Investigation on [OH−]-responsive systems for construction of one-dimensional hydroxyapatite via a solvothermal method

Abstract

An oleic acid-assisted solvothermal method has been utilized to prepare hydroxyapatite (HA) nanofibers with a high flexibility and aspect ratio. Understanding the role of oleic acid in the synthesis of HA may provide effective routes for the design of advanced biomaterials. The concentration of OH⁻ ions ([OH⁻]) has a great impact on the reaction system, which in turn affects the nucleation and crystal growth of HA. In this work, the effect of oleic acid on the morphology and structure of the as-prepared products under different concentrations of NaOH was investigated by XRD, FTIR and FE-SEM. The formation process of HA was also explored to better explain the role of oleic acid based on structured characteristics and morphology evolution. These results showed that oleic acid molecules absorbed on the surface of HA would effectively induce a one-dimensional crystal growth, even if the crystal growth habit had been changed under different [OH⁻]. For [OH⁻] < 1.50 M, [OH⁻]-responsive oleic acid and its corresponding behavior as a pH buffer can regulate pH at a relatively constant value. Besides, the flexible ultralong HA nanofibers can be formed at [OH⁻] = 1.25–1.50 M, while the crystallite size and preferred growth along the c-axis were both improved with an increase in [OH⁻] added.