Synergistic effects of Mg-substitution and particle size of chicken eggshells on hydrothermal synthesis of biphasic calcium phosphate nanocrystals

Abstract

Magnesium (Mg2+) ion plays important roles in biomineralization of bone, teeth and calcium carbonate skeletons. Herein, chicken eggshells mainly comprising of Mg-calcite nanocrystals (Mg/(Mg + Ca) ∼2.0 mol.%) were used to fabricate biphasic calcium phosphate (BCP), a mixture of hydroxyapatite (HA) and β-tricalcium phosphate (β-TCP) nanocrystals, through hydrothermal reactions at 200 °C for 24 h. Our results indicated that β-TCP nanocrystals formed through the ion-exchange reactions of Mg-calcite, while HA nanocrystals were mainly produced by dissolution-reprecipitation reactions on the surfaces of eggshell samples in the hydrothermal system. Mg substitution in calcite resulted in formation of β-TCP nanocrystals instead of HA crystals through ion-exchange reactions. BCP samples with different compositions (∼28.6–77.8 wt.% β-TCP) were produced by controlling particle sizes of eggshells for hydrothermal reactions. The larger particles lead to the larger proportion of β-TCP in the BCP composition. Therefore, Mg substitution and particle size had synergetic effects on the hydrothermal synthesis of BCP using chicken eggshells through balance of ion-exchange and dissolution-reprecipitation reactions. Cell culture results showed that the BCP products were non-cytotoxic to MC3T3-E1 cells, which may be used for bone substitute materials in future.