|Accidents, surgery and disease often result in the use of biomimetic materials that can
replace human hard tissue and calcium phosphate bioceramics are ideally suited for this
purpose. Indeed, biological apatite is a poorly crystalline, non-stoichiometric carbonated
hydroxyapatite. The composition, crystallinity and particle size of synthetic calcium
phosphate bioceramics directly affect their biological, mechanical and thermal
performance. Hence control over these properties in synthetic bioceramics is essential in
order to mimic human hard tissue in functionality. The existing methods of synthesis of
calcium phosphate bioceramics are multi-step, time consuming and require strict control
over synthesis conditions. Therefore, there is a requirement of a one-step, rapid
synthesis technology which allows control over particle properties. The continuous
hydrothermal flow synthesis (CHFS) technique addresses all such issues but it has not
been used to synthesise calcium phosphate based nano-bioceramics.
The work in this thesis involves the use of CHFS technology to synthesise calcium
phosphate bioceramics. It was demonstrated that the rapid crystallising environment in a
CHFS system resulted in phase-pure crystalline hydroxyapatite (HA). Traditionally
required long ageing times and heat-treatment were avoided. Furthermore, variations in
the CHFS system parameters were correlated with properties of the synthesised nanobioceramics.
The CHFS system was also used to substitute biologically beneficial ions (C03'-, Si044-,
Mg2+ and Zn2) into HA. Some ionic substitutions affected thermal stability and phase
composition. For example, increase in magnesium contents in solution resulted in
precipitation of a phase pure Mg-Whitlockite phase.
Conventional consolidation methods of HA powders require several hours of exposure
to elevated temperatures which results in large grains, phase decomposition and poor
mechanical properties. Spark Plasma Sintering on the other hand is capable of very high
heating and cooling rates. Phase-pure and ion-substituted calcium phosphates and
zirconia-hydroxyapatite phase mixtures were spark plasma sintered to high densities
with these materials displaying good mechanical properties.