Shape and structure controlling of calcium oxalate crystals by a combination of additives in the process of biomineralization

The origin of complex hierarchical superstructures of biomaterials and their unique self-assembly mechanisms of formation are important in biological systems and have attracted considerable attention. In the present study, we investigated the morphological changes of calcium oxalate (CaO(x)) crystals induced by additives including chiral aspartic acid, sodium citrate, Mg(2+), casein and combinations of these molecules. The morphology and structure of CaO(x) were identified with the use of various techniques. The morphogenesis of CaO(x) crystals were significantly affected by chiral aspartic acid, sodium citrate or Mg(2+). However, they only formed calcium oxalate monohydrate (COM). It was observed that the chiral aspartic acid, sodium citrate and casein adhered to the surface of the crystals. The adherence of Mg(2+) to crystals was not evident. Casein significantly affected the formation of COM and calcium oxalate dihydrate (COD). The ratio of different CaO(x) crystal forms is associated with the casein concentration. In combination with Mg(2+) or citrate ions, casein showed improved formation of COD. The present study mimics biomineralization with a simple chemical approach and provides insight into the complicated system of CaO(x) biomineralization as well as facilitates the understanding of urinary stone treatment.