Key Engineering Materials Vols. 396-398 (2009) pp 229-232
Online available since 2008/Oct/21 at www.scientific.net
© (2009) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/KEM.396-398.229
Effect of Saline Solution on the Development of Compressive
Strength in Apatite Based Bone Cement Containing Demineralized Bone
Matrix
Young-Woo Kim1,a, Tai-Joo Chung1,b, Ju-Woong Jang2,c, and
Kyung-Sik Oh1,d*
1
School of Advanced Materials Engineering, The Center of Green Materials Technology,
Andong National University, 388 Songchon-dong, Andong, Kyungbuk,760-749, Korea
2
Korea Bone Bank, AcetechnoTower IX 402 Gasan-dong, Geumcheon-Gu, Seoul, 153-782, Korea
b
c
d
a
[email protected], [email protected], [email protected], [email protected]
*To whom correspondence should be addressed.
Keywords: Bone Cement, Storage, Compressive Strength, DBM, Saline solution
Abstract. Compressive strength of apatite type bone cement was analyzed with respect to the
concentration of setting agent and types of saline solution used for storage after setting. With the
increase of the concentration to 2 M, the density of paste decreased. However, the compressive
strength of cement was not necessarily correlated with the density and dependent on the type of saline
solution used for storage after setting. One solution led rather porous paste and the strongest specimen
from the series was obtained under the maximized amount of apatite within the paste. The other saline
solution induced the more dense paste after setting. In this series, the strongest specimen was obtained
under the coexistence of low crystalline apatite and dicalcium phosphate dihydrate. The difference
between two saline solutions was explained in terms of the solidity of skeleton formed by apatite.
Introduction
Calcium phosphate based bone cement has aroused orthopaedic surgeon’s interest in the recovery of
damaged bone. Among the various types of calcium phosphate bone cement, combination of
α-tricalcium phosphate (α-TCP), tetracalcium phosphate (TTCP) and dicalcium phosphate dihydrate
(DCPD) produces calcium deficient apatite (CDHA) or octacalcium phosphate (OCP) as product and
it features the strength far greater than that of cancellous bone. In the bone cement, osteogenic
additives such as demineralized bone matrix (DBM) are often introduced [1]. However, such an
addition of compliant phase usually reduces the mechanical properties. Therefore, the compressive
strength of matrix needs to be further increased to compensate the decrease of strength caused by the
addition of any possible functional agents.
The mechanical properties of bone cements are dependent on the parameters such as powder to liquid
ratio, particle size, composition and so on [2]. However, little attention was paid on the environment
before and after setting. In case of the brushite cement, it was shown that the temperature and
humidity before setting were important factors controlling properties of cement [3]. In apatite based
cement, the specimens are usually conserved in the simulated body fluid or saline solution to mimic
the in vivo setting behavior and therefore the storing condition after setting requires systematic
investigation. In this work, effects of the types of saline solution and concentration of setting agent on
compressive strength were investigated in apatite cement. It was found that the type of saline solution
was an important parameter affecting the porosity of hardened paste and consequent compressive
strength. For the specimen with little porosity, it was suggested that the strength could be further
increased by incorporating secondary phase over the main product phase that play a skeletal role.
Materials and Methods
TTCP and α-TCP were prepared by stoichiometrically (Ca:P=2 for TTCP and 1.5 for α-TCP)
reacting CaCO3 and CaHPO4 at temperatures between 1350 and 1550oC. Successive quenching was
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230
Bioceramics 21
carried out to avoid the formation of unwanted phase like β-TCP. Prepared α− TCP, TTCP and
DCPD were mixed at a ratio of 6:2:2 in weight. As a setting agent, 0.5 ml of citric acid was used per
one gram of powder mixture. The concentration of citric acid was varied between 1.0 and 2.0 M. The
paste was molded into cubic with an edge of 10 mm and was conserved in commercially available
saline solutions designated as saline-A and saline-B, respectively. Both salines contained 9 g of
sodium chloride per 100 ml of solution, but they were different in preservatives. 0.002 g of
benzalkonium chloride was used in saline-A, while same amount of polyhexamethylene hydrochloric
acid was selected in saline-B. After conserving for 3 or 6 days, the hardened pasted was crushed for
the X-ray diffraction analysis. Also the compressive strength was estimated for cubic specimens using
an Instron 4204 at a crosshead speed of 0.5 mm/min. The porosities of cement were evaluated by
Archimedes immersion technique. For the cement paste exhibiting superior compressive strength, 10
volume % of DBM was introduced during preparation of paste and compressive strength was
measured.
Results and Discussion
Figure 1 shows the compressive strength of cement stored in either saline-A or B with respect to the
concentration of setting agent. For both types of saline solutions, the compressive strengths were not
much dependent on the stored days. However, the concentration of setting agent was found to strongly
affect the compressive strength of hardened paste. It was common for both types of saline solutions
that the decrease of compressive strengths took place at the concentration of 2 M. The decrease of
compressive strength was more serious in saline-A. In saline-A, the strength decreased to less than 20
MPa, while more than 30 MPa was maintained in saline-B. The results between two saline solutions
are drastically distinguished at 1.5 M. The greatest compressive strength (68 MPa) in this work was
recorded with saline-B, while the least value was observed with saline-A.
In saline-A, the compressive strength showed clear correlation behavior with density and porosity. As
summarized in Table 1, the density decreased from 1.432 to 1.272 g/ml with the increase of the
concentration. At the same time, the porosity increased from 21.9 to 37.4%. The cement conserved in
saline-B was generally less porous compared with saline-A. The generally superior strength observed
in saline-B series is thus attributed to the smaller porosity of hardened paste. In both saline solutions,
the porosities are found to increase with respect to the concentration. The greater viscosity of
concentrated setting agent might leave the pore bubbles incorporated in the paste under the
circumstance of less possibility of escape or elimination during setting or storage.
80
. 80
ht
3day
3day
thg
g
6day
6day
n
ne 60
er 60
rt
S )a
ev P
is M40
se (
rp
m
oC 20
0
tS )
evi aP 40
ss M
(
rep
20
m
oC
Saline-A
1.0M
1.5M
Citric acid
(a)
2.0M
0
Saline-B
1.0M
1.5M
Citric acid
2.0M
(b)
Fig. 1 Compressive strength of cement stored in (a) saline-A and (b) saline-B with respect to the
concentration of setting agent. The specimens were stored for 3 or 6 days.
Key Engineering Materials Vols. 396-398
231
Table 2 Density and porosity of cement stored in saline-A and B with respect to the concentration of
setting agent.
Concentration of
Setting Agent
1.0 M
1.5 M
2.0 M
Saline-A
Density (g/ml)
Porosity (%)
1.432
21.9
1.346
27.6
1.272
37.4
Saline-B
Density (g/ml)
Porosity (%)
1.455
18.7
1.398
21.8
1.361
29.9
Figure 2 shows the microstructure of specimens. Comparing the specimens between saline-A and B,
specimens of saline-A are found to have more interconnected large pores. On the contrary, specimens
stored in saline-B show more dense microstructure. Such a dense structure is supposed to be a key in
exhibiting good compressive strength when 1.5 M of setting agent is used.
Fig. 2 Microstructure of cements stored in saline-A or B using 1.0 or 1.5 M of setting agent.
(A) saline-A with 1.0 M, (B) saline-A with 1.5 M, (C) saline-B with 1.0 M, and (D) saline-B with 1.5
M
Figure 3 shows the X-ray diffraction patterns of hardened specimens. From Fig.3 (a), it can be
realized that the cement stored in saline-A is composed of CDHA and DCPD. With the increase of
concentration, the amount of DCPD increases and that of CDHA decreases. Therefore, in saline-A
series, it is found that formation of the sufficient CDHA as product phase leads to strong cement.
Fig.3 (b) shows formation of some unknown phase along with CDHA and DCPD when stored in
saline-B. It is also distinguished from Fig.3 (a) that amount of DCPD is generally limited. It is
worthwhile to notice that best compressive strength (~68 MPa) in this work was obtained from the
specimen mixed with CDHA and DCPD.
CDHA is the major product phase in apatite type bone cement and it contributes to hardening of paste
by formation of interconnected skeleton. The connectivity of skeleton should be proportional to the
density and therefore, the specimens of saline-B have better connected skeleton than those of saline-A.
Once the solid skeleton is provided, incorporation of secondary phase such as DCPD can contribute to
increase the strength by replacing voids. Therefore, it is suggested that good compressive strength can
be obtained in the sample composed of CDHA and DCPD provided that it has sufficient density and
232
Bioceramics 21
consequent solid skeleton. Introduction of 10 wt% of DBM in the cement evidently decreased the
strength to 35 MPa, but it still featured the strength greater than that of cancellous bone.
DCPD
CDHA
Cit2.0M
Cit1.5M
Cit1.0M
Saline-A
Cit2.0M
Cit1.5M
Cit1.0M
SBF-B
Saline-B
2.0 M
INTENSITY
INTENSITY
2.0 M
1.5 M
1.5 M
1.0 M
1.0 M
10
20
30
2θ
(a)
40
50
10
20
30
40
50
2θ
(b)
Fig. 3 X-ray diffraction patterns of specimens from (a) saline-A and (b) saline-B with respect to the
concentration of setting agent.
Conclusions
Properties of apatite type bone cement were compared with respect to the concentration of setting
agent and types of saline solution used for storage after setting. The increase of the concentration
generally led to the decrease of density. However, the compressive strength of cement was not
necessarily correlated with the density and dependent on the type of saline solution. One solution led
to the more porous paste and the strongest specimen had maximized amount of product phase. The
other saline solution induced the more dense paste after setting. In this series, the strongest specimen
was obtained under the coexistence of low crystalline apatite and dicalcium phosphate dihydrate. The
difference between two series was explained in terms of the solidity of skeleton formed by apatite.
References
[1] K.-Y. Lee et al. (2007) Key Engineering Materials. 330-332, 803-806.
[2] K.-S. Oh and S.-R. Kim. (2005) Key Engineering Materials. 284-286, 141-144.
[3] S.-A.Lee et al. (2008) Key Engineering Materials. 361-363, 351-354.
Acknowledgements
This work was carried out by a grant from Technology Innovation Program supported by Small and
Medium Business Administration of Korea.
Bioceramics 21
doi:10.4028/www.scientific.net/KEM.396-398
Effect of Saline Solution on the Development of Compressive Strength in Apatite
Based Bone Cement Containing Demineralized Bone Matrix
doi:10.4028/www.scientific.net/KEM.396-398.229
References
[1] K.-Y. Lee et al. (2007) Key Engineering Materials. 330-332, 803-806.
doi:10.4028/www.scientific.net/KEM.330-332.803
[2] K.-S. Oh and S.-R. Kim. (2005) Key Engineering Materials. 284-286, 141-144.
doi:10.4028/www.scientific.net/KEM.284-286.141
[3] S.-A.Lee et al. (2008) Key Engineering Materials. 361-363, 351-354.
doi:10.4028/www.scientific.net/KEM.361-363.351