Browsing by Subject "Defects"
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Item Open Access Tensile Fatigue Characterization of High Strength Hydrogels for Soft Tissue Applications(2021) Koshut, William JosephSynthetic cartilage implants have the potential to deeply transform the treatment of articular cartilage degeneration as well as the progression of osteoarthritis in load-bearing applications of various joints in the human body. To reduce patient morbidity and enhance range of motion, surgeons and material scientists alike are looking to synthetic alternatives re-establish articular cartilage function without introducing higher cost and health burdens. These implants are rigorously tested for their compressive and wear properties over longer timeframes, with the first instance of approved human use coming in the 1st metatarsophalangeal (MTP) joint with poly(vinyl alcohol) (PVA) being the predominant polymer in composition. Despite their promise of dissipating stress and providing smooth joint movement, these synthetic cartilage implants are not well-studied for their tensile fatigue properties which are extremely critical to in vivo performance and implant survival. As a synthetic substitute to match the properties of cartilage in human beings, hydrogels are extensively researched due to their potential biocompatibility. This research describes work dedicated to the advanced mechanical study of synthetic hydrogel systems for cartilage-based applications. The materials of interest are designed to have enhanced monotonic tensile properties for supplementary investigation via tensile fatigue testing. Superior mechanical behavior was achieved through the use of bio-friendly additives, freezing-thawing cyclic processing, and fiber reinforcement. Lastly, the long-term failure mechanisms through flaw development for these synthetic hydrogel systems and biological tissue will be explored.
Item Open Access The Roles of Capping Agents and Defects in the Anisotropic Growth of Ag Nanocrystals(2023) Xu, HengSynthetic control of metal nanocrystal shape is a common strategy to control their properties. Shape control is often achieved by controlling the crystal structure of the seed crystals, as well as through the use of additives which are thought to block atomic addition to certain facets. However, the effect of crystal structure or additives on the rate of atomic addition to a specific facet is not usually quantified, making it difficult to design nanocrystal syntheses. This work combines seed-mediated growth, single-crystal electrochemistry measurements and Raman spectroscopy to understand the roles of capping agents and planar defects in the anisotropic growth of silver nanocrystals. The roles of citrate, polyvinylpyrrolidone (PVP), and halides have been investigated. Synthetic results show citrate is a {111} capping agent, PVP is a weak {111} capping agent, chloride and bromide are weak {100} capping agents. However, when chloride or bromide is added with PVP, they become strong {100} capping agents. Electrochemical measurements show the anisotropic growth is caused by capping agents selectively suppressing the oxidation of ascorbic acid (a reducing agent) on a specific crystal facet. The effect of capping agents on silver ion reduction is not facet-selective. Further comparison between the growth of single-crystal seeds and seeds with planar defects indicates defects can catalyze silver atom deposition by up to 100 times and cause greater anisotropic growth than can be explained by facet-selective passivation. Overall this work advances our understanding of nanocrystal chemistry, and informs the design of nanocrystal synthesis to obtain a desired nanocrystal morphology with a desired set of properties.