Formation of Stable\nZinc-Rich Amorphous Calcium Phosphate

Metal ion-rich amorphous calcium phosphate (ACP) is an\nessential\nmineral component in biogenic hard tissues, such as bones and teeth.\nHowever, the formation mechanism of ion-doped ACP and the role of\nmetal ions in this process remain elusive. Herein, taking Zn as an\nexample, we develop a series of Zn-substituted calcium phosphate materials\nthat serve as models for investigating the formation process of Zn-ACP.\nIt is found that entirely pure Zn-ACP can be successfully achieved\nwhen the precursor Zn/Ca ratio is maintained between 0.1 and 0.2.\nThe resulting Zn-ACP nanoparticles exhibit a homogeneous distribution\nof Zn at the nanoscale, excellent cytocompatibility, and exceptionally\nhigh amorphous stability in aqueous media, including water and simulated\nbody fluid. Furthermore, we fabricate monolithic Zn-ACP bioceramics\nthrough the application of pressure, resulting in remarkable hardness\n(1.7 GPa) and modulus (25.5 GPa) that exceed those of human bones.\nThis work presents a novel approach to producing Zn-ACP monoliths\nand advances our understanding of the biomineralization processes\ninvolving Zn and ACP, thus opening potential applications in biomedicine.