Browsing by Author "James, Susan, advisor"
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Item Open Access Alternative heart assistance pump(Colorado State University. Libraries, 2021) Sharifi, Alireza, author; Bark, David, advisor; James, Susan, advisor; Scansen, Brian, committee member; Popat, Ketul, committee member; Gao, Xinfeng, committee memberOn average, the human heart beats around 115,000, and pumps around 2,000 gallons of blood daily. This essential organ may undergo systolic or diastolic dysfunction in which the heart cannot properly contract or relax, respectively. To help hearts pump effectively should these types of failures occur, ventricular assist devices (VAD) are implemented as a temporary or permanent solution. The most common VAD is the left ventricular assist device (LVAD) which supports the left ventricle in pumping the oxygen-rich blood from the heart to the aorta, and ultimately to the rest of the body. Although current VADs are an important treatment for advanced heart failure, generally VADS come with many complications and issues after implantation. These complications include incidents of hemolysis (tearing of the blood cells), thrombosis (clotting of the blood), bleeding (especially in the gastrointestinal tract), and infection at the driveline site. Specifically, the current continuous flow pumps are associated with a much higher incidence of gastrointestinal bleeding, myocardial perfusion, kidney problems, among others, compared with the earlier generation pulsatile pumps. However, the presence of several moving mechanical components made the pulsatile pumps less durable, bulky, and prone to malfunction, ultimately leading to favor toward continuous flow designs. The goal of the present study is to develop a novel heart assist pump, overcoming drawbacks to current commercially available pumps, by improving hemodynamic (blood flow) performance, pulsatility, and eliminating bleeding disorders. Our design will overcome the current pumps which suffer from non-physiological flow, and blood damage. The impact of this work goes beyond heart assist devices and would be applicable to other blood pumps. The fundamental biological and physical principles of designing a blood pump will be reviewed in chapter one. In addition, recent studies on current LVADs and the motivation behind these studies will also be discussed. Then, the idea of using a contractive tubular heart as an alternative pump will be presented in chapter two. To understand the pumping mechanism of the tubular heart, a detailed study on the embryonic heart is presented in this chapter. Subsequently, the effect of flow forces on blood cells will be studied in chapter 3. Moreover, the relation between flow regime and bleeding disorders have been studied in the same chapter. A discussion of our design, including the pump design, testing set up, experimental results will be presented in chapter 4. Finally, the limitations of the present study and future work will be presented in chapter 5.Item Open Access Catalytic biomass conversion and upgrading into platform chemicals and liquid fuels(Colorado State University. Libraries, 2014) Liu, Dajiang, author; James, Susan, advisor; Chen, Eugene, advisor; Williams, John, committee member; Marchese, Anthony, committee member; Fisk, Nick, committee memberThe development of novel, efficient catalytic processes for plant biomass conversion and upgrading into versatile platform chemicals as well as oxygenated biodiesel and premium hydrocarbon kerosene/jet fuels is described in this dissertation. The chief motivation of using annually renewable biomass as the source of chemical building blocks and transportation fuels is to reduce societal dependence on depleting fossil fuels. Towards this goal, 5-hydroxymethylfurfural (HMF), the dehydration product from C6 (poly)sugars, has been intensively investigated as it has been identified as a versatile C6 intermediate or platform for value-added chemicals and biofuels. This work has developed several highly efficient and cost-effective catalyst systems for C6 (poly)sugars conversion to HMF under mild conditions, including ubiquitous and inexpensive aluminum alkyl or alkoxy compounds, recyclable polymeric ionic liquid (PIL)-supported metal (Cr, Al) catalysts, and thiazolium chloride, a recyclable Vitamine B1 analog. An integrated, semi-continuous process for the HMF production from fructose has also been developed, affording the high-purity HMF as needle crystals. Towards HMF upgrading into higher-energy-density fuel intermediates, developing new strategies of C-C bond formation or chain extension is of particular interest. In this context, this study has discovered that N-heterocyclic carbenes (NHCs) are highly effective organic catalysts for HMF self-condensation to 5,5'-dihydroxymethylfuroin (DHMF), a new C12 biorefining building block. This new upgrading process has 100% atom economy, can be carried out under solvent-free conditions, and produces the C12 DHMF with quantitative selectivity and yield, the hallmarks of a "green" process. More significantly, the C12 DHMF has been transformed catalytically into oxygenated biodiesels, high-quality alkane jet fuels, and sustainable polymers, thereby establishing DHMF as a new C12 biomass platform chemical.Item Open Access Characterization of osseointegrative phosphatidylserine and cholesterol orthopaedic implant coatings(Colorado State University. Libraries, 2013) Rodgers, William Paul, author; James, Susan, advisor; Popat, Ketul, committee member; Ehrhart, Nicole, committee member; De Long, Susan, committee memberTotal joint arthroplasties/replacements are one of the most successful surgeries available today for improving patients’ quality of life. By 2030 in the US, demand for primary total hip and knee arthroplasties are expected to grow by 174% and 673% respectively to a combined total of over 4 million procedures performed annually, driven largely by an ageing population and an increased occurrence of obesity. Current patient options for load-bearing bone integrating implants have significant shortcomings. Nearly a third of patients require a revision surgery before the implant is 15 years old, and those who have revision surgeries are at an increased risk of requiring additional reoperations. A recent implant technology that has shown to be effective at improving bone to implant integration is the use of phosphatidylserine (DOPS) coatings. These coatings are challenging to analyze and measure due to their highly dynamic, soft, rough, thick, and optically diffractive properties. Previous work had difficulty investigating pertinent parameters for these coating’s development due in large part to a lack of available analytical techniques and a dearth of understanding of the micro- and nano-structural configuration of the coatings. This work addresses the lack of techniques available for use with DOPS coatings through the development of original methods of measurement, including the use of scanning white light interferometry and nanoindentation. These techniques were then applied for the characterization of DOPS coatings and the study of effects from several factors: 1. the influence of adding calcium and cholesterol to the coatings, 2. the effect of composition and roughness on aqueous contact angles, and 3. the impact of ageing and storage environment on the coatings. This project lays a foundation for the continued development and improvement of DOPS coatings, which have the promise of significantly improving current patient options for bone integrating implants. Using these newly developed and highly repeatable quantitative analysis methods, this study sheds light on the microstructural configuration of the DOPS coatings and elucidates previously unexplained phenomena of the coatings. Cholesterol was found to supersaturate in the coatings at high concentration and phase separate into an anhydrous crystalline form, while lower concentrations were found to significantly harden the coatings. Morphological and microstructural changes were detected in the coatings over the course of as little as two weeks that were dependent on the storage environment. The results and understanding gained pave the path for focused future research effort. Additionally, the methods and techniques developed for the analysis of DOPS coatings have a broader application for the measurement and analysis of other problematic biological materials and surfaces.Item Open Access Compatibility of hydrophobic ionic liquids with high performance cathode materials for lithium ion batteries(Colorado State University. Libraries, 2012) Carnes-Mason, Ezekial Robert, author; James, Susan, advisor; Wilkes, John, committee member; Strauss, Steven, committee memberLithium batteries are widely seen as the best choice for the future of energy storage but significant improvements are still required. One important area for improvement is searching for new cathode materials that incorporate lithium at higher capacities and voltages. This increases the energy and power available from an individual electrochemical cell, which reduces the number of cells required thereby reducing the size of a battery pack. While several high voltage cathode materials have been discovered, research has been hindered due to safety concerns with current standard electrolytes at high voltages. Ionic liquids are a new class of materials that exhibit excellent electrochemical and thermal stability as well as high ionic conductivity. These qualities make them excellent candidates to replace current battery electrolytes but difficulties in purification and the sheer number of possible chemistries have inhibited their study. In this study four hydrophobic ionic liquids based on pyrrolidinium and piperidinium cations paired with bis(trifluoromethylsulfonyl)imide anions were synthesized using bench top methods. These ionic liquids were successfully incorporated into working half-cells with LiNi1/3Mn1/3Co1/3O2, a high capacity layered cathode and LiNi0.5Mn1.5O4, a high voltage spinel type cathode. By comparing the behavior of the ionic liquids a clear relationship between cation size and rate capability was shown. The improved performance and safety at elevated temperatures was also demonstrated showing that ionic liquids are excellent candidates for use as battery electrolytes.Item Open Access Method for creating functionally graded materials with spark plasma sintering and a continuous machine for future scalability(Colorado State University. Libraries, 2017) Colasuonno, Paul S., author; James, Susan, advisor; Ma, Kaka, committee member; Neilson, James, committee memberThis work develops a quantitative process to sinter functionally graded materials (FGMs) to specific porosity gradients using Spark Plasma Sintering (SPS). The powder densification in SPS is modeled using the Master Sintering Curve (MSC) calculated from shrinkage due to three different heating rates. The meaning of the apparent sintering activation energy is discussed along with the MSC's applicability to SPS. The MSC is adjusted for the additional sintering that occurs during cooling, such that porous materials can be produced by interrupting the heating schedule. The temperature in the powder is then spatially resolved by a constructed thermal-electric FEA model. Tooling is designed to apply a steady state temperature gradient (50°C/mm) on zirconia (+3% mol yttria) powder. The MSC, coupled to the thermal-electric model, is used to spatially predict densification in a temperature gradient. Resulting FGM microstructures and grain size distributions are discussed. Design problems found while attempting to scale the FGMs process to larger diameters are quantified. As an alternative to traditional SPS batch processes, a Continuous Electric Field Assisted Sintering (CEFAS) machine is developed to address these practical limitations from a new direction. The proof of concept CEFAS machine uses Joule heated rollers to continuously heat, compress, and extrude material under conditions analogous to SPS. Design considerations, lessons learned, and control variables for future iteration CEFAS machines are illustrated.Item Open Access Penetrative osseointegrative phospholipid coatings on 3D titanium lattice structures(Colorado State University. Libraries, 2012) Hudson, Hannah Katherine, author; James, Susan, advisor; Prawel, David, committee member; Ehrhart, Nicole, committee memberTitanium is a commonly used material for implantable metallic devices though these devices still have many issues. The cost of implant surgery and the likely revision surgery that will follow is high. Cementless implants frequently fail due to aseptic loosening of the device, typically as a result of poor osseointegration. Phospholipids are naturally occurring substances that have been used to enhance new bone growth and integration of this bone with the implants. Electrospraying (e-spraying) is a method that uses electrical forces to drive source material to a target conductor. It typically has very high efficiency because it uses electrical charge to carry the material. This process also provides good control of coating morphology as this can be effected by the parameters used to e-spray. In our work the E-spraying technique was used to apply coatings of 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS) to Ti-6V-4Al porous lattice structures. These lattice structures are created using Electron Beam Melting (EBM). This manufacturing process is an additive process, part of the solid free form fabrication group, a subset of rapid prototyping. EBM enables precise control of complex geometries. When e-spraying these lattice structures can become Faraday cages when an electric field is applied to them. A Faraday cage is a conductor that becomes an equipotential surface when an electric field is applied and thus in its interior lacks an electric field. The exclusion of an internal electric field can inhibit to the e-spray process which relies on field lines to carry material to the target. In our work the Faraday cage effect was observed in two conditions, one in which the lattice structures were externally, circumferentially insulated and one in which the lattices were not insulated. Three different porosity lattices, with different pore sizes, were tested and all became Faraday cages when insulated and only the lowest porosity lattice became a strong Faraday cage when not insulated. The lattices that did coat did not exhibit conformal and uniform coatings when the Faraday cage effect was present. E-spray parameter variation was not able to mitigate the Faraday cage effect nor was it able to affect the morphology of the coatings. The surface topography of the structures is important for preferential cell adhesion and can be controlled using acid etching to modify the surface. In attempt to coat titanium lattice structures with a phospholipid coating this work discovered the Faraday cage effect as it relates to the electrospraying of phospholipids. It currently defines the limitations of the e-spray process as well as outlines what has been tried to mitigate the Faraday cage effect and discover how the Faraday cage effect changes coating morphology. In the future continuing work on mitigating the Faraday cage effect will be done as well as combining the e-spray process with one that uses a mechanical force to accelerate particles.Item Open Access Phosphatidylserine and antibiotic coatings for allograft bone(Colorado State University. Libraries, 2014) Tait, Douglas, author; James, Susan, advisor; Ehrhart, Nicole, committee member; Deines, Susan, committee memberOsteosarcoma is the most common type of primary bone tumor in humans. Treatment usually involves both surgical resection of the tumor and chemotherapy. Limb sparing often necessitates the use of massive bone allografts, however patients on anticancer drug regimens are at increased risk of infection, non-union and mechanical failure. The purpose of this work was to develop and test antibiotic eluting phospholipid coatings for massive bone allografts which may be useful in revision surgery for patients with osteomyelitis infection. This project was motivated by previous research performed on coatings of the phospholipid 1,2-dioleoyl-sn-glycero-3-phospho-l-serine (DOPS) and the antibiotic Gentamicin Sulfate (GS) applied to metallic implants. The potential of these coatings to combat infection and enhance osseointegration was evaluated in vivo using massive femoral allografts in a murine model with a well established osteomyelitis infection. Phospholipid coatings were applied to decellularized mouse femur segments using an electrospray method. Antibiotic was incorporated between two DOPS layers. The presence of both DOPS and GS was verified by examining the treated allografts with a scanning electron microscope (SEM). Allografts were then prepared and implanted into 50 mice in seven different treatment groups. In four of these treatment groups the mice were deliberately infected with osteomyelitis one week prior to allograft implantation using a genetically modified bioluminescent strain of Staphylococcus aureus that enabled tracking of the infection in vivo. Mice were sacrificed at 28 days post allograft implantation and allografts were evaluated histologically. After completing the in vivo portion of the study, the antibiotic eluting characteristics of the coatings were analyzed in vitro with a total sink elution method and antibiotic in the eluent was quantified using an agar diffusion test. Results showed that mice receiving antibiotic coated allografts displayed significantly reduced infection up to fifteen days post allograft implantation. Measurable infection remained until the end of the study however and none of the infected mice exhibited any osseointegration with the allograft. These results were most likely due to the severity of the osteomyelitis infection and the rapid elution of the antibiotic from the allografts, as confirmed by the in vitro elution study. Osseointegration was observed in the uninfected mice however no statistically significant differences were found between the DOPS coated treatment groups and the uncoated control group. This was attributed to the small sample size of the uninfected groups and the small number of histological sections, and was perhaps exacerbated by inconsistent host-graft apposition. Further research is therefore necessary to validate the potential of DOPS/GS allograft coatings to fight infection and enhance osseointegration.Item Open Access Spectroscopic ellipsometry as a process control tool for manufacturing cadmium telluride thin film photovoltaic devices(Colorado State University. Libraries, 2013) Smith, Westcott P., author; Kirkpatrick, Allan T., advisor; James, Susan, advisor; Puttlitz, Christian, committee member; Sampath, W. S., committee member; Wu, Mingzhong, committee memberIn recent decades, there has been concern regarding the sustainability of fossil fuels. One of the more promising alternatives is Cadmium Telluride (CdTe) thin–film photovoltaic (PV) devices. Improved quality measurement techniques may aid in improving this existing technology. Spectroscopic ellipsometry (SE) is a common, non-destructive technique for measuring thin films in the silicon wafer industry. SE results have also been tied to properties believed to play a role in CdTe PV device efficiency. A study assessing the potential of SE for use as a quality measurement tool had not been previously reported. Samples of CdTe devices produced by both laboratory and industrial scale processes were measured by SE and Scanning Electron Microscopy (SEM). Mathematical models of the optical characteristics of the devices were developed and fit to SE data from multiple angles and locations on each sample. Basic statistical analysis was performed on results from the automated fits to provide an initial evaluation of SE as a quantitative quality measurement process. In all cases studied, automated SE models produced average stack thickness values within 10% of the values produced by SEM, and standard deviations for the top bulk layer thickness were less than 1% of the average values.Item Open Access The development of hyaluronan enhanced expanded polytetrafluoroethylene and linear low density polyethylene for blood contacting applications(Colorado State University. Libraries, 2019) Bui, Hieu T., author; James, Susan, advisor; Reynolds, Melissa, committee member; Popat, Ketul, committee member; Olver, Christine, committee memberCardiovascular disease is the number one cause of death in high income, industrialized countries. Designing cardiovascular implants from synthetic polymers is a cost-effective solution to the growing demand for medical treatments such as heart valve replacements and cardiovascular bypass procedures. Synthetic polymers are often known for their tunability, durability, and low production cost. Unfortunately, these materials are also prone to induce thrombosis. Therefore, improving the blood compatibility of these polymers is still a major challenge in the biomedical field. This dissertation discusses the alteration of two synthetic polymers, linear low density polyethylene (LLDPE) and expanded polytetrafluoroethylene (ePTFE), using hyaluronan (HA) to improve their blood compatibility. HA, a naturally occurring polysaccharide in the human body, is known for its wound healing and anticoagulant properties. In this work, two unique methods were developed for HA enhancement of ePTFE (HA-ePTFE) and LLDPE (HA-LLDPE). This was a process driven research that aimed at designing HA-ePTFE and HA-LLDPE by analyzing the effect of different treatment parameters on the properties of the resultant materials. In the case of ePTFE, it was demonstrated that HA can be incorporated into vascular ePTFE grafts by exploiting the micro pores of the polymer and adjusting the spraying treatment. In the HA-LLDPE fabrication process, its parameters were varied to assess their effects on the interpenetrating polymer network (IPN) formation. Surface characterization such as water contact angle goniometry, infrared spectroscopy, and toluidine blue O (TBO) staining prove that HA treatment successfully changed the surface chemistry and increased the hydrophilicity of ePTFE and LLDPE. Thermal analysis and gas chromatography-mass spectrometry were used to quantify the effects of different treatment conditions on material properties. Tensile properties such as elastic modulus, tensile strength, yield stress and ultimate strain are unchanged by HA enhancement for both polymers. The biological results reveal that HA-ePTFE and HA-LLDPE are not cytotoxic and result in less blood clotting and platelet activation than ePTFE and LLDPE.Item Embargo Thermally-assisted frontal polymerization for rapid curing of fiber-reinforced polymer composites(Colorado State University. Libraries, 2024) Naseri, Iman, author; James, Susan, advisor; Bailey, Travis, committee member; Herrera-Alonso, Margarita, committee member; Ma, Kaka, committee memberFiber-reinforced polymer composites (FRPCs) are widely used in a variety of applications owing to their excellent specific mechanical properties, chemical stability, and fatigue resistance. However, the state-of-the-art technologies for manufacturing FRPCs are intensive in terms of time and energy, generate a significant carbon footprint, and require costly resources. In addition, FRPCs lack key non-structural functionalities (e.g., de-icing, damage sensing) required for many applications. Despite the enormous efforts made to improve the manufacturability of FRPCs and address the shortcomings associated with the performance of FRPCs, there is still a pressing need for alternative manufacturing technologies to enable the rapid, energy-efficient, and low-cost manufacturing of multifunctional fiber-reinforced polymer composites. In this dissertation, a novel technique for rapid and cost-effective manufacturing of multifunctional fiber-reinforced polymer composites is developed by exploiting the frontal polymerization concept and joule heating of nanostructured materials. A nanostructured paper or fabric is integrated into the composite layup to supply the energy required to trigger frontal polymerization via the Joule heating effect. In addition, the nanostructured paper remains advantageous in in-service conditions and imparts new functionalities to the host composite structure. In the first chapter, the recent developments in material systems, as well as heating techniques reported for improving the manufacturability of FRPCs, are reviewed, and frontal polymerization (FP) as a rapid and energy-efficient technique for curing thermoset matrix composites is introduced. In the second chapter, frontal curing of multifunctional composites via a commercial nanostructured heater (buckypaper) is demonstrated, and the curing behavior of composite laminate is studied under various layup conditions. It is demonstrated that the through-thickness FP manufacturing strategy using an embedded buckypaper surface heater allows for rapid and energy-efficient manufacturing of fully cured composite panels using the conventional tooling materials utilized in the composite industry. However, the temperature profiles developed during the cure cycle, as well as the degree of cure of resin in produced composites, are greatly affected by the thermal properties of the tooling materials, where lower front temperatures and degree of cure are measured for composite panels manufactured using thermally conductive tooling materials such as aluminum. This issue can be effectively addressed by preheating the dry composite layup for a few minutes. Despite the relatively uniform heat generation in nanostructured buckypaper heaters, the infrared thermal imaging of the curing process reveals that the front initiates from multiple locations and propagates in both the through-thickness and in-plane directions. In addition, the de-icing functionality is demonstrated in the cured composite as one of the several possible functionalities imparted to composite structures due to the presence of a buckypaper layer. In the third chapter, a fabric heater is developed by writing laser-induced graphene on aramid fabric using a CO2 laser and used as an integrated heater for manufacturing FRPCs via the through-thickness FP manufacturing technique. A 10 cm × 10 cm composite panel is successfully cured within only 1 minute with a total energy consumption of 4.13 KJ, which is comparable to the time and energy required for producing a similar composite panel using a buckypaper heater. In addition to composite manufacturing, flexible heaters are prepared with the addition of silicone rubber to fabric heaters. Although the addition of electrically insulating rubber negatively affects the electrothermal performance of fabric heaters, it greatly improves the durability of fabric heaters. In the fourth chapter, a facile and rapid technique for the preparation of mechanically robust nanocomposite film heaters is developed based on a frontally polymerizable resin system. The mechanical and electrothermal properties of the nanocomposite film heaters are characterized, and the produced heaters are used for out-of-oven manufacturing composite laminates. In the final chapter, the main research findings are summarized, and the recommendations for future studies are presented.