UCLA

Biodegradable metals have emerged as a promising class of materials for medical implants, particularly in cardiovascular applications where the long-term presence of foreign materials can lead to complications such as chronic inflammation and restenosis. Among these materials, zinc (Zn) has garnered significant attention due to its optimal corrosion rate and excellent biocompatibility. However, Zn's inherent mechanical limitations, including low strength and long-term instability, have hindered its application in load-bearing biomedical devices. This dissertation explores the use of nanoparticles to enhance the mechanical performance and long-term stability of Zn alloys for biomedical applications, with a particular focus on biodegradable stent materials.

To address Zn’s limitations, this research systematically develops and characterizes Zn-matrix nanocomposites incorporating various nanoparticles, including TiC, TiB₂, and Fe-Si intermetallic phases. These nanocomposite systems were designed to achieve small nanoparticle size and uniform nanoparticle dispersion, thereby improving tensile properties, fatigue resistance, and microstructural stability while maintaining biocompatibility. A combination of experimental techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD), and mechanical testing, was used to evaluate the effects of nanoparticle incorporation on Zn alloys. The results demonstrate that nanoparticles significantly refine Zn’s microstructure, inhibit grain growth, and enhance mechanical properties through multiple strengthening mechanisms, while preserving Zn’s favorable biodegradability and superior biocompatibility.

Furthermore, this study systematically investigates the long-term stability of Zn nanocomposites under physiological conditions, emphasizing the role of nanoparticles in mitigating material instability, particularly in fatigue performance. The results demonstrate that nanoparticle incorporation significantly enhances fatigue resistance across various temperatures. Microstructural analyses reveal key mechanisms underlying this improvement, including crack deflection by nanoparticles and a more uniform distribution of localized stress. Additionally, calculations based on Basquin’s Equation indicate that nanoparticles not only enhance fatigue resistance but also reduce the temperature sensitivity of Zn materials. Unlike conventional Zn alloys, which experience pronounced fatigue deterioration at elevated temperatures, Zn nanocomposites exhibit greater resistance to thermal effects with increasing nanoparticle content. Moreover, microstructural evolution and material aging behavior were examined to assess the long-term stability of Zn-based materials. The findings highlight that nanoparticle-stabilized Zn alloys demonstrate superior fatigue resistance, reduced aging effects, and enhanced microstructural stability compared to conventional Zn alloys, making them promising candidates for biomedical applications.

Beyond material development, this dissertation presents a comprehensive approach to biodegradable stent design, encompassing pattern optimization, manufacturing, and in vivo validation. Optimized Zn nanocomposite stents were fabricated and evaluated in preclinical models to assess their mechanical integrity, degradation profile, and biocompatibility. The findings support the feasibility of Zn-based nanocomposites as next-generation biodegradable stent materials.

This work provides a fundamental understanding of how nanoparticles influence the mechanical and degradation properties of Zn alloys, paving the way for their broader application in biomedical devices. The insights gained from this research contribute to the advancement of biodegradable metals and have the potential to significantly impact the future of cardiovascular stent technology and other medical implant applications.