Theses and Dissertations

Permanent URI for this collectionhttps://hdl.handle.net/10217/197901

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Open Access
Advanced nanostructured materials for enhancing bioactivity
(Colorado State University. Libraries, 2024) Bhattacharjee, Abhishek, author; Popat, Ketul C., advisor; Sampath, Walajabad, committee member; Herrera-Alonso, Margarita, committee member; Wang, Zhijie, committee member
Health hazards such as pathogenic infection, communicable diseases, and bone damage and injuries cause enormous human suffering and pain worldwide. Biomaterials such as orthopedic implants and biosensors are crucial tools to remedy these complications. Development of novel biomaterials and modifying existing materials can help enhance medical device efficacy. One of the key aspects of improving biomaterials is the utilization of nanotechnology. Nanoscale surface features can improve the interaction between materials and biological agents, thus improving their bioactivity. In this dissertation research, two different biomaterials were used for two distinct applications. Firstly, titanium, a common material for orthopedic implants, was used. Ti is a popular implant material because of its superior corrosion resistance, lightweight, and excellent biocompatibility. However, 10% of Ti implants fail each year due to pathogenic bacterial infection and poor osseointegration resulting in revision surgeries and immense suffering of the patients. Nanostructured surface modification approaches can potentially reduce the failure rate of Ti implants. In this study, TiO2 nanotube arrays (NT) were fabricated followed by zinc (Zn) and strontium (Sr) doping. These elements provide important signals to mesenchymal stem cells to differentiate into osteoblasts which helps in bone healing. Zn also reduces bacterial adhesion to the implant surface. Results showed that the modified surfaces could significantly reduce bacterial adhesion and improved osseointegration properties of the mesenchymal stem cells. Secondly, a polydiacetylene (PDA)-based electrospun nanofiber biosensor was prepared that is flexible in nature for monitoring bacterial or viral infection. The nanofiber biosensor could selectively detect Gram-negative bacteria via a vivid blue-to-red color transition. Since the color transition is visible to the naked eye, the biosensor offers immense potential to be used as a screening device for Gram-negative bacterial infection in various industries such as food packaging, medical, intelligence, and national security. During the COVID-19 pandemic, the PDA biosensing platform was utilized to detect the spike (S) protein of the SARS-CoV-2. For this, the surface chemistry of the PDA fibers was modified, and a receptor protein was conjugated at the end of the PDA polymer chain. When the modified PDA fibers were incubated with the S protein, the blue-to-red color transition happened, thus sensing the presence of S protein in the environment. This result indicated that PDA nanofiber biosensor is a flexible sensing platform for effectively detecting both bacteria and viruses. The two biomaterials investigated in this research indicated that the use of nanotechnology can help in enhancing their bioactivity.
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Degradation and nano-scale structural evolution of geopolymers: effect of temperature, stress and mine process solutions
(Colorado State University. Libraries, 2025) Piyathilake, S. A. K. V. M., author; Bareither, Christopher, advisor; Shackelford, Charles D., committee member; Yourdkhani, Mostafa, committee member; Herrera-Alonso, Margarita, committee member
Waste containment barrier systems commonly employ geosynthetics to protect human health and the environment against contaminant release. An example of a robust, composite liner system used to contain mine waste includes a textured polyethylene geomembrane (PE GMX) and a geosynthetic clay liner with two layers of polypropylene geotextiles (PP GCL). A key challenge in barrier system design is forecasting long-term performance of geosynthetic materials in various waste containment applications. A design objective in engineering practice is to predict material stability and lifespan of geomaterials used in waste containment infrastructure. With that objective in mind, this research focused on understanding the degradation mechanisms of polymers used in GMXs and GCLs (i.e., polyethylene and polypropylene), with particular emphasis on micro- and nano-scale changes to chemical and mechanical properties. A preliminary study was conducted to characterize oxidation behavior of geopolymers at room temperature. The analysis confirmed the formation of free radicals and oxidation degradation in the geopolymers. Subsequent studies on the same materials were conducted using in situ small/wide angle X-ray scattering (SAXS/WAXS) experiments with simultaneous tensile tests at elevated temperatures. These novel experiments revealed that chemical and mechanical treatments led to the degradation of the geopolymer, causing it to transition into a more crystalline state and lose its original elasticity. This understanding is vital for the effective use of geopolymers in applications like waste containment. Accelerated exposure experiments were conducted on samples of PE GMXs and PP GCLs in three different solutions (i.e., de-ionized water, bauxite mine process solution, and copper mine process solution) and at three temperatures (i.e., 20 °C, 50 °C, and 80 °C). Differential scanning calorimetry (DSC) and tensile tests were conducted on geopolymers at different durations of exposure up to 300 d. The study found that PE GMX and PP GCL degrade differently under various pH environments and temperature gradients. The degradation is influenced by factors such as the type of polymer, temperature, specific transition metals present, their concentration, and the conditions of the liquid medium. A model to predict the lifetime was developed, and the activation energies for the high and low exposure solutions were extracted.
Open Access
Development of surface modifications on titanium for biomedical applications
(Colorado State University. Libraries, 2021) Maia Sabino, Roberta, author; Popat, Ketul C., advisor; Martins, Alessandro F, advisor; Herrera-Alonso, Margarita, committee member; Li, Yan Vivian, committee member; Wang, Zhijie, committee member
For decades, titanium-based implants have been largely employed for different medical applications due to their excellent mechanical properties, corrosion resistance, and remarkable biocompatibility with many body tissues. However, even titanium-based materials can cause adverse effects which ultimately lead to implant failure and a need for revision surgeries. The major causes for implant failure are thrombus formation, bacterial infection, and poor osseointegration. Therefore, it is essential to develop multifunctional surfaces that can prevent clot formation and microbial infections, as well as better integrate into the body tissue. To address these challenges, two different surface modifications on titanium were investigated in this dissertation. The first one was the fabrication of superhemophobic titania nanotube (NT) surfaces. The second approach was the development of tanfloc-based polyelectrolyte multilayers (PEMs) on NT. The hemocompatibility and the ability of these surfaces to promote cell growth and to prevent bacterial infection were investigated. The results indicate that both surface modifications on titanium enhance blood compatibility, and that tanfloc-based PEMs on NT improve cell proliferation and differentiation, and antibacterial properties, thus being a promising approach for designing biomedical devices.

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Browsing Theses and Dissertations by Author "Herrera-Alonso, Margarita, committee member"