Facile preparation of hydroxyapatite nanotubes assisted by needle-like calcium carbonate

A cost-effective way to prepare hydroxyapatite (HA) nanotubes with no post-processing template removal step was presented through Kirkendall effect-assisted ion-exchange process by using inexpensive needle-like CaCO3 nanoparticles as templates and calcium sources. The as-prepared HA nanotubes had uniform tubular hollow structures with big openings, a length of 2-4 μm, the average inner diameters at the two ends of 300-400 nm and 150-250 nm, respectively, as well as a wall thickness of approximately 35 nm and a specific surface area of 60 m2/g. Due to its special hollow tubular structure and biocompatibility, HA nanotubes may find wide applications in many fields.