Synthesis and Characterization of Hydroxyapatite Nanoparticles and β-TCP Particles

Maisara S.M. Arsad & *Pat M.Lee Materials Technology Program,

Faculty of Applied Sciences, Universiti Teknologi MARA,

40450 Shah Alam, MALAYSIA * patmlee.1@gmail.com

Lee Kong Hung Malaysia University of Science & Technology,

Petaling Jaya, MALAYSIA

Abstract - Hydroxyapatite (HA) was prepared by co-precipitation of calcium chloride and phosphoric acid while β-TCP was prepared using ammonium hydrogen phosphate and calcium chloride. The wet powders from both preparations were centrifuged, sonicated, autoclaved and calcinated to produce nanoparticles. They were characterized by SEM, XRD and FTIR. Green and sintered disc of both samples were also prepared. The hydroxyapatite nanoparticles were of rod shape structure with dimension of 65±1.0 nm for length and 25±1.0 nm for width while β-TCP was larger with dimension of 200±10 nm for length and 100±10 nm for width. The hardness of sintered hydroxyapatite disc was found to be stronger than the sintered β-TCP.

Keyword: Hydroxyapatite; β-TCP; nanoparticles: SEM; XRD; FTIR; Vickers Microhardness Tester

I. INTRODUCTION Synthetic calcium phosphates, such as calcium

hydroxyapatite, HA; Ca10(PO4)6(OH)2, and β-tricalcium phosphate, β-TCP; Ca3(PO4)2 and biphasic mixtures of these two have found use as bone substitutes [1-3]. HA or β-TCP implants exhibit relatively good tissue compatibility, and new bone is formed directly on the implants with no fibrous encapsulation [4]. However, sintered and well-crystallized HA ceramics usually demonstrated minimal in vivo resorption, with resorption times lagging the new bone formation rates [5-9]. Kilian et al. [10] showed that nonsintered HA could even be phagocytized and dissolved by macrophages and osteoclasts, while sintered ceramics were not degraded and remained at the site of implantation for years following the surgery. The β-TCP, on the other hand, has a significantly high solubility [11, 12] and typically fades away from the defect site even before the completion of new bone formation. An ideal skeletal repair implant should readily take part in the bone remodeling processes, and also allow for the direct anchorage by the bony tissues surrounding it (osteoconduction) [13].

Nanosized size HA can provide large interfaces, giving high catalic activity and great adsorption capability in the catalysis and separation fields. Hydroxyapatite is non-inflammatory, causes no immunological and irritating response [14]. These scaffolds provide the necessary support as artificial extracellular matrices and permit cells to proliferate and differentiated functions. A new tissue will generate on the scaffold as the function of the scaffold as a template to guide the new tissue formation. For

biodegradable scaffold in bone tissue engineering, the scaffold will be a temporary template that introduced at the defective area or lost bone. It initiated bone tissue regeneration and new bone tissue will be form. The biodegradable scaffold is gradually degrade and replaced by newly formed bone tissue. An ideal scaffold should be biocompatible, cytocompatible, controllable biodegradable, porous and have good mechanical strength [15, 16]. The objectives of this work were to synthesize hydroxyapatite and β-TCP nanoparticles and to characterize these particles by various instrumental methods and their properties were compared.

II. MATERIALS AND METHODS

A Materials

Calcium chloride was purchased from Merck. Phosphoric acid was purchased from Systems. Tween 80 and ammonium hydrogen phosphate were purchased from Sigma-Aldrich. Liquid ammonia was purchased from R & M Chemicals. Ammonium hydrogen phosphate was purchased from Reidel-de Haën.

B. Synthesis of Sample HAP-A

The method conducted was according to the method reported [17] but with some modifications. A five neck flask was used. The flask was kept in a water bath at a temperature of 45˚C. Different solutions were added through different necks of the flask while one neck of the flask was inserted with a thermometer and the other was for pH electrode. Aqueous solution of 1.0 M calcium chloride was vigorously stirred at room temperature. A solution of 0.6 M phosphoric acid was added slowly in a dropwise manner to the vigorously stirred calcium chloride solution. An aqueous solution of 5% Tween 80 was added into the vigorously stirred solution mixture of calcium and phosphate. A certain volume of 25% (v/v) ammonia solution was then added dropwise into the solution to maintain the pH of the solution at pH10. After 4 h reaction at 40 ˚C, the reaction mixture was allowed to age for another 16 h at room temperature to complete the reaction. The suspension was centrifuged at 10,000 rpm using a table-top centrifuge for 5 min. Wet powder of sample HAP-A was obtained. C. Synthesis of Sample HAP-B

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2011 2nd International Conference on Biotechnology and Food Science IPCBEE vol.7 (2011) © (2011) IACSIT Press, Singapore

Aqueous solution of calcium chloride was vigorously stirred at room temperature. A solution of ammonium hydrogen phosphate was slowly added dropwise to the calcium chloride solution. Ammonia solution was added dropwise into solution to adjust the pH 10 [18]. After reaction at 40 ˚C for 4 h and the reaction maintain was stirred for another 16 h at room temperature. The white precipitate of HAP-B was formed.

D. Autoclaved, Sonicated and Calcined

After aging of both samples, the solutions were transferred to the autoclave (HICLAVE HVE-50, HIRAYAMA), and autoclaved at 105˚C for 4 h and 130 ˚C for another 4 h. The resultant wet powder was centrifuged using 10,000 rpm for 5 min. Ethanol was added to the pellet and the suspension was sonicated using ultrasonicator for 20 min and dried in an oven at 100oC for 3 hours. The dried powder was calcinated at 900 ˚C for 4 hours before sample analysis. E. Preparation of Green and Sintered Disc

Powder samples were compressed into cylindrical tablets with a diameter of 12.80±0.02 mm and thickness of 2.00±0.03 mm under a uniaxial pressure of 5.0 MPa for 5 min to prepare green disc. The sintered disc were prepared by sintered the green disc at 1200ºC for 2 hours with same diameter and thickness. F. X-ray Diffraction (XRD)

The structure of HAP-A and HAP-B were examined using XRD Rigaku Geiger-Flex Japan. The powder was examined with Ni filtered CuKα radiation generated at 40 kV and 30 mA. The powders were scanned from 3-100˚ 2θ with a scan speed of 2˚ per minute. The peaks obtained were compared with standard references in JCPDS file available in software for hydroxyapatite (09-0432) [19] G. Fourier-transformed Infrared Spectroscopy (FTIR)

The functional groups of the hydroxyapatite were identified by FTIR Perkin Elmer using the KBr-disc method. The FTIR spectrum was scanned from 4000-400cm-1 [20]. H. Vicker’s Microhardness Tester

Hardness measurements were performed on a Vickers microhardness tester (MITUTOYO MVK-HI). Loads of 2, 5 and 10 N was applied to the surface of each compressed disc for 15 s through a pyramidal diamond indenter. Diagonal length of the indentation was measured through a micrometric eyepiece with an objective lens of 40º. The tests were repeated 5 times for each sample. The Vickers hardness number was calculated using the equation VHN = (2Fsinθ/2)/d2, where F is the applied load in grams, θ is the angle between opposite faces of indenter (136º), and d is the diagonal length of indentation in micrometers [21].

III. RESULTS AND DISCUSSION XRD pattern of the sample HAP-A showed the structure

of the prepared sample was similar to the hydroxyapatite standard as shown in Fig. 1. There is a high consistency between the data of HAP-A and that from the standard data base, with lattice dimensions of a = b = 0.9418 nm, c = 0.6884 nm. No other impurity was observed in the XRD pattern, indicating that the chief inorganic phase of the sample is hydroxyapatite crystal. The result obtain was similar to [22] as reported.

Figure 1. XRD of (a) HAP-A nanoparticles and (b) library standard of hydroxyapatite.

XRD pattern of HAP-B as shown in Fig.2 showed that it is similar in structure to the standard β-TCP which has Ca:P ratio of 3:2. The result obtained for β-TCP was similar to that reported by [23]. No α-TCP phase and HA phase were detected in the XRD pattern of the powder β-TCP with lattice dimensions of a = b = 1.0429 nm, c = 3.7380 nm.

Figure 2. XRD of (a) HAP-B nanoparticles and (b) library standard of β-TCP.

FTIR spectrum as shown in Fig. 3 showed the characteristic absorption peaks of sample HAP-A

(b)

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185

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187187

post-graduate scholarship was awarded to Maisara S.M. Arsad. The authors would also like to thank the University for providing facilities for conducting this research and Research Management Institute, UiTM for the support.

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