Growth Morphologies, Fragmentation Patterns, and Hardness in Sodium Hydrogen Urate Monohydrate
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Growth Morphologies, Fragmentation Patterns, and Hardness in Sodium Hydrogen Urate Monohydrate A. B. Brune and W.T. Petuskey Department of Chemistry and Biochemistry, Arizona State University, PO Box 871604, Tempe, AZ, USA ABSTRACT Mechanical properties and new morphological data on synthetic sodium hydrogen urate monohydrate are reported and interpreted. Crystals formed in supersaturated aqueous solutions were identified by powder x-ray diffraction. Intact grains and separate needles were examined by several microscopy techniques, some reported here for the first time. The dominant morphology was spherulite-type, comprising tapered, branched blades (needles) radiating out of a common core. The pointed blade tips were truncated by (011) planes, corresponding to hydrogen-bonded planes. Branching was at about a 5° angle or its multiples, suggesting it accommodated by dislocation arrays at the low angle boundaries, as is often seen in twinning. Vicker’s microhardness, extrapolated to zero porosity, was 0.90 GPa, which is greater than the hardness measured by nano-indentation. Present results are anticipated to be useful in interpreting the mechanical characteristics of the material crystallized in vivo and its action concerning gout, and affording inferences on the role of the milieu on morphologies, fragmentation, and hardness. INTRODUCTION Inflammatory crystals of NaC5H3N4O3.H2O, commonly named sodium hydrogen urate monohydrate or monosodium urate monohydrate, and abbreviated MSUM or MSU, accumulate in humans with gout disease. According to published work, MSUM crystal structure was solved on a triclinic unit cell [1]. The habit is needle (blade) shaped, fastest growing along [001] and comprising blunt or sharp tips [2]. Oftentimes the crystallites grow from a central nucleation core as a spherulitic mass of many blades; blades and spherulites have been found in vivo and in vitro [3-5]. Bulk crystallization in solution is controlled by surface nucleation. On a single crystal, two dimensional islands nucleate and subsequently spread [6]. In mimicking MSUM crystallization in vivo, albumin acts as a nucleating agent, explained by interactions between carboxylate groups and sodium ions [7]. No information is found in the literature on mechanical properties and fragmentation in synthetic MSUM, or the corresponding biomaterial. With the present work we aim at complementing the available data set on synthetic MSUM, by reporting new morphological data, fragmentation patterns, and mechanical properties. We prepared crystalline MSUM following published procedures [6] and identified it by powder x-ray diffraction (XRD). Morphologies were examined by several microscopy techniques. Mechanical properties were measured by micro-indentation and nano-indentation. Results from this work will permit to assess MSUM capability in inflicting tissue damage, and provide the basis for comparisons with the biomaterial, yielding insights on the role of the biological environment on MSUM morphologies, fragmentation, and mechanical properties.
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