Matching Items (4)
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- All Subjects: Biomedical Engineering
- All Subjects: Soft matter
Description
Sensitivity is a fundamental challenge for in vivo molecular magnetic resonance imaging (MRI). Here, I improve the sensitivity of metal nanoparticle contrast agents by strategically incorporating pure and doped metal oxides in the nanoparticle core, forming a soluble, monodisperse, contrast agent with adjustable T2 or T1 relaxivity (r2 or r1). I first developed a simplified technique to incorporate iron oxides in apoferritin to form "magnetoferritin" for nM-level detection with T2- and T2* weighting. I then explored whether the crystal could be chemically modified to form a particle with high r1. I first adsorbed Mn2+ ions to metal binding sites in the apoferritin pores. The strategic placement of metal ions near sites of water exchange and within the crystal oxide enhance r1, suggesting a mechanism for increasing relaxivity in porous nanoparticle agents. However, the Mn2+ addition was only possible when the particle was simultaneously filled with an iron oxide, resulting in a particle with a high r1 but also a high r2 and making them undetectable with conventional T1-weighting techniques. To solve this problem and decrease the particle r2 for more sensitive detection, I chemically doped the nanoparticles with tungsten to form a disordered W-Fe oxide composite in the apoferritin core. This configuration formed a particle with a r1 of 4,870mM-1s-1 and r2 of 9,076mM-1s-1. These relaxivities allowed the detection of concentrations ranging from 20nM - 400nM in vivo, both passively injected and targeted to the kidney glomerulus. I further developed an MRI acquisition technique to distinguish particles based on r2/r1, and show that three nanoparticles of similar size can be distinguished in vitro and in vivo with MRI. This work forms the basis for a new, highly flexible inorganic approach to design nanoparticle contrast agents for molecular MRI.
ContributorsClavijo Jordan, Maria Veronica (Author) / Bennett, Kevin M (Thesis advisor) / Kodibagkar, Vikram (Committee member) / Sherry, A Dean (Committee member) / Wang, Xiao (Committee member) / Yarger, Jeffery (Committee member) / Arizona State University (Publisher)
Created2012
Characterization of a Lipid Coating on the Surface of Silk Produced by the Embiid Antipaluria urichi
Description
Insects of the order Embiidina spin sheets of very thin silk fibers from their forelimbs to build silken shelters on bark and in leaf litter in tropical climates. Their shelters are very stiff and hydrophobic to keep out predators and rain. In this study, the existence of an outer lipid coating on silk produced by the embiid Antipaluria urichi is shown using scanning and transmission electron microscopy, FT-IR, and water drop contact angle analysis. Subsequently, the composition of the lipid layer is then characterized by 1H NMR and GC-MS.
ContributorsOsborn Popp, Thomas Michael (Author) / Yarger, Jeffery (Thesis director) / Holland, Gregory (Committee member) / Barrett, The Honors College (Contributor) / Department of Chemistry and Biochemistry (Contributor)
Created2014-05
Description
The egg cases of spiders are commonly multilayered, complex structures that contain several silk fibers. This study uses optical and polarized microscopy, scanning electron microscopy, and infrared spectroscopy to compare the morphology and secondary protein structure of egg case silk of two orb-web spider species (A. aurantia and A. trifascita), two cobweb species (L. hesperus and L. geometricus), and one nursery web species (D. okefinokensis). A common feature of all six spiders' egg cases was a more dense and rigid outer layer, which was typically comprised of both tubiliform and aciniform silk fibers, along with a less dense inner layer of pure tubiliform silk. Infrared spectroscopy revealed that tubiliform silk from all egg cases contain a significant proportion (30-50%) of beta-sheet nanocrystalline aligned regions that are embedded in an amorphous random coil matrix, which does not change appreciably with hydration. While the native as-spun aciniform silk fibers primarily incorporated into the outer shell layer of egg cases are observed to be dominated by alpha-helical and random coil secondary structures, where the alpha-helical component undergoes a partial hydration-induced conversion to beta-sheet. Akin to egg case silk’s biochemical structure, its potential uses encompass a wide variety of industries, especially medicine. Synthetic materials have served in roles where silk often caters best to with its high mechanical/chemical robustness and biocompatability while also ushering in novel treatment avenues. An arachnid-based film hybridized with a photothermal converter nanoparticle such as copper salt or silver nanoprisms, which serve to weld the suture to the dermal tissue, is a promising strategy in the goal of ever improving patient outcomes.These two studies in parallel, one of a fundamental focus and one of an applied outlook, seek to understand and exploit the properties of spider silk in order to advance our knowledge of this amazing material and harness its potential for a wide range of practical applications.
ContributorsDeCambra, Weston (Author) / Yarger, Jeffery (Thesis advisor) / Rege, Kaushal (Committee member) / Birkel, Christina (Committee member) / Arizona State University (Publisher)
Created2024
Description
In disordered soft matter system, amorphous and crystalline components might be coexisted. The interaction between the two distinct structures and the correlation within the crystalline components are crucial to the macroscopic property of the such material. The spider dragline silk biopolymer, is one of such soft matter material that exhibits exceptional mechanical strength though its mass density is considerably small compare to structural metal. Through wide-angle X-ray scattering (WAXS), the research community learned that the silk fiber is mainly composed of amorphous backbone and $\beta$-sheet nano-crystals. However, the morphology of the crystalline system within the fiber is still not clear. Therefore, a combination of small-angle X-ray scattering experiments and stochastic simulation is designed here to reveal the nano-crystalline ordering in spider silk biopolymer. In addition, several density functional theory (DFT) calculations were performed to help understanding the interaction between amorphous backbone and the crystalline $\beta$-sheets.
By taking advantage of the prior information obtained from WAXS, a rather crude nano-crystalline model was initialized for further numerical reconstruction. Using Markov-Chain stochastic method, a hundreds of nanometer size $\beta$-sheet distribution model was reconstructed from experimental SAXS data, including silk fiber sampled from \textit{Latrodectus hesperus}, \textit{Nephila clavipes}, \textit{Argiope aurantia} and \textit{Araneus gemmoides}. The reconstruction method was implemented using MATLAB and C++ programming language and can be extended to study a broad range of disordered material systems.
By taking advantage of the prior information obtained from WAXS, a rather crude nano-crystalline model was initialized for further numerical reconstruction. Using Markov-Chain stochastic method, a hundreds of nanometer size $\beta$-sheet distribution model was reconstructed from experimental SAXS data, including silk fiber sampled from \textit{Latrodectus hesperus}, \textit{Nephila clavipes}, \textit{Argiope aurantia} and \textit{Araneus gemmoides}. The reconstruction method was implemented using MATLAB and C++ programming language and can be extended to study a broad range of disordered material systems.
ContributorsMou, Qiushi (Author) / Yarger, Jeffery (Thesis advisor) / Benmore, Chris (Committee member) / Holland, Gregory (Committee member) / Ros, Robert (Committee member) / Arizona State University (Publisher)
Created2015