Polymer–Mineral\nInteraction Influences the\nMineralization of Hydroxyapatite in Hydrogels

Bone mineralization relies on the\ninteraction between\ncollagen\nand minerals to control bone growth and multiscale hierarchical structure.\nUrged by the increasing need for bone defect repairs, tissue engineering\nsearches for biocompatible materials to assist and enhance repairs.\nOne potential avenue is to use hydrogels as organic scaffolds to control\nnucleation and growth of bonelike minerals. Here, two biocompatible\npolymers, polyacrylamide and agarose, were selected for the mineralization\nof hydroxyapatite, and the mineralization kinetics was investigated\nin the presence of calcium carbonate (to simulate early bone formation\nconditions) and in its absence. The results of this work show that\nagarose and polyacrylamide lead to different polymer–mineral\ninteractions, which influence the stabilization of carbonate and phosphate\nprecursors and thereby the onset of the crystallization of hydroxyapatite\nand more so in the presence of carbonate. In both hydrogels, amorphous\ncalcium carbonate and hydroxyapatite are noncongruent, and amorphous\ncalcium phosphate forms as a precursor. This distinct interaction\nbetween the mineral and agarose vs polyacrylamide leads to different\nmicrostructures and thereby mechanical responses. This research not\nonly advances our understanding of the influence of mineral–polymer\ninteractions on hydroxyapatite mineralization but also provides new\nopportunities for designing biomaterials for specific applications.