Browsing by Author "Kim, Keekyoung"
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Item Embargo A Scalable Fabrication Methodology for the Manufacturing of Cardiovascular Perfusion and Drainage Cannulae(2024-09-20) Feddema, Joshua; Dalton, Colin; Sundararaj, Uttandaraman; Badv, Maryam; Kim, KeekyoungCannula manufacturing techniques are held as trade secrets by their respective companies, including large biomedical companies such as Medtronic Cardiopulmonary, Getinge, and Edwards [1]. While exact details are not available, polyvinyl chloride (PVC) plastisol dip molding is a known commercial method used to fabricate cannula. Through exploratory experimentation and the investigation of different fabrication techniques, this project aimed to refine a basic dip molding process into the controlled precision fabrication of cannulae. Crude tube-shaped structures can be produced with basic dip molding; however, significant research and development was required to refine the process to a clinically relevant level. For medical applications, cannulae require embedded coils, good surface finish, uniform and reproduceable geometries, acceptable tip and connector joints, and clinically relevant markings. This project investigated precision dip molding and subsequent cannula assembly to meet these requirements. The result of this work was a viable 18 step fabrication methodology that takes 56 minutes to produce cardiovascular cannula shafts specifically for placement into the aorta. These prototypes were considered clinically acceptable by an ICU physician, supporting the credibility of the research. Additional prototyping of cannula for the drainage of venous blood was conducted, showing the versatility of the fabrication methodology. Flow testing on the cannula prototypes showed excellent lumen reinforcement with a <2% flow reduction when bent according to ISO 18193 standards. Simulation based tools were built to aid in the future development of cannula designs. Beyond manufacturing, this research presents the underlying physics believed to govern fabrication with PVC plastisol, an atypical plasticizer polymer material. With this understanding, appropriate plastisol handling, and fabrication troubleshooting are achievable.Item Embargo Chemically and Electrochemically Synthesized Graphene-Based Inks for 3D Printing of Advanced Electronics and Electromagnetic Shields(2024-04-26) Erfanian, Elnaz; Sundararaj, Uttandaraman; Natale, Giovanniantonio; Bryant, Steve; Ewoldt, Randy H; Kim, KeekyoungThis thesis explores new approaches for the development of graphene-based inks for 3D printing of macro-scale patterned scaffolds for advanced applications, e.g., electronics and electromagnetic (EM) shields. These approaches include multiscale design of the inks, from nano-scale chemistry to micro-scale assembly. To achieve this, the chemical features of the nanosheets were fine-tuned by synthesizing different graphenes via both the electrochemical and chemical synthesis methods. The electrochemical method is considered safer, faster, and more environmentally friendly than chemical methods, primarily yielding pristine graphene with high electrical conductivity. However, due to the lack of surface functional groups, electrochemically synthesized graphene is challenging to disperse in water. In contrast, the chemical method produces highly oxidized graphene nanosheets, GO, which are easily dispersible in water due to their oxygen-containing functional groups but feature low electrical conductivity. In the first part of this thesis, graphene oxide (GO) is synthesized using modified Hummer method, selected for its water dispersibility, the most environmentally friendly medium. The resulting nanosheets exhibit both hydrophobic and hydrophilic characteristics; the hydrophobicity stems from the carbon basal plane, while the hydrophilicity originates from their functional groups. This duality makes it ideal for stabilizing Pickering emulsions featuring yield stress and proper rheological features, required for printing. Hence, utilizing emulsion templating, a non-printable graphene oxide dispersion was transformed into a printable yield-stress fluid, with the printing quality adjustable by modifying operational conditions. Although printable inks were developed by emulsion templating, the main constituent of these inks is GO, which is not conductive, limiting the application potential of the printed structure. GO can be transformed to reduced GO (rGO) via harsh chemical or thermal reduction post-processing methods. Thus, the second part of the thesis addresses the challenges of enhancing electrical conductivity in the conventional GO-based systems. Herein, an electrochemical synthesis approach was adopted, eliminating the need for harmful chemicals. However, this method introduced problems related to the graphene's limited water dispersibility. In this regard, electrochemically synthesized graphene (EGO) posed challenges in 3D printing, particularly its tendency to form droplets rather than a continuous filament. Thus, bio-based materials, i.e., TEMPO-oxidized cellulose nanofibrils (TOCNF), were employed as dispersants and rheological modifiers to improve the water compatibility of the highly conductive, nonpolar, electrochemically synthesized graphene nanosheets. A meticulous balance and optimization of TOCNF and EGO concentrations were required to achieve a printable ink that maintains the post-printed structure. This formulation allowed the identification of a 'window of printability,' creating a roadmap for fabricating 3D printed EGO-TOCNF ink. The high-fidelity printed structures maintained their form during drying and post-processing steps, enabling the fabrication of aerogels with tunable nano- and micro-scale designs. Hence, the multi-scale materials design of this work provided a unique opportunity to control the mechanical and electrical properties of the printed structures. Aerogels with a compression modulus ranging from 250-1096 kPa were obtained, and for the optimized ink, an EMI shielding effectiveness as high as 55.6 dB was achieved, eliminating the need for post-printing reduction processes. Although TOCNF bestows printability to graphene-based suspensions, it deteriorates the overall electrical conductivity due to its insulating nature. Thus, the third part of the thesis addresses the drawbacks of multicomponent inks, including the compromise in electrical conductivity when incorporating additives into graphene. A highly conductive all-graphene 3D printable aqueous ink was developed using a novel two-step electrochemical method with a specially designed intercalation step to control the surface functionality of the synthesized graphene nanosheets. Comprehensive characterization revealed the significant impact of graphene nanosheets’ physicochemical properties on the homogeneity, rheology, electrical conductivity, and EMI shielding effectiveness of their resultant aqueous-based inks. Phosphoric acid treatment was found to be the most effective in enhancing both printability and conductivity, achieving an electrical conductivity of 158 S/cm and an EMI shielding effectiveness of 50 dB at a 50 µm thickness, without the need for any post-processing reduction. Systematic experimentation with varying durations of phosphoric acid intercalation established that 10-minute intercalation produces inks with superior 3D printing fidelity, which can be converted to 3D patterned aerogels. This innovative approach enables rapid, continuous, and scalable manufacturing of lightweight, porous materials, avoiding environmentally harmful reductant chemistries or high-temperature processing. The elimination of a reduction step in the fabrication process aligns with industrial demands for energy-efficient production processes and high output rates, marking a significant advancement in the field of materials science. Thus, this work offers promising prospects for the application of graphene-based inks in advanced manufacturing technologies.Item Embargo Development of a Multi-Axis Robotic Embedded Bioprinting Platform and its Process Chain(2024-05-14) Shin, Joonhwan; Lee, Jihyun; Kim, Keekyoung; Wong, Joanna; Kim, Kangsoo3D bioprinting is a tissue engineering technology, and it has successfully developed simple tissues. However, the current bioprinting methods that rely on layer-based cartesian mechanisms face significant challenges in creating complex and vascularized tissues necessary for developing fully functional tissues. This limitation highlights the need for innovative approaches that enhance bioprinting's flexibility and precision. This thesis presents the development and application of a multi-axis robotic bioprinting platform and its process chain that overcomes traditional constraints and enables the fabrication of complex 3D scaffolds from all directions within the expanded workspace. This research involves embedded bioprinting, an extrusion-based method that can bioprint soft and low-viscosity bioinks while maintaining desired printing fidelity using a viscoplastic suspension bath. The multi-axis robotic bioprinting platform, equipped with a 6-degree-of-freedom robotic arm and a pneumatic extrusion system, integrates computer-aided design (CAD) extraction, computer-aided manufacturing (CAM) slicing, robot simulation, script adjustment, and robot control. This process chain facilitates the seamless transition from digital models to physical bioprinted constructs. Two case studies experimentally validate the platform's superiority over traditional bioprinting techniques. The first focuses on freeform surface bioprinting, highlighting the system's adaptability in reproducing intricate tissue contours. The second explores the fabrication of a hollow tubular structure essential for engineering complex vascular networks. In summary, this thesis contributes to developing the technology and processes necessary to standardize in situ/in vivo bioprinting for fabricating artificial tissues and organs directly on damaged sites.Item Open Access Development of Multifunctional Polymer Nanocomposites with Hybrid Structures for Fabrication of Stretchable Strain Sensing and Wearable Electronic Devices(2020-06-25) Shajari, Shaghayegh; Sudak, Sudak, Leszek Jozef; Sundararaj, Uttandaraman; Kim, Keekyoung; Dalton, Colin; Roberts, Edward P. L.; Naguib, Hani E.Stretchable and flexible electronics have been proposed and practiced as promising alternatives to traditional rigid electronics for the next generation of smart devices in the fields of biomedicine, soft robotics, and energy harvesting. Particularly, the next generation of personal portable devices for remote health assessment requires wearable and attachable smart systems. Examples of these monitoring devices are stretchable and skin-mountable strain sensors for human motion detections, sport activities monitoring, soft robotics, and entertainment technology. Several requirements such as high stretchability, flexibility, a wide working strain ranges, durability, fast response, easy signal collections are considered for wearable sensing systems. Polymer nanocomposites are well established in wearable fashion due to their light weight, flexibility, deformability and easy processing. In this thesis, unique processing techniques were employed to develop novel filler network structures in polymers to improve electrical conductivity and mechanical properties and electromechanical properties and thus strain sensing performances. One dimensional (1D) nanofillers such as carbon nanotubes (CNTs), silver nanowires (AgNWs) and stainless steel fibers (SSFs) were employed due to their effective network connections in polymers. Developing effective filler network structures in polymers even facilitated reducing electrical and strain sensing percolations. In this regard, firstly, a new double percolated network was introduced in CNT combined with fluoroelastomer FKM using an internal melt-mixing process. The two percolation networks provided wide range of low to high stretchability with high sensitivities. High strain sensing of more than 200% with high sensitivity or gauge factor (GF) of greater than 8×(10)^3 was achieved. Very long AgNWs (70-100 µm) with high aspect ratio of >500 and high conductivity of (10)^5 S.cm-1 were synthesized via a modified polyol process. Novel 3D hybrid network structures of AgNWs with CNTs in fluoroelastomer FKM including bridging and shell like structures were developed using optimized solution processing techniques such as solution mixing and layer by layer assembly (LBLA) methods. These hybrid network morphologies led to high conductivity of 2× (10)^5 S. m-1, ultra-high stretchability of up to 300% with ultra-high sensitivity at GF of 2× (10)^6. In LBLA method, only small hybrid nanofiller loadings of 0.88 wt% were employed for ultra-thin sensing elements with less than 10 µm in thickness. Compared to the recent stretchable strain sensors based on polymer nanocomposites reported in the literature, this is the best reported combination of strain sensing performances including stretchability, sensitivity and conductivity in thin film structures and using low filler concentrations. Moreover, the hierarchical hybrid network of SSFs and CNTs in polypropylene (PP) was developed via an internal melt-mixing process. This synergistic network structure in a semicrystalline polymer contributed to the simultaneous enhanced EMI shielding effectiveness (SE) of 57.4 dB and mechanical properties such as strain to failure at 3.5 vol% hybrid filler concentrations. The hybrid nanocomposite with SSFs and CNTs in PP is a good coating candidate to protect the sensor signals by 99.99% from any interference by electromagnetic (EM) waves in the X-band freq. The reliability and usability of wearable sensors made from CNT/FKM nanocomposites was verified for human motion monitoring and as flexible interconnectors for fabricating stretchable light emitting diodes (LEDs) circuits. These inexpensive and simple fabrication techniques satisfy the new demands for cost-effective and high performance flexible and wearable electronics.Item Open Access Development of Rapid, Low-cost, and Portable Device to Detect Infectious Diseases(2022-09-22) Lee, Yoonjung; Kim, Keekyoung; Wong, Joanna; Curiel, LauraWith the spread of COVID-19, which started the global pandemic in 2019 and continues to be prevalent these days, the importance of developing effective diagnostic methods to limit the spread of infectious diseases has emerged. The standard method used to diagnose severe acute respiratory syndrome coronavirus 2 is reverse transcriptase polymerase chain reaction (RT-PCR). Still, its disadvantages include high cost, complex equipment, and long diagnostic time. This study developed two loop-mediated isothermal amplification (LAMP) based diagnostic methods (Saliva-Dry LAMP and Direct Dry-LAMP) which are rapid, sensitive, and near-patient to overcome the limitations of RT-PCR. Saliva-Dry LAMP has the advantages of the LAMP method and requires saliva samples using a customized portable all-in-one box. Direct Dry-LAMP has a more rapid detection time with a heat inactivation step instead of RNA extraction, and the customized device can be executed with batteries and the developed application. The development of these devices reduces the capital cost of instruments significantly, and both methods have shown great performances with excellent positive percent agreement and negative percent agreement compared to each reference RT-PCR. Another convection-based device combined with real-time detection was developed to perform Direct Dry-LAMP. Although this device is still in development, it underscores the growing need for a random-access platform with real-time detection. Overall, Saliva-Dry LAMP and Direct Dry-LAMP can provide rapid and accurate detection of COVID-19 with portable and low-cost devices. With more widespread use, both these methods could play a central role in efficiently limiting the spread of infectious diseases, especially in resource-limited regions.Item Open Access Effects of imperfect bonding on three-phase inclusion-crack interactions(2004) Kim, Keekyoung; Sudak, Les JozevThe solution for the elastic three-phase circular inclusion problem plays a fundamental role in many practical and theoretical applications. In particular, it offers the fundamental solution for the generalized self-consistent method in the mechanics of composites materials. In this thesis, a general method is presented for evaluating the interaction between a pre-existing radial matrix crack and a three-phase circular inclusion. The bonding at the inclusion-interphase interface is considered to be imperfect with the assumption that the interface imperfections are constant. On the remaining boundary, that being the interphase-matrix interface, the bonding is considered to be perfect. Using complex variable techniques, we derive series representations for the corresponding stress functions inside the inclusion, in the interphase layer and in the surrounding matrix. The governing boundary value problem is then formulated in such a way that these stress distributions simultaneously satisfy the traction free condition along the crack face, the imperfect interface condition and the prescribed asymptotic loading conditions. Stress intensity factor (SIF) calculations are performed at the crack tips for different material property combinations and crack positions. The results illustrate convincingly the role of an interphase layer as well as the effects of an imperfect interface on crack behavior. Moreover, the conclusions reached in this dissertation provide a quantitative description of the interaction problem between a three-phase circular inclusion with interface imperfections and a radial matrix crack.Item Open Access Electrokinetic Transport of Silica Nanoparticles in a Biomimetic Porous Medium(2024-04-18) Sreeram, Priyanka; Natale, Giovanniantonio; Benneker, Anne; Kim, Keekyoung; Hejazi, HosseinColloidal particles can be manipulated under an applied external field, one of which is an electric field, to transport them to their desired location. The movement of charged particles or fluids due to an applied electric field is known as electrokinetics. This has widely been used in drug delivery and electrokinetic soil remediation. This phenomenon allows for an easy way to manipulate charged particles. Previous work investigating the application of drug delivery has focused on porous mediums that is homogeneous and physiochemically different from that found in tissues. The electrokinetic and hydrodynamic transport of nanoparticles in biomimetic porous medium has not been studied extensively. In this work, we have incorporated Gelatin methacrylamide (GelMA) hydrogel in a microfluidic chip to explore the transport of silica nanoparticles through the hydrogel. To accomplish this, we studied the transport of silica nanoparticles at varying crosslinker concentration, pressure driven flow and electric field intensity. Our results indicate that by increasing the crosslinker concentration, the pore size gets smaller and the nanoparticle transport is more constrained. Increasing the flow rate increases the distance that the nanoparticles can travel while also increasing the number of aggregates formed. We also explore the transport of silica nanoparticles at varying electric field strengths. We observed that increasing the electric field strength increases the distance travelled by the nanoparticles through the hydrogel and reduces the number of aggregates formed which benefits the transport of the nanoparticle. The experimental results in this thesis open up routes for electrokinetic drug delivery through heterogeneous porous media, and allow for further investigation of the effect of electric fields and more directed drug delivery.Item Embargo Engineering a High Throughput Lung-on-a-Chip System with Intravascular Shear Stress to Better Represent In Vivo Lung Physiology and Characterize Acute Respiratory Distress Syndrome(2024-08-13) Volek, Kelsie Lena; Gillrie, Mark Robert; Yipp, Bryan George; Kim, KeekyoungAcute Respiratory Distress Syndrome (ARDS) is an inflammatory condition often requiring mechanical ventilation due to severe lung injury, frequently leading to fatal outcomes. Traditional models, including animal studies and 2D cell cultures, fail to capture the complexities of human lung physiology, limiting our understanding of ARDS. To address these limitations, we developed a sophisticated lung-on-a-chip (LoC) platform integrating human endothelial cells forming microvessels within a fibrin hydrogel containing fibroblasts alongside an alveolar epithelial cell-lined air-liquid interface. We use this novel LoC to investigate ARDS disease mechanisms and drug responses. First, we demonstrate marked microvascular damage and tissue biomechanical changes induced by double-stranded RNA (PolyI:C), a common inflammatory agonist which mimics viral lung infections. Additionally, we identified a clinically available drug that blocks JAK/STAT inflammatory signaling, ruxolitinib, and prevented this lung damage. With the addition of continuous vascular fluid flow (and hence shear stress), we found enhanced vascularization under standard conditions but retained disruption following polyI:C treatment. A computational fluid dynamics model was also used to provide insight into fluid velocities and shear stresses present in the ‘healthy’ LoC, parameters that are difficult to measure using empiric testing. This modeling along with empiric vascular bulk flow and bead velocity measurements, points towards significant intravascular obstruction during viral lung infection. These results significantly advance our understanding of lung physiology and ARDS disease progression, paving the way for novel therapeutic interventions in respiratory health, particularly targeting the pulmonary vasculature.Item Open Access Enhanced Longitudinal Analysis of Bone Strength Estimated by 3D Bone Imaging and the Finite Element Method(2020-10-06) Plett, Ryan Michael; Boyd, Steven Kyle; Duncan, Neil A.; Manske, Sarah Lynn; Kim, Keekyoung; Edwards, William BrentThree-dimensional (3D) imaging with high-resolution peripheral quantitative computed tomography (HR-pQCT) and micro-finite element (FE) analysis provides important insight into bone health. Longitudinal analyses of bone morphology maximize precision by using 2D slice-matching registration (SM) or 3D rigid-body registration (3DR) to account for repositioning error between scans, however, the compatibility of these techniques with FE for longitudinal bone strength estimates is limited. This work developed and validated a FE approach for longitudinal HR-pQCT studies using 3DR to maximize reproducibility by fully accounting for misalignment between images. Using a standard imaging protocol, ex vivo (N=10) and in vivo (N=40) distal radius HR-pQCT images were acquired to estimate the efficacy of 3DR to reduce longitudinal variability due to repositioning error and assess the sensitivity of this method to detect true changes in bone strength. In our proposed approach, the full common bone volume defined by 3DR for serial scans was used for FE. Standard FE parameters were estimated by no registration (NR), SM, and 3DR. Ex vivo reproducibility was estimated by the least significant change (LSC) in each parameter with a ground truth of zero change in longitudinal estimates. In vivo reproducibility was estimated by the standard deviation of the rate of change (σ) with an ideal value that was minimized to define true changes in longitudinal estimates. Group-wise comparisons of ex vivo and in vivo reproducibility found that FE reproducibility was improved by both SM (CVRMS<0.80%) and 3DR (CVRMS<0.62%) compared to NR (CVRMS~2%), and 3DR was advantageous as repositioning error increased. Although 3D registration did not negate motion artifacts, it played an important role in detecting and reducing variability in FE estimates for longitudinal study designs. Therefore, 3D registration is ideally suited for estimating in vivo effects of interventions in longitudinal studies of bone strength.Item Open Access In-Situ Hydrogel based Device Application for Donor Sites in Skin Grafting Surgery(2024-08-21) Liu, Daichen; Hu, Jinguang; Kim, Keekyoung; Kibria, Golam; Du, KeSkin grafting is a recent technological advancement in surgical procedures, involving the replacement of skin from healthy areas and providing coverage for wound regions. Grafting is primarily employed for various wound indications, such as deep burns, skin cancer, trauma, or reconstructive surgeries. In these scenarios, doctors need to harvest healthy skin from the patient. The freshly harvested skin requires immediate medical attention, often leaving the donor site unattended for a period. Considering the above, we aim to design a hydrogel application device that directly substitutes the dermatome blade guard. This device is intended to apply wound-healing hydrogel evenly to the donor site wound while the surgery. Using computational fluid dynamics (CFD) simulations and 3D printing, we developed a functional prototype. Our research first focuses on a hydrogel composed of 0.5% TEMPO-oxidized bacterial cellulose (TOBC) mixed with 2% sodium alginate. This hydrogel is designed to cover the wound, protect it, absorb exudates and blood, and maintain a moist environment, which is essential for healing. The hydrogel has a tensile strength of 228 kPa and a compressive strength of 449 kPa after cross-linking, providing substantial protection. It also exhibits a swelling capacity of approximately 1000%, ensuring a moist environment and efficient absorption of wound exudates. Recognizing the need for antimicrobial properties, we incorporated silver nanoparticles (AgNPs) into the hydrogel by attaching them to TOBC through ion exchange and thermal reduction reactions, creating TOBC-AgNp. Although this modification slightly reduced the hydrogel's tensile strength to 85 kPa and compressive strength to 240 kPa, it endowed the hydrogel with significant antimicrobial efficiency, providing 99.0% and 90.1% efficacy against Gram-negative and Gram-positive bacteria in 12hr, respectively, effectively reducing the risk of wound infection. The synergistic interaction between advanced hydrogel formulations and precision application devices represents a significant advancement in surgical wound management. This research focuses on improving operational efficiency, enhancing patient care, and reducing infection risks. The device's ability to provide immediate and uniform hydrogel application not only aids in faster and more effective healing of the donor site but also enhances patient comfort and reduces postoperative complications.Item Open Access Metal-Organic Framework Reinforced Highly Stretchable and Durable Conductive Hydrogel-Based Triboelectric Nanogenerator for Biomotion Sensing and Wearable Human-Machine Interfaces(Wiley, 2023-07-17) Rahman, Muhammad Toyabur; Rahman, Md Sazzadur; Kumar, Hitendra; Kim, Keekyoung; Kim, SeonghwanFlexible triboelectric nanogenerators (TENGs) with multifunctional sensing capabilities offer an elegant solution to address the growing energy supply challenges for wearable smart electronics. Herein, a highly stretchable and durable electrode for wearable TENG is developed using ZIF-8 as a reinforcing nanofiller in a hydrogel with LiCl electrolyte. ZIF-8 nanocrystals improve the hydrogel's mechanical properties by forming hydrogen bonds with copolymer chains, resulting in 2.7 times greater stretchability than pure hydrogel. The hydrogel electrode is encapsulated by microstructured silicone layers that act as triboelectric materials and prevent water loss from the hydrogel. Optimized ZIF-8-based hydrogel electrodes enhance the output performance of TENG through the dynamic balance of electric double layers (EDLs) during contact electrification. Thus, the as-fabricated TENG delivers an excellent power density of 3.47 Wm–2, which is 3.2 times higher than pure hydrogel-based TENG. The developed TENG can scavenge biomechanical energy even at subzero temperatures to power small electronics and serve as excellent self-powered pressure sensors for human-machine interfaces (HMIs). The nanocomposite hydrogel-based TENG can also function as a wearable biomotion sensor, detecting body movements with high sensitivity. This study demonstrates the significant potential of utilizing ZIF-8 reinforced hydrogel as an electrode for wearable TENGs in energy harvesting and sensor technology.Item Open Access MIL-100(Fe)-Based Composites for Photocatalytic Dye Degradation: Harnessing UV and Visible Light with Enhanced Performance(2024-07-03) Hosseini, Seyedehfateme; Kim, Seonghwan; Mahinpey, Nader; Kim, KeekyoungThis study explores the photocatalytic degradation efficiencies MIL-100(Fe)-Based composites under both UV and visible light. The synthesized ZnO/MIL-100(Fe), ZnO/Ni@MIL photocatalysts were assessed based on their ability to degrade Rhodamine 6G (R6G), a cationic dye. The main aim of integrating MIL-100(Fe) into ZnO nanoparticles is to enhance the surface area of the photocatalyst to improve adsorption and photocatalytic performance, which is crucial for effective dye degradation. Under UV light, ZnO/MIL-100(Fe) exhibited the highest degradation efficiency, achieving complete degradation within 60 minutes. This exceptional performance is attributed to the enhanced adsorption and charge separation and transfer between ZnO and MIL-100(Fe). ZnO/Ni@MIL-100(Fe) followed closely with a 96% degradation efficiency, highlighting the role of Ni nanoparticles in enhancing photocatalytic performance through improved adsorption kinetics and charge carrier dynamics. Under visible light, ZnO/Ni@MIL-100(Fe) demonstrated the highest efficiency, reaching nearly 98% degradation within 60 minutes following by ZnO/MIL-100(Fe) with 88% degradation efficiency. This superior performance is due to the synergistic effects of enhanced light absorption and electron scavenging of Ni nanoparticles. Both synthesized composites exhibit significantly higher efficiency compared to ZnO NPs, MIL-100(Fe), and Ni@MIL-100(Fe). The findings suggest that ZnO/Ni@MIL-100(Fe) is a highly effective photocatalyst under visible light, while ZnO/MIL-100(Fe) excels under UV light. This study underscores the potential of these composites for practical applications in environmental remediation, driven by their enhanced photocatalytic activities and adsorption properties, primarily due to the increased surface area provided by MOFs.Item Embargo Piezoelectric Systems for Force Sensing and Tunable Dynamics(2024-04-03) Rezvani, Sina; Park, Simon; Lee, Jihyun; Kim, Keekyoung; Xue, DeyiThe measurement and suppression of vibrations are crucial for modern-day devices and structures. Piezoelectric materials stand out as exceptional for vibration measurement and control due to their rapid response time. Among these materials, lead zirconate titanate (PZT) is particularly favoured for its high piezoelectric coefficients and stiffness. However, the manufacturing process of PZT can be optimized to reduce both time and energy consumption. Designing and implementing measurement systems incorporating PZT elements contributes to cost reduction and increased accuracy. Moreover, piezoelectric materials not only serve for vibration measurement but can also function as elements for active, and semi-active vibration control. Notably, they possess the capability to perform both sensing and actuation functions simultaneously, a technique known as self-sensing actuation. In this study, the hybrid microwave sintering of PZT and PZT/CNT samples is explored, investigating the effect of incorporating carbon nanotubes (CNTs) on microwave absorption. Furthermore, the effect of adding CNTs and adjusting microwave power on microstructures, and mechanical and electrical properties are investigated. A comparative analysis with conventional sintering is also conducted. A thermal modelling based on FEM is introduced to simulate the temperature variations throughout the sintering process. A vise-based force sensor system is introduced for simultaneous measurement of cutting and clamping forces in milling operations. By integrating PZT piezoelectric sensors and strain gauges, the system achieves accurate force measurement in terms of DC and AC components. Experiments are conducted to validate the effectiveness of the setup. For the purpose of vibration suppression and tuning dynamics, a friction damper based on the discrete layer jamming concept is developed, utilizing a piezoelectric actuator to change the normal force. The study conducts an in-depth exploration of the behaviour of piezoelectric friction dampers under various loading conditions. The investigation covers factors such as load stiffness, preload settings, and the damper’s response in free and forced vibrations, including flexural and axial cyclic loads. The potential applications of the damper are also highlighted.Item Open Access PVA-SbQ Bioinks for Biofabrication(2024-08-23) Li, Zhangkang; Hu, Jinguang; Kim, Keekyoung; Lu, Qingye; Natale, Giovanniantonio; Badv, Maryam; Zhao, BoxinBiofabrication, an advanced additive manufacturing process, employs computer-controlled 3D printing devices to construct objects layer by layer. Unlike traditional 3D printing, bioprinting utilizes cells and bioinks to create organ-like hydrogels, facilitating the proliferation of living cells. Despite its potential, the advancement of biofabrication is constrained by the limited availability of suitable bioinks. The emergence of biofabrication technologies highlights the critical need for biocompatible, printable, and multifunctional bioinks. To address this challenge, this dissertation investigates a novel material: polyvinyl alcohol bearing a styrylpyridinium group (PVA-SbQ). PVA-SbQ demonstrates exceptional capabilities for creating multifunctional hydrogels using various light-activated printing methods. Importantly, this process eliminates the need for toxic crosslinkers or photoinitiators, thereby enhancing cell viability and proliferation. This dissertation commences with an in-depth exploration of the design principles underlying PVA-SbQ hydrogels, elucidating their superior crosslinking performance and hydrogel properties. Subsequently, advanced techniques such as laser-direct writing, stereolithography (SLA) printing, and embedded printing are meticulously introduced as effective methods for biofabricating PVA-SbQ hydrogels. Furthermore, the synergistic combination of PVA-SbQ with other biomaterials such as cellulose is examined to enhance its properties. The findings demonstrate that high-resolution and biocompatible PVA-SbQ hydrogels can be printed rapidly by different methods. Beyond its potential in organ printing and cell behavior regulation, PVA-SbQ shows significant promise in biomedical applications such as organ patches, wearable devices, pattern encryption, and 4D printing. This dissertation provides a profound understanding of PVA-SbQ hydrogels in terms of rational design, biofabrication strategies, and their promising applications in biomedical engineering. We anticipate that this material, in conjunction with advanced printing techniques, will offer a robust strategy for biofabrication and propel advancements in the biomedical field.Item Open Access Rapid and Highly Controlled Generation of Multiple Emulsions via a Hybrid Microfluidic Device(2022-01) Azarmanesh, Milad; Mohamad, Abdulmajeed; Sanati Nezhad, Amir; Hejazi, Hossein; Kim, KeekyoungMultiple Emulsions (MEs) consist of droplets containing one or more microdroplets. Microfluidic approaches have been used to create monodisperse MEs in both a rapid and controlled manner. To generate monodisperse ME constructs, the design relies on the interaction between immiscible fluids in subsequent droplet formation steps. The microfluidic chip used to create the MEs consists of three liquid phases flowing through two subsequent compartments, each with a T-junction and a cross-junction. Creating high shear stress at the cross-junctions induces instability of liquid flow at the first junction, which splits the first immiscible phase into micrometer droplets surrounded by the second phase. The resulting structure is then supported by the third phase at the T-junction to generate and transport MEs. In this work, the ME formation within microfluidic chips is experimentally investigated and numerically simulated. Several critical parameters are examined concerning their effects on the physical properties of MEs. Dimensionless modelling is exploited to enable the change of one parameter at a time while assessing the system's sensitivity to that parameter. Following the optimization of ME formation, highly controlled and high-throughput MEs are formed within the microfluidic chips. It is shown that the consecutive MEs are monodisperse in size, allowing for the generation of controlled MEs for various applications, including bacterial and cell culture. Furthermore, polydimethylsiloxane (PDMS) microchannels are fabricated using conventional soft lithography techniques and coated with Tetraethyl Orthosilicate (TEOS) and Ethylamine (EA) to form a nanometer silicon oxide layer inside the microchannels. TEOS coated PDMS chips provide several advantages over bare PDMS chips. The first benefit of the TEOS coating is the prevention of fluid absorption by the PDMS bulk, which is a major challenge for long-term culture of cells in PDMS microchannels. Using the TEOS coating, bacteria successfully grow for several hours inside nanoliter-sized droplets in a controlled microenvironment, wherein the TEOS coating prevents droplets from being absorbed by the PDMS. Further engineering of this coating makes it a switchable coating, where its hydrophilic properties change to hydrophobic upon exposure to the ambient air. This feature provides selective hydrophobicity and hydrophilicity conditions and allows for the formation of diverse double and multiple emulsions. The hydrophilic property of the coating is further used for cell culture. As a proof-of-concept, MCF7 breast cancer cells and endothelium cells are cultured on the TEOS-coated PDMS chips, enabling further high-throughput drug screening on MEs containing multiple cell types and drugs.