Browsing by Author "Stefan, Mihaela C."
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Item A Green Chemistry Approach to Designing Bio-based Resins for 3D Printing(May 2023) Sparacin, Marissa Lauren 1998-; Smaldone, Ronald A.; Nielsen, Steven O.; Stefan, Mihaela C.Sustainability has become a great topic of interest in recent years. Most associate sustainability with how a material is produced, consumed, and disposed of, and how this continuous cycle effects the environment. However, sustainability is a much more complex concept with nuance regarding its reach on societal issues such as resource inequality and access, as well as, economic availability and convenience. The reliance on petroleum-based materials, such as plastics, in modern day society has been discussed in great depth in relation to sustainability. This is due to fossil fuels being main contributors to environmental pollution, resource degradation, and rising global temperatures. On the other hand, the dependence on plastics in almost every industry is a result of their ease of production, favorable mechanical properties, and cost effectiveness. Because of this, it will be difficult to influence a shift from petroleum-based materials to more bio-based materials if these new materials do not perform similarity to industrially used plastics. It is also crucial to consider the manufacturing processed used to produce the materials. Competitive manufacturing techniques such as 3DP (3D printing) has become a desired technique due to its ability to fabricate complex, uniform, and flexible products without the use of molds or machining, its ability to provide fast, on-site production, and its cost-effective nature without wasting unnecessary materials or excessive waste production. The main goal of this research was to develop bio-based resins that are compatible with digital light processing 3D printing technologies (DLP 3DP) and optimize these materials such that they have comparable properties to commonly utilized plastics. Not only that, but a focus on designing materials that can be chemically recycled, thermally healed, and mechanically reprocessed while maintaining their mechanical properties, will help to produce a movement toward the implementation of more eco-friendly materials. Here, a background on the sustainability movement and its evolution, as well as, the issues associated with plastics will be discussed. Additionally, the implementation of bio-based feedstocks within the design of recyclable, self-healable, and reprocessable thermosets will be investigated and looked at through a green chemistry lens. The concepts explaining the various 3DP technologies, the pros of utilizing such techniques, and the fabrication of 3D printable resins will be explored. Finally, applications of such concepts utilizing bio-based feedstocks such as functionalized vanillin, guaiacol, and eugenol with scientific, peer-reviewed research with the reported findings will be presented.Item Benzodithiophene Homopolymers Synthesized by Grignard Metathesis (GRIM) and Stille Coupling Polymerizations(Royal Soc Chemistry, 2014-04-16) Magurudeniya, Harsha D.; Kularatne, Ruvini S.; Rainbolt, Elizabeth A.; Bhatt, Mahesh P.; Murphy, John W.; Sheina, Elena E.; Gnade, Bruce E.; Biewer, Michael C.; Stefan, Mihaela C.; 0000 0003 8371 1336 (Gnade, BE); 00049719 (Gnade, BE); 55039821 (Stefan, MC); Gnade, Bruce E.; Biewer, Michael C.; Stefan, Mihaela C.Poly{4,8-bis(95-dodecylthiophene-2-yl) benzo[1,2-b: 4,5-b'] dithiophene} has been synthesized by both Grignard metathesis (P1) and Stille coupling polymerizations (P2). Polymers P1 and P2 were characterized and their optoelectronic properties, charge carrier mobilities, and photovoltaic properties were compared. The field-effect mobilities of the polymers were measured on both untreated and heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane (FS) treated organic field effect transistor (OFET) devices. The polymers were also evaluated in bulk heterojunction (BHJ) solar cells with [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) as the acceptor.Item Bi-tensor Free Water Model With Positive Definite Diffusion Tensor and Fast Optimization(2021-08-01T05:00:00.000Z) Wang, Siyuan; Cao, Yan; Stefan, Mihaela C.; Lou, Yifei; Dabkowski, Mieczyslaw K.; Minkoff, Susan E.Diffusion tensor imaging is a widely used imaging methodology to infer the microstructure of brain tissues. When an image voxel contains partial volume of brain tissue with free water, the traditional one tensor model is not appropriate. A bi-tensor free water elimination model has been proposed to correct for the mixing effects. Moreover, recent studies have shown that the free water volume derived from this model could be a biomarker for brain aging and numerous brain disorders such as Parkinson’s and Alzheimer’s disease. However, the problem of fitting this model is ill-posed without additional assumptions. Models by adding spatial constraints or using data from multi-shell acquisition are proposed to stabilize the fitting, but none of them restricts the diffusion tensor D to be positive definite, which is a necessary condition. In this work, we formulate the bi-tensor model fitting as an optimization problem over the space of symmetric positive definite matrices and show that the objective function is a ratio of two geodesically convex functions. We also demonstrate by simulation that the estimation may be highly biased with single-shell data in the presence of noise, so multi-shell data are needed for the fitting of the bi-tensor free water elimination model. Inspired by the Cholesky decomposition, we treat the diffusion tensor D as the product LLT where L is a lower triangular matrix. The optimization is performed on L which guarantees the positive definiteness of D. Our model are evaluated with both simulations and real human brain data. Simulation results show that the model is computationally efficient and the two-shell acquisition gives the best estimation.Item Biocompatible Organic Charge Transfer Complex Nanoparticles Based on a Semi-Crystalline Cellulose Template(Royal Society of Chemistry, 2015-06-19) Nagai, A.; Miller, J. B.; Du, Jia; Kos, P.; Stefan, Mihaela C.; Siegwart, D. J.; 55039821 (Stefan, MC); Stefan, Mihaela C.Using a bio-inspired cellulose template, new charge transfer (CT) nanoparticles (NPs) with unique and intriguing emission properties are reported. Pyrene-modified 2,3-di-O-methyl cellulose formed CT complexes with small molecule acceptors, e.g. 7,7,8,8-tetracyanoquinodimethane (TCNQ), and exhibited aggregation-induced emission (AIE) in aqueous medium upon nanoparticle formation. The TCNQ-CT NPs showed multicolor fluorescence emissions at 370-400 nm, 602 nm and 777 nm, when excited at 330 nm, 485 nm and 620 nm respectively. The cellulose-TCNQ NPs are biocompatible and demonstrate an advance in the use of the CT mechanism for biomedical imaging applications both in vitro and in vivo.Item Bioinspired Wet Pressure-sensitive-adhesives and Shape Memory Polymers for Biomedical Applications(December 2022) Suzuki, Yuta; Smaldone, Ronald A.; Summers, Joshua; Voit, Walter E.; Auciello, Orlando; Stefan, Mihaela C.Neural interfaces-integrated devices provide a promising technology enabling the diagnosis and treatment of neurological diseases and disorders by detecting and stimulating nervous action using bioelectronics. Nerve cuff electrodes are a class of neural integrated devices that consist of a flexible polymeric substrate that wraps a target nerve in cuff-shaped and single- or multi-channel electrodes that detect and/or stimulate nerves via excitation or inhibition of the target nervous action for neuromodulation. In this study, a new cuff-closing method is described, which uses shape memory polymer (SMP) cuffs and wet pressure-sensitive-adhesives (PSAs), for less invasive implantation. SMP cuffs wrap around a target nerve through shape recovery induced by exposure to physiological conditions, then fixed by wet PSA instead of suturing, to facilitate snugly fitting and easier and quicker setup for implantation. To demonstrate the feasibility of the proposed cuff devices, research was performed on three key scientific/technological issues, namely: 1) bioinspired wet PSA suitable for physiological conditions, 2) SMPs with enhanced softening and shape recovery properties, and 3) underwater adhesion of the designed SMPs and wet PSAs. First, the relationship between cohesion and adhesion of bioinspired catecholic PSAs, containing various amines, was studied to develop wet PSAs. The cation- interaction between catechol and amine groups contributed to the high cohesion of the PSAs and their high cohesion significantly increased adhesion under physiological conditions. Second, new thiol-ene/acrylamide SMPs were designed to improve shape recovery properties for facile implantation, using dopamine acrylamide (DAc) as a hydrophilic monomer. Finally, adhesion tests, for the designed wet PSAs to SMPs, demonstrated that the adhesion of PSAs to DAc-modified SMPs increased with an increase in the DAc molar ratio of SMPs to reach a sufficiently high ratio for permanent joints to be formed under physiological conditions. The closure method using wet PSA and SMP substrates, discussed in this study, is proposed as an advantageous method for designing minimally invasive nerve cuffs.Item Carbon Nanofibers Derived From Polymer Blends as Electrodes for High Performance Supercapacitors(2021-12-01T06:00:00.000Z) Malekpour, Soheil; Ferraris, John P.; Dragovic, Vladimir; Balkus, Jr., Kenneth J.; Smaldone, Ronald A.; Stefan, Mihaela C.Nowadays, generation and storage of energy is vital in our life. Supercapacitors as one the energy storage devices are safe and can store high amount of energy and deliver it in a fast manner. Also, they can be used in a wide range of temperatures and show a high cyclability, which make them proper candidates for broad range of applications. However, compared to other common energy storage systems such as batteries, their energy density is low. Carbon materials are known as the most common materials for making electrodes for supercapacitors. To achieve supercapacitors with high energy density it is important to use the right materials as electrodes with proper morphologies. Two main energy storage mechanisms include electric double layer capacitance which energy is stored electrostatically, in the interface of electrode and electrolyte and pseudocapacitance, in which fast redox reactions occur at or near surface of electrodes. In double layer capacitors, high surface area and controlled pore size and pore distribution is required hence, choice of carbon precursors to obtain these properties is essential. Chapter 1 gives basic information about energy storage systems and mechanisms involved in supercapacitors. Also, carbon nanofibers as one of the popular materials for making electrodes are introduced and how they are made is explained. Chapter 2 introduces polymer blends derived from polyacrylonitrile (PAN) and polymethacrylic acid (PMAA) as suitable candidates for making high surface area carbon fibers with high performance. It shows PMAA can be used as a new degrading polymer which, blended with PAN, can result in phase-separation in carbon fibers. Chapter 3 describes fabricating hybrid materials as electrodes for supercapacitors using PANPMAA blend as carbon source and cobalt oxide. It is shown how using PMAA as a chelating polymer can enhance the distribution and uniformity of metal oxide nanoparticles on the carbon fibers which improve the performance of supercapacitors compared to the ones that are made only with PAN.Item Coupling Physical Measurement with Machine Learning for Holistic Environmental Sensing(2021-05-01T05:00:00.000Z) Wijeratne, Lakitha Omal Harindha; Lary, David J.; Stefan, Mihaela C.; Glosser, Robert; Chen, Lunjin; Slinker, Jason D.; Heelis, Roderick A.The interest in characterizing the abundance and nature of airborne particulates has been increasing over the last decade, driven in large part by the rising awareness of the manifold health impacts of airborne particulates. Since regulatory observations of airborne particulates are usually made with expensive instruments, the number of sensors that can be deployed is naturally limited by the costs involved. This dissertation describes the substantial progress we have made in the physical sensing of airborne particulates by providing low-cost, high-quality observations of airborne particulates by utilizing advances in low-cost laser-based sensors, that can be deployed at scale, coupled with machine learning used for accurate calibration of these low-cost sensors. The abundance of airborne particulates is usually quantified by an integrated mass density in µg/m3 over the airborne aerosol size distribution (e.g. PM2.5, the integrated mass density of all airborne particulates with a diameter of up to 2.5 microns). A persistent feature of all airborne observations of particulates is the variability over small temporal and spatial scales. This persistent and ubiquitous variability underscores the value of being able to deploy a large number of low-cost sensors that can make accurate measurements every few seconds, 24/7. Taking this into account, I have built, calibrated, and deployed a large number of sensors across the Dallas-Fort Worth (DFW) Metroplex in Texas as a part of my dissertation work. Other physical measurements can also be utilized in accurate assessment of airborne particulates. Just as weather RADARs are used to examine the spatial and temporal distribution of atmospheric precipitation, we show that if we use machine learning, we can also employ the weather RADARs to examine the spatial distribution of airborne particulates. CO2 has gained a lot of attention in recent years due to global warming. It is considered the principal anthropogenic greenhouse gas driving global warming. As a result, CO2 levels must be monitored and controlled. The present study describes how machine learning can be used to calibrate a low-cost CO2 sensor which is already part of the sensor systems that I have built and deployed. This dissertation provides an overview of how low-cost physical sensing can be combined with machine learning to provide environmental sensing systems at scale, thus using physics in service of society.Item Development of Graphene-like Carbons for Energy Storage and the Sequestration of Lanthanide and Actinide Elements(2021-12-01T06:00:00.000Z) Brown, Alexander Travis; Balkus, Jr., Kenneth J.; Akbar, Mohammad; Ferraris, John P.; Stefan, Mihaela C.; Yang, Duck J.Porous materials are solids which contains voids also known as pores. Porous materials are used in a variety of applications that require a high surface area as well as controllable pore sizes and pore architectures. Porous silica and carbons can be used in applications like as drug delivery, gas separations, energy storage, and the sequestration of elements. Particularly, porous carbona can be synthesized by chemical vapor deposition and can have exceptional porosity as well as high electrical conductivity. The development of carbons that have both high porosity and high electrical conductivity has surged since the discovery of graphene-like carbons. The ability to form various type of porous carbons and understanding of the underlying growth mechanism is a trending research topic. Furthermore, porous carbons can be used for extracting and selectively separating rare earth elements, which are critical elements vital to the production of magnets, batteries, metals, catalysts, glass, lighting, pigments, ceramics, aerospace products, and various other textiles. Herein various high surface area and electrically conductive porous carbons are synthesized and characterized; and a mechanism for the carbon synthesis is proposed. Then the porous carbons are evaluated for the performance in liquid-solid extractions of lanthanide and actinide elements and supercapacitors applications.Item Development of Neodymium-Based Catalysts for the Polymerization of Dienes and Cyclic Esters(2019-05) Ren, Yixin; Stefan, Mihaela C.High-quality elastomeric materials from the polymerization of dienes are in high demand in industry. However, polymerizing the dienes with greater than 98% cis-1,4 content, with controlled molecular weight remains a prominent challenge. Therefore, the development of new catalysts that polymerize dienes with improved cis-1,4 content, well-defined molecular weights, and high catalytic activity is a topic of substantial interest in industry and academia. Neodymium-based Ziegler-Natta type catalysts are promising to achieve such goals and are the focus of the majority of fundamental studies. A variety of useful neodymium-based catalysts have been developed with oxygen-containing electron-donating ligands such as carboxylates and phosphates. These catalysts are often either highly active or highly stereospecific (yielding high cis-1,4), but seldom both and very often result in high polydispersity index. Recently, nitrogen-containing electron-donor ligands, such as β-diketiminiate and acenaphthene-diimine which offer greater potential for tunable steric and electronic properties, have shown promising results for achieving improved cis1,4 content, with well-defined molecular weight and narrow molecular weight distribution. While neodymium-based catalysts have shown high catalytic activity and stereoregularity for polymerizing dienes, their catalytic activities for ring opening polymerization of cyclic esters has seldom been explored. In this dissertation, two neodymium-based catalysts have been developed and their catalytic activities for the polymerization of dienes and the ring opening polymerization of cyclic esters are investigated. In Chapter 1, the development of neodymium-based catalysts for the polymerization of dienes and ring opening polymerization of cyclic esters are discussed. The effect of polymerization conditions and the mechanistic studies of the catalytic systems are also discussed in this chapter. Chapter 2 discusses the development of a new type of halide-free neodymium-based catalytic system for diene polymerization. The catalytic system consists of the neodymium diethylphosphate catalyst [Nd(μ-DEP)3]x and the co-catalyst triisobutyl aluminum (TIBA) and was used to polymerize β-myrcene. This catalytic system shows promising results and produced polymer with high cis-1,4 content and relatively narrow molecular weight distribution. The kinetic studies demonstrated the pseudo-living characteristics. Chapter 3 focuses on developing neodymium-based catalysts containing bis-diimine ligands. The diimine ligands offer greater potential for tunable steric and electronic properties compared to carboxylate and phosphate ligands. In an attempt to synthesize NdCl3·(L)1 and NdCl3·(L)2 with L = bis(2-pyridinal)ethylenediimine ligand, using azeotropic distillation, we instead obtained [NdCl(L)(H2O)3]Cl2·2(H2O) and L[Nd3Cl6(L)3(O)2]Cl. The crystal structures, luminescent properties, and the magnetic properties of these two complexes will be discussed in this chapter. Chapter 4 discusses the development of neodymium-based catalysts bearing phosphate ligands NdCl3·3L; L = triethyl phosphate (TEP) or tris(2-ethylhexyl) phosphate (TEHP) for the ring opening polymerization (ROP) of ε-caprolactone. These Nd catalysts were tested for ROP of ε- caprolactone (ε-CL) in the presence of benzyl alcohol to generate polymers with relatively narrow polydispersity indices and tunable molecular weights. An important result from the kinetic studies revealed that the catalyst with the sterically bulkier ligand TEHP gave a higher rate of polymerization and lower amount of the transesterified product. The livingness of this catalytic system was demonstrated by kinetic studies and by successful synthesis of the block copolymer poly(ε-caprolactone)-block-poly(L-lactide). In situ NMR studies by monitoring the reaction of NdCl3·3TEP and benzyl alcohol at room temperature are also discussed in this chapter.Item Developments of Furan and Benzodifuran Semiconductors for Organic Photovoltaics(Royal Society of Chemistry, 2015-02-13) Huang, Peishen; Du, Jia; Biewer, Michael C.; Stefan, Mihaela C.; 55039821 (Stefan, MC); Biewer, Michael C.; Stefan, Mihaela C.This review describes the developments of organic photovoltaic materials containing furan or benzo[1,2-b:4,5-b']difuran (BDF) building blocks. Promising power conversion efficiencies above 6% have been achieved in the past two years for the BDF donor-acceptor polymers. Fundamentals of organic photovoltaics are briefly introduced at the beginning of this review. The uniqueness and advantages of BDF building block in semiconducting materials are discussed and compared with benzo[1,2-b:4,5-b']dithiophene analogues.Item Donor-Acceptor Organic Semiconductors: Investigations of Optical, Electronic, and Morphological Properties(2017-05) Du, Jia; Stefan, Mihaela C.Organic semiconductors have drawn remarkable attention due to their light weight, feasible fabrication and flexibility in the field of organic photovoltaics and field effect transistors. The rapidly increasing world population and the accompanied with huge energy demands are becoming a big concern for the future, which makes harvesting unlimited solar power using photovoltaic devices extremely important. A remarkable amount of research has been done to improve the power conversion efficiency in terms of the materials design, morphology investigations and device engineering. Organic field effect transistors utilizing solution-processed conjugated polymers can be fabricated efficiently at a low cost roll-to-roll technique over a large area. Designing high performing conjugated polymers and investigating their morphology is essential. In this dissertation, the fundamentals and the recent developments of organic semiconductors are covered in Chapter 1. The basic operation mechanism of organic photovoltaics and field effect transistors are introduced. Semiconducting molecules and polymers that have been reported using benzo[1,2-b;4,5-b’]dithiophene (BDT), benzo[1,2-b;4,5-b’]difuran (BDF), 2,1,3-benzothiadiazole (BT), and diketopyrrolopyrrole (DPP), are discussed and summarized. Chapter 2 describes the isomeric effect of two small molecules containing BDT and BT units on the photovoltaic performance. The influence on UV-vis absorption, frontier molecular orbital energy level, and morphology due to the position of the BT unit was systematically investigated. The photovoltaic performance was studied in bulk heterojunction solar cells with [6, 6]-phenyl-C71-butyric acid methyl ester used as the acceptor. Chapter 3 describes the synthesis of novel conjugated polymers built from BDF and furan substituted DPP unit. Furan and its derivatives are regarded as green and renewable building units. This polymer was tested in bulk heterojunction solar cells with the highest power conversion efficiency of 5.55% and high fill factor of 0.73 achieved when 4% diphenyl ether was applied to optimize the phase separation. The morphology of the blend films was investigated by atomic force microscopy, grazing incident wide-angle X-ray scattering and transmission electron microscopy. In Chapter 4, an alternative copolymer built from furan substituted DPP and (E)-1,2-di(furan-2-yl)ethene was synthesized by Stille coupling and employed in organic field effect transistors. Hole mobility of 0.42 cm2 V-1 s-1 was achieved with current on/off ratio of 104 after annealing the thin film at 150 oC for 5 minutes. The higher mobility after thermal annealing was explained by the increased crystallinity, which was revealed by atomic force microscopy and grazing incident X-ray diffraction. At the end, the prospective and future work for the organic photovoltaics and field effect transistors are discussed in Chapter 5.Item Fine-tuning Thermoresponsive Functional Poly(ε-caprolactone)s to Enhance Micelle Stability and Drug Loading(Royal Society of Chemistry, 2015-01-16) Rainbolt, Elizabeth A.; Miller, J. B.; Washington, Katherine E.; Senevirathne, Suchithra A.; Biewer, Michael C.; Siegwart, D. J.; Stefan, Mihaela C.; 55039821 (Stefan, MC); Biewer, Michael C.; Stefan, Mihaela C.Block copolymers synthesized by the ring-opening polymerization of γ-2-[2-(2-methoxyethoxy)ethoxy]ethoxy-ε-caprolactone (ME₃CL), γ-2-methoxyethoxy-ε-caprolactone (ME₁CL), and ε-caprolactone (CL) are reported. Previously, diblock copolymers of PME₃CL-b-PME₁CL displayed excellent thermoresponsive tunability (31-43 ⁰C) and self-assembled into micelles with moderate thermodynamic stability. In this report, two strategies are employed to enhance thermodynamic stability of PME₃CL/PME₁CL-type block copolymer micelles while maintaining their attractive thermoresponsive qualities: modification of the end group position and alteration of hydrophobic block composition by using both ME₁CL and CL. These new thermoresponsive amphiphilic block copolymers showed lower critical micelle concentration (CMC) values by one order of magnitude and formed thermodynamically stable micelles. Furthermore they demonstrated good biocompatibility and up to 4.97 wt% doxorubicin loading, more than double the amount loaded into the PME₃CL-type polymeric micelles previously reported.Item Functional Polymers for Drug Delivery and Opto-Electronic Applications(2018-11-16) Karmegam, Vasanthy; Stefan, Mihaela C.Polymers are promising macromolecules that have been extensively used in a range of applications such as biomedical, optoelectronic, and catalysts. These polymer materials can be designed with a wide range of architecture and functionalities. The functionalization of the polymer backbone offers new properties to improve the existing polymer material. This study focuses on the synthesis of functionalized polycaprolactone and pyrimidine polymers and improvement in properties to apply in drug delivery and opto-electronic applications. Chapter 1 discusses the recent advances in biodegradable polyesters for drug delivery systems. Polyesters are an attractive material which has been extensively used in biomedical application. There has been a significant amount of attention on modification of polyesters and its application in drug delivery systems. This chapter discusses the synthesis and design of aliphatic polyester materials and its various applications. Chapter 2 describes the synthesis of thermo-responsive linear and star-like block copolymers from functionalized polycaprolactones, a class of biodegradable polyesters. The functionalized polycaprolactone was used to develop polymer micellar carrier to encapsulate anti-cancer drug, Doxorubicin. The effect of polymer functionalization and architecture in polymer property and drug loading are discussed. Chapter 3 discusses co-delivery of Doxorubicin and Resveratrol in linear and star-like polymer micellar drug carriers. The favorable interaction between drugs and functional groups of the polymer backbone significantly enhances the drug loading. The simultaneous delivery of DOX and Resveratrol is a promising approach for improving drug loading and antitumor activity. Chapter 4 discusses the synthesis and characterization of a series of pyrimidine-containing donor acceptor conjugated polymers. The pyrimidine polymer was functionalized with electron with drawing and -donating pendent groups. The electron-withdrawing strength of the pendent groups was systematically varied to study its effect on opto-electronic properties of the conjugated polymer.Item Halide-Free Neodymium Phosphate Based Catalyst for Highly cis-1,4 Selective Polymerization of Dienes(Royal Soc Chemistry, 2019-01-24) Ren, Yixin; Miller, Justin T.; Polderman, Stefanie T.; Vo, Trinh D.; Wallace, Adele C. M.; Cue, John Michael O.; Tran, Sarah T.; Biewer, Michael C.; Stefan, Mihaela C.; 0000-0001-5374-8600 (Stefan, MC); Ren, Yixin; Miller, Justin T.; Polderman, Stefanie T.; Vo, Trinh D.; Wallace, Adele C. M.; Cue, John Michael O.; Tran, Sarah T.; Biewer, Michael C.; Stefan, Mihaela C.Neodymium-based Ziegler-Natta type catalytic systems are known to produce polydienes with high cis-1,4 content. It is generally believed that in Ziegler-Natta catalytic systems, a halide or pseudohalide, whether in the catalyst itself or a separate source, is required for the success of the polymerization. In this work, we have synthesized an unusual halide-free neodymium diethyl phosphate catalyst for diene polymerization. This neodymium complex combined with triisobutylaluminum (TIBA), formed a binary catalytic system and was used to polymerize β-myrcene. The catalytic system displays high stereospecificity and produces poly(β-myrcene) with 96% cis-1,4 content and a relatively narrow molecular weight distribution (Mᵥᵥ/Mₙ = 1.80). Also, kinetic studies indicated the catalytic system gives a pseudo-living polymerization. The block copolymer poly(β-myrcene)-b-poly(isoprene) was successfully synthesized by sequential monomer addition, further demonstrating the pseudo-living nature of polymerization with the neodymium diethyl phosphate catalyst.Item Linear and Star-Like Substituted Polycaprolactones for Enhanced Delivery of Doxorubicin(2017-08) Washington, Katherine E.; Stefan, Mihaela C.Doxorubicin is a poorly water soluble chemotherapeutic drug used in the treatment of many cancers. However, due to its toxic side effects, there has been a lot of effort to develop better delivery methods for this drug to alleviate some of the toxicity and to improve its efficacy. Encapsulation of doxorubicin in polymeric micellar drug delivery systems offer an opportunity to improve this delivery by improved solubility and a more controlled release of the drug to tumor sites. Substituted poly(caprolactone)s are a desirable material to use to form amphiphilic block copolymers due to their tunable properties. Depending on the substituent used, the size, stability, degradation rate, and hydrophilicity or hydrophobicity of the micelle can be adjusted. One drawback of micelle drug delivery systems is their tendency to have low drug loading capacities. In this dissertation, several drug delivery systems were designed in order to increase the amount of doxorubicin loading in polymeric micelles. The design and recent advances of polymeric drug delivery systems featuring polyesters is discussed in Chapter 1. Polyesters are attractive drug delivery materials due to their biocompatibility and biodegradability. Many systems have been designed using these systems including those that are stimuli-responsive, designed for a more controlled release of the encapsulated cargo, and those that have targeting to allow for a better accumulation of the drug delivery vehicles at tumor sites. Different systems that have been developed in recent years using polyesters are discussed in this chapter. Chapter 2 describes a comparison of linear and 4-arm star-like block copolymers synthesized from amphiphilic polycaprolactones with a tri(ethylene glycol) substituted polycaprolactone as the hydrophilic block and unsubstituted poly(caprolactone) as the hydrophobic segment. The linear and star-like block copolymers are compared in terms of their thermodynamic stability, degradation, size, and drug loading capabilities, with the star-like structure used as a way to improve the loading of doxorubicin. In Chapter 3, two star-like polycaprolactones featuring either four or six arms are compared in terms of their properties and drug loading abilities. In addition, these polymers are synthesized with a tri(ethylene glycol) substituted poly(caprolactone) hydrophilic block and a ethoxy substituted hydrophobic block, which are shown to have thermally controlled drug release. Chapter 4 focuses on improving the loading of doxorubicin in polymeric micelles through the combination loading of doxorubicin with resveratrol, a polyphenolic compound that has cardioprotective and chemosensitizing properties. Resveratrol, when loaded in combination with doxorubicin, increases the amount of doxorubicin encapsulated in the micelle significantly. This can be a way to improve loading of the chemotherapeutic drug, while also decreasing some of its toxic side effects.Item Magnetic and Catalytic Properties of Lanthanide Complexes(2021-05-01T05:00:00.000Z) Miller, Justin Todd; Stefan, Mihaela C.; Choudhary, Pankaj K.; Biewer, Michael C.; Nielsen, Steven O.; Pantano, PaulLanthanides are an intriguing family of elements possessing unique properties useful in many diverse applications. The first chapter of this work describes the origins of some of these properties and their catalytic and magnetic applications. The second chapter will highlight a highly unusual neodymium catalyst for diene polymerization. This coordination polymer catalyst contains no halides and makes use of no halide donor, yet produces desirable 96% 1,4- cis stereospecific material. The third chapter is concerned with the surprising formation and superparamagnetism of a neodymium-peroxide diimine cluster and the associated crystals. The cluster is formed by a rare example of anion-templated assembly in which the anion is derived from dissolved atmospheric oxygen. The resulting structural motif featured an array of tight three-metal clusters separated by a distance long enough to prevent long-range magnetic order, which resulted in superparamagnetic behavior in the solid state. This is believed to be the first report of superparamagnetism in a bulk crystal state. The fourth and final chapter is concerned with MRI contrast agents and presents an example of a new variety of potential next-generation agents composed of coordination polymers. The gadolinium diethylphosphate polymer features a far longer rotational coordination time than conventional small gadolinium complexes and thus offers dramatically improved T1 relaxation performance at low-fields common in clinical imaging applications. All of these lanthanide complexes are synthesized using an azeotropic distillation method. This method avoids the need for strict water-free techniques and also occasionally allows for novel structures to be obtained, as demonstrated in Chapter 3 in particular.Item Magnetic Properties and Coordination Polymerization of Lanthanide Phosphate Complexes(2021-12-01T06:00:00.000Z) Cue, John Michael; Stefan, Mihaela C.; Choudhary, Pankaj; Meloni, Gabriele; Biewer, Michael C.; Sibert IV, John W.The intrinsic properties of lanthanides give steric and electronic advantages in rare earth organometallics. Lanthanides have the potential to accomplish unique applications which cannot be done using transition metals. The first chapter describes the structure of the lanthanide complexes and the potential applications of the f block chemistry because of their magnetic and catalytic properties. The second chapter highlights a discrete neodymium complex for the polymerization of dienes and polar vinyl monomers. The study of the kinetics of polymerization shows a quasi-living polymerization which is beneficial to control the molecular weight and synthesize new materials using block copolymers. The third chapter focuses on the application of polynuclear lanthanide organophosphate complexes as molecular magnets. Lanthanide organophosphate complexes based on a triethyl phosphate ligand have been prepared using azeotropic distillation to explore their structure and properties. Single crystal X-ray diffraction studies show isomorphic complexes having a unique one-dimensional polymer with the bridging ligand connecting the LnIII ions. A series of the three lanthanide coordination polymers display the phosphate groups as an irregular distorted tetrahedron. These complexes were synthesized in search of new single-molecule magnets. SQUID magnetometry studies show high magnetic susceptibility.Item Microfabrication of an Organ-on-a-chip Device to Model Cardiotoxicity Induced by Chemotherapies for Cancer Nanomedicine Evaluation(2020-12-03) Soltantabar, Pooneh; Stefan, Mihaela C.Cancer is the leading cause of death worldwide, and more efficient treatments and pre-clinical tests for the evaluation of novel therapies are in high demand. Chemotherapy, as the most common cancer treatment, is facing severe challenges, including low water solubility of anti-cancer drugs and the cardiotoxicity induced by them. Nanotechnology has made significant contributions to the development of drug delivery systems by reducing the toxicities, which leads to improvement in conventional chemotherapies. Chapter 2 describes a micellar drug delivery system's design using benzyl substituted poly(ε-caprolactone) as the hydrophobic block, and co-loaded doxorubicin anticancer drug and quercetin cardioprotective agent to increase the solubility of the anticancer drug in water and reduce the cardiotoxicity induced by the anticancer drug. Oligo(ethylene) glycol substituted poly(ε-caprolactone)s were used as hydrophilic blocks and make the polymer thermoresponsive. Our proposed biodegradable and thermoresponsive micellar DDS can open the door to developing a more effective platform for cancer treatment. Although many therapeutics have been developed so far, the pharmaceutical industry is still facing challenges for drug discovery, which is mostly attributed to the lack of proper pre-clinical testing. In Chapter 3, we try to model the cardiotoxicity induced by anticancer drugs on an organ-on-achip device to improve conventional pre-clinical cell culture. Organ-on-a-chip devices can mimic the whole-body response to therapeutics by fluidically connecting microscale cell cultures and generating a realistic model of human organs of interest. We described a pumpless heart/liver-ona-chip (HLC) using the HepG2 hepatocellular carcinoma cells and H9c2 rat cardiomyocytes to reproduce the cardiotoxicity induced by Doxorubicin (DOX) in vitro. Our designed HLC device represents a unique approach to assess the off-target toxicity of drugs and their metabolites, which will eventually improve current pre-clinical studies.Item Molecular Dynamics Investigation of Fluoride Ion Permeation and Mechanism in Fluoride Export Protein Bordetella Pertussis (Bpe)(December 2022) Akintayo, Abiola Damilare; Torabifard, Hedieh; Stefan, Mihaela C.; Nielsen, Steven O.; Meloni, GabrieleMicroorganisms struggle to survive numerous chemical threats, one of which is fluoride ions to which they developed fluoride channels (Fluc) for exporting fluoride out of their cytoplasm. The crystallographic structure and previous studies have spotted an unusual tetrahedrally coordinated non-transported central sodium cation and highlighted certain conserved polar residues along the Fluc pores. However, the exact coordination number of the central sodium and the mechanism of fluoride permeation in relation to these conserved polar residues remains elusive. In this study, we applied the all-atoms molecular dynamics method on WT Fluc-Bpe (Bordetella pertussis) with single fluoride in its pore and with four fluorides alongside its arginine mutants (R23A and R23K). We investigated the possible hydration of central sodium ion to ascertain its coordination, the role of arginine 23, which is an important conserved polar residue, and the permeation mechanism of fluoride. We found out using the watershell analysis that sodium was anhydrous in the WT Fluc and its mutants but hydrated to form a 5-ligand coordination in WT Fluc systems with single fluoride in Fo and F2 binding sites. The dihedral analysis of arginine 23 revealed that it plays a pivotal role in the stabilization of fluoride ions by electrostatic non-bonded interactions made possible by its guanidinium side chain which undergoes dihedral shift for fluoride permeation and efflux. The mechanism of fluoride export for each protein system under study provides insight into the structural dynamics of Fluc’s important arginine polar residue.Item Molecularly-Engineered, 4D-Printed Liquid Crystal Elastomer Actuators(WILEY-VCH Verlag GmbH, 2018-11-27) Saed, Mohand O.; Ambulo, Cedric P.; Kim, Hyun; De, Rohit; Raval, Vyom; Searles, Kyle; Siddiqui, Danyal A.; Cue, John Michael O.; Stefan, Mihaela C.; Shankar, M. Ravi; Ware, Taylor H.; 0000-0001-5154-6378 (Saed MO); 0000-0001-7996-7393 (Ware, TH); Saed, Mohand O.; Ambulo, Cedric P.; Kim, Hyun; De, Rohit; Raval, Vyom; Searles, Kyle; Siddiqui, Danyal A.; Cue, John Michael O.; Stefan, Mihaela C.; Ware, Taylor H.Three-dimensional structures that undergo reversible shape changes in response to mild stimuli enable a wide range of smart devices, such as soft robots or implantable medical devices. Herein, a dual thiol-ene reaction scheme is used to synthesize a class of liquid crystal (LC) elastomers that can be 3D printed into complex shapes and subsequently undergo controlled shape change. Through controlling the phase transition temperature of polymerizable LC inks, morphing 3D structures with tunable actuation temperature (28 ± 2 to 105 ± 1 °C) are fabricated. Finally, multiple LC inks are 3D printed into single structures to allow for the production of untethered, thermo-responsive structures that sequentially and reversibly undergo multiple shape changes.
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