Biomedical Engineering Reference
In-Depth Information
of carbonates helped in suppressing formation of ACP phases with
apatitic structure and its transformation into poorly crystalline
(almost amorphous) CDHA and favored the formation of β-TCP
phase [441]. Nano-sized particles of both FA and β-TCP were
synthesized by a simultaneous combustion of calcium carboxylate
and tributylphosphate based precursors in a flame spray reactor
[410]. The same technique was used to synthesize nano-sized
particles of amorphous TCP of 25-60 nm size [442-445], those after
calcinations transformed into α-TCP or β-TCP. Nanodimensional
β-TCP powders with an average grain size of ~100 nm [147, 446]
and less [447] were prepared by wet precipitation methods,
followed by calcining at elevated temperatures. Furthermore, a sol-
gel technique [448], reverse micelle-mediated synthesis [449], and
a polystyrene template method [450] are also applicable. In wet
precipitation techniques, dialysis might be applied as a separation
method [446]. When wet-precipitation methods were used, initially
nanodimensional CDHA with Ca/P ratio of ~1.50 was precipitated,
that was transformed into nano-sized β-TCP at calcination.
To synthesize nano-sized TCP, both milling [451, 452] and a
high temperature flame spray pyrolysis [453] techniques might be
employed as well. Afterwards, the nanodimensional β-TCP powders
can be compacted into 3D specimens, followed by sintering to
achieve the appropriate mechanical strength [147]. The maximal
values of the bending strength, elastic modulus, Vickers hardness,
and compressive strength of the samples fabricated from nano-sized
β-TCP powders were more than two times higher as compared to those
of bioceramics obtained from micron-sized β-TCP powders. However,
the degradability of bioceramics sintered from nanodimensional
powders was just about one fourth of that sintered from micron-
sized powders. Thus, the degradability of β-TCP bioceramics could
be additionally regulated by the particle dimensions [147].
Nano-sized whiskers of several calcium orthophosphates (HA,
β-TCP, and BCP (HA + β-TCP)) were produced by using a novel
microwave-assisted “combustion synthesis (auto ignition)/molten
salt synthesis” hybrid route. Aqueous solutions containing NaNO
,
3
Ca(NO
(with or without urea) were irradiated in a
household microwave oven for 5 min at 600 watts of power. The as-
synthesized precursors were then simply stirred in water at room
temperature for 1 h to obtain the nano-sized whiskers of the desired
calcium
)
, and KH
PO
3
2
2
4
orthophosphate
[454].
Furthermore,
nanostructured
Search WWH ::
Custom Search