synthesis nano biphasic calcium phosphate by untrasound assisted process for biomaterial application

SYNTHESIS NANO BIPHASIC CALCIUM PHOSPHATE BY
UNTRASOUND ASSISTED PROCESS FOR BIOMATERIAL
APPLICATION
Ngoc Quyen Tran
1
, Cuu Khoa Nguyen
1

Hoang Nguyen
1
, Kim Lien Pham
2
and Thị Phuong Nguyen
1

1
Institute of Applied Materials Science, Vietnam Academy of Science and Technology,
2
Lac Hong University, Dong Nai province
*Email: ;
Tóm tắt

Nano calcium phosphat vật liệu được ứng dụng trong lĩnh vực y sinh. Các hạt nano biphasic
calcium phosphat (hỗn hợp của Hydroxyapatite và tricalcium phosphat) được tổng hợp bằng
phương pháp kết tủa calcium chloride và tri-sodium phosphat kết hợp sóng siêu âm. pH của phản
ứng được duy trì ở 7, 9 và 11 bằng cách thêm dung dịch natri hydroxide vào hệ phản ứng. Cấu trúc
của BCP được xác định bằng phương pháp nhiễu xạ tia X (XRD), phổ hồng ngoại (FTIR). Hình thái
của nano BCP được xác định bằng phương pháp kính hiển vi điện tử quét (SEM).
Từ khóa: biphasic calcium phosphat, calcium phosphate, sóng siêu âm

Abstract

Nanoscale calcium phosphates is a promising material for biomedical applications. Biphasic
calcium phosphate nanopowders (mixture of Hydroxyapatite and tricalcium phosphate) were
prepared by precipitation method under ultrasonic irradiation using calcium chloride and tri-
sodium phosphate. The pH of the reaction system was maintained at 7, 9 and 11 by adding of
sodium hydroxide solution. The calcined powders were characterized by using X-ray powder
diffraction(XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron
microscopy (SEM).
Key words: biphasic calcium phosphate, ultrasonic, calcium phosphate.
1. INTRODUCTION
Calcium phosphates have received most attention for bone repair applications because
they have the requisite characteristics to be excellent candidates for biomaterial applications
[1-2]. Moreover, calcium phosphates have a high adsorption capacity for serum proteins,
such as fibronectin and vitronectin. Therefore, using of calcium phosphates as bone repair
materials could result in enhancing attachment of osteoblast cells. On the other hand,
calcium phosphate gradually dissolved to release calcium and phosphate ions, which are
beneficial to bone formation [3-5].
Among calcium phosphate ceramics, such as hydroxyapatite (HAp) and TCP
(tricalcium phosphate), osteoinductivity of BCP (HAp and TCP) has been reported as more
efficient than HAp alone for repair of periodontal defects, and having better osteoinduction
than single phasic HAp or TCP. HAp is stable in body fluid, while TCP is rather soluble.
On the other hand, the dissolution rate of HAp in human body after implantation is too low
to achieve the optimal results while the dissolution rate of TCP is too fast for bone bonding.
Their range of biodegradation rate still cannot satisfy the requirement for biodegradable
biomaterials. The degradation rate of the biomaterials should not exceed remodeling rate
and bone ingrowth. Therefore, biphasic calcium phosphate, the combination of HAp, TCP
may present a scope for optimal biodegradable calcium phosphates, were developed. For
these materials constituted of HAp and TCP mixture, the adjustment of Ca/P ratio value
allows controlling the resorption rate. The combination of HAp, TCP can improve the
mechanical properties, induce the proper biodegradation and promote the osteointegration
that is increasing the bioactivity [2, 3, 6, 7].

Recent advancements in nanoscience and nanotechnology, investigation of nanoscale
calcium phosphate has been revitalized because of its good biocompatibility and bone
integration ability. Due to greater surface area which may improve fracture toughness, nano
calcium phosphate powders exhibit improved sinterability and enhanced densification.
Nevertheless, having better bioactivity, its particles can be utilized for engineered tissue
implants with improved biocompatibility over other implants [8].
However, to effectively control the size and morphology of the resulting nanoparticles
can be a hindrance. One of the solutions for this problem is to use ultrasonic irradiation, and
its preferably used for many reasons: (1) increasesreaction speed, (2) decreases processing
time, and (3) an overall improvement in the efficiency of energy consumption. The particle
size relates to nucleation and the growth pattern of the material. Ultrasonic irradiation is
used in the synthesis process promote both physical effects and chemical reactions that
directly influence the synthesis procedure of materials in liquid [9].
In this research,BCP nanopowder were prepared by wet precipitation method under
ultrasonic irradiation. The influences of pH of the starting solution on BCP microstructures
and crystal structures were investigated using X-ray diffraction (XRD), field emission
scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FT-
IR).
2. MATERIAL AND METHODS
2.1 Material
Calcium chloride dihydrate (CaCl
2
.2H
2
O, 99%), tri-sodium phosphate dodehydrate
(Na
3
PO
4
.10H

2
O, 98%) and sodium hydroxyte were obtained from Merck, Germany.
2.2 Experimental procedure
Calcium chloride dihydrate and tri-sodium phosphate dodehydrate as calcium and
phosphorous precursors were weighed to coincide the stoichiometric BCP with molar ratio
of Ca/P = 1.57. Calcium phosphates were synthesized in aqueous solutions with constant
pH at 50
o
C. The pH of the system was maintained by adding of sodium hydroxide solution.
A white precipitate was formed and the suspension was kept under ultrasonic irradiation for
1 h. After cooling to room temperature, the precipitate was washed thoroughly with de-
ionized water several times and dried in an oven at 90◦C. Finally, the calcination was
carried out at 750 ◦C in air.
2.3 Characterization
The influence of pH on BCP nanopowder’s phase was identified using X-ray
diffractometer (XRD, D8/Advance, Bruker, UK) with CuKα, (λ=1.5406 Å) as a radiation
source over the 2θ range of 20 - 80º at 25ºC. Morphology and microstructure of the
synthesized powders were investigated using FESEM (JSM-635F, JEOL).
Infrared spectra were performed by FTIR (Equinox 55, Bruker, UK) in range of 400–
4000 cm
-1
wave number region. For infrared spectroscopy, samples were pulverized and
mixed with a given amount of potassium bromide (KBr) and pressed in very thin tablets.
3. RESULTS AND DISCUSSION

Fig. 1 FESEM images of BCP and HAp nanopowders depending on the pH of the
starting solution: (a,d) pH 7, (b, e) pH 9 and (c, f) pH 11
The morphology of synthesized BCP and HAP powders were shown in Fig 1. Both of
them are nano particles which distribute uniformly. The particle size is related to nucleation
and growth pattern of the material that is highly influenced by the degree of super saturation

in the liquid phase. These effects increase chemical and physical effects, thus ultrasound
can be used for the synthesis of materialsin liquid phase. Nano calcium phosphate, having
better bioactivity, its particles can be utilized for biomaterial with improved
biocompatibility.

Fig. 2 XRD patterns of BCP and HAp nanopowders depending on the pH of the
solution: (a) pH 7, (b) pH 9 and (c) pH 11.
XRD spectra of the synthesized BCP and HAP nano powders are shown in fig 2. These
graphs allowed calculating the Ca/P ratio of precipitated powders and the proportion of TCP
(Table 1). Because of partial peak superposition, it appears that the most appropriate peaks
for quantitative analysis correspond to the plane (2 1 0) at 2θ = 29° for HAP and to the
plane (0 2 10) at 2θ = 31° for TCP. Therefore, the intensity ratios are used for quantitative
analysis of biphasic calcium phosphates containing HAP and TCP [10]. They are defined as
follows:
R =
𝐼
𝑇𝐶𝑃 (0210 )
𝐼
𝐻𝐴𝑝 (210)

R  C  wt% TCP
where C is a constant.
Table 1: Synthesis parameters and compositions of BCP and HAp


pH
R
7
2,4
9

1,6
11
0
The intensity ratios of the plane (2 1 0) at 2θ = 29° for HAP and to the plane (0 2 10) at
2θ = 31° for TCP (R) decreased as the pH of the solution increased. The XRD pattern in
Fig. 2 indicated that the sample (a) and (b) contained two crystalline phases (tricalcium
phosphate and hydroxyapatite). On the other side, HAp existed in the sample (c), at pH 7
and 9 the synthesized powder shown mixed phases with TCP and HAp. On the other hand,
at pH 11, the TCP phase disappeared due to its high solubility. Increasing the pH value
caused the yield of TCP powders to gradually decrease [11, 12].

Fig. 3 FTIR spectrum of BCP and HAp nanopowders depending on the pH of the
solution: (a) pH 7, (b) pH 9 and (c) pH 11.
Fig. 3 shows typical FT-IR spectra of nano powders.The sharp peak at 3573 cm-
1

corresponds to the vibrations of the lattice OH
–
ions in HAp. The peak at 635 cm-
1
is

stretching vibration of the HAp hydroxyl group. The very strong bands at 1032 cm
-1
and
1092 cm
-1
correspond to the PO
4
-3

functional group. The observation of the asymmetric P-O
stretching vibration of the PO
4

3-
bands at 962 cm
-1
as a distinguishable peak, together with
the sharp peaks at 635, 603 and 570 cm
-1
correspond to the triply degenerate bending
vibrations of PO
4
in hydroxyapatite. Our FTIR results were similar to the literature data [9,
13, 14].
4. CONCLUSIONS
In this study, the synthesis of nano HAp and BCP powder obtained by untrasound
assisted process. The sample prepared at pH 7 and 9 is BCP powders, where-as the powder
prepared at pH 11 had HAp powders. Thus, our results confirmed that increasing pH
changed phase composition of the synthesized powders. The intensity ratios of the plane (2
1 0) at 2θ = 29° for HAp and to the plane (0 2 10) at 2θ = 31° for TCP (R) decreased as the
pH of the solution increased since the TCP phase disappeared due to its high solubility. The
prepared powders could be widely used for biomedical applications.
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