Journal of Medical and Biological Engineering, 32(3): 201-204
201
Properties of TTCP/DCPA/CSH Cement Immersed in Hanks’
Solution
Jiin-Huey Chern Lin1
Sen-Hsiang Hung1
Jing-Wei Lee3
Wei-Luen Chen2
Ruey-Mo Lin4
Chang-Keng Chen1
Chien-Ping Ju1,*
1
Department of Materials Science and Engineering, National Cheng Kung University, Tainan 701, Taiwan, ROC
2
Joy Medical Devices Corporation, Luzhu Township, Kaohsiung 821, Taiwan, ROC
3
Division of Plastic Surgery, Department of Surgery, National Cheng Kung University Hospital, Tainan 704, Taiwan, ROC
4
Department of Orthopedics, National Cheng Kung University College of Medicine and Hospital, Dou-Liou Branch, Yunlin 640, Taiwan, ROC
Received 17 Jan 2011; Accepted 21 Jun 2011; doi: 10.5405/jmbe.889
Abstract
As bone substitute materials, most commonly used calcium phosphates exhibit relatively low bioresorption rates.
Most calcium sulfates exhibit relatively low mechanical strength and excessively high dissolution rates. The structure
and properties of tetracalcium phosphate (TTCP)/dicalcium phosphate anhydrous (DCPA)/calcium sulfate hemihydrate
(CSH) cement immersed in Hanks’ solution are investigated in the present study. Results indicate that this cement has a
working time of 6.6 min and setting time of 7.7 min. The maximum compressive strength is obtained when the cement
is immersed in Hanks’ solution for 1 day, at which point the TTCP/DCPA-hydroxyapatite (HA) phase transformation
has been largely completed. The long-term pH value of the Hanks’ solution wherein the cement is immersed remains
between 6 and 7. The HA phase remains the dominant phase throughout the entire 42 days of immersion.
Keywords: Calcium phosphate, Calcium sulfate, Bone cement, Hanks’ solution
1. Introduction
Most currently used calcium phosphate and calcium
sulfate materials have excellent biocompatibility, osteoconductivity, and bioresorbability, and are non-exothermic and
X-ray detectable. However, most calcium phosphates,
especially the commonly used highly crystalline hydroxyapatite
(HA), exhibit relatively low bioresorption rates [1] and most
calcium sulfates exhibit relatively low mechanical strength and
unfavorably high dissolution rates [2].
Calcium sulphate hemihydrate (CSH, CaSO4, 0.5H2O),
commonly known as plaster of Paris, has been extensively used
in construction, ceramics, and medicine. It undergoes virtually
complete resorption in vivo without eliciting a significant
inflammatory response [2]. However, for many applications,
insufficient mechanical strength may cause premature
disintegration of the implant and an excessively high
dissolution rate may not allow new bone cells to effectively
grow into a bone cavity [3].
A tetracalcium phosphate (TTCP)/dicalcium phosphate
* Corresponding author: Chien-Ping Ju
Tel: +886-6-2748086, Fax: +886-6-2748086
E-mail: [email protected]
anhydrous (DCPA)/CSH composite system has recently been
developed in the present authors’ laboratory. The present study
investigates the changes in the structure and properties of
TTCP/DCPA/CSH cement immersed in Hanks’ solution for
various periods of time.
2. Materials and methods
TTCP powder was fabricated in-house using the method
suggested by Brown and Epstein [4]. TTCP/DCPA/CSH
cement was prepared by mixing TTCP/DCPA/CSH composite
powder with a TTCP:DCPA:CSH weight ratio of 2.91:1.09:1
(or a TTCP/DCPA:CSH weight ratio of 80:20) with a
phosphate-containing hardening solution. The prepared
TTCP/DCPA/CSH cement paste exhibited a working time of
6.6 min and setting time of 7.7 min, which are suitable for most
orthopedic and dental surgeries.
The methods used for measuring the working and setting
times and the pH values of the cement during hardening and the
Hanks’ solution [5] wherein the cement paste sample was
immersed are described elsewhere [6]. The Hanks’ solution
was maintained at 37 °C throughout testing and continually
stirred to maintain uniform ion concentrations in the solution.
The phases of the cement were analyzed using an X-ray
diffractometer (XRD, D-MAX B, Rigaku, Tokyo, Japan) with
Ni-filtered CuKα radiation operated at 30 kV and 20 mA at a
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scanning speed of 1°/min. The porosity values of the samples
were measured according to the ASTM C830-00 (2006)
method. The compressive strength (CS) values were measured
using a desk-top mechanical tester (AGS-500D, Shimadzu,
Tokyo, Japan) at a crosshead speed of 1.0 mm/min. The test
method was according to the ASTM 451-99a method.
To determine the weight loss values of the
TTCP/DCPA/CSH cement immersed in Hanks’ solution for
various periods of time, the weights of the cement samples
before and after immersion (W0 and Wt, respectively) were
measured using an electronic balance with an accuracy of
0.001 g. After being removed from the Hanks’ solution, the
samples were dried in anhydrous ethanol at 50 °C for 1 day.
The weight loss ratio of each sample was determined as:
Weight loss ratio (% ) = (W0 -Wt) / W0 × 100
the porosity level of the cement did not change significantly.
After 42 days, the porosity value increased to 32.8 % from its
1-d value of 27.7%. The dissolution of CSH, CSD (formed by
the hydration of CSH during immersion), and phosphates
(TTCP and DCPA) could contribute to the increases in porosity
and weight loss.
3. Results and discussion
As shown in Fig. 1, during hardening, the pH value of the
cement paste slightly increased with time until it reached a
plateau (8.1) at 30 min. It has been reported that the early
dissolution of TTCP in phosphate-containing solution could
cause the pH value to increase [7]. The mildly basic nature of
the solution at the early stage may be a result of the balance
between the dominant phosphate component, specifically TTCP,
that dissolved in the solution and caused the solution to turn
basic [8], and the sulfate component, i.e., CSH, that caused the
solution to turn acidic [2].
Figure 2. Weight loss and porosity values of cement immersed in
Hanks’ solution.
Figure 3 shows typical XRD patterns of the various
starting powders and the hardened cement immersed in Hanks’
solution for various periods of time. The characteristic peaks of
CSD are also given as a reference. The XRD peaks of TTCP
and DCPA can be easily identified in the 1-h sample. The CSH
peaks are largely diminished in the 1-h sample, indicating a
quick CSH dissolution process in the solution. In the 1-d
sample, the HA phase was found to dominate the XRD patterns,
indicating that the TTCP/DCPA-HA phase transformation had
been largely completed after 1 day. In the same duration, all
three starting phases (TTCP, DCPA, and CSH) became
insignificant. The HA phase remained dominant throughout the
entire 42 days of immersion. The absence of CSD peaks in the
XRD patterns is considered to be due to the relatively small
quantity and/or quick dissolution of CSD after it formed from
the hydration of CSH in the solution.
Figure 1. Variations in pH value of cement during hardening and
Hanks’ solution during immersion.
The long-term variation in the pH value of the Hanks’
solution wherein the cement was immersed is also shown in
Fig. 1. The pH value gradually decreased, which is probably
due to a combined effect of the formation of HA [10], the
hydration of CSH, and the dissolution of calcium sulphate
dihydrate (CSD) [2], each of which could cause the pH value of
the solution to decrease.
As shown in Fig. 2, the cement lost 11.4% of its weight
after being immersed in Hanks’ solution for 1 day, with no
significant weight loss thereafter. After 42 days, the weight loss
of the cement increased to 16.8%. The porosity data
demonstrates the same trend. After being immersed for 1 day,
Figure 3. XRD patterns of starting powders and cement immersed in
Hanks’ solution.
As shown in Fig. 4, the CS value of the cement continued
to increase at the early stage. The maximum CS value was
observed in the 1-d sample. After 1 day, the CS value gradually
decreased, reaching 35 MPa on day 42. The increase in CS at
Structure and Properties of TTCP/DCPA/CSH Cement
the early stage might be explained by the increased amount of
HA that formed from the reaction of TTCP and DCPA [9]
during the hardening and immersion processes. This
HA-induced increase in strength has also been observed in
many calcium phosphate cement (CPC) systems [6,9-11]. The
long-term gradual decrease in CS of the immersed cement
might be a direct result of the dissolution-induced increase in
its porosity level, since the HA content of the cement remained
mostly unchanged after the cement had been immersed for a
few days.
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immersed for 1 day; thereafter, the weight loss and porosity did
not change significantly. XRD patterns indicate a quick
dissolution of CSH in the solution. After immersion for 1 day,
the TTCP/DCPA-HA phase transformation was largely
completed. The HA phase remained dominant throughout
long-term immersion. The CS value of the hardened cement
increased for 1 day, and then gradually decreased, reaching
35 MPa on day 42.
Acknowledgment
The authors would like to acknowledge the support for
this research by the Southern Taiwan Science Park (Kaohsiung
Science Park), Taiwan, R.O.C., under grant BZ-07-18-43-98.
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Figure 4. Variation in compression strength of cement immersed in
Hanks’ solution.
Several implantable calcium sulfate/calcium phosphate
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4. Conclusion
[11]
The structure and properties of TTCP/DCPA/CSH cement
immersed in Hanks’ solution were investigated. The cement
paste exhibited average working and setting times of 6.6 min
and 7.7 min, respectively, making it suitable for most
orthopedic and dental surgeries. The pH value of the cement
paste slightly increased during hardening. The pH value of the
Hanks’ solution wherein the cement was immersed remained
between 6 and 7 over the long term. The hardened cement lost
11.4% of its weight and had a porosity of 27.7% after being
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