Master's Thesis : Tailored hydroxyapatite for bone reconstruction

Abstract

Hydroxyapatite (HA), Ca5(PO4)3(OH), is a bioceramic well-known in the biomaterial field. Through the last decades, efforts have been particularly developed in the synthesis of nanostructured hydroxyapatite and in the control of its properties, mainly to increase its specific surface area. In order to achieve that, surfactants acting as template during synthesis represent a promising research field. However, no study depicts clearly the behaviour of surfactants in the conditions of HA synthesis, as well as the effect of surfactant concentration on the structure of hydroxyapatite. The goal of this work is to study the behaviour of a cationic surfactant, cetrimonium bromide (CTAB), in conditions of HA synthesis (pH 10.5 and presence of phosphate ions) and to perform HA synthesis with CTAB. To achieve that, different CTAB concentrations ranging from 0.4 to 100 mmol/L were analysed through Dynamic light scattering (DLS) at temperatures of 25 and 50 °C. Results showed that temperature does not impact significantly the CTAB micelles behaviour. Moreover, CTAB forms aggregates at concentrations lower than 10 mmol/L. These aggregates tend to disappear when CTAB concentration increases and unimodal size micelles are formed. HA syntheses were performed using appropriate CTAB concentrations determined by means of DLS results. After synthesis, HA powders have been characterized by FT-IR, TGA, XRD, BET and TEM techniques and have been compared to commercialized HA powder. It is observed that surface area can be undoubtedly increased (up to 150 m²/g) by the use of CTAB surfactant. Moreover, morphology and size of HA particles are impacted by CTAB concentrations. These results are promising and show the importance of surfactant behaviour's comprehension in HA synthesis. This opens new perspectives in the biomaterials domains and especially in bone reconstruction.