J. Biomedical Science and Engineering, 2011, 4, 583-590 JBiSE
doi:10.4236/jbise.2011.49074 Published Online September 2011 (http://www.SciRP.org/journal/jbise/).
Published Online September 2011 in SciRes. http://www.scirp.org/journal/JBiSE
Fabrication and characterization of the Ti-Ca-P composites by
vacuum sintering
Dibakar Mondal1, Swapan Kumar Sarkar1, Dong-Won Lee2, Young-Seon Lee2, Byong-Taek Lee1*
1Department of Biomedical Engineering and Materials, College of Medicine, Soonchunhyang University, Chungnam, Korea;
2Department of Materials Processing, Korea Institute of Materials Science, Changwon, Kyungsangnam-Do, Korea.
Email: lbt@sch.ac.kr
Received 14 February 2011; revised 25 April 2011; accepted 23 May 2011.
Using Ti and biphasic calcium phosphate (BCP) pow-
ders, Ti-Ca-P composites which contained 0 - 30
vol.% BCP powders initially, were fabricated by vac-
uum sintering at two different sintering temperatures,
1300˚C and 1400˚C. Detailed microstructural char-
acteristics of the resulting composites were investi-
gated. Mechanical properties like compressive stren-
gth, Vickers hardness were evaluated and they sh ow-
ed decreasing trend with the increasing initial BCP
content. The x-ray diffraction (XRD) profiles revealed
that extensive chemical reaction occurred and the
initial BCP was degraded and formed CaO, TiO2, TiP,
CaTiO3. However, the cell viability by MTT assay
and cell proliferation behavior through one cell mor-
phology analysis showed excellent increasing trend in
biocompatibility which makes this materials suitable
for hard tissue aid material. And the composite con-
taining 30 vol.% BCP content with Ti sintered at
1400˚C showed excellent biocompatibility with the
Vickers Hardness value 108.8 HV and the compres-
sive strength value 303.7 MPa.
Keywords: Ti; Calcium Phosphate; Biocompatibility;
Biocompatible metals such as Ti and its alloys, Co-Cr
alloys are still the most preferred implant materials for
applications that require load bearing conditions,
whether it is in dense form or porous. Titanium and its
alloys are corrosion resistant, biocompatible, and self-
passivating materials that have a much lower elastic
modulus than Co-Cr alloys and stainless steel. The me-
chanical properties of titanium and its alloys are good
enough for load-bearing implants, but their biocompati-
bility is much lower than that of calcium phosphate ce-
ramics [1,2]. In addition, the interface between titanium
and host bone is a simple interlocking bonding owing to
the bio-inert nature of titanium metal, which can lead to
the loosening of the implant and the eventual failure of
implantation [3]. The lack of biological bonding between
the metal and host bone can cause wear and associated
debris which can lead to particle induced inflammation.
The implantation of metal in place of the damaged bone
can cause the stress shielding effect, due to the dissimi-
larity of elastic modulus between bone and the implant
materials, which weakens new bone formation and
causes severe damages to the whole bone structure in the
long run. The skeleton grows more bone tissue in re-
gions where the load on the skeleton is large and the net
result is a more closely packed and stronger skeleton that
has the strength to sustain the increased load. In areas
with diminished load, the skeleton retains only enough
bone tissue necessary to sustain the diminished load.
Thus, the skeleton in unloaded areas is weaker [4-6].
Surgeons believe that stress shielding is harmful because
the weaker skeleton may fracture. The stress shielding
effect depends on the difference between the stiffness of
the shaft component and the stiffness of the bone. This
only can be avoided by matching the elastic modulus of
the implant and bone closely. The problems with tita-
nium metals are obvious and only could be addressed
with a systemic approach to incorporate features to im-
prove the biocompatibility and modify the mechanical
BCP, which is a mixture of Hydroxyapatite,
Ca10(PO4)6(OH)2 and Tri Calcium Phosphate, Ca3(PO4)2,
has a similar crystallographic structure to bones mineral
phase. Several studies have demonstrated that BCP is
biocompatible with hard tissues and exhibits osseocon-
ductive properties [5-9]. It is also well known that BCP
forms a direct bond with surrounding tissue after bone
implantation. However, its poor mechanical properties,
especially the fracture toughness less by an order of
D. Mondal et al. / J. Biomedical Science and Engineering 4 (2011) 583-590
Copyright © 2011 SciRes. JBiSE
magnitude, are the most serious obstacles for applica-
tions as load-bearing implants [10].
Many efforts have been made to improve the me-
chanical properties of Hydroxyapatite (HAp) [11,12] and
the biological properties of titanium and its alloys [13,
14]. Achieving a good combination of the bioactivity of
HAp and the favorable mechanical properties of metals
are considered a promising approach to fabricate more
perfect biomedical devices for load-bearing applications
in hard tissue engineering. This could be achieved by
using appropriate metallic reinforcing materials with
hydroxyapatite [15-17]. Functionally graded materials
consisting of metallic and ceramic components [18] have
been shown to improve the properties of several systems
such as medical implant devices.
Several studies have examined the potential of coating
of Hydroxyapatite on Ti with or without combination of
Ti to improve the biocompatibility of the metallic system
in terms of biological fixation with the host site. Several
methods of coating Ti have been developed such as
plasma spraying, dip-spin, electrochemical etc. [19-22].
However, coating Ti is complex because the bonding
strength of the interface of Ti and BCP is very low.
Therefore, it is very difficult to prepare a uniform coat-
ing on an implant with a complex structure using this
technique. The most widely used coating method is
plasma spray coating, which severely damages the Hy-
droxyapatite [19-21]. BCP and Ti duplex metal-matrix
composites can be viewed as a potential alternative but
there are also some unique problems using this approach.
Due to severe oxidation of titanium in air, sintering of
the Ti-BCP composites has to be done in vacuum or un-
der the protection of an inert atmosphere. However, un-
der such sintering conditions, dehydration and decompo-
sition temperatures of HAp will decrease remarkably
[23], which decreases its mechanical properties as well
as the excellent biocompatibility of the HAp is lost.
However, a comprehensive investigation is still to be
reported with the aim to incorporate HAp in titanium
matrix with a nano-structured HAp phase inclusion and
the improvement of biocompatibility along with the
modification of mechanical properties with in favorable
range of magnitude.
In this study, Ti-BCP composites were fabricated us-
ing the vacuum sintering method to combine the bioac-
tivity of BCP and the mechanical properties of titanium.
Two sintering temperatures, 1300˚C and 1400˚C, were
used to investigate the sintering behaviors. In addition,
four compositions at each sintering temperatures were
examined; pure Ti or 0% BCP as the controls, 10 vol.%
BCP, 20 vol.% BCP and 30 vol.% BCP. These experi-
ments were conducted to investigate changes in the
properties of the composite as a function of BCP content.
Especially using MTT assay and observation of single
cell growth the cell viability and biocompatibility of
Ti-Ca-P based composites were investigated.
2.1. Preparation of the Composite
The BCP powder was prepared at room temperature by
mixing calcium nitrate tetrahydrate (Ca(NO3)2.4H2O)
(Samchun Chemicals, 98.5% pure) and ammonium
phosphate dibasic ((NH4)3PO4·2H2O) (Samchun Chemi-
cals, 98.5% pure) in an ultrasonic bath [24]. NH4OH was
added to the solution to bring the pH > 9 and the sample
was ultrasonciated for 4hrs. The solution was then al-
lowed to precipitate for 24 hr. Then, the precipitated
BCP was washed to remove NH4OH and filtrated. After
filtration the cake was dried at 80˚C for 72 hr in an oven
and then crushed. The BCP powder was then calcined at
750˚C for 2 hr. Commercially pure titanium powder
(325 mesh, 99.5%, Alfa Aesar, USA) and BCP were
mixed with alcohol and ball milled for 24 hr. Four dif-
ferent compositions were fabricated; pure Ti powder, 10
vol.% BCP, 20 vol.% BCP and 30 vol.% BCP powder
with Ti. The mixture was then dried at 80˚C for 3 hr. For
the characterization of microstructure and material prop-
erties, pellets of 1.3 cm diameter were made in a hydrau-
lic pressure unit (Carver Inc., USA) with 5 tons force.
Then, the composite pellets were sintered in vacuum at a
temperature of 1300˚C and 1400˚C for 1 hr.
2.2. Characterization
The density of the composites was measured using the
Archimedes method. The Vickers’ hardness was meas-
ured using a hardness testing machine (Microvicker,
Akashi, Japan) and the compressive strength was meas-
ured using universal testing machine (Unitech TM, R&B,
Korea). The microstructure of the composites was char-
acterized using a Scanning Electron Microscope (JSM-
6701F, JEOL Ltd, Japan). In addition, the composites
composition and crystal structure of composites were
determined by X-Ray diffraction (Miniflex II, Rigaku,
2.3. In Vitr o Study
The in vitro properties of the composite were character-
ized by cytotoxicity test for L929 cell line with a MTT
bromide, a tetrazole) solution and the cell morphology of
individual cells using MG63 cell line.
BCP-Ti composites pellets were first chemically
etched with a 20% H2SO4 solution for 5 minutes in an
ultrasonic bath. Then, they were cleaned with acetone,
alcohol and deionized water sequentially in an ultrasonic
bath for 5 minutes each. The pellets were placed in fal-
D. Mondal et al. / J. Biomedical Science and Engineering 4 (2011) 583-590
Copyright © 2011 SciRes. JBiSE
con tubes and sterilized in an autoclave.
The pellets were then submerged in 12 ml solution of
Roswell Park Memorial Institute medium (RPMI). The
mixture is then incubated 5% CO2 atmospheres for 72
hrs in a shaking incubator. After that medium was fil-
trated and the extract was taken in 50 ml falcon tube.
Previously cultured L929 cells were seeded into 96-well
microtiter plates (Nunclon™, Nunc, Wiesbaden, Ger-
many) at a density of 7 × 104 cells/well. After washing
with PBS the extract and medium solution were pour
into the well and moved those in CO2 incubator for 72
hrs. After that the medium was removed and in each well
20 μl of 5 mg·ml–1 MTT was added including one set of
wells with MTT but no cells (control). Then Incubated
for 3.5 hours at 37˚C in culture hood media was re-
moved carefully. With adding 150 μl MTT solvent the
plate was covered with Al foil and agitates cells on or-
bital shaker for 15 min, then the absorbance was read at
590 nm using an HP 8453 spectrophotometer.
For one cell morphology the MG63 cells were seeded
onto the composite pellets in a 24-multiwell plate at a
final density 10,000 cells·cm2. After 1 hr and 24 hrs, the
media was removed and after dehydratationin ethanol
solutions of 75%, 90%, 95% and 100%specimens were
fixed with 4% glutaraldehyde in PBS (pH 7.2) and keep
at room temperature for drying. After drying the samples
were sputter-coated with Pt. The surface of the speci-
mens was finally examined with backscattered (BSE)
mode and secondary electrons (SE) modeby scanning
electron microscopy (SEM) under a voltage of 15 kV.
3.1. Microstructure and Morphologies of
Ti-Ca-P Composites
SEM images of sintered composites body had shown in
Fig.1, as the amount of initial BCP in composites in-
creases so does the porosity in the composites. This
trend was common for both of the sintering temperature
of 1300˚C and 1400˚C as shown in Figures 1(a-d), re-
spectively. From the SEM images, we could easily see
that the titanium surface was barely visible except for
the polished surface.
3.2. Phase Composition of the Composites
The SEM microstructure and energy dispersive X-ray
spectroscopy (EDS) profile of the Ti-10% BCP compos-
ite sintered at 1400˚C shown in Figure 2. As shown in
Figure 2(b), in selected point Pon the titanium metal
surface, significant amounts of titanium were observed as
expected. In addition, in point Q contained more Ca and
P (Figure 2(c)); however, a significant amount of Ti was
Figure 1. SEM morphologies of (a) 10% BCP-Ti; (b) 30% BCP-Ti vacuum sintered at 1300˚C and (c) 10%
BCP-Ti; (d) 30% BCP-Ti vacuum sintered at 1400˚C.
D. Mondal et al. / J. Biomedical Science and Engineering 4 (2011) 583-590
Copyright © 2011 SciRes. JBiSE
1 2 3 4 5 6 1 2 3 4 5 6
Figure 2. (a) SEM image of a small area of 10% BCP-Ti based composites surface sin-
tered at 1400˚C and Energy dispersive spectroscopy (EDS) profiles of (b) point P on tita-
nium surface and (c) point Q on Ca-P surface.
also there, which revealed that Ti in the composite body
got reacted with the initial BCP phase, which was the
reason for the decomposition of the calcium phosphate
phase. Ti reacted with BCP and formed TiO2, TiP and
CaTiO3. By analyzing the x-ray diffraction data (XRD)
in Figure 3, the phase can be mostly detected. From
Figure 3(a) for pure Ti, no TiO2 or CaO or CaTiO3was
observed. But for 90% Ti with 10% initial BCP and both
for vacuum sintered at (b) 1300˚C and (d) 1400˚C, some
amount of TiO2, CaO and CaTiO3had formed. In addi-
tion, for 70% Ti with 30% initial BCP, the amount of all
these components increased. At all compositions and
both sintering temperatures, no BCP phase was detected
(for BCP major peak occurs at 2θ value of 31).
3.3. Mechanical Characteristics of the
As shown in Figure 4(a), the density of the Ti based
composites decreasedat increasing initial BCP content
for vacuum sintered composites both at 1300˚C and
1400˚C. Pure Ti had almost the same value as the theo-
retical value near 4.50 g·cm–3. The hardness and com-
pressive strength also showed the same tendency, there
was a decrease in the mechanical properties at higher
initial BCP contents as shown in Figures 4(b) and (c).
From these figures it can be seen that at the same initial
Ti-BCP composition, composites sintered at 1400˚C had
better mechanical properties than composites sintered at
1300˚C due to enhanced densification at higher tem-
perature, although the composition reacted at high tem-
perature to form different reaction product and the initial
BCP phase was almost entirely disappeared. For pure
titanium, this effect was not significant. The hardness
value was drastically fallen after introducing the ceramic
phase but kept steady afterwards with minor declination
with the increased BCP content. Compressive strength
value showed steadily declination as the initial BCP
content was increasing.
3.4. In Vitro Experiments
To evaluate the cytotoxicity of the composites, cell vi-
ability and cell proliferation on the composites were de-
termined through in vitro experiments with MTT assay
and by examining the morphology of surface grown in-
dividual cells. These experiments were conducted with
the composites sintered at a temperature of 1400˚C. It
was expected that the 70% Ti based composite would
show the best results relative to the other compositions
because of high initial Ca-P content. As expected, after
60 minutes of incubation, the cells on the 70% Ti com-
D. Mondal et al. / J. Biomedical Science and Engineering 4 (2011) 583-590
Copyright © 2011 SciRes. JBiSE
Figure 3. XRD pattems of (a) pure Ti sintered at 1400, (b) 10% BCP-Ti
and (c) 30% BCP-Ti sintered at 1300˚C, (d) 10% BCP-Ti and (e) 30%
BCP-Ti sintered at 1400˚C. Unmarked peaks are TiP.
(a) (b) (c)
Figure 4. Density, (b) Vikers, Hardness and (c) compressive strength of Ti-BCP composites at two different sintering temperatures.
posites had divided daughter cells were observed in the
SEM images; however, no daughter cells were observed
on the 80% Ti based composites and others.
Prior to mixing, the biphasic calcium phosphate and tita-
nium powders consisted of different particle size which
made a non uniform mixing with a bimodal particle dis-
tribution with two sharp peaks (Figure 1). BCP powder
consisted of nano size particles (<100 nm particle size)
with spherical morphology [25] and the Ti powder con-
sisted of micro size particle (less than 43 μm) with ir-
regular spongy shape [26]. The nano sized BCP covered
the much larger Ti particles and make a soft coating like
layer. This prevented the grain diffusion of the Ti and
sintering was hindered. The BCP particles themselves
were sintered in the mean time and the inter-particular
space of the Ti particles remained barely unaltered to
make the residual pores. However there were some
necking zones among the Ti particles that facilitate sin-
The XRD (Figure 3) and EDS (Figure 2) profiles in-
dicated that there was a reaction between titanium and
BCP. And BCP degraded into CaTiO3, CaO, TiO2and TiP.
The reaction [27] between the titanium and BCP is,
Ti + Ca10(PO4)6(OH)2 CaTiO3 + CaO + TiO2 + TiP
+ H2O.
Soas desired, no Hydroxyapatite or tri-calcium phos-
phate was found in the final sintered sample as shown in
the XRD profiles of Figure 3. The SEM images of the
composite bodies as shown in Fig.1demonstrated that the
surface of the titanium particles was degraded. The tita-
nium particles were wrapped by the other materials pro-
duced after the sintering. As the BCP concentration in-
creased so did the porosity and surface degradation. This
is due to the thicker covering of the Ti particles by in-
D. Mondal et al. / J. Biomedical Science and Engineering 4 (2011) 583-590
Copyright © 2011 SciRes. JBiSE
creased amount of BCP, which reduced the necking zone
of Ti.
The phases of the sintered composites did not change
significantly at the two different vacuum sintering tem-
perature 1300˚C and 1400˚C. In the XRD patterns (Fig-
ure 3), small amounts of CaO, TiO2, TiPand CaTiO3
were observed in the 90% Ti based composites sintered
at both 1300˚C and 1400˚C. However, for the 70% Ti
based composites, the amount of these compounds in-
creased at both sintering temperatures. Both HAp and
TCP degraded and the disproportionate peak intensity
between the metal and nonmetal composition made it
difficult to detect the phases.
The mechanical properties of TiO2 as shown in figure
4 vary drastically from Ti. Ti, being a metal has superior
strength value and fracture toughness and microstruc-
tural defects like cracks or pores does not affect the
properties overwhelmingly. Composites were denser at
higher sintering temperature of 1400˚C than 1300˚C.
The density of commercially pure Ti, TiO2, CaTiO3 and
TiP are 4.506 g·cm3, 4.23 g·cm3, 3.98 g·cm3 and 4.08
g·cm3 respectively. So that with increasing BCP content
in the composites the density decreased very rapidly. The
Vickers Hardness showed a steep decline with the intro-
duction of BCP powder from 400 HV to about its one
third values, but did not change drastically with the in-
creasing of BCP. This is because of the introduction of
porosity with the addition of BCP phase. In this study
the 70% Ti based composites sintered at 1400˚C showed
Vickers hardness value 108.8 HV and compressive
strength value 303.7 MPa. These values are closer to the
natural bones mechanical properties than that of the pure
Ti. For a human cortical bone Vickers hardness and
compressive strength are approximately 40.4 HV and
138 - 224 MPa, [28] respectively.
For a biomaterial, good cell viability is the most im-
portant pre-condition. MTT assay for the fabricated ma-
terials shown in Figure 5 revealed that all the compos-
ites composition exhibited good cell viability. MTT was
performed with L929 cell line which is a fibrosarcoma
cell line. 70% Ti based composite showed most cell vi-
ability than any other composition with more than 80%
absorbance for 100% extract as shown in Figure 5.
From the XRD data we knew that with increasing BCP
the amount of TiO2, CaO and CaTiO3 also increased and
from the MTT assay graph the cell compatibility also
increased with increasing of initial BCP concentration.
This infers that even after reaction was occurred, the
composites remained biocompatible. The interface be-
tween the implant and the host bone is one of the most
important issues for biomaterials used in hard tissue re-
pair applications. The bonding type is considered to be a
vital criterion for evaluating the biocompatibility and
bioactivity of biomaterials. When the morphology of
individual cells that had been incubated with the com-
posites for 60 minutes was analyzed, all composites ex-
cept pure Ti displayed a good cell proliferation and cell
attachment behavior as shown in Figure 6. On pure Ti
surface cells cannot proliferate in such short time [29].
Osteosarcoma MG63 cell line was used for one cell mor-
phology analysis. The cells were bound to the compos-
ites surfaces and proliferated well. After 60 minutes of
cell seeding the filopodial activity for 100% and 80% Ti
based composites were same as shown in Figure 6(a)
and (b). But in 70% Ti case composites (Figure 6(c))
cells started to divide into new daughter cells and mi-
grated. Filopods of cells in 70% Ti based composites
surface were most elongated. And one day after the cells
Figure 5. MTT assay results of composites vacuum sintered at 1400˚C.
D. Mondal et al. / J. Biomedical Science and Engineering 4 (2011) 583-590
Copyright © 2011 SciRes. JBiSE
Figure 6. Cell morphology on the surfaces of Ti based composites vacuum sintered at 1400˚C with MG63 cells; (a) pure Ti, (b)
20% BCP-Ti, (c) 30% BCP-Ti and after 1 hrs of cell seeding and (d) pure Ti, (e) 20% BCP-Ti and (f) 30% BCP-Ti after 24 hrs of
cell seeding.
were seeded, the surface of the 70% Ti based composite
body was completely covered with cells that wereprolif-
erating (Figure 6(f)). In the case of pure Ti, no signifi-
cant change in cell attachment was observed for one day
after cell seeding.
From the above discussion it can be drawn that the
mechanical properties shows better resemblance to that
of the cortical bone for the fabricated 70% Ti composites
compared to the pure titanium metal or even with that of
the titanium alloy. Moreover, the biocompatibility of the
70% Ti also showed remarkable improvement over that
of the pure Ti as shown in the MTT assay experiment
and cell proliferation after 24 hours. These two facts
indicate that the 70% Ti composites can be a potential
candidate for better hard tissue implant material for load
bearing condition. This would potentially minimize the
risk of stress shielding effect that is caused by the im-
plantation of pure Ti or its alloy or any other metallic
Although the initial materials were not fully preserved
after carrying out the fabrication process and a whole
new group of reaction products appeared, the biocom-
patibility of the fabricated materials were not compro-
mised. In contrast to the pure titanium, all the materials
had superior cell viability and cell proliferation behavior.
The material was not fully densified as the CaP phase
created a barrier for the Ti particles to sinter. This sig-
nificantly decreases the mechanical properties of the
pure Ti as shown by the hardness and compressive
strength value which was roughly one fourth of the pure
metals properties for 70% Ti containing composites.
However, the values were high enough for the successful
application as implant materials.
The in vitro bioactivity of Ti based composite is de-
pendent on their initial composition, i.e. the phase com-
position of the composites. The bioactivity was in the
order of 70% Ti > 80% Ti > 90% Ti > pure Ti. For the
70% Ti based composite, the cells started to divide into
daughter cells on the composite surfaces within 60 min-
utes. In addition, the mechanical properties were suitable
enough for use as a load bearing hard tissue implant. The
results of this work suggest that the Ti based composites
containing 70% Ti are potential candidates for load bear-
ing bone replacement applications.
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