The study of biocompatible materials has intensified over the last decade d
riven by the growing awareness of an aging population. The need for alterna
tive medical solutions has not only extended the requirement for biomedical
devices to offer more than just functionality but also bioactivity. A new
generation of bioactive materials has emerged promising better properties o
ver existing biomaterials because of their ability-to promote intimate bone
growth and rapid fixation. In particular, hydroxyapatite (HA) has been rec
ognised as one bioactive material having the potential and opportunity for
development as bone substitutes. Although HA has a similar chemical composi
tion to that of natural bone, it lacks sufficient strength and toughness fo
r use in load bearing applications. Very often it requires blending with a
low modulus polymer to achieve adequate toughness. However, the properties
of HA composites is highly dependent on the particle size and morphology of
the HA filler. Much has been suggested on the benefit of nano particulate
materials in achieving higher mechanical properties. The need now arises in
developing and processing HA of sufficient fineness for this purpose. As s
uch the synthesis of ultra-fine HA was initiated using RF induction suspens
ion plasma spraying with a wet suspension of HA as feedstock. This was axia
lly injected into the RF plasma at various plate powers (plasma energies),
chamber pressures, probe distances and plasma gas flow rates. The processed
powders varied in size according to the cyclones designed to collect the p
owders from medium to ultra-fine. The chamber collecting ultrafine powder c
ontained particles ranging from 10 nm to 4 mum. The particle size, morpholo
gy and phase concentration of the powders were characterised using SEM, TEM
, XRD and FTIR. In general, the particle size decreased with increasing pla
te power, while the reverse was observed for the volume of nano-sized parti
cles produced. Decomposition into other phases such as tricalcium phosphate
(TCP), tetracalcium phosphate (TTCP) and calcium oxide (CaO) increased wit
h increasing plate power. This study suggests that the processing parameter
s associated with the production of the ultra-fine powders interact in a co
mplex manner but can be rationalised by considering the overall thermal tre
atment experienced by the particulates during plasma treatment. (C) 2001 El
sevier Science B.V. All rights reserved.