Crystal growth and dissolution of brushite crystals by different concentration of citric acid solutions

Calcium hydrogen phosphate dihydrate (CHPD) or brushite crystals are well-known urinary crystals and frequently found in urinary stones. The CHPD crystals were grown by the single diffusion gel growth technique in sodium metasilicate gel. The grown crystals were having platelet and star shape morphologies. The maximum growth was observed for the first five days, thereafter, the growth became almost steady. After achieving maximum growth of CHPD crystals, the aqueous solutions having different molar concentrations of citric acid were added into the supernatant solution containing calcium chloride. In the case of low concentrations of citric acid, the inhibition of the growth of CHPD crystals was observed, whereas for the higher concentrations of citric acid the dissolution of the grown crystals was observed. This indicates that the citric acid inhibits the growth of CHPD crystals in the lower concentrations and dissolves them in the higher concentrations. This supports the citrate inhibition theory of urinary calculi and crystals.