Theses and Dissertations
Permanent URI for this collection
Browse
Browsing Theses and Dissertations by Author "James, Susan P., advisor"
Now showing 1 - 2 of 2
Results Per Page
Sort Options
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 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.