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Table 1 The different assays used in studies of MSU crystallization. These criteria were used to categorize each article into one or more of the main MSU crystallization steps

From: Factors influencing the crystallization of monosodium urate: a systematic literature review

Crystallization category Assay
Solubility Two different methods were used to measure the solubility of MSU in vitro. The first method involved changing the conditions of the solvent, or adding specific factors to the solvent and then measuring the change in urate concentration. The second method measured the maintenance of MSU in crystalline form whereby one or more synthesized MSU crystals (seed crystals) were added to the solvent and the dissolution of these crystals was measured. The solvents used for both types of assays were usually solutions of sodium urate or water.
Nucleation Nucleation assays were typically done in supersaturated sodium urate solutions. Various factors were added to the system and endpoints included whether new crystals formed in the presence of the given factor or change in condition, the time taken to form new crystals, and measurement of the total weight of crystals formed at the end of the experiment. Any studies that used MSU seed crystals in the assay for measuring crystal weight were assigned to this category.
Crystal growth Crystal growth assays involved exposing one or more MSU seed crystals to a solution of sodium urate and measuring the rate of growth of the seed crystals over time and/or the change in length of the crystals. Changes in crystal morphology in the presence of a given factor were typically examined using microscopy.