Production, characterization and dispersion of nanohydroxyapatite

Abstract

Over the past few decades, various investigations have highlighted the importance of mimicking bone for tissue engineering and bone replacement applications. The hierarchy, chemistry and morphology existing in bone are aspects reflected in the synthesis of biomaterials. Thus, composite materials consisting of a polymeric collagen matrix containing well dispersed nanocrystals of hydroxyapatite (HA) are often the goal in many works. Different HA synthesis routes have been widely developed by several researchers. However, a few studies have shone a light on the successfulness of treatments for deagglomerating and dispersing hydroxyapatite, which is critical when mimicking hierarchy in bone. The present work attempts to synthesize and evaluate the dispersion ability of nanohydroxyapatite particles and to establish a procedure to prepare stable nanosuspensions in order to provide a reliable framework for biomaterials production. With that purpose, this work is first focused on the study of three different synthesis routes of HA; and second, in the dispersion of the synthesized particles with the help of dispersants and physical treatments. The synthesis routes studied are mechanosynthesis, precipitation and sonochemical precipitation, which allow obtaining nano-sized calcium deficient hydroxyapatites with different properties. The mechanosynthesis route provides more agglomerated hydroxyapatites than the precipitation routes, which results in poor suspension yields. Precipitated and sonochemical routes provide needle-like carbonated nanohydroxyapatites with enhanced suspensions stability. Dispersion of nanohydroxyapatite has been studied through the application of high and lowfrequency ultrasonic irradiation in order to deagglomerate hydroxyapatite particles, together with the addition of biocompatible dispersant agents. The dispersion efficiency has been quantified according to the particle content in suspension, which can be related to the amount of sediment obtained. Sonochemical precipitated hydroxyapatite (spHA) has the best yield and stability in suspension; higher particle content in suspension is achieved when using spHA with sodium tripolyphosphate as dispersant. However, there is a high influence of the treatment applied to deagglomerate hydroxyapatites obtained. It has been shown that high frequency ultrasonic irradiation enhances deagglomeration of particles facilitating in turn the adsorption of dispersants. However the nature of the particles plays an important role in their behaviour in suspension. It has been demonstrated that ultrasound irradiation during synthesis is a useful tool to obtain enhanced yields in suspension; since ultrasound irradiation is deagglomerating particles; the effect of dispersants is also enhanced.