The Effect of the Two-Step Sintering Process on Consolidation of Fluoridated Hydroxyapatite and its Mechanical Properties and Bioactivity Mohammadhossein Esnaashary,* Mohammadhossein Fathi, and Mahdi Ahmadian Biomaterials Research Group, Department of Materials Engineering, Isfahan University of Technology, Isfahan 8415683111, Iran The aim of this work was to evaluate the effect of the two-step sintering process on consolidation of fluoridated hydroxyapatite (FHA). In addition, the effect of fluorine content on sinterability, mechanical properties, and bioactivity of FHA bulks was studied. Nanostructured FHA bulks were obtained under the conditions of 1000 and 900°C for the initial and secondary temperatures, respec- tively, without any structural decomposition. In addition, by increasing the fluorine content, the sinterability of FHA bulks was decreased and the hardness of FHA bulks was improved. Moreover, FHA bulks showed acceptable bioactivity. Introduction For decades, scientists have researched among suitable substitutable materials for injured bones. One of them is hydroxyapatite (HA). HA attracted much attention because of its chemical and structural similarities to the natural hard tissues. 1 Under in vitro condition, HA has the innate ability to promote apatite formation and growth. 2 In addition, cell culture experiments indicated acceptable cell attachment, proliferation, and differentiation on HA. 3 However, its low chemical and thermal stability decreases HA sinterability and introduces poor mechanical properties of HA bulk. 4 So, HA applications have restricted in unloaded conditions such as coating 5 and combination with various com- pounds. 6 Due to the ionic contamination of biological HA, much research has focused on the ion doping of HA struc- ture. 7–11 Ion doping such as strontium (Sr), magnesium (Mg) and/or, fluorine (F) on HA structure improves HA properties for different uses. Sr and Mg hinder the growth of HA particles and increase their solubility and positive surface charges, which make HA as a good candidate for gene delivery. 7,8 On the other hand, F increases the structural *mh.esnaashary@yahoo.com © 2013 The American Ceramic Society Int. J. Appl. Ceram. Technol., 1–10 (2013) DOI:10.1111/ijac.12053