fibroblast growth factor-basic (bFGF), and brain-derived neurotrophic factor (BDNF) to induce differentiation to dopaminergic neurons (DN). The constructs were analyzed for expression of neural markers, dopamine release, and electrophysiological activity. The cells expressed DN-specific and early neuronal markers (tyrosine hydroxylase (TH) and class III beta-tubulin (TUJ1), respectively) after 12 days of differentiation. Additionally, the tissues exhibited immature electrical signaling after treatment with potassium chloride (KCl). Overall, this work shows the potential of bioprinting engineered neural tissues from patient-derived MSCs, which could serve as an important tool for personalized disease models and drug-screening.Item 3D bioprinting of human induced pluripotent stem cells derived neural progenitors using bioinks containing drug-releasing microspheres(2022-05-03) Sharma, Ruchi; Willerth, StephanieTissue engineering employs biological and engineering principles to create functional substitutes for damaged tissue by combining biomaterial scaffolds with drug delivery devices. 3D (three-dimensional) bioprinting has grown into a potential manufacturing technology for creating such scaffolds. The key problem with this technology is printing scaffolds while preserving cell viability, functioning, and structural integrity. This dissertation explores the features of bioink formed from the combination of natural biomaterials and their influence on the bioprinting process. This work aims to explain the development of bioprinting processes for producing tissue with neural progenitor cells (NPCs) derived from human induced pluripotent stem cells (hiPSCs) and fibrin-based bioink encapsulated with microspheres for neural tissue engineering applications. Moreover, hiPSCs are stem cells made from skin or blood cells that have been reprogrammed into an embryonic-like pluripotent state, which means they can be used to make any kind of human cell that is needed for therapeutic use. To accomplish these goals, this study pursues three objectives: first, to bioprint healthy hiPSC-derived NPCs with guggulsterone microspheres; second, to examine the physical and mechanical properties of bioink with and without guggulsterone microspheres; and finally, to bioprint Parkinson’s disease (PD) patient-specific hiPSC-derived NPCs with guggulsterone microspheres for advanced drug-screening. The RX1 bioprinter from Aspect Biosystems, which is based on microfluidics, was used to manufacture domes of 1 cm in diameter using our fibrin-based bioink containing guggulsterone microspheres and hiPSC-derived NPCs. Bioprinted healthy brain tissues had over 90% cellular viability one day after printing. Tissues healthy brain tissues had over 90% cellular viability one day after printing. Tissues displayed early and mature neuronal markers TUJ1 (15.3%), dopamine marker TH (8.1%), and other genes (NURR1, LMX1B, TH, and PAX6) that expressed in midbrain dopaminergic neurons. The storage and loss modulus, viscosity, and shear rates of bioprinted constructs with and without microspheres were also determined. Physical properties such as microstructure, porosity, swelling, and biodegradability were also studied. According to our findings, the elastic modulus of constructs with microspheres was higher than without microspheres. The integration of microspheres resulted in mechanical strength, indicating their potential for use in neural tissue engineering in the future. A bioprinted model of PD was generated utilising hiPSC-derived NPCs from PD patients. NPCs were differentiated into dopaminergic neurons. These models can efficiently identify viable compounds in the early phases of drug development. Finally, I validated that using a microsphere-laden bioink to bioprint hiPSC-derived NPCs can stimulate neural tissue development.Item 3D Bioprinting Patient-Derived Induced Pluripotent Stem Cell Models of Alzheimer’s Disease using Drug Releasing Microspheres(2022-09-27) Benwood, Claire; Willerth, StephanieAlzheimer’s disease (AD), a progressive neurodegenerative disorder, is becoming increasingly prevalent in aging populations. It is characterized by the buildup of amyloid beta plaques and neurofibrillary tangles containing hyperphosphorylated-tau. The current treatments for AD are only symptomatic and do not prevent the long-term progression of the disease. Basal forebrain cholinergic neurons (BFCNs), responsible for memory and spatial learning, are the first to be affected and degenerate in AD. Microspheres are small spherical particles that can release their encapsulated drugs at a controlled rate. Their ability to release drugs slowly over a long period of time is beneficial when differentiating human induced pluripotent stem cells (hiPSCs) into neural progenitor cells (NPCs) and more specialized neurons. Here, I differentiated patient derived hiPSCs into NPCs and used the Aspect RX1 microfluidic printer to produce dome-shaped constructs. The combination of cells, bioink that mimics the extracellular matrix (ECM), and purmorphamine (puro) releasing microspheres directs the differentiation of NPCs into BFCNs. These AD tissue models were then characterized with cell viability, immunocytochemistry, and electrophysiology to evaluate their functionality and physiology for use as disease-specific neural models. The neuronal and cholinergic markers Tuj1, FOXG1, and ChAT were identified as well as the Alzheimer markers Amyloid beta and tau. Further, immature electrical activity was observed when the cells were excited with potassium chloride (KCl) and acetylcholine (ACh).These tissue neural tissue constructs show potential for the use of patient-specific drug screening as well as a model to increase understanding about the progression of AD.Item 3D finite element model for predicting cutting forces in machining unidirectional carbon fiber reinforced polymer (CFRP) composites(2019-01-04) Salehi, Amir Salar; Jun, Martin Byung-Guk; Ahmadi, KeivanExcellent properties of Carbon Fiber Reinforced Polymer (CFRP) composites are usually obtained in the direction at which carbon fibers are embedded in the polymeric matrix material. The outstanding properties of this material such as high strength to weight ratio, high stiffness and high resistance to corrosion can be tailored to meet specific design applications. Despite their excellent mechanical properties, application of CFRPs has been limited to more lucrative sectors such as aerospace and automotive industries. This is mainly due to the high costs involved in manufacturing of this material. Machining, milling and drilling, is a critical part of finishing stage of manufacturing process. Milling and drilling of CFRP is complicated due to the inhomogeneous nature of the material and extreme abrasiveness of carbon fibers. This is why CFRP parts are usually made near net shape. However, no matter how close they are produced to the final shape, there still is an inevitable need for some post machining to obtain dimensional accuracies and tolerances. Problems such as fiber-matrix debonding, subsurface damage, rapid tool wear, matrix cracking, fiber pull-out, and delamination are usually expected to occur in machining CFRPs. These problems can affect the dimensional accuracy and performance of the CFRP part in its future application. To improve the efficiency of the machining processes, i.e. to reduce the costs and increase the surface quality, researchers began studying machining Fiber Reinforced Polymer (FRP) composites. Studies into FRPs can be divided in three realms; analytical, experimental and numerical. Analytical models are only good for a limited range [0° – 75°] of Fiber Orientations , to be found from now on as “FO” in this thesis. Experimental studies are expensive and time consuming. Also, a wide variety of controlling parameters exist in an experimental machining study; including cutting parameters such as depth of cut, cutting speed, FO, spindle speed, feed rate as well as tool geometry parameters such as rake angle, clearance angle, and tool edge/nose radius. Furthermore, the powdery dust created during machining is known to cause serious health hazards for the operator. Numerical models, on the other hand, offer the unique capability of studying the complex interaction between the tool and workpiece as well as chip formation mechanisms during the cut. Large number of contributing parameters can be included in the numerical model without wasting material. Three main objectives of numerical models are to predict principal cutting force, thrust force and post-machining subsurface damage. Knowing these, one can work on optimization of machining process by tool geometry and path design. Previous numerical studies mainly focus on the orthogonal cutting of FRP composites. Thus, the existing models in the literature are two-dimensional (2D) for the most part. The 2D finite element models assume plain stress or strain condition. Accordingly, the reported results cannot be reliable and extendable to real cutting situations such as drilling and milling, where oblique cutting of the material occurs. Most of the numerical studies to date claim to predict the principle cutting forces fairly acceptable, yet not for the whole range of fiber orientations. Predicted thrust forces, on the other hand, are generally not in good agreement with experimental results at all. Subsurface damage is reported by some experimental studies and again only for a limited FO range. To address the lack of reliable force and subsurface damage prediction model for the whole FO range, this thesis aims to develop a 3D finite element model, in hope of capturing out-of-plane displacements during stress formation in different material phases (Fiber, Matrix and the Interface bonding). ABAQUS software was chosen as the most commonly used finite element simulation tool in the literature. In present work a user-defined material subroutine (VUMAT) is developed to simulate behavior of carbon fibers during the cut. Carbon fibers are assumed to behave transversely isotropic with brittle (perfectly elastic) fracture. Epoxy matrix is simulated with elasto-plastic behavior. Ductile and shear damage models are also incorporated for the matrix. Surface-based cohesive zone technique in ABAQUS is used to simulate the behavior of the zero-thickness bonding layer. The tool is modeled as a rigid body. Mechanical properties were extracted from the literature. The obtained numerical results are compared to the experimental and numerical data in literature. The model is capable of capturing principal forces very well. Cutting force increases with FO from zero to 45° and then decreases up to 135°. The simulated thrust forces are still underestimated mainly due to the fiber elastic recovery effect. Also, the developed 3D model is shown to capture the subsurface damage generally by means of a predefined dimensionless state variable called, Contact Damage (CSDMG). This variable varies between zero to one. It is stored at each time step and can be called out at the end of the analysis. It was shown that depth of fiber-matrix debonding increases with increase in FO.Item 3D printed hydrogel microneedle arrays for interstitial fluid biomarker extraction and colorimetric detection(Polymers, 2023) Razzaghi, Mahmood; Seyfoori, Amir; Pagan, Erik; Askari, Esfandyar; Najafabadi, Alireza Hassani; Akbari, MohsenTo treat and manage chronic diseases, it is necessary to continuously monitor relevant biomarkers and modify treatment as the disease state changes. Compared to other bodily fluids, interstitial skin fluid (ISF) is a good choice for identifying biomarkers because it has a molecular composition most similar to blood plasma. Herein, a microneedle array (MNA) is presented to extract ISF painlessly and bloodlessly. The MNA is made of crosslinked poly(ethylene glycol) diacrylate (PEGDA), and an optimal balance of mechanical properties and absorption capability is suggested. Besides, the effect of needles’ cross-section shape on skin penetration is studied. The MNA is integrated with a multiplexed sensor that provides a color change in a biomarker concentration-dependent manner based on the relevant reactions for colorimetric detection of pH and glucose biomarkers. The developed device enables diagnosis by visual inspection or quantitative red, green, and blue (RGB) analysis. The outcomes of this study show that MNA can successfully identify biomarkers in interstitial skin fluid in a matter of minutes. The home-based long-term monitoring and management of metabolic diseases will benefit from such practical and self-administrable biomarker detection.Item 3D Printing Breast Tissue Models: A Review of Past Work and Directions for Future Work(Micromachines, 2019) Cleversey, Chantell; Robinson, Meghan; Willerth, Stephanie M.Breast cancer often results in the removal of the breast, creating a need for replacement tissue. Tissue engineering offers the promise of generating such replacements by combining cells with biomaterial scaffolds and serves as an attractive potential alternative to current surgical repair methods. Such engineered tissues can also serve as important tools for drug screening and provide in vitro models for analysis. 3D bioprinting serves as an exciting technology with significant implications and applications in the field of tissue engineering. Here we review the work that has been undertaken in hopes of generating the recognized in-demand replacement breast tissue using different types of bioprinting. We then offer suggestions for future work needed to advance this field for both in vitro and in vivo applications.Item 3D Printing for Medical Applications: Current State of the Art and Perspectives during the COVID-19 Crisis(Surgeries, 2021) Hagen, Andrew; Chisling, Megan; House, Kevin; Katz, Tal; Abelseth, Laila; Fraser, Ian; Bradley, Stephen; Kirsch, Rebecca; Morris, Jacob; Giles, Joshua W.; Willerth, Stephanie M.The coronavirus SARS-CoV-2 pandemic has affected over one hundred million people worldwide and has resulted in over two million deaths. In addition to the toll that coronavirus takes on the health of humans infected with the virus and the potential long term effects of infection, the repercussions of the pandemic on the economy as well as on the healthcare system have been enormous. The global supply of equipment necessary for dealing with the pandemic experienced extreme stress as healthcare systems around the world attempted to acquire personal protective equipment for their workers and medical devices for treating COVID-19. This review describes how 3D printing is currently being used in life saving surgeries such as heart and lung surgery and how 3D printing can address some of the worldwide shortage of personal protective equipment, by examining recent trends of the use of 3D printing and how these technologies can be applied during and after the pandemic. We review the use of 3D printed models for treating the long term effects of COVID-19. We then focus on methods for generating face shields and different types of respirators. We conclude with areas for future investigation and application of 3D printing technology.Item 3D-Printed Tumor-on-a-Chip Model for Investigating the Effect of Matrix Stiffness on Glioblastoma Tumor Invasion(Biomimetics, 2023) Amereh, Meitham; Seyfoori, Amir; Dallinger, Briana; Azimzadeh, Mostafa; Stefanek, Evan; Akbari, MohsenGlioblastoma multiform (GBM) tumor progression has been recognized to be correlated with extracellular matrix (ECM) stiffness. Dynamic variation of tumor ECM is primarily regulated by a family of enzymes which induce remodeling and degradation. In this paper, we investigated the effect of matrix stiffness on the invasion pattern of human glioblastoma tumoroids. A 3D-printed tumor-on-a-chip platform was utilized to culture human glioblastoma tumoroids with the capability of evaluating the effect of stiffness on tumor progression. To induce variations in the stiffness of the collagen matrix, different concentrations of collagenase were added, thereby creating an inhomogeneous collagen concentration. To better understand the mechanisms involved in GBM invasion, an in silico hybrid mathematical model was used to predict the evolution of a tumor in an inhomogeneous environment, providing the ability to study multiple dynamic interacting variables. The model consists of a continuum reaction–diffusion model for the growth of tumoroids and a discrete model to capture the migration of single cells into the surrounding tissue. Results revealed that tumoroids exhibit two distinct patterns of invasion in response to the concentration of collagenase, namely ring-type and finger-type patterns. Moreover, higher concentrations of collagenase resulted in greater invasion lengths, confirming the strong dependency of tumor behavior on the stiffness of the surrounding matrix. The agreement between the experimental results and the model’s predictions demonstrates the advantages of this approach in investigating the impact of various extracellular matrix characteristics on tumor growth and invasion.Item A comparative analysis of mould growth on exterior sheathing of a brick masonry wall in different Canadian climate zones(2024) Singh, Jasveer; Mukhopadhyaya, Phalguni; Valeo, CaterinaThis study investigates the risk of mould growth on sheathing boards in brick masonry walls in four Canadian cities: Vancouver, Ottawa, Calgary, and Saskatoon. The hygrothermal simulation tool WUFI® Pro 6.8 (1D) and the VTT Mold Index were used to conduct this investigation. The impact of moisture penetration through brick veneer cladding on the potential for mould growth in Oriented Strand Board (OSB), Fiberboard (FB), and Plywood (Ply) sheathing was assessed. For hygrothermal simulations, a severe weather year was selected based on a 31-year historical weather dataset (1986-2016) using the severity index (Isev) method prescribed in the ASHRAE Standard 160-2021. The calculation period was set for seven years, and two wall orientations were considered: (i) direction with the least solar radiation and (ii) maximum wind-driven rain direction. For each orientation, three rain penetration cases (1%, 2% and 3% of wind-driven rain) were considered, and two Air Change Rates (ACH 0 and ACH 15) were considered in the drainage cavity for each of the three rain penetration cases. As per ASHRAE 160-2021, the rain penetration was deposited on the outer layer of the water-resistive barrier (WRB). The results showed that for the 1% rain penetration and no ventilation, the mould growth index (MGI) for all three sheathing boards remained at zero (i.e., No mould growth) for Vancouver’s north-oriented wall (least solar radiation); however, the southeast-facing wall (maximum wind-driven rain) experienced a higher MGI (up to 5.3). For the same case (i.e. 1% rain penetration), the remaining simulated cities experienced MGI>5 (i.e., 50% visually covered surface). In the case of increased rain penetration and no ventilation, each sheathing board’s mould growth performance significantly decreased (MGI>5) for all four cities in both orientations; however, an air change rate of 15/hour (ACH 15) in the drainage cavity reduced the mould growth (MGI<1, local growth microscopic level) in Calgary, Ottawa and Saskatoon. In contrast, ACH 15 was insufficient to reduce the MGI < 3 (i.e., visuals of mould <10% surface coverage) for the Vancouver location, except for the 1% rain penetration case.Item A droplet-based microfluidic impedance flow cytometer for detection of micropollutants in water(Environments, 2024) Aghel, Mohammadreza; Fardindoost, Somayeh; Tasnim, Nishat; Hoorfar, MinaMicroplastics as micropollutants are widely spread in aquatic areas that can have a toxic effect on aquatic life. To reduce the potential risk they pose, it is essential to detect the microplastics and the source of the contamination of the environment. Here, we designed and developed a droplet-based microfluidic impedance flow cytometer for in situ detection of microplastics in water. Impedance spectroscopy enables the direct measurement of the electrical features of microplastics as they move in water, allowing for sizing and identification of concentration. To show the feasibility of the developed method, pure and functionalized polystyrene beads ranging from 500 nm to 6 ?m in four size groups and different concentrations were used. Focusing on three different frequencies (4.4 MHz, 11 MHz, and 22.5 MHz), the changes in the signal phase at frequencies of 4.4 MHz and 11 MHz are a strong indicator of microplastic presence. In addition, the functionalized microplastics showed different magnitudes of the measured signal phase than the pure ones. A k-nearest neighbors classification model demonstrated our developed system’s impressive 97.4% sensitivity in accurately identifying microplastics based on concentration. The equivalent circuit model revealed that the double-layer capacity of water droplets is significantly impacted by the presence of the microplastics. Our findings show the potential of droplet-based microfluidic impedance flow cytometry as a practical method for detecting microplastics in water.Item A Laboratory Study on the Influence of Guided Drop Tower Carriage Mass and Kinematic Differences to Full-Surrogate Free Falls Toward Enhanced Helmet Certification Methods(2024) Brice, Aaron; Dennison, ChristopherFalling from height presents a significant risk for military personnel due to the frequency at which they perform high exposure maneuvers, such as walking along unstable structures, repelling from buildings or aircrafts, and low altitude egressing. Traumatic brain injury (TBI) resulting from falls from height (FFH) account for approximately 20% of TBIs with a reported cause in the military, despite the presence of protective head gear. This is likely because current certification testing performed on military helmets emphasize protection against ballistic threats over blunt impacts, such as falls. Military personnel have identified the need for the next generation of helmets to provide better protection against blunt impacts. To develop such helmets, a method for helmet evaluation in scenarios that are representative of real-life falls must be established as the new standard for helmet impact testing. Guided vertical drop towers are a test device commonly used to evaluate the impact attenuating properties of protective headgear in headfirst falls during certification testing. These devices provide a simple, low cost, repeatable means for conducting certification tests over using full-body surrogates to replicate a person experiencing a headfirst fall. However, there are some limitations to the guided drop tower that may limit their ability to properly replicate a fall from height. The most notable limitations are that guided drop towers are constrained to only a single degree of freedom and the impact mass of a drop tower assembly typically only includes the mass of a human head and neck rather than the mass of a full-body. At present there is little work on how these limitations may yield a differing kinematic response between a guided drop tower and that of an actual fall. The objectives of this thesis was to determine if kinematic differences exist between a guided drop tower and a free-falling person, in unhelmeted and helmeted scenarios. The outcomes of this thesis will contribute toward the development of enhanced test standards that evaluate protective headgear in scenarios that are more representative of real-life falls. iii A custom guided drop tower equipped with a Hybrid III head/neck and adjustable weight drop carriage along with a full-body Hybrid III 50th percentile male surrogate, to represent a falling person, were subjected to two experimental series 1) unhelmeted impacts at four angles between 30° and 75° and four impact velocities between 1.50 m/s and 3.00 m/s and, 2) helmeted impacts at 30° and 75° with impact velocities of 3.00 m/s and 4.50m/s. Impacts in both series were conducted onto a rigid impact surface and kinematic measures of head center of gravity linear acceleration, angular acceleration, and angular velocity were measured. Results of the unhelmeted impact series identified that the drop tower can provide an acceptable approximation of the linear acceleration but not the angular velocity that is likely to be experienced by a person in a headfirst frontal impact. This is due to the angular velocity differing in either the magnitude of the peak angular velocity or direction and time instance of peak measures. Changes to the mass of the drop carriage, to be closer to that of a full dummy, did not bring angular velocity closer to that measured for the full dummy. The helmeted impact study identified that a drop tower is likely to yield an underestimate of peak kinematics in shallow angle impacts and an overestimate of peak kinematics in steep angle impacts. This suggests that the drop tower, in its current form, provides a varying estimate of the resultant peak kinematics in helmeted impacts which is dependent on impact angle. These differences in response are primarily attributable to variances in helmet liner engagement when comparing the drop tower and a person falling. The results of this research found that in their current form guided drop towers do not provide a true representation of the kinematic response that is likely to result in a headfirst fall, either unhelmeted or helmeted. Further the addition of mass to the drop carriage in either scenario did not alter the drop tower’s response to a point where it matched the measured response of the falling surrogate .These differences in kinematic responses between the drop tower and what is likely to be experienced by a falling person, specifically in the case of underestimated responses in shallow angle helmeted falls emphasizes the need to further develop testing methods to ensure that future helmets are evaluated in a way that effectively tests the helmet’s impact-attenuating abilities in an actual fall.Item A microfluidics device integrated with Surface Enhanced Raman Spectroscopy (SERS) for characterizing microplastics in aqueous samples(2024) Vahidi, Mohsen; Akbari, MohsenMicroplastic contamination is an emerging contaminant and concern that can be found all over the planet. These microplastics are often very tiny in size; therefore, they can readily pass though bedrock and infiltrate water bodies such as rivers, lakes, and seas. Whenever such environmental contamination occurs, the first step in order to address the issue is to characterize the contamination in order to define its origin. This project proposes a design of a microfluidic chip, which is integrated with a Surface Enhanced Raman Spectrometer to characterize microplastic particles in various aqueous solutions such as water. The proposed design is capable of sorting and collecting microplastics based on their size without any need for a membrane. It also has a flat architecture, which makes it easy to manufacture at a reasonable cost. SolidWorks was used for the computer aided design (CAD) of the microfluidic chip and COMSOL Multiphysics was utilized for computer aided engineering (CAE) calculation to verify the design. According to the calculations, this microfluidic chip is capable of size-based sorting of microplastics.Item A microgel-based approach for optimized wound healing(2025) Moretti de Andrade, Thiago Antonio; Akbari, MohsenSkin tissue engineering strategies that leverage the properties of biomaterials for in vitro wound healing investigation have emerged as an effective approach to creating more realistic models providing ethically and scientifically preferable models to animal experimentation. Granular material with spherical-shape and rod-shape have stood out in this scenario, creating a biocompatible interface for cell proliferation and migration. Gelatin Methacryloyl (GelMA) is a pivotal crosslinkable hydrogel in the fabrication of granular biomaterials due to its versatile properties in enhancing the mechanical strength, and biocompatibility. Therefore, the combination of GelMA’s cell-friendly properties and the enhanced porosity generated among its particles in microgel mimicking the extracellular matrix underscores the novelty of this study in the investigation of the keratinocytes’ viability and migration in GelMA microgel-based to optimize the wound healing process in a more effective and realistic method than the regular 2D methods. To address this investigation, it was strategically designed and printed (by Anycubic 4K Mono printer - DLP-based) one structure to be used as a mold of the 7.5% GelMA with keratinocytes (1.0 × 106 / mL of GelMA) in the 12-well plates after its crosslinking by 405 nm LEDs. The middle of this mold was designed to form one vat in the middle of the 7.5% GelMA that is intended to be placed the microgel (10% GelMA spherical-shape with 2.5% GelMA between the particles to crosslink all microgel in the 7.5% GelMA ring) with no keratinocytes. As the microgel was surrounded by keratinocytes in 7.5% GelMA (from its bottom and around), it was possible to investigate the viability and migration of the keratinocytes from the GelMA to the microgel layer naturally and by themselves, with neither stimulation nor chemotaxis. The control group was the 10% GelMA bulk (non-microgel, no droplets) placed in the vat, in the same conditions as the experimental group (10% GelMA spherical-shape droplets). Live/dead was performed to qualitatively evaluate the keratinocytes’ viability and migration; DAPI stain analyses (from the 3D construct samples and from the 2D cryostat-slices’ samples) were performed to qualitatively confirm keratinocytes’ migration. All analysis were investigated on days 1, 3 and 7. Overall, the model has been shown to be feasible, more realistic and promising for studying cell migration, taking advantage the own GelMA’s porosity and the additional GelMA microgel’s porosity, making suitable for short-term in vitro wound healing investigation with no vascularization. The model established here was more effective and realistic to investigate keratinocyte migration from the bottom and across surrounding the microgel area, providing a more relevant system than traditional 2D cultures, such as scratch assays or Transwells. With the second mold design, the most suitable method has been established, and the optimal GelMA bioink concentration (2.5% of GelMA bioink) for promoting keratinocyte migration has been identified. Beyond this, the established method offers a foundation for future studies and broader applications in wound healing and regenerative medicine, for example, investigating the potential effects of the microgel in the wound healing in vitro and in vivo, associated or not with pathologies, such as diabetes, that can impair the wound healing process.Item A novel electrocatalytic Fe-TiO2 reactor for degrading persistent pollutants in wastewaters(2025) Jahanshahi, Zahra; Herring, Rodney A.The pervasive presence of persistent organic pollutants in water systems presents a major threat to the environment and public health. Being based on physicochemical properties of contaminants, conventional wastewater treatment techniques proved ineffective in eliminating these contaminants due to their widely variable and complex nature. With vast urbanization and limited water resources, the need for innovative and scalable solutions that can target these contaminants of emerging concern is crucial. This study presents the development and optimization of a novel Fe-doped TiO₂-based electrocatalytic reactor for the degradation of methyl orange, a representative organic pollutant. The degradation studies showed that the rate of methyl orange (MO) removal increases consistently with electric current, achieving up to 95.6% degradation at 16 A in 40 min without saturation, confirming steady hydroxyl radical generation. Using titanium electrodes, particularly when modified with a native TiO₂ layer, significantly improved degradation efficiency while reducing voltage requirements compared to stainless steel setups, achieving up to 94.7% degradation in 12 minutes at lower voltages. The efficiency of this process relative to electron density can be calculated as 22.4%, meaning generation of each hydroxyl radical consumes 4 to 5 electrons, which is orders of magnitudes more efficient than currently used methods, such as using chemicals and photonic activation. This work strives to address key limitations of current approaches in utilizing titanium dioxide crystals in treating water and wastewater, including catalyst immobilization, energy efficiency, and operational simplicity, paving the way for industrial applicability.Item A patient-oriented and musculoskeletal modeling approach to guide prosthetic design improvements and rehabilitation priorities for females with transtibial amputations(2025) Carswell, Tess MR; Giles, Joshua W.Females with lower limb amputations are underrepresented in research and they experience unique challenges when compared to males. Addressing this research need, this PhD utilized principles of User-Centered Design, Patient-Oriented Research, gait analysis, and musculoskeletal modeling to recommend improvements of sex-specific rehabilitation and prosthetic design for people with transtibial amputations. A Patient-Oriented Research committee was developed, engaging females with lower limb amputations to inform research plans. This committee co-developed a behavioural research study, including novel questionnaire and interview instruments that actively engaged females with lower limb amputations in their development. From this study, quantitative and qualitative sex differences in the priorities of people with lower limb amputations were elucidated and informed plans for subsequent research efforts as well as recommendations put forward. A scoping review and evaluation of existing transtibial amputation musculoskeletal models was performed to determine the best to proceed with for computational modeling of sex differences in the gait of people with transtibial amputations. This resulted in a database of existing models, including the selected model to proceed with. With this model, computational analyses of biomechanical gait study data were performed. For the gait study, people with transtibial amputations and able-bodied participants completed level and sloped walking trials. Findings demonstrated sex differences in gait biomechanics of people with transtibial amputations and unique differences between females with transtibial amputations and able-bodied females not observed in the male comparisons, informing recommendations. Ultimately, findings were compiled to propose recommendations for further investigation of sex-specific rehabilitation priorities and prosthetic design. Namely, recommendations to perform sex-specific comparisons of gait for the purposes of rehabilitation or assessment of prosthetic technology, prioritize sex-specific rehabilitation towards female mobility needs, and investigate female-specific prosthetic ankle designs with additional propulsion and range of motion.Item A portable animation facility for the design of autonomous underwater vehicles(1998) Hackett, Georgina Bronwyn; Nahon, Meyer A.The development process of an Autonomous Underwater Vehicle (AUV) typically requires evaluation of the stability and controllability of a large number of candidate vehicle configurations. The three-dimensional animated simulation presented in t his thesis provides a computer-based tool with which initial screenings of candidate vehicle configurations can be performed. The three dimensional animation includes an animated AUV and instrument panel. The application is written with Open Inventor, a C++ graphics library developed by Silicon Graphics and based on OpenGL. The entire package was initially developed on a Silicon Graphics Indy workstation and then ported to a PC running Windows NT and equipped with an OpenGL compatible graphics card.