Structure and Properties in Synthetic MSUM and the Corresponding Biomaterial
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Structure and Properties in Synthetic MSUM and the Corresponding Biomaterial Alicia B. Brune1, Gregory P. Holland2, Jeffery L. Yarger1, William T. Petuskey1 1. School of Molecular Sciences, Arizona State University, Tempe, AZ, United States. 2. Department of Chemistry and Biochemistry, San Diego State University, San Diego, CA, United States. ABSTRACT At the MRS Fall 2014 Meeting, Symposium E, we reported on morphologies, fragmentation, and hardness in synthetic hydrogen urate monohydrate (monosodium urate monohydrate, MSUM, or MSU) crystals. We are now presenting further characterization results, including some from the biomaterial that forms in humans with gout disease: The fanning of radiating blades (needles) in spherulitic grains of synthetic MSUM was examined by microscopy techniques. These and previous data are consistent with an interpretation in terms of the crystallographic parameters in the unit cell, and the presence of dislocation arrays at low angle boundaries. The kinetics of such branched growth is here related to thermodynamic properties and super-saturation levels. Secondary nucleation is an additional mechanism leading to more complex morphologies. Differences in overall growth rates, under conditions of either branched or single needle growth, are considered in relation to gout. Novel powder XRD and solid state NMR data show, respectively, preferred orientation in the biomaterial, and the potential of NMR for identifying and characterizing MSUM in specific environments, helping to resolve pending questions in gout. Present results are anticipated to be useful for designing bio-inspired and biomimetic materials, regarding morphologies, overall growth rates, and mechanical properties. INTRODUCTION MSUM crystals accumulate in humans with gout disease. Anisotropic growth, with both single needle and spherulitic-type shapes, is known to occur in the synthetic and the biomaterial [1 - 3]. In the former, we earlier reported and interpreted growth morphologies, fragmentation, and mechanical properties [4]: Branching of the crystals, producing spherulitic morphologies, was illustrated by several microscopy methods, and it was proposed that branching was accommodated by dislocation arrays, as seen in twinning. Because crystals can accumulate faster when branched shapes develop, the conditions and mechanisms of branched growth are central to gout studies. Furthermore, dislocations can alter mechanical properties and fragmentation. Super-saturation is a salient factor among those affecting MSUM crystallization [5]; super-saturation levels have not been explicitly correlated with branching, but synthetic spherulites reportedly formed at lower cooling temperatures than needles [1, 2]. In gout, supersaturation may be promoted by local conditions and peculiar tissue structures; additional factors can favor bio-crystallization, such as the presence of strained tissue acting as a template for nucleation [3], and stresses developed under spatial constraints. Laboratory studies on the kinetics of MSUM crystallizatio
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