Monosodium urate monohydrate crystallization

The crystallization of monosodium urate monohydrate (MSU) in the synovial fluid has long been associated with the joint disease gout, which is characterized by recurring attacks of pain and inflammation within the joints. In this work, in situ atomic force microscopy (AFM) on single crystal (010) MSU surfaces and dynamic light scattering were used complementarily to investigate the growth of MSU in 2–10 mM urate solutions under model physiological conditions (37 °C, pH = 7.4, 150 mM NaCl). In this solution regime, crystal growth rates normal to the (010) surface followed the square of supersaturation, which is consistent with a two-dimensional island nucleation and spread mechanism. Islands observed under in situ AFM imaging conditions had sizes consistent with dynamic light scattering measurements but exhibited unique faceting not typically observed in fully developed crystals or predicted by previous theoretical work. Preferred alignment of the islands' long axis and the underlying ±c axis of the MSU (010) was observed, as was island overgrowth over time.