Mediating the Enhanced Interaction between Hydroxyapatite and Agarose through Amorphous Calcium Carbonate

The masterful control of physical and chemical interactions between minerals and organic matter allows living organisms to model complex shapes and microstructures and thereby to achieve remarkable properties. Calcium phosphate is the mineral component in vertebrate skeletal and dental systems. There is recent evidence that calcium carbonate, especially in its amorphous role, may play an important role in mineralizing vertebrate tissues like bone. Here, we study the mineralization of hydroxyapatite in agarose hydrogels via an amorphous calcium carbonate (ACC) precursor and compare both the mineralization kinetics and the crystal properties with those obtained in the absence of the carbonate precursor. While under both conditions, hydroxyapatite forms via amorphous calcium phosphate, the presence of ACC delays the onset of hydroxyapatite crystallization but enables equilibrium to be achieved in a shorter time. Furthermore, ACC promotes the interaction of hydroxyapatite crystallites with the agarose polymer, which alters the crystal morphology. This bioinspired pathway opens new possibilities to control mineralization in an organic matrix and thereby to modulate the microstructure. More broadly, our work holds promise to advance the fields of biomineralization and tissue engineering.