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

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) (similar to)2.0 mol.%) were used to fabricate biphasic calcium phosphate (BCP), a mixture of hydroxyapatite (HA) and beta-tricalcium phosphate (beta-TCP) nanocrystals, through hydrothermal reactions at 200 degrees C for 24 h. Our results indicated that beta-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 beta-TCP nanocrystals instead of HA crystals through ion-exchange reactions. BCP samples with different compositions ((similar to)28.6-77.8 wt.% beta-TCP) were produced by controlling particle sizes of eggshells for hydrothermal reactions. The larger particles lead to the larger proportion of beta-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. (C) 2019 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.