Hydrothermal synthesis of hydroxyapatite nanorods in the presence of sodium citrate and its aqueous colloidal stability evaluation in neutral pH.

In this paper, colloidal hydrophilic hydroxyapatite nanorods were synthesized in the presence of sodium citrate via thermal-decomplexing method. The influence of sodium citrate/Ca ions molar ratio (CT/CM) on the synthesis of HA nanorods was characterized in term of structure, size, morphology, and colloidal stability through TEM, XRD, Zeta potential, DLS and long-term standing test. The results show that increasing CT/CM would evidently facilitate high aspect ratio and enhance colloidal stability of nanorods. When the CT/CM is above 1/3, well crystallized HA nanorods with mean aspect ratio up to 5 would be obtained and kept colloidally stable for over two months in neutral pH (7.3-7.5). The origin responding to the results is that increasing CT/CM would enhance the inhibiting growth effect of sodium citrate and increasing absorption density of citrate ions on the particle surface. This work provides new insights into the role of citrate on both the crystallization and tailoring of colloidal stability. Moreover, the synthesized HA nanorods are promising materials for use as carriers for local targeted drug delivery systems as well as building blocks for the preparation of nanostructured scaffolds for cells in bone tissue engineering.