Highly repeatable synthesis of nHA with high aspect ratio

• A highly repeatable synthesis method for nHA fibers has been developed.
• Altering the pH of solutions can control the aspect ratio in a repeatable way.
• Nano HA particles with the aspect ratio of 50 can be synthesized by both precipitation and hydrothermal methods.

Hydroxyapatite with different aspect ratios such as nano dots, sheets, rods and fibers were synthesized by the hydrothermal and precipitation methods respectively. It is not difficult to synthesize nanohydroxyapatite (nHA) with a low aspect ratio using published methods. However, it is still a challenge to synthesize nHA particles with a high aspect ratio, such as nHA fibers, using a well-controlled and repeatable method. In this study, we describe a method to control the aspect ratio of nHA by controlling the initial pH of the solution. A highly repeatable synthesis method for nHA fibers has been developed, and the mechanism to control the aspect ratio is discussed.