Carbonate Chemistry Regulates Ion Transport from Polymer–Calcium Condensates for Bioinspired Calcification

Amorphous calcium carbonate phases are common intermediates in multistep crystallization processes. In many cases, it was shown that these dense and liquid-like phases function as transient metastable precursors that transform into mature crystalline phases. However, some biological systems consist of inorganic condensates that serve only as ion carriers and dissolve prior to the formation of the mineral. In this work, we study the chemical conditions that regulate the release of calcium ions from polymer condensates toward the formation of calcium carbonate. It is shown that the presence of bicarbonate ions tunes the stability of biogenic and bioinspired polymer–Ca condensates. In specific conditions of the carbonate system, condensate dissolution is induced, affecting calcium carbonate supersaturation and crystallization kinetics. This behavior recapitulates observations on the roles of such condensates in vivo, suggesting that bicarbonate ions indirectly affect mineralization by turning inorganic condensates from mineral precursors into sacrificial ion pools.