Effect of Magnesium on the Mechanical and Bioactive Properties of Biphasic Calcium Phosphate

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Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 982-988

Published Online October 2012 (http://www.SciRP.org/journal/jmmce)

Effect of Magnesium on the Mechanical and Bioactive

Properties of Biphasic Calcium Phosphate

Ponnusamy Kanchana, Chinnathambi Sekar

Department of Bioelectronics and Biosensors, Alagappa University, Karaikudi, India

Email: [email protected]

Received August 12, 2012; revised September 15, 2012; accepted September 25, 2012

ABSTRACT

Incorporation of trace elements into calcium phosphate structure is of great interest for the development of artificial

bone implants. Biphasic calcium phosphate (BCP) composed of hydroxyapatite (HA) and β-tricalcium phosphate

(β-TCP) have been synthesized in the presence of magnesium (5 M% - 20 M%) by gel method under physiological

conditions. Crystallization of Mg-BCP in the gel medium mimics the Mg intake in the human body. Powder X-ray dif-

fraction and Fourier transform infrared analyses confirmed that the Mg doping leads to the enrichment of β-TCP phase

and suppresses the HA content in BCP. Nanoindentation studies indicate a significant decrease in hardness and elastic

modulus values of BCP due to Mg doping. In vitro bioactivity study has confirmed the formation of apatite layer on the

Mg doped samples making it suitable for bone replacement. The results suggest that the optimum Mg doping promotes

the bioactivity which is perquisite for biomedical applications.

Keywords: Biphasic Calcium Phosphate; Crystal Growth; X-Ray Diffraction; Mechanical Properties

1. Introduction

Biphasic calcium phosphate (BCP) composed of a mix-

ture of hydroxyapatite (HA, Ca10(PO4)6(OH)2) and β-tri-

calcium phosphate (β-TCP, β-Ca3(PO4)2) are interesting

candidates in reconstructive surgery [1-3]. They are par-

ticularly suitable for synthetic bone substitution appli-

cations because the HA provides a permanent scaffold

for new bone formation via osteoconduction and the re-

sorption of the β-TCP oversaturates the local environ-

ment with Ca2+ and ions to accelerate this new

bone formation. The HA/β-TCP ratio dominantly deter-

mines the rate and extent of BCP resorption in vivo, in

that higher β-TCP contents allow faster and more exten-

sive resorption [4]. Magnesium, one of the most impor-

tant divalent ions associated with the biological apatite,

has its own significance in the calcification process and

on bone fragility and has indirect influence on mineral

metabolism. BCP with Mg incorporation has been the

subject of extensive research because of its potential for

developing artificial bone and other biomedical appli-

cations [5]. The amount of HA and β-TCP in BCP can be

tailored by the insertion of Mg. Independently, Mg doped

HA is of great interest for the development of artificial

bones. The presence of Mg2+ within HA lattice sensibly

affects apatite crystallization in solution promoting the

formation of β-TCP and thus forming BCP [6].

PO 

Several methods have been reported to prepare Mg

substituted HA, β-TCP and BCP [6-9]. Ryu et al. [7]

showed that the MgO-doped HA/β-TCP synthesized by

conventional solid state reaction method exhibited high

density and improvements in compressive strength and

fracture toughness. In particular, the compressive strength

shows 1203 MPa, which is three times greater than the

undoped HA/β-TCP composite. Gomes et al. [1] have

reported that the bioactivity of the BCP has improved

due to the presence of Mg atoms in the structure of the

β-TCP phase. Kannan and Ferreira [8] have reported that

the sodium, magnesium and fluorine co-substituted

HA/β-TCP composites have higher thermal stability upto

1400˚C. In general, sol-gel and precipitation methods

need high temperature heating to produce BCP phases,

and the high temperature treatments results in the forma-

tion of minor phases such as CaO and MgO [1].

Earlier we have demonstrated that the strontium (Sr)

doped BCP synthesized by gel method was free from

these impurities [10]. As the gel medium offer the possi-

bility to mimic the growth of various biominerals in en-

vironments similar to natural biomineralization [11,12],

we have carried out the synthesis of BCP in sodium me-

tasilicate gel with various concentration of magnesium.

Effect of Mg addition on the HA/β-TCP ratio, morpho-

logy, bioactive properties and mechanical behavior of

BCP have been investigated.

2. Materials and Method

BCP was prepared by gel method using AR grade re-

P. KANCHANA, C. SEKAR 983

agents. Single diffusion gel method was employed to

prepare BCP using sodium metasilicate (SMS,

Na2SiO3·9H2O) gel. The gel was prepared by mixing

SMS solution of specific gravity 1.03 g/cm3 and 0.6 M of

disodium hydrogen phosphate (Na2HPO4) in the ratio 1:1.

The pH of the solution was adjusted to 7.4 using 10%

glacial acetic acid. About 10 ml of this solution was al-

lowed to gel in a test tube over a period of 2 days. After

the gelation, 1 M anhydrous CaCl2 solution was poured

on the gel without disturbing it. Growth experiments

were carried out at room temperature for a period of

three weeks. Finally, samples were harvested by decant-

ing the test tubes and the gel was removed by washing.

The samples were kept in hot air oven (60˚C) for 2 hours.

In another series, supernatant solution was prepared by

mixing 1 M of anhydrous CaCl2 with 0.05, 0.1, 0.15 and

0.2 M of magnesium chloride (MgCl2·2H2O) and the

growth was carried out as described above. BCP crystal-

lites collected from middle layers of each test tube were

subjected to systematic studies to understand the role of

Mg on the growth and mechanical properties. Both the

pristine and Mg doped BCP were sintered at 1000˚C in

ambient atmosphere for 5 hours and the resulting pow-

ders were characterized by commonly used techniques.

Powder X-ray diffraction pattern was recorded on

Bruker AXS D8 advanced diffractometer within the 2θ

range of 10 to 55˚ using CuKα1 as X-ray source (λ =

1.5406 Å). Surface analyses were carried out on BCP

samples using scanning electron microscopy (SEM) JSM

5610 LV JEOL make. Elemental analyses were done us-

ing the OXFORD INCA energy dispersive X-ray spec-

trometer (EDX) attached to SEM. Thermogravimetry of

samples was performed using TA instruments SDT Q600

V8.3 in the temperature range of 30˚C - 1200˚C at the

heating rate of 20˚C/minute in nitrogen atmosphere.

FTIR spectra were recorded on a Perkin Elmer (Spec-

trum RXI) spectrometer in transmission mode in the

wave number range between 400 and 4000 cm−1 using

KBr pellets.

To test the in vitro bioactivity, the samples were im-

mersed in simulated body fluid (SBF). The SBF was

prepared according to the procedure described by Ko-

kubo [13]. Samples were pressed into pellets of about 8

mm diameter and 1 mm thickness and the pellet was

immersed in 15 ml of SBF solution in airtight plastic

container. The solution was renewed every 48 h for a

period of three weeks. Then the samples were taken out,

washed with deionized water and dried. The morpho-

logical variation of the pellets surface after soaking in

SBF was studied by SEM.

For characterizing the mechanical response, both pris-

tine and Mg doped BCP were die-pressed and sintered at

600˚C for 5h in ambient atmosphere. Indentation impres-

sions were made by nanobased indentation system

NHTXS/S: 50-0172 with diamond Berkovich indenter.

The force used for all the samples was 100 mN with

loading and unloading rate of 20 mN/min. A minimum of

10 indents were made on each sample. Distance between

two separate indents was more than 20 μm to avoid the

influence of residual stresses from adjacent impressions.

From the load (P)-penetration depth (h) curves, the shape

of the unloading curve can be used as a means of obtain-

ing the elastic properties and hardness of the sample. The

slope S is the initial unloading stiffness, A is the pro-

jected area of contact and Er is the reduced modulus de-

termined by a method that has been developed and de-

scribed by Oliver and Pharr [14].

dπ

(or) 2





The elastic modulus of the sample Es can be calculated

using the relation





rs i

EE E







where Ei is elastic modulus of the indenter tip, νs and νi

are the Poisson ratio of the sample and indenter tip re-

spectively. The hardness (H) which is defined as the

mean pressure that the material will support under load is

determined by the following relation

max



where Pmax is the maximum applied load.

3. Result and Discussion

3.1. Synthesis of BCP

Biphasic calcium phosphate consisting of HA and β-TCP

was successfully synthesized by gel method. Upon the

addition of CaCl2 solution on the top of the set gel in the

test tubes, Ca2+ diffuses into the gel and reacts with



producing white precipitate at the gel solution

interface. Just below this, a circular white disc was ob-

served after one day. Subsequently, 12 discs of about 3

mm thickness each have grown in the gel medium over a

period of three weeks. The space between successive

white discs was found to increase towards the bottom of

the test tube from the interface due to the lack of diffu-

sion of “Ca” from top of the gel down to the bottom of

the tube. These white colored circular discs, commonly

known as Liesegang rings, were identified as BCP (Fig-

ure 1(a)).

In Mg added experiments, Liesgang rings have ap-

peared 4 to 5 days after the addition of supernatant solu-

P. KANCHANA, C. SEKAR

984

Figure 1. BCP in the form of Liesegang rings (a) undoped

BCP; (b) 0.05 M; (c) 0.1 M; (d) 0.15 M; and (e) 0.2 M Mg

doped BCP.

tion which indicate that the initial nucleation and growth

rate were retarded due to the presence of Mg in the

growth environment. The number of white discs got de-

creased as the concentration of Mg (0.05 - 0.2 M) in-

creased in the supernatant solution (Figures 1(b)-(e)).

We could collect the products grown with 0.05 and 0.1

M Mg only. The white discs formed at higher Mg levels

(0.15 and 0.2 M) were very fragile and got mixed up with

the gel at the time of harvest. It should be noted that the

amount of Ca present in the growth environment re-

mained the same as that of pristine BCP and Mg was

added as additive only. Thus the presences of Mg seem

to inhibit the formation of BCP. This inhibitory effect

may be attributed to the incorporation of smaller Mg2+

(0.66 Ǻ) at larger Ca2+ site (1.00 Ǻ) [15]. The presence of

strontium (Sr2+, 1.13 Å) in the growth environment is

also known to inhibit the formation of BCP [10]. Com-

pared to Sr2+, the Mg2+ has a strong influence on the

growth rate and total yield of BCP. The solubility of the

ionic impurity in the mother solution has been considered

as an indicator of the strength of the interfacial coor-

dination, the highest solubility corresponding to the

weakest interaction [16]. The addition of MgCl2·2H2O

with relatively high solubility affects the solubility of the

growth environment. Thus the Mg addition seems to in-

hibit the less soluble HA growth and lead to the forma-

tion of initial transient phases such as TCP [17]. In both

pure and Mg added growth experiments (0.05, 0.1 M %),

DCPD crystals (CaHPO4·2H2O) have grown in between

the rings. No such crystals were found at higher concen-

tration of Mg. Bigi et al. [18] also found significant inhi-

bition by Mg2+ on DCPD crystals.

3.2. Powder XRD Analyses

The as prepared BCP (undoped) and Mg-BCP (Mg

doped BCP) samples were identified as a mixture of HA

and



-TCP (Figures 2(a) and (b)) in agreement with the

JCPDS standards (09-0169 for β-TCP and 09-0432 for

HA). For Mg-BCP, XRD peaks corresponding to β-TCP

planes (0 2 10, 1 1 0) were found to be highly intensed

and the planes (2 1 1) corresponding to HA was less in-

tensed. Contrary to the BCP, Mg doping enriches β-TCP

content and suppresses the HA formation. A number of

ions are known to inhibit and disrupt nucleation of Ca-P

phases. Salimi et al. [19] showed that the Mg2+ has a

marked inhibiting effect on HA growth. They attributed

the inhibitory effect of Mg2+ to its adsorption at active

growth sites. This kinetically hinders nucleation of HA.

In our earlier work, we found that the Sr2+ doping has

enhanced the formation of HA and reduced the β-TCP

content in the BCP composites which was attributed to

the difference in ionic size of the dopant Sr2+ (1.13 Ǻ) in

place of Ca2+ (1.00 Ǻ).

High temperature annealing (1000˚C) of pristine BCP

resulted in the occurrence of more distinct and sharp

XRD peaks of β-TCP (Figures 3(a) and (b)). Contrary to

this, Mg-BCP samples have mainly β-TCP with traces of

γ-Ca2P2O7 phase. Further, the XRD peaks of the Mg

doped samples have been slightly and continuously

shifted to higher diffraction angles and there was a slight

decrease in their peak intensity (see inset of Figure 3).

Table 1 shows the variation of lattice parameters of the

investigated samples. These results suggest that Mg is

preferentially incorporated into the β-TCP phase, the

replacement of Ca by Mg induces lattice contraction and

the respective displacement toward higher 2θ angles [7].

Gomes et al. [1] reported the occurent of minor impurity

phases CaO, CaCO3 and MgO in the pristine and Mg-

BCP samples sintered at high temperature (500˚C -

Figure 2. XRD patterns of (a) pure BCP and (b) 0.1 M Mg

doped BCP.

P. KANCHANA, C. SEKAR 985

Figure 3. XRD patterns of sintered (1000˚C) (a) pure BCP

and (b) 0.1 M Mg doped BCP. Inset figure shows a system-

atic shift towards the higher angle side (2θ values between

30˚ to 35˚).

Table 1. Lattice parameters of pure and Mg doped



-TCP

(1000˚C).

Lattice parameters (Å)

Samples

a c

Volume (Å3)



-TCP 10.4147 37.2776 3501.57



-TCP + 0.1M Mg 10.3408 37.1926 3444.17

1100˚C). In the present case, both the as prepared and

sintered (1000˚C) samples synthesized by gel method did

not indicate the presence of any such impurity phases up

to the resolution limit of the XRD measurement.

3.3. SEM- EDX Analyses

Define abbreviations and acronyms the SEM pictures of

the pure and 0.1 M Mg-BCP samples are shown in Fi-

gures 4(a) and (b). The micrograph of BCP consisted of

fibers with an anisotropic aspect of approximately 6 - 10

m in length and 0.5 - 1.0 m in width (Figure 4(a)).

The Mg-BCP consisted of agglomerates of fibers on the

surface (Figure 4(b)), which confirmed that the presence

of Mg changed the growth pattern. An in vitro bioactivity

test of pure and 0.1 M Mg-BCP samples are shown in

Figures 4(c) and (d). Mg-BCP has revealed the forma-

tion of apatite layer on the surface of the pellets when

compared to that of pure BCP. The newly formed apatite

layer consisted of tiny spherical particles of calcium

phosphates (Figure 4(d)). This is in accordance with the

fact that a bioactive material would form a layer of apa-

tite between bones and implant which helps in bonding

of the implant to bone [13].

EDX measurements were made at different points on

Figure 4. SEM pictures of (a) pure BCP; (b) 0.1 M Mg

doped BCP and SBF soaked samples of (c) pure BCP (d) 0.1

M Mg doped BCP.

the samples and the results show that the BCP is prima-

rily composed of calcium and phosphorus without the

presence of other impurities (Figures 5(a) and (b)). In

BCP, the Ca/P ratio was found to be 1.58 [20]. In

Mg-BCP, (Ca+Mg)/P ratio was estimated at 1.42. The

average atomic percentages of the individual elements

are shown in Table 2. It can be noticed that the addition

of Mg leads to the “Ca” reduction when compared to

BCP sample. The average Mg value in the 0.1 M

Mg-BCP was estimated to be 3.52 atm%.

3.4. Thermogravimetric Analyses

TG curves of BCP and Mg-BCP are shown in Figure 6.

In both the cases, initial weight loss up to ≈450˚C was

due to the loss of adsorbed water (up to 200˚C) and

lattice water (up to 450˚C) [21]. Above this, weight loss

occurred in several steps between 450˚C and 900˚C

which indicate the transformation of HA into β-TCP

phase in the BCP [22].

The total weight loss up to the measured temperature

of 1200˚C was found to be 10.02% and 12.02% re-

spectively for pristine and Mg doped BCP. In addition, a

slight decrease in the decomposition temperature for Mg

doped sample was observed in the TG curve. These

observations suggest that the Mg doping lead to the re-

duced thermal stability of BCP.

3.5. FTIR Analyses

The FTIR spectra of BCP and Mg-BCP show vibrational

bands characteristic of calcium phosphate compounds

(Figure 7). The band at 1031 cm−1 is assigned to the tri-

P. KANCHANA, C. SEKAR

986

Table 2. EDX data of pure and Mg doped BCP.

Element Pure BCP (atm. %) Mg doped BCP (atm. %)

Ca 61.25 55.18

P 38.75 41.30

Mg - 3.52

Ca/P = 1.58 (Ca+Mg)/P = 1.42

Figure 5. EDX spectra of (a) BCP and (b) 0.1M Mg doped

BCP.

Figure 6. TG curves of (a) BCP and (b) 0.1 M Mg doped

BCP.

ply degenerate ν3 asymmetric P-O stretching mode. The

peak at 961 cm−1 is attributed to ν1, the non-degenerate

P-O symmetric stretching mode. The peaks at 601 and

562 cm−1 correspond to the triply degenerate ν4, O-P-O

bending mode and the band at 460 cm−1 is attributed to

the doubly degenerate ν2, O-P-O bending mode. The

bands at 1640 and 3441 cm−1 are assigned to the ad-

sorbed water [23]. The low intensity hydroxyl group at

3553 cm−1 indicates the presence of HA/TCP [24]. The

low intensity OH− group at 3553 cm−1 of the BCP was

not visible in the case of Mg-BCP sample. Moreover,

broadening of phosphate band at 1000 - 1100 cm−1 and

the weak bands at 869, 1371 cm−1 due to the P-O(H)

stretching in groups have appeared in the Mg-

HPO 

Wave number (cm–1)

Figure 7. FTIR spectra of (a) BCP and (b) 0.1 M Mg doped

BCP.

BCP only [25,26]. The peak broadening of phosphate

group and new peaks have confirmed the formation of

tricalcium phosphate due to Mg doping.

3.6. Nanoindentation Studies

Mechanical behavior of the BCP samples was investi-

gated in terms of hardness and elastic modulus obtained

by nanoindentation. Figure 8 shows the typical load-

penetration depth (p-h) curves obtained for BCP and

Mg-BCP samples. For comparative analysis, the p-h

curve of Sr doped BCP is also incorporated [10]. In all

the three cases, the p-h curves are associated with the

displacement bursts or pop-ins as indicated by arrow

marks in Figure 8. Similar pop-ins observed in the p-h

curves were reported to be associated with pile-ups

around the indent mark for HA and β-TCP single crys-

tals [27]. The mean value of elastic modulus (E) and

hardness values (H) of BCP, Sr and Mg doped BCP cal-

culated from the p-h curves are shown in Table 3. It can

be noticed that the E and H values for the Mg doped BCP

is lower when compared to that of pure and Sr doped

samples. The observed decrease in hardness values could

be attributed to the enrichment of β-TCP phase and the

difference in sizes between Ca (1.00 Å) and the dopants

Sr (1.13 Å) and Mg (0.66 Ǻ). However, all the p-h curves

show an elastic recovery after the removal of the applied

load.

4. Conclusion

The Mg doped biphasic calcium phosphate was success-

fully synthesized by the simple gel method. The as pre-

pared and sintered (1000˚C) samples did not indicate the

presence of impurities like CaO, CaCO3, MgO and ni-

trates. The presence of Mg2+ ions in the growth environ-

P. KANCHANA, C. SEKAR 987

Figure 8. Load vs displacement curves of BCP, Sr and Mg

doped BCP.

Table 3. The mean value of elastic modulus (E) and hard-

ness values (H) of pure, Sr and Mg doped BCP calculated

from the p-h curve.

Sample Elastic modulus (E)

(GPa)

Hardness (H)

(GPa)

BCP 23.41 (±3.14) 0.613 (±0.107)

BCP + 0.1M Sr 16.81 (±4.00) 0.427 (±0.081)

BCP + 0.1M Mg 10.64 (±2.24) 0.349 (±0.100)

ment suppresses the nucleation and subsequent growth of

BCP. Powder XRD results confirmed phase formation

and the variation in HA/TCP content in BCP as a func-

tion of Mg in the starting compound. When compared to

undoped BCP, Mg-BCP samples exhibited a higher pro-

portion of β-TCP content. XRD and EDX analyses con-

firmed Mg doping into BCP. The SEM micrographs

showed that the microstructural morphology of BCP

changes from fibrous for pristine BCP to agglomerates of

fibers for Mg-BCP. The nanoindentation results revealed

that the hardness (H) and elastic modulus (E) of BCP

slightly decreases due to Mg doping. The in vitro bio-

activity study showed that the Mg doped BCP could in-

duce apatite formation on their surface after three weeks

of soaking in simulated body fluid which is desirable for

bone replacement applications.

5. Acknowledgements

P.K. acknowledges with thanks the Council of Scientiﬁc

and Industrial Research (CSIR), India for providing the

Research Associateship (F. No. 9/688(0022)/12 EMR-I).

REFERENCES

[1] S. Gomes, G. Renaudin, E. Jallot and J. M. Nedelec,

“Structural Characterization and Biological Fluid Interac-

tion of Sol-Gel-Derived Mg-Substituted Biphasic Cal-

cium Phosphate,” Applied Materials and Interfaces, Vol.

1, No. 2, 2009, pp. 505-513. doi:10.1021/am800162a

[2] S. Mondal, B. Mondal, A. Dey and S. S. Mukhopadhyay,

“Studies on Processing and Characterization of Hy-

droxyapatite Biomaterials from Different Bio Wastes,”

Journal of Minerals & Materials Characterization & En-

gineering, Vol. 11, No. 1, 2012, pp. 55-67.

[3] D. Luna-Zaragoza, E. T. Romero-Guzmán and L. R.

Reyes-Gutiérrez, “Surface and Physicochemical Charac-

terization of Phosphates Vivianite, Fe2(PO4)3 and Hy-

droxyapatite, Ca5(PO4)3OH,” Journal of Minerals & Ma-

terials Characterization & Engineering, Vol. 8, No. 8,

2009, pp. 591-609.

[4] R. W. N. Nilen and P. W. Richter, “The Thermal Stability

of Hydroxyapatite in Biophasic Calcium Phosphate Ce-

ramics,” Journal of Minerals & Materials Characteriza-

tion & Engineering, Vol. 19, No. 4, 2008, pp. 1693-1702.

doi:10.1007/s10856-007-3252-x

[5] F. Ren, Y. Leng, R. Xin and X. Ge, “Synthesis, Charac-

terization and Ab Initio Simulation of Magnesium-Sub-

stituted Hydroxyapatite,” Acta Biomater, Vol. 6, No 7,

2010, pp. 2787-2796. doi:10.1016/j.actbio.2009.12.044

[6] I. Cacciotti, A. Bianco, M. Lombardi and L. Montanaro,

“Mg-Substituted Hydroxyapatite Nanopowders: Synthesis,

Thermal Stability and Sintering Behavior,” Journal of the

European Ceramic Society, Vol. 29, No. 14, 2009, pp.

2969-2978. doi:10.1016/j.jeurceramsoc.2009.04.038

[7] H. S. Ryu, K. S. Hong, J. K. Lee, D. J. Kim, J. H. Lee, B.

S. Chang, D. H. Lee, C. K. Lee and S. S. Chung, “Mag-

nesia-Doped HA/β-TCP and Evaluation of Their Bio-

compatibility,” Biomaterials, Vol. 25, No. 3, 2004, pp.

393-401. doi:10.1016/S0142-9612(03)00538-6

[8] S. Kannan and J. M. F. Ferreira, “Synthesis and Thermal

Stability of Hydroxyapatite-β-Tricalcium Phosphate Com-

posites with Cosubstituted Sodium, Magnesium, and

Fluorine,” Chemistry of Materials, Vol. 18, No. 1, 2006,

pp. 198-203. doi:10.1021/cm051966i

[9] S. R. Kim, J. H. Lee, Y. T. Kim, D. H. Riu, S. J. Jung, Y.

J. Lee, S. C. Chung and Y. H. Kim, “Synthesis of Si, Mg

Substituted Hydroxyapatites and Their Sintering Behav-

iors,” Biomaterials, Vol. 24, No. 8, 2003, pp. 1389-1398.

doi:10.1016/S0142-9612(02)00523-9

[10] P. Kanchana and C. Sekar, “Influence of Strontium on the

Synthesis and Surface Properties of Biphasic Calcium

Phosphate (BCP) Bioceramics,” Journal of Applied Bio-

materials and Biomechanics, Vol. 8, No. 3, 2010, pp.

153-158.

[11] P. Kanchana and C. Sekar, “Influence of Sodium Fluoride

on the Synthesis of Hydroxyapatite by Gel Method,”

Journal of Crystal Growth, Vol. 312, No. 6, 2010, pp.

808-816. doi:10.1016/j.jcrysgro.2009.12.032

[12] C. K. Chauhan, M. J. Joshi and A. D. B. Vaidya, “Growth

Inhibition of Struvite Crystals in the Presence of Herbal

Extract Boerhaavia Diffusa Linn,” American Journal of

Infectious Diseases, Vol. 5, No. 3, 2009, pp. 170-179.

doi:10.3844/ajidsp.2009.170.179

[13] T. Kokubo, H. Takadama, “How Useful is SBF in Pre-

P. KANCHANA, C. SEKAR

988

dicting in Vivo Bone Bioactivity?” Biomaterials, Vol. 27,

No. 15, 2006, pp. 2907-2915.

doi:10.1016/j.biomaterials.2006.01.017

[14] W. C. Oliver and G. M. Pharr, “An Improved Technique

for Determining Hardness and Elastic Modulus Using

Load and Displacement Sensing Indentation Experi-

ments,” Journal of Materials Research, Vol. 7, No. 6,

1992, pp. 1564-1583. doi:10.1557/JMR.1992.1564

[15] J. F. Ferguson and P. L. McCarty, “Effects of Carbonate

and Magnesium on Calcium Phosphate Precipitation,”

Environmental Science and Technology, Vol. 5, No. 6,

1971, pp. 534-540. doi:10.1021/es60053a005

[16] S. Veintemillas-Verdaguer, “Chemical Aspects of the

Effects of Impurities in Crystal Growth,” Progress in

crystal growth and characterization of materials, Vol. 32,

No. 1-2, 1996, pp. 75-109.

doi:10.1016/0960-8974(96)00005-8

[17] E. Boanini, M.Gazzano and A. Bigi, “Ionic Substitutions

in Calcium Phosphates Synthesized at Low Tempera-

ture,” Acta Biomaterialia, Vol. 6, No. 6, 2010, pp. 1882-

1894. doi:10.1016/j.actbio.2009.12.041

[18] A. Bigi, M. Gazzano, A. Ripamonti and N. Roveri, “Ef-

fect of Foreign Ions on the Conversion of Brushite and

Octacalcium Phosphate into Hydroxyapatite,” Journal of

inorganic biochemistry, Vol. 32, No. 4, 1988, pp. 251-257.

doi:10.1016/0162-0134(88)85004-9

[19] M. H. Salami, J. C. Heughebaert and G. H. Nancollas,

“Crystal Growth of Calcium Phosphates in the Presence

of Magnesium Ions.” Langmuir, Vol. 1, No. 1, 1985, pp.

119-122. doi:10.1021/la00061a019

[20] E. C. Victoria and F. D. Gnanam, “Synthesis and Charac-

terization of Biphasic Calcium Phosphate,” Trends in

Biomaterials & Artificial Organs, Vol. 16, No. 1, 2002,

pp. 12-14.

[21] W. L. Suchanek, K. Byrappa, P. Shuk, R. E. Riman, V. F.

Janas and K. S. Ten Huisen, “Mechanochemical-Hydro-

thermal Synthesis of Calcium Phosphate Powders with

Coupled Magnesium and Carbonate Substitution,” Jour-

nal of solid state chemistry, Vol. 177, No. 3, 2004, pp.

793-799. doi:10.1016/j.jssc.2003.09.012

[22] P. N. Kumta, C. Sfeir, D. H. Lee, D. Olton and D. Choi,

“Nanostructured Calcium Phosphates for Biomedical Ap-

plications: Novel Synthesis and Characterization,” Acta

Biomaterialia, Vol.1, No. 1, 2005,pp. 65-83.

doi:10.1016/j.actbio.2004.09.008

[23] I. Sopyan and A. N. Natasha, “Preparation of Nanostruc-

tured Manganese-Doped Biphasic Calcium Phosphate

Powders via Sol-Gel Method,” Ionics, Vol. 15, No. 62009,

pp. 735-741. doi:10.1007/s11581-009-0330-8

[24] I. Manjubala and M. Sivakumar, “In-Situ Synthesis of

Biphasic Calcium Phosphate Using Microwave Irradia-

tion,” Materials Chemistry and Physics, Vol. 71, No. 3,

2001, pp. 272-278. doi:10.1016/S0254-0584(01)00293-0

[25] J. Pena and M. Vallet-Regi, “Hydroxyapatite, Tricalcium

Phosphate and Biphasic Materials Prepared by a Liquid

Mix Technique,” Journal of the European Ceramic Soci-

ety, Vol. 23, No. 10, 2003, pp. 1687-1696.

doi:10.1016/S0955-2219(02)00369-2

[26] K. P. Sanosh, M. C. Chu, A. Balakrishnan, T. N. Kim, S.

J. Cho, “Sol-Gel Synthesis of Pure Nano Sized β-Tricalcium

Phosphate Crystalline Powders,” Current Applied Physics,

Vol. 10, No. 1, 2010, pp. 68-71.

doi:10.1016/j.cap.2009.04.014

[27] B. Viswanath, R. Raghavan, U. Ramamurthy and N. Rav-

ishankar, “Mechanical Properties and Anisotropy in Hy-

droxyapatite Single Crystal,” Scripta Materialia, Vol. 57,

No. 4, pp. 361-364. doi:10.1016/j.scriptamat.2007.04.027