Browsing by Author "James, Susan P., advisor"
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Item Open Access A drug eluting, osseointegrative phospholipid coating for orthopedic implants(Colorado State University. Libraries, 2011) Prawel, David A., author; James, Susan P., advisor; Popat, Ketul C., advisor; Kipper, Matt J., committee member; Ryan, Stewart D., committee memberMillions of implant surgeries are performed each year. Titanium is commonly used for implantable metallic devices, especially total hip and knee replacements. However, titanium implants are far from perfect. Although the absolute failure rate is not particularly high, the case-by-case direct and human cost of each device implant failure is tremendous. Cementless titanium implant devices, although preferred by surgeons, frequently fail due to loosening of the device, often as a result of poor integration of naturally forming bone with the metallic implant, and by infection. Phospholipids are naturally occurring substances that are shown to enhance integration of new bone with implants, and to help reduce inflammation, a common precursor to infection. In addition, numerous studies have shown phospholipids to be effective drug delivery agents. To date, dip and drip coating techniques for applying phospholipid coatings have been used on titanium. Both coating techniques are easy to perform, but result in coatings too thick and non-conformal for in vivo use. Electro-spraying (E-spray) is a method of atomizing a liquid by means of electrical forces. E-spraying provides the advantage of being able to create coatings with relatively high efficiencies because the electrical charge difference "carries" the liquid source material, which also provides good control of coating morphology, especially on rough and intricately shaped surfaces. Other advantages of this technique are low cost and easy setup. In our work, the E-spraying technique was successfully adapted to apply thin, conformal, consistent coatings of 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS) to small, flat, commercially pure titanium plates. DOPS coatings were E-sprayed, then loaded with gentamicin sulfate (GS), a popular antibiotic used in treatment of osteomyelitis. An elution study was completed to assess drug delivery capabilities of the coatings. This work demonstrated that elution profile could be modified by changing E-spray parameters. Rat marrow stromal cells were harvested, and seeded onto the test coatings. Mesenchymal stem cells (MSCs) were selected from the general cell population, successfully cultured and differentiated into osteoblasts. Cytotoxicity of the coatings, along with cell viability, cell differentiation, biomineralization activity, cell morphology and early osseogenesis markers were evaluated at multiple time points in dual multi-week studies. DOPS coatings were found to be non-cytotoxic, and cell viability and biomineralization were higher on DOPS-coated surfaces and gentamicin-loaded coatings than on plain titanium samples. At the two week time point, excessive delamination of the coatings occurred in the cell growth environment. Research was undertaken to identify and test techniques to enhance coating retention. Surface chemistry was modified by passivation and pretreatment with calcium-chloride, and cholesterol was added to the DOPS E-spray. A repeated elution study demonstrated that elution profile could be modified as a result of changes in coating chemistry. An additional MSC cell study was completed to reconfirm the effects of enhanced coating chemistry on the cytotoxicity, cell viability and biomineralization. Cell morphology was re-evaluated at all time points via SEM imaging. Hydroxyapatite formation was confirmed. Preliminary osseogenesis biomarkers were also measured, showing deposition of osteocalcin and osteopontin, important protein precursors to normal bone growth, on enhanced coatings. This work demonstrates the viability of electro-sprayed DOPS coatings on titanium orthopedic implant material, and the enhanced osseogenic characteristics of these coatings. We also demonstrated that DOPS coatings can carry and release an antibiotic over time at clinically relevant dosages, and that this release profile can be engineered by modifications to E-spray process parameters, surface chemistry and E-sprayed material formulation.Item Open Access A nanoparticulate-reinforced hyaluronan copolymer hydrogel for intervertebral disc repair(Colorado State University. Libraries, 2011) Yonemura, Susan S., author; James, Susan P., advisor; Bailey, Travis S., committee member; Kisiday, John D., committee member; Wheeler, Donna L., committee memberDegenerative disc disease (DDD) is an inevitable consequence of aging, commonly resulting in low back pain (LBP). Current clinical treatment options for disc degeneration exist at two extremes: conservative management or extensive surgical intervention. Given the economic impact of lost productivity and disability associated with low back pain, there is significant interest in earlier, less invasive intervention. Biomimetic disc replacement and regenerative therapies offer an attractive alternative strategy for intervertebral disc repair, but materials employed to date have not exhibited a successful combination of mechanical and biological properties to achieve viable solutions. The composite material developed and characterized in this work consisted of a novel hyaluronan-co-poly(ethylene-alt-maleic anhydride) (HA-co-PEMA) hydrogel matrix reinforced with nanoparticulate silica; the hydrogel matrix provided a compliant hydrated matrix conducive to integration with the surrounding tissue while the nanoparticulate reinforcement was manipulated to mimic the mechanical performance of healthy ovine nucleus pulposus (NP) tissue. HA-co-PEMA was formed via an esterification reaction between a hydrophobically-modified HA complex and PEMA, and candidate formulations were characterized by chemical, thermal, and physical means to select an appropriate base hydrogel for the reinforced composite. Three grades of commercially-available fumed silica, varying by degree of hydrophobic surface modification, were evaluated as nanoparticulate reinforcement for the composite materials. Mechanical testing of two reinforced composite formulations (620-R and 720-R) emphasized dynamic shear properties and results were directly compared to ovine nucleus pulposus (NP) tissue. The complex shear modulus (G*) for 620-R ranged from 1.8±0.2 KPa to 2.4±0.3 KPa over the frequency range 0.1 Hz < f < 10 Hz, while G* for 720-R varied from 4.4 ± 0.5 KPa to 6.1 ± 0.6 KPa over the same frequency range. Ovine NP tissue tested using identical methods exhibited G* of 1.7 ± 0.2 KPa at 0.1 Hz up to 3.8 ± 0.5 KPa at 10 Hz. Thus, the complex shear moduli (G*) for 620-R and 720-R effectively bracketed G* for NP over a physiologically-relevant frequency range. Subsequent in vitro cytotoxicity and biocompatibility experiments suggest that the 720-R formulation warrants consideration for future in vivo modeling.Item Open Access Applications and advanced sintering techniques of functionally graded ZnO-based thermoelectric material(Colorado State University. Libraries, 2017) Cramer, Corson Lester, author; Ma, Kaka, advisor; James, Susan P., advisor; Williams, John D., committee member; Sampath, Walajabad, committee member; Neilson, Jamie R., committee memberThermoelectric generator (TEG) materials provide a unique solid-state energy conversion from heat to electricity. Nanostructured TEGs experiencing transient thermal loads at medium to high-temperatures are susceptible to degradation due to thermal stress cracking, which subsequently causes decreased lifetime. Previous efforts to prevent the thermal degradation have led to the following approaches: geometric pinning, compositional gradients, and segmentation of different materials. In the present research, functionally graded zinc oxide (ZnO) materials with graded grain size distribution were fabricated using a water sintering strategy via spark plasma sintering (SPS) with a thermal gradient in combination with modified tooling and strategic mechanical load schedules. Samples with homogeneous grain size distribution were also fabricated as a baseline for comparison. The primary objective of the work is to investigate the correlation between the processing conditions, formation of graded microstructure, and the resultant thermoelectric (TE) output performance and lifetime of the ZnO materials. The fundamental understanding of this correlation will contribute to future design of TEG materials using the approach of graded microstructure. The hypothesis is as follows: in a TEG material with graded grain size distribution, one side that consists of coarse (micron-sized) grains is exposed to the heat source. This coarse-grained side of the material can mitigate thermal stress cracking by spreading the heat more quickly during transient heating and thus provide improved thermal stability. The other side of the TEG material consists of fine grains (submicron-sized) and still exhibits high efficiency. In the current study, both continuously graded ZnO materials and a five-layer discretely graded ZnO material were fabricated. Microstructural characterization shows that the grain size gradient of the continuously graded materials across a 10-mm thickness goes from submicron scale (average size ~ 180 nm) to micron scale (~1.2 μm). The thermoelectric properties of the baseline ZnO materials with uniform grain sizes were measured. Using the data obtained from those samples with uniform grain sizes, the peak efficiencies of the continuously graded materials and the five-layer graded materials were simulated and compared to the experimentally measured values. The lifetime of the ZnO samples was evaluated from the electrical resistance at the cycling temperature. The results of the final efficiencies suggest that the thermoelectrical performance of the ZnO materials benefit from the grain size gradation. In addition, the sintering behavior of the continuously graded ZnO system is investigated and compared to that of the isothermally sintered samples to establish a predictive model of the microstructure (density-grain size-time relation). A discrepancy is observed between the prediction of the continuously graded materials and the experimental results. This discrepancy is attributed to a stress shielding that develops during sintering due to differential sintering from the temperature gradient. The stress shielding occurs when denser, and thus stiffer material develops adjacent to less dense and less stiff material causing the stress to vary because the stress is not evenly distributed. The stress shielding effect during sintering is further investigated through theoretical sintering equations. Using the viscoelastic analogy in sintering, the stress to be added to the sample during sintering in a thermal gradient is quantified to compensate the discrepancy from the samples sintered isothermally based on an average strain rate difference.Item Open Access Development of a hyaluronan-polyethylene copolymer for use in articular cartilage repair(Colorado State University. Libraries, 2009) Oldinski, Rachael, author; James, Susan P., advisorArticular cartilage is the connective tissue which covers the ends of long bones, providing a lubricious, hydrodynamic surface for articulation and energy dissipation. Articular cartilage has a limited ability to repair itself; once the native tissue has become damaged, either from injury or disease (e.g., arthritis), it is irreversible and the tissue will degrade with time resulting in joint pain. The goal of this research was to develop a permanent (i.e., non biodegradable/bioerodible) bioactive material and assess its applicability for articular cartilage repair and/or replacement. Utilizing two constituents, polyethylene (the 'gold standard' bearing material for total joint replacements) and hyaluronan (HA, a native component of articular cartilage), a hyaluronan-polyethylene graft copolymer (HA-co-HDPE) was developed. The novel HA- co-HDPE material was successfully synthesized using an interfacial polymerization reaction in a non-aqueous environment. Although the material has limited melt-processability, it is more processable than HA and was successfully compression molded into samples for physical, mechanical and in vitro biological characterization (e.g., swell ratio, dynamic mechanical analysis). HA-co-HDPE exploits the strength, rigidity and melt-processability associated with HDPE, and achieves increased osteogenic potential by incorporating the highly hydrophilic biopolymer HA. In conclusion, the swelling, mechanical and degradation properties of the copolymer can be custom-optimized for biomedical applications by tailoring chemical or physical crosslinking strategies and varying the amount and molecular weights of HA and HDPE incorporated into the copolymer.Item Embargo Development of bioinspired hyaluronan enhanced synthetic polymers for medical applications(Colorado State University. Libraries, 2023) Gangwish, Justin Phillip, author; James, Susan P., advisor; Bailey, Travis S., advisor; Dasi, Lakshmi Prasad, committee member; Popat, Ketul, committee member; Monnet, Eric, committee memberThe first transcatheter aortic valve replacement (TAVR) was performed in 2002, and over the past two decades has become as prevalent as surgical aortic valve replacements in America. TAVR's have significant potential to provide relief for patients with aortic valve disease, but due to their high cost remain accessible primarily in wealthy nations. Furthermore, TAVR's have limited lifespans and are radiotransparent so they can only be evaluated for function through echocardiography. Thus, an expensive medical implant with limited durability is only replaced after it has begun to fail and cause the patient further stress on their heart. To address these issues this dissertation reviews the research performed in generating a novel heart valve leaflet material that is radiopaque, made primarily out of linear low-density polyethylene (LLDPE), and incorporates the biological polymer hyaluronan (HA). These leaflets could significantly reduce the cost of TAVR's potentially allowing for global adoption of the technology. They are radiopaque and easily imaged using x-ray fluoroscopy allowing changes in leaflet shape or movement to be identified prior to when the echocardiography would have shown a deleterious effect to function. They incorporate HA which is found in the interior lumen of blood vessels and has been shown to decrease calcification and thrombosis, both of which have caused polymeric leaflets to fail in previous research. Finally, they can be easily shaped and reinforced allowing for a potentially far greater device lifespan. The leaflets are made by melt pressing in radiopaque powders of either tungsten or bismuth trioxide into sheets of LLDPE followed by treatment with HA to form an interpenetrating polymer network. The material properties of the leaflets were evaluated for their tensile mechanical properties, their hydrophilicity, their radio transparency (or lack thereof), and their hemodynamics. The biocompatibility of the leaflets was evaluated through a cytotoxicity assay, whole blood clotting on the surface of the material, and the ability for platelets to adhere and activate on the material surface. The results demonstrate the material has significant potential to function as a heart valve leaflet in a TAVR. Beyond evaluating this novel material, the process by which HA is incorporated into LLDPE was examined and optimized for commercial scale up. First, the need for solvent distillation and nitrogen blankets during treatment were determined to be unnecessary to produce an HA IPN with LLDPE. Then the rate at which the LLDPE is drawn from the HA solution as well as the vacuum pressure and temperature during this process was found to affect the amount of active HA at the surface of the material. Finally initial evidence was found that shows that HA IPN does not form through the bulk of the material, but rather in the first few microns of the LLDPE. Unrelated to TAVR's a study was performed to enhance the non-woven polypropylene used in surgical masks and N-95 masks against COVID-19 using HA and polyethylene glycol (PEG). HA was used to form a microcomposite on the surface of the non-woven polypropylene while PEG was grafted to the surface with oxygen plasma. The resulting materials were evaluated for their tensile mechanical properties, breathability, chemical composition, hydrophilicity, cytotoxicity, and ability to adsorb COVID-19 spike protein. The results indicate the material has notable potential to make masks more effective at preventing the transfer of COVID-19, however further studies using live SARS-CoV-2 virus beyond the capabilities of this laboratory are necessary before that potential can be fully confirmed.Item Open Access Effect of destabilized reactions using lithium amide (LiNH2) and doping using titanium based catalyst on the desorption characteristics of lithium aluminium hydride (LiAlH4)(Colorado State University. Libraries, 2012) Paravasthu, Siddharth, author; James, Susan P., advisor; Sampath, Walajabad S., committee member; Wu, Mingzhong, committee memberIn the past few decades there has been a tremendous increase in hydrogen storage research. Numerous materials and material systems have been studied as potential candidates for hydrogen storage, but unfortunately none of those materials demonstrate enough hydrogen releasing capacity under suitable temperature range to be used for hydrogen storage. Research promises to unlock the potential of these materials and ultimately lead to the commercialization of this technology. LiAlH4 is one of those materials that have been exclusively studied as a candidate for hydrogen storage due to its high theoretical hydrogen storage capacity, and its ability to release hydrogen in more than one step at different temperature ranges. Jun Lu and Zhigang Zak Fang studied the effects of titanium based catalyst (TiCl3.1/3AlCl3) and destabilization reactions using LiNH2 on LiAlH4, but did not demonstrate the effects of ball milling on the system. In the present work we have investigated the effects of ball milling, and the effects of destabilization reaction using LiNH2 on the hydrogen release characteristics of LiAlH4 doped with TiCl3. The current market scenario for fuel cell technology and the possibility and consequences of introducing the current system in the market has been briefly discussed. X-ray powder diffraction, thermo-gravimetric analysis and scanning electron microscopy were employed for the characterization of the samples. Both the compounds LiNH2, and TiCl3 worked in effecting the dehydrogenation kinetics of LiAlH4. The duration of ball milling required to affect the dehydrogenation kinetics of LiAlH4 using TiCl3 was optimized. A hydrogen release of 7.3 wt% was observed from the final system i.e. (LiAlH4/LiNH2 doped with 2% TiCl3) at temperatures below 4000C.Item Embargo Failure analysis and durability enhancement of polymeric heart valve leaflets(Colorado State University. Libraries, 2024) Khair, Nipa, author; James, Susan P., advisor; Bailey, Travis S., advisor; Li, Vivian, committee member; McGilvray, Kirk, committee memberRheumatic and calcified aortic heart valve disease is prevalent globally among all aged people, and the number is rapidly increasing. Clinically accepted, minimally invasive xenograft-based transcatheter aortic heart valve replacement (TAVR) shows limited durability (<10 years). Hyaluronic acid (HA) enhanced polyethylene polymeric TAVR shows excellent in vitro and in vivo anti-calcific, anti-thrombotic, and hydrodynamic performance, making it a suitable candidate for heart valve leaflets. The main problem, however, is during durability testing, cyclic impact loading causes premature failure in a consistent fashion related to TAVR assembly. This dissertation investigates leaflet premature failure mechanisms and provides two plausible solutions to upgrade heart valve durability without sacrificing performance. With regard to the failure mechanism, representative areas of retrieved failed leaflets are examined under electron microscopy and small angle x-ray scattering. The investigation finds abrasive wear, wear polishing, fine scratching, and imprints of the metal stent of the leaflet surface, indicating surface wearing from soft plastic rubbing against hard metal. A strong permanganate oxidizer etches away low-energy amorphous domain to unveil stable spherulitic structures of approximately 3 µm, bridging and tie molecular domains of pristine LLDPE. The oxidizer partially etches away polymeric buildups of failed leaflets only to reveal thinned-out and fractured spherulites beneath them, identifying the buildups as stress precursors. SAXS study reports local lamellar disruption further confirming the SEM results. Most. Notably, this is the first study that, to our knowledge, to directly image stable craze cross-tie microstructure that formed due to chain disentanglement from high amplitude cyclic stress. The SEM images validate previous theoretical and computational molecular dynamics models of cross-tie structure architecture. Therefore, leaflet premature failures are the compound effect of cyclic fatigue-initiated crazing and surface wear. Heart valve leaflet durability can be upgraded by controlling crazing and surface wearing. Both the crazing and surface wearing can be controlled by crosslinking of randomly folded amorphous chains. Because they are direct impacts of chain disentanglement under high amplitude cyclic stress. Crosslinked covalent bonds of polymer limit chain movements. LLDPE thin sheets are crosslinked at 50, 70, 100, and 150 kGy doses using 200 KeV (low energy) and 4 MeV (low energy) electron beams at room temperature in the air. Their effects are characterized by measuring gel content percentage, tensile testing, Differential Scanning Calorimetry (DSC), nanoindentation, and nano scratch test. Crosslinked LLDPE heart valve leaflet tested in in vitro flow loop and wear tester to determine valve performance and durability, respectively. Low energy electron beam (LEEB) forms 28% xylene insoluble gel whereas high energy electron beam (HEEB) forms 58 % gel at 100 kGy doses. LEEB does not affect mechanical properties, but HEEB significantly increases stiffness and yield strength. A slight reduction of melting temperature is found for LLDPE crosslinked by both of the energy sources. Nanomechanical tests show crosslinking improves hardness and coefficient of friction, an indication of improving surface wear resistance, which can explain durability improvement. Heart valve durability can also be improved by strengthening the leaflet with fiber reinforcement. A thin plastic sheet is assembled into a cylindrical form by welding two ends, which never fails. The weld at the commissure post is found to be mechanically stronger than the rest of the leaflet, which protected this region. Braided fibers are embedded on the leaflet regions of the commissure post perpendicular to the valve circumference, mimicking the weld but at a much higher strength. Leaflet durability skyrockets from a few million ISO 5840-2005 cycles to 73 million. The entire cardiac cycle of the heart valve with embedded fibers of varying angles, lengths, and numbers is simulated in Finite Element Analysis (FEA) to study their effects on leaflet maximum principal stress and leaflet opening dynamics. Horizontal fibers wrap the leaflet 360° to relax the leaflet completely during peak diastolic. However, the leaflet has a higher coaptation gap and delayed opening. The heart valve with embedded horizontal fibers is physically manufactured and tested in an in vitro flow loop and wear tester, which showed improved durability, but compromised hemodynamics. Finally, strategically crosslinked leaflet was simulated in FEA where leaflet regions of the commissure post and stent line are assigned with stiff crosslinked LLDPE material property, but the rest of the cusps undergo maximum bending are assigned with uncrosslinked LLDPE material property. Results show that strategically crosslinked leaflets open more easily than fully crosslinked leaflets. The final chapter discusses 3D shaped LLDPE leaflet bio enhancement process. Leaflets are 3D shaped in a vacuum thermoformer followed by the HA enhancement. Whole blood clotting resistance, platelet adhesion, activation, and cytotoxicity studies are conducted to determine at 10-4 µmol/mm2 ranged HA population density is required to achieve the best biocompatibility. Generally, water contact angle, Toluidine Blue O (TBO) elution assays, ATR-FTIR are used to determine overall HA presence on the leaflet. This study reports TBO staining and elution is the most effective and accurate measurement tool for determining HA population density. Fiber-reinforced LLDPE, and crosslinked LLDPE are HA-treated, and TBO staining predicts heavily populated HA surface density.Item Open Access Hyaluronic acid enhancement of expanded polytetrafluoroethylene for small diameter vascular grafts(Colorado State University. Libraries, 2014) Lewis, Nicole R., author; James, Susan P., advisor; Popat, Ketul C., committee member; Bailey, Travis, committee memberCardiovascular disease is the leading cause of mortality and morbidity in the United States and other developed countries. In the United States alone, 8 million people are diagnosed with peripheral arterial disease per year and over 250,000 patients have coronary bypass surgery each year. Autologous blood vessels are the standard graft used in small diameter (<6mm) arterial bypass procedures. Synthetic small diameter grafts have had limited success. While polyethylene (Dacron) and expanded polytetrafluoroethylene (ePTFE) are the most commonly used small diameter synthetic vascular graft materials, there are significant limitations that make these materials unfavorable for use in the low blood flow conditions of the small diameter arteries. Specifically, Dacron and ePTFE grafts display failure due to early thrombosis or late intimal hyperplasia. With the shortage of tissue donors and the limited supply of autologous blood vessels available, there is a need for a small diameter synthetic vascular graft alternative. The aim of this research is to create and characterize ePTFE grafts prepared with hyaluronic acid (HA), evaluate thrombogenic potential of ePTFE-HA grafts, and evaluate graft mechanical properties and coating durability. The results in this work indicate the successful production of ePTFE-HA materials using a solvent infiltration technique. Surface interactions with blood show increased platelet adhesion on HA-modified surfaces, though evidence may suggest less platelet activation and erythrocyte lysis. Significant changes in mechanical properties of HA-modified ePTFE materials were observed. Further investigation into solvent selection, uniformity of HA, endothelialization, and dynamic flow testing would be beneficial in the evaluation of these materials for use in small diameter vascular graft bypass procedures.Item Open Access Hydroxyapatite structures created by additive manufacturing with extruded photopolymer(Colorado State University. Libraries, 2019) López Ambrosio, Katherine Vanesa, author; James, Susan P., advisor; Ma, Kaka, committee member; Prawel, David A., committee memberBone tissue has the ability to regenerate and heal itself after fracture trauma. However, this ability can be affected by different risk factors that are related to the patient and the nature of the fracture. Some of the factors are age, gender, diet, health, and habits. Critical-sized defects are particularly difficult, if not impossible, to heal correctly. Particularly in large defects, bone regeneration ability is impeded, disrupting normal healing processes, resulting in defective healing, integration, and non-union. To prevent and treat defective healing or non-union, surgical intervention is needed. Surgeons implant various forms of devices between the ends of the broken bone, usually with external fixation. Implants function by guiding and enabling new bone ingrowth while giving support to the healing tissue. Some of the most common implants are autografts, allografts, and metallic endoprostheses. Unfortunately, these common techniques have drawbacks such as the risk of infection and relatively poor biological or mechanical compatibility with host tissue, in addition to the limited source of donor tissue and high cost, often resulting from secondary surgical interventions. Critical defects are particularly problematic. Hence, there is a necessity for bone implant substitutes that diminish the risk of infection and incompatibility while also providing similar mechanical properties to real bone tissue. Hydroxyapatite (HAp) is a ceramic with a chemical composition similar to bone tissue that has shown biocompatibility and osteoconductive properties with host bone tissue, but it is difficult to manufacture into complex structures with mechanical properties comparable to bone tissue. Therefore, significant efforts are directed to produce materials and methods that could produce HAp synthetic implants to treat bone defects. This research aimed to create and characterize a hydroxyapatite photo-polymeric resin suitable for 3D printing, which could produce dense HAp ceramic parts in complex shapes without requiring support material. We created a HAp-based photopolymer slurry that achieved 41 vol% HAp loading in homogenous slurries. The HAp slurries presented a strong shear thinning behavior and dispersion stability over 20 days under dark storage conditions. The resultant rheological behavior of HAp slurries enabled 3D printing of HAp green bodies in complex shapes using a combination of viscous extrusion and layer-wise photo-curing processes. Complex structures with concave and convex forms and scaffolds with interconnected pores ranging from 130 µm to 600 µm pore sizes and 10% to 40% porosity were successfully built with high resolution and no support material. Moreover, HAp/PEGDMA green bodies presented complete layer cohesion. After 3D printing, sintering was used to densify HAp structures and eliminate the polymer matrix. The resultant HAp structures maintained their complex details, had a relative density of ~78% compared to fully dense HAp and a dimensional shrinkage of ~15% compared to its green body. Sintered HAp structures were found to be non-cytotoxic for ADSCs cells. Flexural properties of HAp green and sintered structures were also determined. It was found that green bodies had a flexural strength of ~30.42MPa comparable to trabecular bone. To summarize, a photopolymerizable resin with 41 vol% of HAp was created to produce ~78% dense HAp complex structures. This was achieved by using additive manufacturing that combined viscous extrusion and layer-wise photo-curing and a sintering process. HAp/PEGDMA showed flexural strength comparable to the trabecular bone, and HAp sintered structures demonstrated non-cytotoxic behavior.Item Open Access Improving hydrophilicity of silicone elastomer by IPN formation with hyaluronan(Colorado State University. Libraries, 2016) Koch, Richard L., author; James, Susan P., advisor; Bailey, Travis, committee member; Popat, Ketul C., committee memberSoft contact lenses have been available to consumers for the past several decades. By far, the most popular form on the market today is the silicone hydrogel, with nearly 70% of the market share. However, many contact lens wearers still have issues which cause them to discontinue lens use. It is estimated that between 25-35% of people discontinue use permanently. This can be traced back to two main issues with modern hydrogel lenses: a lack of adequate oxygen permeability across the lens; and lens-induced dehydration of the cornea. The corneal epithelium lining the lens of the eye is an avascular environment. As such, the cells must get their oxygen by diffusion through the tear film, or any material covering the lens. The silicone hydrogel SCLs have reduced oxygen gas permeability compared to traditional silicone elastomers. Additionally, when the hydrogel lenses lose water to evaporation, they pull water from the wearer's eye, contributing to dryness. Beyond simple discomfort, these issues can lead to pathologies such as hyperemia and even corneal cell death in severe cases. It was determined that a solution to these issues would be a new ocular lens material which had superior oxygen gas permeability and was hydrophilic without containing water in its bulk. The aim of this research was to create an interpenetrating polymer network (IPN) materials of poly(dimethyl siloxane) (PDMS) and hyaluronan (HA) with such properties. The results in this work indicate the successful synthesis of these HA-PDMS IPN materials. These elastomeric materials had improved hydrophilicity compared to untreated PDMS. Additionally, new chemical species (ATR/FTIR and XPS spectroscopy) and surface morphologies (SEM imaging) indicated the introduction of HA into the PDMS. Furthermore, analysis of the oxygen gas permeability showed no significant change for the treated samples as compared to the PDMS base material. As silicone materials have use in many biomedical fields, the material was also tested for platelet adhesion/activation and whole blood clotting. However, studies showed unfavorable results as the treated samples still caused platelet activation and blood clotting. Additionally, overall optical transmittance of the treated materials was significantly decreased. Further refinement of the treatment methods may yield more favorable results in the areas of thrombogenicity and platelet adhesion.Item Open Access In vivo efficacy of antibiotic-eluting phospholipid coated implants(Colorado State University. Libraries, 2011) Triffo, Thomas, author; James, Susan P., advisor; Criswell, Marvin E., committee member; Ehrhart, Nicole P., committee memberImplant-associated infection can be a serious problem for patients that receive orthopedic implants, such as hip and knee replacements. This is a common cause for early implant loosening, which requires revision surgeries and results in an even greater risk of infection. To address this issue, our lab has developed a novel electrospraying technique for applying phospholipid coatings to orthopedic implants. These coatings consist of two layers of 1,2-dioleoyl-sn-glycero-3-phospho-L-serine (DOPS), with antibiotic loaded in between layers. In vitro tests were performed to evaluate how modifications to these coatings affect coating retention, based on a clinically relevant test, and antibiotic elution from these coatings. Coating retention tests were performed by inserting implants through segments of mouse bone and then examining the implants under SEM. Antibiotic elution was performed using a total sink elution combined with OPA assay for detection of antibiotic. These results showed that the coatings that were retained the most and eluted antibiotic slowest were samples that were pre-treated with calcium and were electrosprayed with a mixture of 6:1 DOPS-to-cholesterol. This coating was selected to be used in an in vivo study to determine the efficacy of the coatings in treating osteomyelitis. Osteomyelitis was induced in a murine model using genetically modified bacteria, which allowed tracking of the infection prior to sacrificing the animals via bioluminescent imaging, a technique that makes use of genetically modified bacteria producing luciferin and luciferase which causes emission of photons. It was observed that antibiotic-eluting implants cleared the infection faster than implants without antibiotic during a 4 week study. Also, no kidney damage was observed based on creatinine, blood urea nitrogen, and urine protein tests. Histology confirmed observations from the bioluminescent imaging. These results show that our antibiotic-eluting implant coatings were able to reduce infection in vivo without resulting in adverse effects. Bioluminescent imaging showed significant reduction of emission of photons, p < 0.05, in the antibiotic loaded group compared to the control samples. The results also suggest that the implants exhausted their supply of antibiotic at the end of the study, and in future studies a greater amount of antibiotic will be loaded onto the implants.Item Open Access Processing and properties of metal open-cell foams with periodic topology(Colorado State University. Libraries, 2018) Nivala, Peter Thompson, author; James, Susan P., advisor; Puttlitz, Christian M., committee member; Popat, Ketul, committee member; Heyliger, Paul R., committee memberMetal open-cell foams are competitively poised to meet the demands of next generation applications due to the ability to tailor their properties to achieve multifunctionality through material selection and control of the pore structure. The topological design of metal foams must consider many factors including pore size, shape, spatial distribution, and interconnectivity; however, the current manufacturing techniques limit the degree to which the tailored pore structures can be realized. In the current research, a novel manufacturing approach to tailoring the pore structure of metal open-cell foams has been conceptually demonstrated based on a structured assembly of porogens. A process integrating space-holder replication and spark plasma sintering (SPS) was developed to fabricate metal open-cell foams exhibiting increased control over the pore size, shape, and position. The pore structure consisted of spherical copper porogens arranged into a hexagonal close-packed pattern. This sacrificial template was co-sintered with nickel-titanium (NiTi) powder using SPS and subsequently leached using nitric acid. The resultant NiTi open-cell foams were characterized for their spatial and mechanical properties, which exhibit uniform, well-replicated pore structures with a high-degree of interconnectivity. During compression testing the open-cell foams displayed unexpected brittle behavior, which was traced to the initiation and inter-particulate propagation of cracks through the NiTi matrix leading to sudden specimen failure. Additionally, the Master Sintering Curve (MSC) concept was utilized to investigate the effect of copper porogens on the densification behavior of NiTi during the fabrication of open-cell foams. Typically, the MSC is used to determine the apparent activation energy (QMSC) for sintering densification of powder materials and to predict the final specimen density under arbitrary time-temperature sintering profiles. The MSC predicted the areal matrix density of the NiTi open-cell foams to within 1.2%. Comparisons of the densification behavior between NiTi and NiTi with copper specimens suggests the porogens have little to no effect on the densification behavior of NiTi powders within the current experimental setup. The manufacturing approach demonstrated within the current research will be extended to leverage advanced manufacturing techniques, such as additive manufacturing, to realize optimum pore structures for multifunctional applications to enable the next generation of open-cell foams exhibiting higher performance at lower cost and less weight.Item Open Access Synthesis and characterization of lithium-ion cathode materials in the system (1-x-y) LiNi0.8Co0.15Al0.05O2.xLi2MnO3.yLiCoO2(Colorado State University. Libraries, 2013) Yerramilli, Anish, author; James, Susan P., advisor; Prieto, Amy, committee member; Wu, Mingzhong, committee memberEnergy storage technology has been dominated by lithium ion batteries, which are considered the most promising with higher energy density compared to any other battery technologies. The market for lithium ion batteries has increased rapidly from 2007. Goals set by the U.S Department of Energy for hybrid electric vehicles have not been met by any of the existing cathode materials. The objective of this thesis was to find a material composition that has better cyclability and lower cost than the standard battery materials. A ternary composition with low cost materials like Al, Mn and Ni were used instead of high amounts of Co to reduce the cost of the battery. It was hypothesized that there are cathode compositions in the system (1-x-y) LiNi0.8Co0.15Al0.05O2.xLi2MnO3.yLiCoO2 that when tested for discharge capacities and cyclability will show better properties than the current generation lithium ion cathode materials. The system (1-x-y) LiNi0.8Co0.15Al0.05O2.xLi2MnO3.yLiCoO2 is synthesized using a simple sol-gel synthesis. The materials LiNi0.8Co0.15Al0.05O2, Li2MnO3 and LiCoO2 were used as end points in a ternary composition diagram. Twenty eight cathode compositions spanning the entire ternary composition diagram were synthesized under the same conditions and characterized using X-ray diffraction (XRD) and an Arbin BT2000 battery testing system. XRD results showed α-NaFeO2 structure with a space group of R3m. The results from electrochemical testing revealed a wide range of electrochemical capacities and cyclabilities. The regions close to Li2MnO3 showed high capacities and cyclability. The material with composition Li1.5 Ni0.133Co0.358Al0.008Mn0.5 had an initial discharge capacity of 216.3 mAh/g and retained this capacity even after multiple cycles in the voltage range of 4.6-2 V at a rate of C/15. Statistical analysis was done using SAS/STAT 9.2 with the ADX procedure to fit a general linear model with three linear terms and three two way interactions to map capacities and cyclabilities. This analysis was used to choose the compositions with best capacities and cyclability. Inductively couple plasma (ICP) analysis was carried out on the chosen samples to find the error between calculated composition and the theoretical composition. XPS (X-ray photoelectron spectroscopy) was conducted for the chosen samples and the oxidation states of the elements were determined. The material with composition Li1.5 Ni0.133Co0.358Al0.008Mn0.5 was found to be the promising material for commercialization. Before going into the market additional changes like synthesis conditions and surface treatments should be conducted on the material.Item Open Access Synthesis and characterization of lithium-ion cathode materials in the system (1-x-y)LiNi1/3Mn1/3Co1/3O2 ∙ xLi2MnO3 ∙ yLiCoO2(Colorado State University. Libraries, 2012) Paravasthu, Rushendra, author; James, Susan P., advisor; Prieto, Amy, committee member; Wu, Mingzhong, committee memberConsidering various technologies for storing energy the usage of lithium (Li) - ion batteries still stands as one of the most promising options, especially for the on-going huge demand for electric and plug-in hybrid vehicles. The main limiting factor in the performance of a Li-ion battery is the cathode material. The current cathode material that is being used in the present market is LiCoO2 cathode which is effective but is expensive and toxic. The objective of this thesis is to find a cathode material which is advantageous and a probable replacement for LiCoO2. Based on the previously studied work on ternary solid solutions and its advantages, this system (1-x-y)LiNi1/3Mn1/3Co1/3O2•xLi2MnO3•yLiCoO2 was chosen. This was made using a ternary composition diagram which is a combination of LiNi1/3Mn1/3Co1/3O2, Li2MnO3 and LiCoO2 materials. Points inside the ternary diagram were chosen in an arrangement conducive to mathematical modeling and compositions of the cathodes were processed accordingly. All the 28 samples in the system were synthesized using the sol-gel method, each sample was characterized using X-ray diffraction (XRD) scans and electrochemical testing was performed by using an Arbin BT2000 battery testing system with MITS Pro Arbin software. The XRD results showed that all the samples established a α-NaFeO2 structure and a space group of R3m with varying degrees of purity in the crystal structure. The compounds in this system showed fairly consistent charge/ discharge curves during the electrochemical testing with initial discharge capacities varying from 122mAh/g to 240mAh/g and high capacity compositions were found in the region of high Li2MnO3 content. The highest capacity found was Li1.222Mn0.5Ni.056Co0.222O2 composition with a discharge capacity of 242mAh/gin the voltage range 4.6 - 2V at a C/15 rate. A statistical based analysis was carried out using JMP version 7.0.1 with the design of experiments (DOE) procedure for a mixture design to find variations in capacity and cyclability trends over the composition triangle. Inductively couple plasma (ICP) analysis was carried out on 4 samples which were found to be most promising basing on the statistical analysis. ICP results confirmed the formation of optimum compositions for the specified synthesis conditions. All these 4 samples were synthesized and tested again to confirm consistent performance across repeat samples. XPS (X-ray photoelectron spectroscopy) was conducted for these samples to determine the chemical environment of transition metals. The composition with the highest capacity was found to be Li1.222Mn0.5Ni0.056Co0.222O2 electrode. Its high capacity is attributed to the Ni+2/Ni+4 and Co+3/Co+4 red-ox couple and the Li-ion extraction form Li2MnO3 at a voltage >4.5V which results in an extended discharge profile. This cathode composition is very promising because it shows high capacity and good cyclability, and would be much cheaper than conventional LiCoO2 cathodes since it has more manganese which is less expensive than cobalt.