Trends Biomater. Artif. Organs. Vol. 16 (1) pp 12-14 (2002) http://www.sbaoi.org
SYNTHESIS AND CHARACTERISATION OF BIPHASIC CALCIUM
E. Caroline Victoria and F.D. Gnanam
Centre for Ceramic Technology
Department of Physics
Chennai 600 025.
Clinical application of pure bioactive hydroxyapatite can be improved with the bioresorbable tricalcium phosphate for
better bone regeneration. Biphasic calcium phosphate (BCP) consisting of hydroxyapatite (HAp) and tricalcium phosphate
(TCP) has been processed by precipitation technique using 1.0 M of Ca(OH) 2 and 0.63 M of H3PO4. The X-ray diffraction
analysis of the as-dried powder reveals that the calcium deficient hydroxyapatite is poorly crystalline and is converted into
a biphasic calcium phosphate when calcined at a temperature of 800oC. The HAp and TCP ratio w as found out to be 70
:30. The particle agglomerates as determined form the laser diffraction method is found out to be 2-3.0 µm. The release of
water and the decomposition of β- Ca(PO3) 2 to the pyrophosphate to form β -TCP is evident from the thermal analysis.
HPO42- band is found in the FTIR of the as-dried sample.
INTRODUCTION the ceramics and displays interesting
mechanical properties. In this study, a
Development of biphasic calcium precipitation route has been used to prepare
phosphate(BCP), especially with BCP. Its evolution and characteristics are
hydroxyapatite (HAp : Ca10(PO4)6(OH)2 ) and discussed.
tricalcium phosphate (TCP : Ca3(PO4)2 ) has
drawn considerable attention. HAp and TCP, MATERIALS AND METHODS
although have similar chemical composition,
they differ in their biological resorbing The BCP in this study with a higher
capacity. The dense HAp ceramics when amount of HAp and TCP was prepared by a
used as bone implant is almost non- precipitation method. 0.63 M of H3PO4 was
resorbable and bio-inert. While the porous β- added dropwise to the well dispersed 1.0M of
TCP containing ceramics displays affinity for Ca(OH)2 at the rate of 7ml/min. The reaction
high speed biological degradation, they are was carried out at 28 ± 3 C. The pH was 12
bioactive and bioresorbable materials (1). The at the initial stage of the reaction and dropped
main attractive feature of bioactive bone graft to 8 at the end of the reaction. A white
materials such as BCP ceramics is their ability gelatinous precipitate was obtained at the
to form a strong direct bond with the host end of the reaction. The precipitate was
bone resulting in a strong interface compared refluxed at 90 ± 5 C for an hour and then
to bioinert or biotolerant materials which form stirred for another hour till it cooled down to
a fibrous interface (2). The bioactivity relies on room temperature . The precipitate was aged
physical and chemical properties of biphasic for 48 hrs without stirring. The water as then
calcium phosphate ceramics(3). BCP has decanned and filtered using a buchner funnel.
been prepared by various methods (4-5). But The filtered cake was then dried in the oven at
Gautier et.al. 1999 (6), have suggested that ~110 C. The as-dried powder was then
the elaboration of BCP ceramics involving the calcined at 800 C.
calcination of a calcium-deficient apatite
obtained by an aqueous precipitation method The powder x-ray diffraction (XRD)
may appear to be an effective process. This was carried out for the as-dried and for the
preparation method conserves the bioactivity calcined powder using Cu-Kα radiation. The
and biodegradability, increases the purity of fourier transformed infra red (FT-IR) spectra
Synthesis and Chatacterisation of Biphasic Calcium Phosphate 13
were taken using KBr pellet technique using
Bruker IFS 66v FT-IR spectrometer. The
thermal analysis was carried out using
TG/DTG using Perkin- Elmer TGA7 . The
particle size was analysed using the laser
diffraction particle size analyser.
RESULTS AND DISCUSSION
Fig.2: TG/DTG analysis of the as-dried samples
Fig.2. Shows the TG/DTG analysis of
the as-dried powder. From the TG/DTG
analysis, the non-stoichiometric calcium
deficient Hydroxyapatite shows a weight loss
around 100 C, that is due to the physically
adsorbed water. The DTG analysis shows a
Fig.1: XRD Patterns of the (a) as-dried and (b) o
calcined at 800oC peak around 290 – 300 C. TenHuisen and
P.W. Brown 1999(8), have reported that the
Fig.1. Shows the XRD pattern for the non-stoichiometric calcium deficient
as-dried and calcined samples. The XRD for hydroxyapatite would transform to a
the as-dried powder shows a broad peak amorphous β- Ca(PO3)2 at 250 C in the
indicating that the powder is poorly crystalline absence of steam and would transform to a β
and calcium deficient. When it is calcined for - Ca(PO3)2 at 450 C-500 C. This
800 C it shows a biphasic nature with HAp transformation has been confirmed by the two
and β TCP. The relative intensity ratio (RIR) of peaks found in the DTG at ∼ 250 C and ∼
the HAp:TCP were found out using the 500 C. A smaller peak has been found around
intensity peaks of (211) and (2 0 10) peaks of 600 C that would be due to the decomposition
HAP and βTCP respectively using the of β- Ca(PO3)2 to a pyrophosphate. The
formula, RIR = IβTCP/(IβTCP +IHAp) and it is reaction of P2O7 + 2OH → 2PO4 + H2O)
found out that the HAP :TCP is 70:30 . would follow immediately (7) and hence
around 750 C, a large amount of β- TCP
The non-stiochiometric, calcium appears in addition to calcium hydroxyapatite
deficient apatite has the general formula of forming a biphasic calcium phosphate.
Ca10-x (HPO4)x (PO4)6-x (OH)2-x (0<x<2) although
it has an apatite structure, the concentration Fig.3. shows the FTIR spectra of the
ratio Ca/P, the index for stoichiometry can as-dried and calcined samples. The FT-IR
vary from 1.67 to 1.33 (7). In this study, BCP spectrum of the calcium deficient HAp shows
was prepared with a Ca/P ratio of 1.59. the presence of OH-, H2O, HPO4 , PO4 and
Hence, this non-stiochiometric apatite can CO3 bands. Typical band of CO3 type B is
have the formula Ca9.58 (HPO4)0.42 (PO4)5.58 present in the region of 1400-1550 cm which
(OH)1.58 (x= 0.42 for Ca/P = 1.59). disappears after calcination. The HPO4 band
14 E. Caroline Victoria et. al.
is observed at 876 cm for the as dried one. The agglomerated particle size is found out to
The FT-IR of the calcined one at 800 C does be 2-3 µm and it has a narrow distribution.
not show this band and so it can be concluded
that the condensation of HPO4 is complete CONCLUSION
and BCP is formed at 800 C. The broad
BCP has been prepared using a
precipitation technique using 1.0M of Ca(OH)2
and 0.63M of H3PO4. From XRD the HAp:
TCP was found out to be 70: 30. The FT-IR
analysis show the HPO4 band in the as-dried
sample. TG/DTG analysis show the formation
of β-Ca(PO4)2 around 500 C and the
subsequent decompostion of its
pyrophosphate around 750 C to the
formation of β-TCP and calcium
Fig:3: FTIR analysis of the as-dried and the calcined One of the authors, E. Caroline
samples Victoria wish to acknowledge R. D. Birla
-1 Medical Research Center , Mumbai for their
stretching mode of OH band in the calcium
financial assistance to carry out this work.
deficient HAP is drastically reduced when
calcined at 800 C.
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