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.
