- Email: [email protected]
A study on bioceramic reinforced bone cements
Materials Letters 61 (2007) 1456 – 1459 www.elsevier.com/locate/matlet
A study on bioceramic reinforced bone cements S. Daglilar ⁎, M.E. Erkan Department of Metallurgical and Materials Engineering, Chemistry–Metallurgy Faculty, Yildiz Technical University, Davutpasa Campus, 34201, Esenler, Istanbul, Turkey Received 23 June 2006; accepted 16 July 2006 Available online 10 August 2006
Abstract This paper presents the mechanical properties and SEM studies of bone cements reinforced by bovine hydroxyapatite (BHA), synthetic hydroxyapatite (HA), and β-tricalcium phosphate (β-TCP). All ceramic fillers were silane treated with γ-methacryloxy-propyl-trimethoxy silane (A-174, 0.2%). The quantities of silane treated ceramic fillers in cement were 1.5 wt.%, 2.5 wt.% and 3.5 wt.%. Commercial CMW™3 bone cement was used as control group. The results showed that there is no decay of mechanical properties if the amount of bioceramic additives does not exceed 2.5 wt.%. Similar microstructures were observed by SEM at the fracture surfaces of the bioceramic reinforced bone cements and the control group. © 2006 Elsevier B.V. All rights reserved. Keywords: Bone cement; Silanation; Bovine hydroxyapatite; β-tricalcium phosphate; Hydroxyapatite; Mechanical properties
1. Introduction Acrylic bone cements, mainly consisting of polymethylmethacrylate (PMMA), have been used in orthopedic surgery and dentistry for more than forty years [1]. Nevertheless, PMMA cement possesses several inherent problems, such as nonbonebonding capability, relatively low mechanical strength, and high heat generation during polymerization [2]. To overcome mechanical weakness, bone cements are usually reinforced with additives, such as carbon, graphite, aramid, bone particles, polyethylene, titanium, ultra-high molecular weight polyethylene, PMMA fibers, tricalcium phosphate, and hydroxyapatite [3]. In our study, we focused our interest only on synthetic hydroxyapatite (HA), bovine hydroxyapatite (BHA), and β-tricalcium phosphate (β-TCP) as additives. Hydroxyapatite (HA) is the principal mineral of bone and teeth, with a chemical formula of Ca10(PO4)6(OH)2. HA can be derived from natural sources, such as bovine bones, or corals via hydrothermal transformation, or it can be synthetically prepared [4,5]. Highly pure synthetic HA can be prepared by solid-state reaction, by hydrothermal or microwave methods, or by sintering of apatite obtained via sol-gel method. Apatites ⁎ Corresponding author. Tel.: +90 212 449 16 43. E-mail addresses: [email protected] (S. Daglilar), [email protected] (M.E. Erkan). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.07.068
derived from bovine bone (BHA) are obtained by chemical and/ or thermal removal of the organic matter whether without sintering or with sintering at temperatures above 1000 °C. Pure β-TCP (Ca3(PO4)2) is prepared either by solid-state reaction or by sintering of calcium-deficient apatite obtained from solutions [5]. To achieve mechanically strong cement composites, the silane treatment of the inorganic filler of the cements is a well-known and widely accepted approach in the technology of such composites. The goal of silane treatment is that it results in formation of strong bonds between the inorganic filler and the organic matrix [6]. The purpose of this study was to compare the mechanical strengths of bone cements which were reinforced with different amounts of silane treated HA, BHA, and β-TCP. Measurements of compressive strength, compressive elastic modulus, and three point bending strength were carried out. Observations of the microstructure of the fracture surfaces were performed by SEM. 2. Materials and methods 2.1. Materials The production procedure of the BHA powder used in this study has been described in an earlier study [7]. Synthetic HA and β-TCP powders were obtained from Merck A.G. (Germany). PMMA prepolymerized powder with average particle
S. Daglilar, M.E. Erkan / Materials Letters 61 (2007) 1456–1459
size of 40 μm and MMA liquid (IMICRYL; Turkey) were used to prepare the bioceramic reinforced bone cements. γmethacryloxy-propyl-trimethoxy silane (A-174) was obtained from General Electric (USA). Commercially available CMW™3 bone cement (DePuy, England) was chosen as a reference. Table 1 shows the chemical composition of CMW™3 as reported by the manufacturer. 2.2. Experimental procedure All ceramic powders were sieved through a sieve of 100-μm mesh. The silane coupling agent (0.2 wt.% with respect to the ceramics powders) was added in 100 ml of distilled water and the pH was maintained at 2.9. The powders of the ceramics were added to the solution and mixed at 50 °C with 350 rpm for 2 h (Velp Arex, Italy). The mixtures were dried at 110 °C for 5 h (Instron, USA) [6,8]. The amount of silane treated ceramic powders added to PMMA powder was 1.5%, 2.5%, and 3.5% (in wt.%). PMMA powder and MMA liquid were mixed manually at a ratio of 2.5/ 1.5. CMW™3 bone cement was prepared according to the instructions suggested by the manufacturer. Table 2 summarizes all the groups of materials tested. To prepare the samples, two 304 stainless steel moulds were designed and prepared. They were preheated at 45 °C before sample preparation. Compressive test samples (6 mm in diameter and 12 mm in height) were prepared according to the ISO 5833 (Instron, USA; speed 1 mm/min). Three point bending test samples, with dimensions of 3 × 10 × 15 mm3, were prepared according to the DIN 53435 (Instron, USA; speed 1 mm/min). SEM images were obtained by Jeol JSM-T330. 3. Results and discussion Table 3 summarizes the results obtained from the mechanical tests, where the values of compressive strength (σcomp), compressive elastic modulus (Ec), and 3-point bending strength (Fs) are presented. Accordingly, bone cement A1 exhibited the highest compressive strength (91.31 ± 5.50 MPa). The C1 bone cement has the highest 3-point bending strength (137.94 ± 30.64 MPa). The results of compressive strength indicate that addition of bioceramics can truly reinforce bone cements since the resultant materials were always stronger than the nondoped D bone cement. The reinforcing effect was more pronounced in the case of BHA (group A) than in HA and β-TCP. That group (A) was the only one that exhibited compressive strength (A1, 91.32 MPa) higher Table 1 The chemical composition of CMW™3 as reported by the manufacturer Powder Polymethyl methacrylate (% w/w) Benzoyl peroxide (% w/w) Barium sulphate (% w/w)
88.00 2.00 10.00
Liquid Methyl methacrylate (% w/w) N,N-Dimethyl-p-toluidine (% w/w) Hydroquinone (ppm)
97.50 ≤2.50 25
1457
Table 2 Experimental groups Sample group
Bioceramic wt.%
A1 A2 A3 B1 B2 B3 C1 C2 C3 D CMW™3
1.5-BHA 2.5-BHA 3.5-BHA 1.5-β-TCP 2.5-β-TCP 3.5-β-TCP 1.5-HA 2.5-HA 3.5-HA No additives Reference
than that of CMW™3 (89.44 MPa). In general, however, less addition of bioceramic (1.5%) resulted in the strongest bone cements, except in the case of C group, where increasing ceramic additives from 2.5% to 3.5% slightly improved compressive strength. Decreasing compressive strength by addition of higher amounts of HA has already been reported in earlier studies. Serbetci et al. and Vallo et al. have reported that addition of HA decreases the mechanical strength of bone cements [3,9]. Those studies have demonstrated that silanation of ceramic additives does not change that general tendency. The beneficial effect of little addition of bioceramic in bone cements was also generally evident in the results of bending strength (except in the case of B2). However, C1 bone cement (1.5% HA) exhibited the highest 3-point bending strength among the group C as well as the other groups, including D and CMW™3. Earlier reports agree fairly well with our experimental findings and the above conclusions. Kim et al. have used 10% chitosan and also HA (derived from trabecular bone blocks of porcine spines) as additives [10]. They have reported that an increase in the amount of HA causes a decrease in the compressive strength of bone cements. B1 bone cement (1.5% β-TCP) exhibited the highest compressive strength among the group B. Further addition of β-TCP caused a decrease in compressive strength. Addition of β-TCP up to 2.5% resulted, however, in an increase of 3-point bending strength. Further addition of β-TCP up to 3.5% caused a decrease of 3-point bending strength as well as compressive strength. The fracture surfaces of samples from A, B, and C groups and those of the reference CMW™3 are similar (Fig. 1). Careful observation of the SEM images suggests that the polymeric matrices were homogeneously and uniformly combined with the ceramic reinforcing additives. Nevertheless, non-polymerized patches are visible in the matrix (except in Fig. 1f). Perhaps, these domains are potential faults
Table 3 The results of mechanical tests Sample group
σcomp (MPa)
Ec (GPa)
Fs (MPa)
A1 A2 A3 B1 B2 B3 C1 C2 C3 D CMW™3
91.31 ± 5.50 89.36 ± 0.89 85.32 ± 1.18 86.48 ± 0.72 84.43 ± 0.78 82.47 ± 2.26 83.82 ± 1.78 80.97 ± 0.72 81.52 ± 1.61 74.00 ± 2.80 89.43 ± 3.92
1.85 ± 0.37 2.13 ± 0.14 2.14 ± 0.06 2.20 ± 0.09 2.22 ± 0.05 2.09 ± 0.14 2.05 ± 0.30 2.16 ± 0.06 1.64 ± 0.19 1.74 ± 0.16 2.37 ± 0.04
125.18 ± 27.22 90.07 ± 40.47 91.68 ± 28.44 86.27 ± 6.98 102.44 ± 17.69 85.06 ± 12.96 137.94 ± 30.64 96.60 ± 16.03 96.23 ± 26.02 128.45 ± 18.49 120.48 ± 17.31
1458
S. Daglilar, M.E. Erkan / Materials Letters 61 (2007) 1456–1459
Fig. 1. SEM images of fracture surfaces. (a) A1, (b) A2, (c) A3, (d) B1, (e) B2, (f) B3, (g) C1, (h) C2, (i) C3, (j) D, (k) CMW™3.
inside actually inhomogeneous microstructures of bone cements, where the occurrence of fracture may have high possibility. We believe that finer PMMA powder with smaller particle size should be used to reduce those poorly polymerized domains in the polymeric matrix. As a result, although ceramic additives reinforced the bone cement, they generally caused a decrease in mechanical properties when they were added in excess. The optimum amount of bioceramic additives
should be in a range between 1.5% and 2.5%. Further studies should be addressed to optimize the amount of bioceramic additives. Silanation is a well-known technique that reinforces the organic– inorganic interface bonds. However, in this study, we observed that the amount of additives is more important than the silanation treatment itself. With regard to ceramic additives, this study showed that BHA has a similar effect on mechanical properties of bone cement like the synthetic
S. Daglilar, M.E. Erkan / Materials Letters 61 (2007) 1456–1459
HA. We did not observe any particular effect of β-TCP on mechanical properties of bone cements. Further studies should be done that are related to additions of BHA and β-TCP in bone cements.
4. Conclusions In this study, we reinforced bone cements with silane treated BHA, HA, and β-TCP additives (1.5, 2.5, 3.5 wt.%) to increase their mechanical strength. Compressive strength tests, measurement of compressive elastic modulus, and 3-point bending strength tests were carried out. To achieve reinforcement by additives, the amount of ceramic additives should be in a range between 1.5% and 2.5%. The role of the amount of ceramic additives is more important than the silane treatment itself. Most of the tested samples exhibited similar mechanical strength with the commercial one, but they also feature the important advantage of bioactivity. Acknowledgments We thank SERBAY Orthopedics and Medical Devices Trade (Turkey), and the Ass. Professors F.N. Oktar and S. Agathopoulos as well as Dr. S. Ozyegin for their support to our study.
1459
References [1] K. Serbetci, F. Korkusuz, N. Hasirci, Turk. J. Med. Sci. 30 (2000) 543–549. [2] T. Yamamuro, T. Nakamura, H. Iida, K. Kawanabe, Y. Matsuda, K. Ido, J. Tamura, Y. Senaha, Biomaterials 19 (1998) 1479–1482. [3] K. Serbetci, F. Korkusuz, N. Hasirci, Polym. Test. 23 (2004) 145–155. [4] G. Goller, F.N. Oktar, Mater. Lett. 56 (2002) 142–147. [5] R.Z. LeGeros, J.P. LeGeros, in: B. Ben-Nissan, D. Sher, W. Walsh (Eds.), Proceedings of the 15th International Symposium on Ceramics in Medicine, vol. 15, 2003, pp. 3–10, (Sydney, Australia). [6] S. Shinzato, T. Nakamura, T. Kokubo, Y. Kitamura, J. Biomed. Mater. Res. 55 (2001) 277–284. [7] L.S. Ozyegin, F.N. Oktar, G. Goller, E.S. Kayali, T. Yazici, Mater. Lett. 58 (2004) 2605–2609. [8] W.F. Mousa, M. Kobayashi, Y. Kitamura, I.A. Zeineldin, T. Nakamura, J. Biomed. Mater. Res. 47 (1999) 336–344. [9] C.I. Vallo, P.E. Montemartini, M.A. Fanovich, J.M. Lopez, T.R. Cuadrado, J. Biomed. Mater. Res. 48 (2) (1999) 150–158. [10] S.B. Kim, Y.J. Kim, T.L. Yoon, S.A. Park, I.H. Cho, E.J. Kim, I.A. Kim, J.-W. Shin, Biomaterials 25 (2004) 5715–5723.
A study on bioceramic reinforced bone cements S. Daglilar ⁎, M.E. Erkan Department of Metallurgical and Materials Engineering, Chemistry–Metallurgy Faculty, Yildiz Technical University, Davutpasa Campus, 34201, Esenler, Istanbul, Turkey Received 23 June 2006; accepted 16 July 2006 Available online 10 August 2006
Abstract This paper presents the mechanical properties and SEM studies of bone cements reinforced by bovine hydroxyapatite (BHA), synthetic hydroxyapatite (HA), and β-tricalcium phosphate (β-TCP). All ceramic fillers were silane treated with γ-methacryloxy-propyl-trimethoxy silane (A-174, 0.2%). The quantities of silane treated ceramic fillers in cement were 1.5 wt.%, 2.5 wt.% and 3.5 wt.%. Commercial CMW™3 bone cement was used as control group. The results showed that there is no decay of mechanical properties if the amount of bioceramic additives does not exceed 2.5 wt.%. Similar microstructures were observed by SEM at the fracture surfaces of the bioceramic reinforced bone cements and the control group. © 2006 Elsevier B.V. All rights reserved. Keywords: Bone cement; Silanation; Bovine hydroxyapatite; β-tricalcium phosphate; Hydroxyapatite; Mechanical properties
1. Introduction Acrylic bone cements, mainly consisting of polymethylmethacrylate (PMMA), have been used in orthopedic surgery and dentistry for more than forty years [1]. Nevertheless, PMMA cement possesses several inherent problems, such as nonbonebonding capability, relatively low mechanical strength, and high heat generation during polymerization [2]. To overcome mechanical weakness, bone cements are usually reinforced with additives, such as carbon, graphite, aramid, bone particles, polyethylene, titanium, ultra-high molecular weight polyethylene, PMMA fibers, tricalcium phosphate, and hydroxyapatite [3]. In our study, we focused our interest only on synthetic hydroxyapatite (HA), bovine hydroxyapatite (BHA), and β-tricalcium phosphate (β-TCP) as additives. Hydroxyapatite (HA) is the principal mineral of bone and teeth, with a chemical formula of Ca10(PO4)6(OH)2. HA can be derived from natural sources, such as bovine bones, or corals via hydrothermal transformation, or it can be synthetically prepared [4,5]. Highly pure synthetic HA can be prepared by solid-state reaction, by hydrothermal or microwave methods, or by sintering of apatite obtained via sol-gel method. Apatites ⁎ Corresponding author. Tel.: +90 212 449 16 43. E-mail addresses: [email protected] (S. Daglilar), [email protected] (M.E. Erkan). 0167-577X/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2006.07.068
derived from bovine bone (BHA) are obtained by chemical and/ or thermal removal of the organic matter whether without sintering or with sintering at temperatures above 1000 °C. Pure β-TCP (Ca3(PO4)2) is prepared either by solid-state reaction or by sintering of calcium-deficient apatite obtained from solutions [5]. To achieve mechanically strong cement composites, the silane treatment of the inorganic filler of the cements is a well-known and widely accepted approach in the technology of such composites. The goal of silane treatment is that it results in formation of strong bonds between the inorganic filler and the organic matrix [6]. The purpose of this study was to compare the mechanical strengths of bone cements which were reinforced with different amounts of silane treated HA, BHA, and β-TCP. Measurements of compressive strength, compressive elastic modulus, and three point bending strength were carried out. Observations of the microstructure of the fracture surfaces were performed by SEM. 2. Materials and methods 2.1. Materials The production procedure of the BHA powder used in this study has been described in an earlier study [7]. Synthetic HA and β-TCP powders were obtained from Merck A.G. (Germany). PMMA prepolymerized powder with average particle
S. Daglilar, M.E. Erkan / Materials Letters 61 (2007) 1456–1459
size of 40 μm and MMA liquid (IMICRYL; Turkey) were used to prepare the bioceramic reinforced bone cements. γmethacryloxy-propyl-trimethoxy silane (A-174) was obtained from General Electric (USA). Commercially available CMW™3 bone cement (DePuy, England) was chosen as a reference. Table 1 shows the chemical composition of CMW™3 as reported by the manufacturer. 2.2. Experimental procedure All ceramic powders were sieved through a sieve of 100-μm mesh. The silane coupling agent (0.2 wt.% with respect to the ceramics powders) was added in 100 ml of distilled water and the pH was maintained at 2.9. The powders of the ceramics were added to the solution and mixed at 50 °C with 350 rpm for 2 h (Velp Arex, Italy). The mixtures were dried at 110 °C for 5 h (Instron, USA) [6,8]. The amount of silane treated ceramic powders added to PMMA powder was 1.5%, 2.5%, and 3.5% (in wt.%). PMMA powder and MMA liquid were mixed manually at a ratio of 2.5/ 1.5. CMW™3 bone cement was prepared according to the instructions suggested by the manufacturer. Table 2 summarizes all the groups of materials tested. To prepare the samples, two 304 stainless steel moulds were designed and prepared. They were preheated at 45 °C before sample preparation. Compressive test samples (6 mm in diameter and 12 mm in height) were prepared according to the ISO 5833 (Instron, USA; speed 1 mm/min). Three point bending test samples, with dimensions of 3 × 10 × 15 mm3, were prepared according to the DIN 53435 (Instron, USA; speed 1 mm/min). SEM images were obtained by Jeol JSM-T330. 3. Results and discussion Table 3 summarizes the results obtained from the mechanical tests, where the values of compressive strength (σcomp), compressive elastic modulus (Ec), and 3-point bending strength (Fs) are presented. Accordingly, bone cement A1 exhibited the highest compressive strength (91.31 ± 5.50 MPa). The C1 bone cement has the highest 3-point bending strength (137.94 ± 30.64 MPa). The results of compressive strength indicate that addition of bioceramics can truly reinforce bone cements since the resultant materials were always stronger than the nondoped D bone cement. The reinforcing effect was more pronounced in the case of BHA (group A) than in HA and β-TCP. That group (A) was the only one that exhibited compressive strength (A1, 91.32 MPa) higher Table 1 The chemical composition of CMW™3 as reported by the manufacturer Powder Polymethyl methacrylate (% w/w) Benzoyl peroxide (% w/w) Barium sulphate (% w/w)
88.00 2.00 10.00
Liquid Methyl methacrylate (% w/w) N,N-Dimethyl-p-toluidine (% w/w) Hydroquinone (ppm)
97.50 ≤2.50 25
1457
Table 2 Experimental groups Sample group
Bioceramic wt.%
A1 A2 A3 B1 B2 B3 C1 C2 C3 D CMW™3
1.5-BHA 2.5-BHA 3.5-BHA 1.5-β-TCP 2.5-β-TCP 3.5-β-TCP 1.5-HA 2.5-HA 3.5-HA No additives Reference
than that of CMW™3 (89.44 MPa). In general, however, less addition of bioceramic (1.5%) resulted in the strongest bone cements, except in the case of C group, where increasing ceramic additives from 2.5% to 3.5% slightly improved compressive strength. Decreasing compressive strength by addition of higher amounts of HA has already been reported in earlier studies. Serbetci et al. and Vallo et al. have reported that addition of HA decreases the mechanical strength of bone cements [3,9]. Those studies have demonstrated that silanation of ceramic additives does not change that general tendency. The beneficial effect of little addition of bioceramic in bone cements was also generally evident in the results of bending strength (except in the case of B2). However, C1 bone cement (1.5% HA) exhibited the highest 3-point bending strength among the group C as well as the other groups, including D and CMW™3. Earlier reports agree fairly well with our experimental findings and the above conclusions. Kim et al. have used 10% chitosan and also HA (derived from trabecular bone blocks of porcine spines) as additives [10]. They have reported that an increase in the amount of HA causes a decrease in the compressive strength of bone cements. B1 bone cement (1.5% β-TCP) exhibited the highest compressive strength among the group B. Further addition of β-TCP caused a decrease in compressive strength. Addition of β-TCP up to 2.5% resulted, however, in an increase of 3-point bending strength. Further addition of β-TCP up to 3.5% caused a decrease of 3-point bending strength as well as compressive strength. The fracture surfaces of samples from A, B, and C groups and those of the reference CMW™3 are similar (Fig. 1). Careful observation of the SEM images suggests that the polymeric matrices were homogeneously and uniformly combined with the ceramic reinforcing additives. Nevertheless, non-polymerized patches are visible in the matrix (except in Fig. 1f). Perhaps, these domains are potential faults
Table 3 The results of mechanical tests Sample group
σcomp (MPa)
Ec (GPa)
Fs (MPa)
A1 A2 A3 B1 B2 B3 C1 C2 C3 D CMW™3
91.31 ± 5.50 89.36 ± 0.89 85.32 ± 1.18 86.48 ± 0.72 84.43 ± 0.78 82.47 ± 2.26 83.82 ± 1.78 80.97 ± 0.72 81.52 ± 1.61 74.00 ± 2.80 89.43 ± 3.92
1.85 ± 0.37 2.13 ± 0.14 2.14 ± 0.06 2.20 ± 0.09 2.22 ± 0.05 2.09 ± 0.14 2.05 ± 0.30 2.16 ± 0.06 1.64 ± 0.19 1.74 ± 0.16 2.37 ± 0.04
125.18 ± 27.22 90.07 ± 40.47 91.68 ± 28.44 86.27 ± 6.98 102.44 ± 17.69 85.06 ± 12.96 137.94 ± 30.64 96.60 ± 16.03 96.23 ± 26.02 128.45 ± 18.49 120.48 ± 17.31
1458
S. Daglilar, M.E. Erkan / Materials Letters 61 (2007) 1456–1459
Fig. 1. SEM images of fracture surfaces. (a) A1, (b) A2, (c) A3, (d) B1, (e) B2, (f) B3, (g) C1, (h) C2, (i) C3, (j) D, (k) CMW™3.
inside actually inhomogeneous microstructures of bone cements, where the occurrence of fracture may have high possibility. We believe that finer PMMA powder with smaller particle size should be used to reduce those poorly polymerized domains in the polymeric matrix. As a result, although ceramic additives reinforced the bone cement, they generally caused a decrease in mechanical properties when they were added in excess. The optimum amount of bioceramic additives
should be in a range between 1.5% and 2.5%. Further studies should be addressed to optimize the amount of bioceramic additives. Silanation is a well-known technique that reinforces the organic– inorganic interface bonds. However, in this study, we observed that the amount of additives is more important than the silanation treatment itself. With regard to ceramic additives, this study showed that BHA has a similar effect on mechanical properties of bone cement like the synthetic
S. Daglilar, M.E. Erkan / Materials Letters 61 (2007) 1456–1459
HA. We did not observe any particular effect of β-TCP on mechanical properties of bone cements. Further studies should be done that are related to additions of BHA and β-TCP in bone cements.
4. Conclusions In this study, we reinforced bone cements with silane treated BHA, HA, and β-TCP additives (1.5, 2.5, 3.5 wt.%) to increase their mechanical strength. Compressive strength tests, measurement of compressive elastic modulus, and 3-point bending strength tests were carried out. To achieve reinforcement by additives, the amount of ceramic additives should be in a range between 1.5% and 2.5%. The role of the amount of ceramic additives is more important than the silane treatment itself. Most of the tested samples exhibited similar mechanical strength with the commercial one, but they also feature the important advantage of bioactivity. Acknowledgments We thank SERBAY Orthopedics and Medical Devices Trade (Turkey), and the Ass. Professors F.N. Oktar and S. Agathopoulos as well as Dr. S. Ozyegin for their support to our study.
1459
References [1] K. Serbetci, F. Korkusuz, N. Hasirci, Turk. J. Med. Sci. 30 (2000) 543–549. [2] T. Yamamuro, T. Nakamura, H. Iida, K. Kawanabe, Y. Matsuda, K. Ido, J. Tamura, Y. Senaha, Biomaterials 19 (1998) 1479–1482. [3] K. Serbetci, F. Korkusuz, N. Hasirci, Polym. Test. 23 (2004) 145–155. [4] G. Goller, F.N. Oktar, Mater. Lett. 56 (2002) 142–147. [5] R.Z. LeGeros, J.P. LeGeros, in: B. Ben-Nissan, D. Sher, W. Walsh (Eds.), Proceedings of the 15th International Symposium on Ceramics in Medicine, vol. 15, 2003, pp. 3–10, (Sydney, Australia). [6] S. Shinzato, T. Nakamura, T. Kokubo, Y. Kitamura, J. Biomed. Mater. Res. 55 (2001) 277–284. [7] L.S. Ozyegin, F.N. Oktar, G. Goller, E.S. Kayali, T. Yazici, Mater. Lett. 58 (2004) 2605–2609. [8] W.F. Mousa, M. Kobayashi, Y. Kitamura, I.A. Zeineldin, T. Nakamura, J. Biomed. Mater. Res. 47 (1999) 336–344. [9] C.I. Vallo, P.E. Montemartini, M.A. Fanovich, J.M. Lopez, T.R. Cuadrado, J. Biomed. Mater. Res. 48 (2) (1999) 150–158. [10] S.B. Kim, Y.J. Kim, T.L. Yoon, S.A. Park, I.H. Cho, E.J. Kim, I.A. Kim, J.-W. Shin, Biomaterials 25 (2004) 5715–5723.