Comparison of dissolution resistance in artificial hydroxyapatite and biologically derived hydroxyapatite ceramics

Comparison of dissolution resistance in artificial hydroxyapatite and biologically derived hydroxyapatite ceramics

ARTICLE IN PRESS Journal of Physics and Chemistry of Solids 69 (2008) 1556–1559 www.elsevier.com/locate/jpcs Comparison of dissolution resistance in...

873KB Sizes 0 Downloads 143 Views

ARTICLE IN PRESS

Journal of Physics and Chemistry of Solids 69 (2008) 1556–1559 www.elsevier.com/locate/jpcs

Comparison of dissolution resistance in artificial hydroxyapatite and biologically derived hydroxyapatite ceramics Young Gook Kima,b, Dong Seok Seob, Jong Kook Leea,b, a

Department of Advanced Materials Engineering, Chosun University, 501-759, Gwangju, Korea BK21 Education Center of Mould Technology for Advanced Materials & Parts, Chosun University, 501-759, Gwangju, Korea

b

Received 6 July 2007; accepted 31 October 2007

Abstract Dissolving behavior of hydroxyapatite (HA) ceramics prepared from bovine bones (BHA) was investigated and compared with artificial HA. BHA and artificial HA were sintered at 1200 1C for 1 h, and they were immersed in distilled water at 37 1C for 3, 7, 14 and 28 days. Detectable peaks in artificial HA were only identical to HA phase, however, BHA consists of mostly HA phase and small amount of MgO. Sintered density of BHA was lower than that of artificial HA. Dissolution of artificial HA was founded after 7 days. The grain boundaries on the surface of artificial HA appeared to initiate dissolution, and grains are pulled out of the artificial HA surface at the end of the immersion period, however, there is no evidence of BHA surface at the end of the immersion period. It was found that HA from bovine bone was more stable than artificial HA in a liquid environment. r 2007 Elsevier Ltd. All rights reserved. Keywords: A. Ceramics; C. Electron microscopy; C. X-ray diffraction; D. Microstructure

1. Introduction

2. Experimental procedures

Calcium phosphates including hydroxyapatite [Ca10 (PO4)6(OH)2, HA] have achieved significant application as a bone graft material in a range of medical and dental applications [1]. In spite of the fact that HA is expected to be stable in body fluid [2], HA was dissolved during exposure to the in vitro and in vivo environment resulting in the presence of loose particles and microstructural degradation [3]. As a result, it will provoke inflammation or third body friction [4]. Therefore, preparing HA with dissolution/degradation resistance should be required. As an alternative method, HA derived from bovine bone can be used. Bovine bone is not dissolved in a biological environment and stable for a long period. Bovine bone is composed of organic and inorganic components. After calcination, it is easy to produce calcium phosphate from bovine bone. The aim of the present work is to prepare HA derived from bovine bone (BHA) and to investigate dissolution of BHA compared with artificial HA.

The biologically derived HA powder used in this study was originated from bovine bones. The bones were irrigated with a brush in running water and dried at room temperature, and organics in each bone were removed by soaking the bones in 0.1 M of NaOH solution at 80 1C for 4 h. After soaking, the bones were dried overnight. After drying, the bones were calcined at 800 1C for 1 h to completely remove organics and to save from infectious diseases like Creutzfeldt Jakob, BSE, HIV, hepatitis B, hepatits C, etc. [5]. Bones calcined manually ground, attritor-milled for 24 h, and then dried overnight. The powders were uniaxially compacted and subsequently cold isostatically pressed into pellets. The pellets were sintered at 1200 1C with a heating rate 5 1C/min for 1 h in humid atmosphere to avoid possible dehydration of the samples. After sintering, the compacts were polished to smoothness using 1 mm diamond paste. The polished disks were soaked in 40 ml of pH 7.4 distilled water (buffered using 0.05 M tris(hydroxymethyl)-aminomethane) at 37 1C for 3–28 days. At the end of these time periods, all samples were washed with distilled water and with alcohol then dried at

Corresponding author. Tel.: +82 62 230 7202; fax: +82 62 230 7899.

E-mail address: [email protected] (J.K. Lee). 0022-3697/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jpcs.2007.10.102

ARTICLE IN PRESS Y.G. Kim et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1556–1559

1557

80 1C overnight. The phases present in the compacts were analyzed by X-ray diffraction (XRD) using Ni-filtered Cu Ka radiation. Morphology of the compacts was also examined using field emission scanning electron microscope (FE-SEM). 3. Result and discussion Fig. 1 shows that XRD and FT-IR patterns of artificial HA sintered at 1200 1C. In artificial HA, all detectable peaks were identical to HA phase without expressing any impurities. From FT-IR analysis, artificial HA was corresponded to a typical spectrum of HA showing the internal mode of PO4 group at (571.8, 601.1, 960.9 and 1049.2 cm 1). The bands at 631 and 3570.6 cm 1 were assigned to structural OH. Fig. 2 shows that XRD and FT-IR patterns of BHA sintered at 1200 1C. BHA consists of mostly HA and small amount of MgO which is not in artificial HA. The FT-IR

Fig. 2. XRD and FT-IR patterns of BHA sintered at 1200 1C.

Table 1 Element analysis of BHA powders

Fig. 1. XRD and FT-IR patterns of HA sintered at 1200 1C.

Elements

Ca

P

Na

Mg

Si

B

Zn Ba Sr

S

Concentration (ppm)

819.80 366.40 23.81 13.20 4.90 2.99 1.35 1.35 1.23 1.11

spectrum (Fig. 2) also shows a typical spectrum of BHA which consists of PO4 derived bands at 572.3, 602.2, 962.2 and 1052.1 cm 1, and the bands of OH at 632 and 3570.4 cm 1 were detected [6]. The band around 1410 cm 1 could be MgO [7], but it is difficult to indicate MgO peaks. Table 1 reveals that elemental constituents of BHA powders. According to the ICP analysis, BHA has Ca/P molar ratio of 1.73, and it contains minor and trace amounts of several elements. Other authors observed Ca/P ratio higher than stoichiometric. It will be shown that, it also exists in BHA powders [8].

ARTICLE IN PRESS 1558

Y.G. Kim et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1556–1559

Fig. 3 presents that SEM micrographs of the surfaces of artificial HA and BHA thermally etched at 1150 1C for 30 min. Sintered density of the artificial HA was about 96%

and that of BHA was about 84%. BHA particles have average of 0.68 mm, however, particle sizes of artificial HA are range of 20–50 nm and needle-shaped (not shown here). BHA particles were larger than artificial HA particles. In addition, particle size distribution of artificial HA was narrow than that of BHA. That is why grain sizes of BHA were larger than that of artificial HA. Fig. 4 indicates that dissolution of artificial HA sintered at 1200 1C. Surface of artificial HA was smooth until 3 days. However, dissolution of artificial HA was occurred from grain boundaries after 7 days. It may be caused by that the presence of non-stoichiometric compositions at grain boundaries having lower Ca/P ratio than within the grains [9]. On the other hand, dissolution of BHA sintered at 1200 1C is different from artificial HA. Fig. 5 illustrates microstructure of BHA during immersion in water. Surface of BHA was smooth after polishing (Fig. 5(a)). At the end of the immersion period, there is no clear evidence of dissolution in BHA compared with the artificial HA. It is interesting that the artificially made HA was soluble in a liquid environment although it was phase-pure with high sintered density [9]. However, BHA was less dissolved HA in spite of having lower sintered density and consisting of HA and MgO. Mg ions can be substituted in the apatite structure. Mg in HA increased in extent of dissolution [10]. As a result, BHA was more stable than artificial HA.

4. Conclusions

Fig. 3. Microstructures of (a) HA and (b) BHA.

HA derived from bovine bones was prepared and its dissolving behavior was compared with artificial HA. Detectable peaks in artificial HA were identical to HA

Fig. 4. Dissolution of HA sintered at 1200 1C: (a) before immersion, and immersed for (b) 3 days, (c) 7 days, (d) 14 days and (e) 28 days.

ARTICLE IN PRESS Y.G. Kim et al. / Journal of Physics and Chemistry of Solids 69 (2008) 1556–1559

1559

Fig. 5. Microstructures of BHA sintered at 1200 1C: (a) before immersion, and immersed for (b) 3 days, (c) 7 days, (d) 14 days and (e) 28 days.

phase, however, BHA consists of mostly HA phase and small amount of MgO. In BHA, there is no clear evidence of dissolution at the end of the immersion period. In artificial HA, initial dissolution was occurred around grain boundaries, and grains are pulled out of the surface at the end of the immersion period. Accordingly, BHA was more resistant to dissolution than artificial HA in spite of lower sintered density. It is believed that biologically derived HA can be a good substance for medical applications, where biological stability of HA is required. Acknowledgment This work was supported by Korea Research Foundation Grant (KRF-2003-041-D20277).

References [1] M. Jarcho, Clin. Orthop. 157 (1981) 259–278. [2] W.E. Brown, L. Chow, Ann. Res. Mater. Sci. 6 (1976) 213–226. [3] J.T. Edwards, J.B. Brunski, H.W. Higuchi, J. Biomed. Mater. Res. 36 (1997) 454–468. [4] M. Rokkum, M. Brandt, K. Bye, K.R. Hetland, S. Waage, A. Reigstad, J. Bone Joint Surg. 81B (1999) 582–589. [5] G. Goller, F.N. Oktar, L.S. Ozyegin, E.S. Kayali, E. Demirkesen, Mater. Lett. 58 (2004) 2599–2604. [6] C.Y. Ooi, M. Hamdi, S. Ramesh, Ceram. Int. 33 (2007) 1171–1177. [7] S. Joschek, B. Nies, R. Krotz, A. Gopferich, Biomaterials 21 (2000) 1645–1658. [8] K. Haberko, M.M. Bucko, J.B. Miecznik, M. Kaberko, W. Mozgawa, T. Panz, A. Pyda, J. Zarebski, J. Eur. Ceram. Soc. 26 (2006) 537–542. [9] T. Nonami, F. Wakai, J. Ceram. Soc. Jpn. 103 (1995) 648–652. [10] D.S. Seo, H. Kim, S.H. Kim, H.J. Kim, J.K. Lee, Key Eng. Mater. 342–343 (2007) 657–660.