Factors determining types and morphologies of calcium oxalate crystals: molar concentrations, buffering, pH, stirring...

Calcium oxalate (CaOx) can be crystallized in several forms and morphologies. We evaluated factors that determine differential types and shapes of CaOx crystals generated in vitro.

CaCl2 and Na2C2O4 solutions at various molar concentrations were mixed in different conditions (with or without Tris-HCl buffer and varying pH, temperature and speed of stirring) and incubated overnight.

A total of 78 conditions were evaluated. The most frequently observed type of CaOx crystals was calcium oxalate monohydrate (COM). In 18.2 MOmega.cm water, typical monoclinic prismatic form of COM was found when 0.5-1 mmol/l CaCl2 and 0.5-1 mmol/l Na2C2O4 were mixed, whereas the COM dendrites were found when higher concentrations were used. Calcium oxalate dihydrate (COD) crystals were observed when 5 mmol/l CaCl2 and 0.5 mmol/l Na2C2O4 were employed. With the same molar concentrations of CaCl2 and Na2C2O4, the sequence of adding these 2 chemicals into the chamber had some effects on crystal types and morphologies. The presence of Tris-HCl buffer in the solution enhanced COM crystal growth and aggregation. The pH greater than 5.0 was associated with the presence of weddellite COD. Magnetic stirring of the supersaturated solution resulted to reduction in size of all crystal forms; the higher speed provided the smaller crystals. Finally, crystallization of CaOx at 4 degrees C was more efficient than performing the experiment at 25 and 37 degrees C.

Molar concentrations, order of adding the substrates, buffering, pH, stirring and temperature have significant effects on CaOx crystal formation, types and morphologies. Cataloging these differential forms of crystals generated in different conditions will be useful for further study on modulations of CaOx crystals and kidney stone disease.