Supervariate Gel Transforms into Various Biominerals in Salt Solutions

Abstract

It is disclosed 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) is 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. This “supervariate” gel is also applied for dental repair and osteogenesis.