Supervariate gel transforms into various biominerals in salt solutions

Abstract We disclose that calcium-based biominerals, particularly hydroxyapatite (as in vertebrate bones and teeth), calcium carbonate (as in plankton and corals), and calcium pyrophosphate (as the cause for pseudogout), can be mineralized from the same precursor—“supervariate” gel, a stable and non-toxic amorphous gel easily prepared by mixing common water-soluble inorganic salt. When dispersed in a Na2CO3 or K2HPO4 solution, this multi-ionic, “supervariate” gel can selectively form the biomineral calcite (CaCO3) or hydroxyapatite, respectively. More remarkable reactions happen when the gel is dispersed in a CaCl2 solution under ambient conditions: dihydrate calcium pyrophosphate (Ca2P2O7·2H2O, CPP) was produced in the morphologically intact gel matrix. The resulting gel further transforms into hydroxyapatite upon drying at room temperature. Because of the ubiquity of pyrophosphate in organisms, such mild formation of calcium pyrophosphate dihydrate (contrasting the high temperatures needed in other non-enzymatic procedures, e.g., as in condensing phosphoric acid), and its transformation into hydroxyapatite, sheds light on 1) the role of pyrophosphate in life’s origin; 2) key biomineralization mechanisms in physiological processes. We also apply this “supervariate” gel for dental repair and osteogenesis.