Advanced Materials Research Vols. 47-50 (2008) pp 928-931 Online available since 2008/Jun/12 at www.scientific.net © (2008) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.47-50.928
Synthesis of Strontium-doped Hydroxyapatite Powder via Sol-Gel Method I. Sopyan 1,a, C.M. Mardziah 1,b, A.R. Toibah 1,c, S. Ramesh 2,d 1
Department of Manufacturing & Materials Engineering, Kulliyyah of Engineering, International Islamic University Malaysia, PO BOX 10, 50728 Kuala Lumpur, Malaysia 2
Ceramics Technology Laboratory, COE, University Tenaga National, Km-7, Jalan KajangPuchong, 43009 Kajang, Selangor, Malaysia a
[email protected],
[email protected], c
[email protected], d
[email protected]
Keywords: Sr-doped hydroxyapatite, synthesis, sol-gel, physical properties
Abstract: Strontium is one of metallic elements found in bones and teeth. It is an essential substance in preventing osteoporosis and has the ability to regenerate, preserve, and even restore bone growth. Synthesizing Sr-doped HA powder is of great importance accordingly. Here we present Sr-doped HA powders prepared via sol-gel procedure using calcium nitrate and diammonium hydrogen phosphate as the precursors. Strontium nitrate was used as the dopant source, and its concentration was varied from 2~15 %. An ammoniacal solution was heated until a white gel was obtained. The obtained gel was then dried and subsequently subjected to 900°C calcination. Characterization on the obtained powder was conducted using XRD, FTIR, and FESEM. XRD measurement had shown that the powder contained hydroxyapatite phase only. Morphological evaluation by FESEM measurement shows that the particles of the Sr -doped HA agglomerates are globular in shape with an average size of 1-2 µm in diameter. Meanwhile, the primary particles have a diameter of 50-150 nm in average. It is likely Sr has played an important role as a calcination or sintering additive, causing more progressive densification of particles. Introduction The capacity of the human body to regenerate bony components that are lost or damaged is limited. For this reason, materials need to be developed that can adequately replace bone tissue, especially mineralized tissue such as bone and teeth. Hydroxyapatite Ca10(PO4)6(OH)2 is particularly attractive for use for human tissue implantation due to its compositional and biological similarity to host materials [1]. HA has a calcium to phosphorous ratio of 1.67 [2] and has an excellent affinity for the living body due to its favourable osteoconductive [3] and bioactive properties [4]. However, synthetic HA exhibits low fracture toughness due to its lack of strength and brittleness, thereby providing an obstacle to its application in implants that must withstand high loads [5]. One strategy to improve its mechanical properties is hydroxyapatite has been doped with metal such as magnesium [6], manganese [7], zinc [7] and strontium [7, 8]. Moreover, minerals and traces of metal elements affect bone formation and resorption on bone cells or bone mineral in vivo and in vitro [9]. Some trace elements chemically related to calcium, such as strontium seemed to have the potential to change the biocompatibility and physicochemical characteristics of HA for implant use [10]. Strontium has been proven to have potential in the treatment of osteoporosis [8]. It has provoked an increasing interest because of its beneficial effects on bone formation and prevention of bone resorption [11]. In this research, strontium doped HA powder was developed via a sol-gel method with an alteration in the amount of Sr ion. The structure and physical characteristics of the materials were evaluated. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 175.140.91.64, International Islamic University Malaysia, Kuala Lumpur, Malaysia-05/01/14,01:39:39)
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Methodology An ammoniacal solution of the monomers was heated and EDTA (Merck KGaA, Germany) was added while stirring until it dissolved. Calcium nitrate tetrahydrate and strontium nitrate (Merck KGaA, Germany) in aqueous solutions were poured into solution. Then di-ammonium hydrogen phosphate (Merck KGaA, Germany) and urea (R & M Chemicals, UK) were subsequently added. This mixture was then refluxed while maintaining the stirring until white gel was obtained. The white gel was then dried. The resultant black gel was crushed into a fine powder and then subjected to 900ºC calcination where white Sr-doped HA powder was obtained. The powder of 2%, 5%, 10% and 15% Sr-HA were prepared to observe the differences in their characteristics. The physical characteristics of each powder was evaluated using FESEM (JEOL, JFM 6700F), XRD (Shimadzu, XRD 6000) and FTIR (Perkin Elmer, Spectrum 100). Results and Discussion Fig. 1 shows the XRD patterns of the HA powders with various Sr additions and pure HA after calcination at 900 ˚C for 3 hours. β-TCP peak was formed in the pure BCP powder and the peak still appeared when 2% Sr was incorporated. With the increasing concentration of Sr (5% and above), the TCP peak disappeared. Previous study shown that TCP peaks will appear when the calcinations temperature is above 500 ºC in order to stabilize the HA system [12]. The disappearance of TCP peak indicates that Sr has substituted Ca ion in the HA. This originates from lattice concentration due to the large radii atom (Sr) substitution for the small radii atom (Ca). Sr atom is larger than Ca atom, so it is likely that replacement of Ca by Sr in β–TCP causes the disappearance of β-TCP peaks.
Fig. 1: XRD Analysis for pure BCP, 2%, 5%, 10% & 15% Sr-HA Fig. 2 shows the FTIR analysis of the calcined powders. A typical HA structure containing sharp O-H band at 3600 cm-1 – 3700 cm-1 and 550 cm-1 – 650 cm-1 as well as P-O band at 1000 cm1 – 1100 cm-1 were observed. As the concentration of Sr increased, the O-H bands at 550 cm-1 – 650 cm-1 (belong to molecularly bonded OH) disappeared gradually. This is because Sr has substituted OH and the reaction is represented by Eq. (1) below:
Ca5(PO4)3OH + SrO Ca5-x Srx(PO4)3OH1-x(SrO)x
(1)
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Fig. 2: FTIR Analysis for pure BCP, 2%, 5%, 10% & 15% Sr-HA Fig. 3 shows the images of the pure HA and 15% Sr-doped HA nano-powder produced by solgel method. It is clear that the powder is tightly agglomerated in globular shape with an average size of 1-2 µm in diameter. Meanwhile, the primary particles have a diameter of 50-150 nm in average. From this result, we can conclude that after doping HA with Sr, the particle will diffuse into a more progressive densification of particles as shown by 15% Sr doping. In this case, we can say that Sr acts as a sintering additive which will improve sintering behaviour of HA leading to improvement in mechanical strength.
0%
15 %
Fig. 3: FESEM images of pure HA and 15% Sr-doped HA powder Summary Sol-gel method has been successfully used to synthesize Sr-doped HA powders with various Sr content. Individual particles of Sr-doped HA are globular in shape with an average size of 50-150 nm in diameter. All powders exhibited highly crystalline characteristics. References [1] [2]
S. Pramanik, A. K. Agarwal, and K. N. Rai: Development of High Strength Hydroxyapatite for Hard Tissue Replacement, Trends Biomater. Artif. Organs, Vol 19(1), p. 46 (2005) M. Komath and H. K. Varma: Development of a Fully Injectable Calcium Phosphate Cement for Orthopedic and Dental Applications, Bull. Mater. Sci., Vol. 26, No. 4, p. 415 (2003)
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S. Agarwala and A. Bhagwat: Hydroxyapatite As A Bone Graft Substitute: Use In Cortical And Cancellous Bone, Indian Journal of Orthopedics, Vol. 39, No. 4, p. 254 (2005) L.L. Hench, J. Wilson: Surface Active Biomaterials, Science, Vol. 226, p. 630 (1984) K. Prabakaran, S.Kannan and S. Rajeswari: Development and Characterisation of Zirconia and Hydroxyapatite Composites for Orthopaedic Applications, Trends Biomater. Artif. Organs, Vol 18 (2) (2005) R. I. Martin, P. W. Brown: The Effects of Magnesium on Hydroxyapatite Formation In Vitro from CaHPO4 and Ca4(PO4)2O at 37.4°C, Calcified Tissue Int., Vol 60, p. 538 (1998) R. Z. LeGeros and J. P. Le.Geros in: An Introduction to Bioceramics: Dense Hydroxyapatite, World Scientific Publishing Co., (1993) H. W. Kim, Y.G. Koh, Y. M. Kong, J. G. Kang and H. E. Kim: Strontium Subtituted Calcium Phosphate Biphasic Ceramics Obtained By A Powder Precipitation Method, Journal of Materials Science: Materials in Medicine 15, p. 1129 (2004) F. S. Kaplan, W. L. Hayes, T. M. Keaveny, A. Boskey, T. A. Einhorn and J. P. Iannotti in: Orthopedic Basic Research, edited by S. P. Simon (American Academy of Orthopedic Surgeons) p.127 (2001) F. Y. Fei and C. D. Min: Influence of Sr2+ on Strontium Substituted Hydroxyapatite's (SrHA), Journal of Oral Tissue Engineering; Vol. 2(2): p. 76 (2005) A. Bigi, E. Boanini, C. Capuccini and M. Gazzano: Strontium-substituted hydroxyapatite nanocrystals, Inorganica Chimica Acta, Vol. 360, Issue 3, p. 1009 (2007) E. Landi, A. Tempieri et. al.: Biomimetic Mg- And Mg,CO3-Substituted Hydroxyqapatite: Synthesis Characterization And In Vitro Behaviour, Journal of the European Ceramic Society 26, p. 2593 (2006)
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Synthesis of Strontium-Doped Hydroxyapatite Powder via Sol-Gel Method 10.4028/www.scientific.net/AMR.47-50.928 DOI References [4] L.L. Hench, J. Wilson: Surface Active Biomaterials, Science, Vol. 226, p. 630 (1984) doi:10.1126/science.6093253 [11] A. Bigi, E. Boanini, C. Capuccini and M. Gazzano: Strontium-substituted hydroxyapatite anocrystals, Inorganica Chimica Acta, Vol. 360, Issue 3, p. 1009 (2007) doi:10.1016/j.ica.2006.07.074 [12] E. Landi, A. Tempieri et. al.: Biomimetic Mg- And Mg,CO3-Substituted Hydroxyqapatite: ynthesis Characterization And In Vitro Behaviour, Journal of the European Ceramic Society 6, p. 2593 (2006) doi:10.1016/j.jeurceramsoc.2005.06.040
