Synthesis and characterisation of biphasic calcium phosphate

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Synthesis and characterisation of biphasic calcium phosphate Powered By Docstoc
					Trends Biomater. Artif. Organs. Vol. 16 (1) pp 12-14 (2002)                                 


                          1                         2
E. Caroline Victoria and F.D. Gnanam
 Centre for Ceramic Technology
 Department of Physics
Anna University
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 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.


                                                       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
                                                                                     o     o
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
                                                                         4-                  2-
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
                                                                                          2-      3-
was prepared with a Ca/P ratio of 1.59.                the presence of OH-, H2O, HPO4 , PO4 and
                                                           2-                              2-
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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