Controllable preparation of ultralong hydroxyapatite nanofibers using the solvothermal method: Effect of initial Ca/P ratios

Hydroxyapatite (HA) is an important component of mammalian bones and teeth. Its superior biocompatibility, biological activity, and bone tissue regenerative properties make it an ideal material for bone tissue replacement and regeneration. The morphological characteristics of HA can affect its selection in various applications. In contrast, one-dimensional (1D) micro/nano-structured HA has received widespread attention in the field of biomedicine. In particular, HA ultra-long nanofibers possess excellent mechanical properties, such as flexibility and deformability, overcoming the brittleness of traditional HA ceramic materials. This work successfully synthesized HA ultra-long nanofibers using oleic acid as a template by a solvothermal method. Particularly, the effects of the initial Ca/P ratios (iCa/P) on the morphologies of HA products were investigated. The microstructure and properties of HA products were characterized by scanning electron microscopy (SEM), X-ray powder diffractometer (XRD) and Fourier transform infrared spectroscopy (FTIR). The results indicated that the uniform and flexible HA nanofibers can be obtained only under the appropriate iCa/P. In addition, the effect of iCa/P on the microstructures of the HA formation stages was investigated using transmission electron microscopy (TEM), and then the formation mechanism of HA nanofibers was proposed. In this process, it is found that HA nanofibers mainly grow selectively along the c-axis, while iCa/P precisely influences the preferential growth direction of HA products.