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, Mg²⁺, 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 Mg²⁺. 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 Mg²⁺ 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 Mg²⁺ 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.