nermin.demirkol09.12.2011_13.36.07diger

Key Engineering Materials Vols. 493-494 (2012) pp 588-593

© (2012) Trans Tech Publications, Switzerland

doi:10.4028/www.scientific.net/KEM.493-494.588

Comparison of Mechanical Properties of Sheep Hydroxyapatite (SHA)

and Commercial Synthetic Hydroxyapatite (CSHA)-MgO Composites

Nermin Demirkol1,2,a, Onur Meydanoglu2,b, Hasan Gokce2,c

Faik Nuzhet Oktar3,d and Eyup Sabri Kayali2,e

1Technical Prog. Dept., Vocational School of Degirmendere Ali Ozbay, Kocaeli University, Kocaeli, Turkey

2Metallurgical & Materials Eng. Dept., Istanbul Technical University, Istanbul, Turkey

3Medical Imaging Techniques Dept., School of Health Related Professions, Marmara University, Istanbul, Turkey

anermin.demirkol@kocaeli.edu.tr, bmeydanoglu@itu.edu.tr, cgokceh@itu.edu.tr,

dfoktar@marmara.edu.tr, ekayali@itu.edu.tr,

Keywords: Sheep hydroxyapatite, synthetic hydroxyapatite, mechanical properties, magnesium oxide.

Abstract. In this study, microstructures and mechanical properties of sheep hydroxyapatite (SHA) and commercial synthetic hydroxyapatite (CSHA)-MgO composites were investigated. The production of hydroxyapatite (HA) from natural sources is preferred due to economical and time saving reasons. The goal of development of SHA and CSHA based MgO composites is to improve mechanical properties of HA. SHA and CSHA composites were prepared with the addition of different amounts of MgO and sintered at the temperature range of 1000-1300 °C.
The physical and mechanical properties were determined by measuring density, compression strength and Vickers microhardness (HV). Structural characterization was carried out with X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies.
In all composites, mean density values and mechanical properties increased with increasing sintering temperature. The increase of MgO content in SHA-MgO composites showed better mechanical properties in contrast to CSHA-MgO composites. Although the highest hardness and compression strength values were obtained at the SHA-10wt% MgO composite sintered at 1300°C, higher hardness and compression strength values were achieved with 5 wt% MgO addition at the CSHA-MgO composites when compared to SHA-MgO composites sintered between 1000-1200°C.
Introduction

In the light of human life expectancy up to 90 years, the improvement of health care and the increase of accidents (due to sport activities and car accidents), the need for effective and inexpensive biomaterials available to everyone, such as HA produces from different sources such as biologically derived and synthetic hydroxyapatite is in great demand [1]. HA possesses exceptional biocompatibility and bioactivity properties with respect to bone cells and tissues, probably due to its similarity with the hard tissues of the body. To date, calcium phosphate biomaterials have been widely used clinically in the form of powders, granules, dense and porous blocks and various composites [2]. HA from natural origins differs from synthetic HA in composition, crystal morphology, size, shape and physico-chemical properties depending on the technology used to obtain the synthetic HA. Synthetic HA can be prepared from an aqueous solution, by solid-state reaction or by hydrothermal methods [3]. To prepare HA from those sources needs analytical pure grade chemicals. The conventional methods for producing HA needs also time. All those make commercial synthetic HA (CSHA) production costly and time consuming. CSHA ceramics do not possess rare minerals like Sr, Si, Mg and many others. Natural HA’s have all kind of those rare minerals. Interest has been increased to prepare rare natural HA’s from natural sources with many

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: 194.27.72.122-23/09/11,12:06:38)

Key Engineering Materials Vols. 493-494 589


methods. Calcination is one of the most used methods. Nowadays natural HA is prepared (calcination method) from bovine, sheep, pig and goat bones. It is already known that the mechanical properties of HA are poor, especially in wet environment. For this reason ceramics of pure HA cannot be suggested for use in heavy-loaded implants, such as artificial bones or teeth. Those HA’s can only be used at non-loading applications, such as graft materials. For improving the mechanical reliability of HA-ceramics, i.e. to increase their fracture toughness, incorporation of metallic materials, ceramic oxides, whiskers or fibers, have been suggested [4-7]. For example MgO is one of the most successful candidates of reinforcement oxides. Magnesium (Mg) is also a very important element in human body, related to mineralization of calcined tissues, apatite crystallization, destabilization of HA and the thermal conversion of HA to β-tricalcium phosphate (β-TCP, Ca3(PO4)2). Mg seemingly reduces risks of cardiovascular diseases, promotes catalytic reactions and controls biological functions of human body[8].
The aim of this study is to compare the mechanical properties of sheep HA (SHA) and commercial synthetic HA (CSHA)-MgO composites to determine the effects of the source and production process of HA.
Materials and Methods
The SHA used in this study was prepared from calcinated sheep bones. Firstly, fresh cut femurs were deproteinized with NaOH and after reirrigation the samples were subjected to calcination at
750°C. Then calcinated sheep bones were wet ball milled for 24 hours and they were dried at the drying oven. SHA powders had an average particle size of 10 µm. The CSHA and SHA powders were mixed with (seperately) 5 and 10 wt% magnesium oxide powder for 4 hours. The samples were prepared according to a British Standard for compression tests (BS 7253) [9]. The powder portions were pressed at 350 MPa between hardened steel dies. Pressed samples were subjected to sintering at different temperatures between 1000°C and 1300°C (with the heating rate of + 5°C min

-1) for 4 h. Compression strength, Vickers microhardness as well as density were measured. SEM and X-ray diffraction studies were also conducted. The compression tests were done with an universal testing machine, at the crosshead speed of 3 mm/min. Microhardness values were determined under 200 g. load. SEM images were taken with Scanning Electron Microscope (JEOL JSM-5410).

Results and Discussion
Table 1 shows the experimental results of density, compression strength and Vickers microhardness of the SHA samples sintered at different temperatures.
Table 1. Experimental results of density, compression strength and Vickers microhardness of the
SHA samples sintered at different temperatures.

Temperature (°C)

Density (g/cm3)

Compression Strength

(MPa)

Vickers Microhardness

(HV)

1000

2,09

31

49

1100

2,16

38

67

1200

2,40

50

138

1300

2,59

69

189

The mean density, compression strength and Vickers microhardness values of SHA increase with increasing sintering temperature, as seen in Table 1. The maximum values were achieved at

1300 °C sintering temperature. Table 2 and 3 show mean values of density, compression strength and Vickers microhardness of SHA-MgO and CSHA-MgO composites at the different sintering temperature, respectively. Fig. 1 and 2 show the results of Table 2 and 3 to compare the properties of SHA and CSHA composites.

590 Bioceramics 23


Table 2. Influence of magnesium oxide content and sintering temperature on density, compression strength and Vickers microhardness of composites made of sheep hydroxyapatite and magnesium oxide (SHA-MgO).

Temperature (°C)

Density (g/cm3)

Compression Strength

(MPa)

Vickers Microhardness

(HV)

 

5wt%

10wt%

5wt%

10wt%

5wt%

10wt%

1000

2,11

2,13

32

42

72

79

1100

2,17

2,26

51

63

89

106

1200

2,57

2,72

70

71

165

212

1300

2,96

2,99

109

116

263

458

Table 3. Influence of magnesium oxide content and sintering temperature on density, compression strength and Vickers microhardness of composites made of magnesium oxide and commercial synthetic hydroxyapatite (CSHA-MgO).

Temperature (°C)

Density (g/cm3)

Compression Strength

(MPa)

Vickers Microhardness

(HV)

 

5wt%

10wt%

5wt%

10wt%

5wt%

10wt%

1000

2,15

2,07

47

38

83

76

1100

2,26

2,18

71

65

156

124

1200

2,77

2,73

78

73

316

282

1300

2,90

2,84

85

78

370

358



(a) (b)


Fig.1. Comparison graphics of compression strength of (a) SHA-5 wt% MgO and CSHA-5 wt% MgO (b) SHA-10 wt% MgO and CSHA-10 wt% MgO composites at different sintering temperatures.
Fig.2. Comparison graphics of Vickers microhardness of (a) SHA-5 wt% MgO and CSHA-5 wt% MgO (b) SHA-10 wt% MgO and CSHA-10 wt% MgO composites at different sintering temperatures.

Key Engineering Materials Vols. 493-494 591


In all composites, mean density values and mechanical properties increased with increasing sintering temperature. Density, compression strength and hardness values of CSHA-5 wt% MgO composites are higher than CSHA-10 wt% MgO composites and higher Vickers microhardness values were achieved with CSHA-MgO composites than SHA-MgO composites at all sintering temperatures. Although, the highest hardness and compression strength values were obtained at the SHA-10wt% MgO composite sintered at 1300°C, the highest hardness and compression strength values were achieved with 5 wt% MgO addition at the CSHA-MgO composites sintered between


1000-1200°C. The MgO addition to SHA improved to strength properties of composites up to 70%.


(a) (b)
(c) (d)
Fig.3. XRD diagrams of (a) SHA-5wt% MgO (b) SHA-10wt% MgO (c) CSHA-5wt% MgO (d) CSHA-10wt% MgO at 1000 and 1300°C sintering temperature.
Fig.3 shows the XRD diagrams of composites at 1000 and 1300°C sintering temperatures. Hydroxyapatite and MgO phases were achieved in the SHA-composites at all sintering temperatures (Fig.3a,b). CSHA-MgO composites include calcium hydrogen phosphate hydrate (CHPH) phase at
1300°C sintering temperature in addition to the phases hydroxyapatite (HA), calcium magnesium phosphate (CMP) and periclase-syn MgO (P) phases present between sintered composites at 1000-
1200°C. The lower compression strengths obtained at CSHA-MgO composites compared to SHA- MgO composites sintered at 1300°C, may be related to calcium hydrogen phosphate hydrate phase formed at 1300°C in CSHA-MgO composites.

592 Bioceramics 23




(a) (b)

(c ) (d)

(e) (f)
(g) (h)
Fig.4 Microstructures of MgO containing composites (a) SHA-5 wt% MgO, 1000°C, (b) SHA-5
wt% MgO, 1300°C, (c) SHA-10 wt% MgO, 1000°C, (d) SHA-10 wt% MgO, 1300°C, (e) CSHA-5 wt% MgO, 1000°C, (f) CSHA-5 wt% MgO, 1300°C, (g) CSHA-10 wt% MgO, 1000°C, (h) CSHA-
10 wt% MgO, 1300°C.
The microstructures of both MgO containing SHA and CSHA composites sintered at different temperatures are given in Fig.4. The microstructures sintered at 1300 °C show better densification as seen in Fig.4.

Key Engineering Materials Vols. 493-494 593


Summary
In this study, the microstructural and mechanical properties of sheep HA and commercial
synthetic HA composites with MgO addition were compared to determine the effects of the source and production process of HA.
The following conclusions were obtained.
1. In all composites, mean density values and mechanical properties increased with increasing sintering temperature.
2. The increase of MgO content in SHA-MgO composites showed better mechanical properties in contrast to CSHA-MgO composites.
3. The highest hardness and compression strength values were obtained at the SHA-10wt% MgO composite sintered at 1300°C.
4. The higher hardness and compression strength values were achieved with 5 wt% MgO
addition at the CSHA-MgO composites for 1000-1200°C sintering temperatures.
5. The MgO addition to SHA improved to strength properties of composites up to 70%.
Biocompatibility studies are going on. If the results of biocompatibility tests are positive, MgO
containing HA composites seems to be very good material for orthopedic applications.
Acknowledgement
The authors would like to thank Prof. Dr. Serdar Salman, Prof.Dr. Mustafa Urgen and Research
Assist. Serdar Pazarlıoglu for their support during experimental studies.
References
[1] O. Gunduz, S. Daglilar, S. Salman, N. Ekren, S. Agathopoulos, F.N. Oktar, Effect of Yttria- doping on Mechanical Properties of Bovine Hydroxyapatite (BHA), Journal of Composite Materials
42 (2008) 1281-1287.
[2] M.P. Ferraz, F.J. Monteiro, C.M. Manuel, Hydroxyapatite nanoparticles: A review of preparation methodologies, Journal of Applied Biomaterials & Biomechanics 2 (2004) 74-80.
[3] E. Damien, P.A. Revell, Coralline hydroxyapatite bone graft substitute: A review of experimental studies and biomedical applications, Journal of Applied Biomaterials & Biomechanics
2 (2004) 65-73.
[ 4] S. Salman, O. Gunduz, S. Yilmaz, M.L. Öveçoğlu , R. L. Snyder, S. Agathopoulos, F.N. Oktar, Sintering effect on mechanical properties of composites of natural hydroxyapatites and titanium, Ceramics International 35 (2009) 2965–2971.
[ 5] F. N. Oktar, Y. Genç, G. Göller, E. Z. Erkmen, L. S. Özyeğin, D. Toykan, H. Demirkıran, H. Haybat, Sintering of Synthetic Hydroxyapatite Compacts, Key Engineering Materials Vol. 264-268 (2004) p. 2087-2090.
[6] N. Demirkol, E.S.Kayali, M.Yetmez, F.N. Oktar, S. Agathopoulos, Hydroxyapatite nano- barium-strontium-titanium oxide composites, Key Engineering Materials Vol. 484 (2011) p. 204-
209.
[7] A. M. Janus, M. Faryna, K. Haberko, A. Rakowska, T. Panz, Chemical and microstructural characterization of natural hydroxyapatite derived from pig bones, Microchim Acta 161 (2008) 349-
353.
[8] F.N. Oktar, S. Agathopoulos, L. S.Ozyegin, O. Gunduz, N. Demirkol, Y. Bozkurt, S. Salman, Mechanical properties of bovine hydroxyapatite (BHA) composites doped with SiO2, MgO, Al2O3, and ZrO2, J Mater Sci: Mater Med (2007) 18:2137–2143

[9] British Standart Non-metallic materials for surgical implants. Part 2: Specification for ceramic materials based on alumina, BS 7253: Part 2:1990 ISO 6474-1981.