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Microstructure and mechanical properties of porous yttria stabilized zirconia ceramic using poly methyl methacrylate powder
Scripta Materialia 54 (2006) 2081–2085 www.actamat-journals.com
Microstructure and mechanical properties of porous yttria stabilized zirconia ceramic using poly methyl methacrylate powder Asit Kumar Gain a, Ho-Yeon Song b, Byong-Taek Lee b
a,*
a School of Advanced Materials Engineering, Kongju National University, 182 Shinkwan-dong, Kongju City, Chungnam 314-701, South Korea Department of Microbiology, School of Medicine, Soonchunhyang University, 366-1, Ssangyoung-dong, Cheonan-city, Chungnam, 330-090, Korea
Received 26 January 2006; received in revised form 28 February 2006; accepted 3 March 2006 Available online 3 April 2006
Abstract Porous t-ZrO2 ceramic was fabricated by pressureless sintering, using commercial t-ZrO2 and different volume percentages of poly methyl methacrylate (PMMA) powders (20–80%). The spherical pores ranged from about 120 to 170 lm in diameter. By increasing the PMMA content, the number of pores, material properties and pore morphology were changed dramatically. The values of relative density, elastic modulus, bending strength and hardness of the 60 vol.% PMMA content sample, sintered at 1550 C, were about 43%, 40 GPa, 170 MPa and 248 Hv, respectively. 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Porous t-ZrO2 ceramic; Microstructure; Material properties
1. Introduction The interest in porous ceramics has significantly increased due to their wide application, e.g., as environmental filters, gas/liquid separators, lightweight structural materials, biomaterials, thermal insulators, and sensors [1,2]. Recently, yttria stabilized zirconia (t-ZrO2) and Al2O3 have been widely used for implants, such as total hip prostheses and dental materials, due to their excellent biocompatibility, as well as their desirable material properties such as strength, chemical stability and wear resistance [3,4]. The mechanical properties of zirconia ceramics are better than those of monolithic Al2O3 ceramics. In particular, t-ZrO2 ceramic showed excellent fracture toughness of about 4–15 MPa.m1/2, as compared with 2– 12 MPa.m1/2 for human bone [5,6], due to the presence of a phase transformation toughening mechanism. The most important factors when considering the application of
*
Corresponding author. Tel.: +82 41 850 8677; fax: +82 41 858 2939. E-mail address: [email protected] (B.-T. Lee).
bioceramics, are their biocompatibility and reasonable mechanical properties. The osteoconduction in porous materials is closely related to the size, shape, connectivity, and porosity of the pores because of their cell attachment, growth behavior and bond strength between the tissue and the artificial implant in the human body [7]. For the fast bone ingrowth of porous materials, it has been reported that the optimum pore size diameter is in the range 150– 250 lm [8]. Another important factor is the fracture strength and elastic modulus, which are inversely dependent on the porosity. Generally, the elastic modulus of dense t-ZrO2 is about 200 GPa, compared with human cortical bone which is only 7–30 GPa [9], and the longitudinal tensile strength of bovine plexiform bone which is about 167 MPa [10]. Recently, many researchers have focused on the fabrication of porous ceramics. It has been recognized that porous ceramics can be fabricated with the following approaches: (1) controlling the particle size of starting ceramic powders to maintain constant pores among particles; (2) reducing the processing parameters such as forming pressure and/ or sintering temperature; (3) mixing the ceramic powders
1359-6462/$ - see front matter 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2006.03.009
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A.K. Gain et al. / Scripta Materialia 54 (2006) 2081–2085
with a bubble former where the large, homogenous pores can be introduced; and (4) mixing ceramic powders with additional organic particles, which burn out at relatively low temperatures and form small, homogenous pores [11]. In this work, porous t-ZrO2 bodies were fabricated using different volume percentages of PMMA powder as a pore-forming agent and by controlling the pore size and shape. This paper also focuses on the relationship between the microstructure and material properties, as well as the elastic modulus, of porous t-ZrO2 bodies, which is compared with that of human bone.
was measured using a Vickers hardness tester (HV-112, Akashi, Japan) by indenting with a load of 2.5 kg (15 points/sample). Some discs of 25 mm in diameter were prepared for the measurement of the elastic modulus with an ultrasonic technique at 5 MHz (pulse receiver 5055PR and Oscilloscope 93354CM, LeCoroy Co., USA). The chemical analysis was performed using Fourier transform infrared spectroscopy (FTIR). The pore size and microstructure of the porous t-ZrO2 bodies were examined by scanning electron microscopy (SEM, JSM-635F, Jeol) with a Pt coating technique.
2. Experimental procedure
3. Results and discussion
The starting materials were yttria stabilized zirconia (3 mol% Y2O3 doped, t-ZrO2) powder (Tosoh Corporation, Nanyo manufacturing complex, Japan) with a particle size averaging about 70 nm and poly methyl methacrylate (PMMA, LG Chemical Company, Korea) powder with a particle size of about 150–200 lm in diameter, used as the pore-forming agent. First, yttria stabilized zirconia and different volume percentages (10–80%) of PMMA powders were mixed for 24 h by a ball mill using Al2O3 balls as the milling media. Then, the mixture of powders was separated from the milling media and compacted by a uniaxial compaction machine into pellets. Finally, the green pellets were heat treated in two steps. First, the pore-forming agent, PMMA powder, was burned out in air at 700 C in an electrically heated furnace. The heating rate was limited to 30 C/h to allow the volatile components to evaporate and prevent bulk defects such as cracks and swelling. Second, the burnout samples were sintered for 2 h at 1550 C in an air atmosphere. Densities of the sintered samples were measured by the Archimedes method. For bending strength measurement, the samples were cut to dimensions of 4 · 3 · 35 mm3 and then each bar was polished with diamond paste to 3 lm. The bending strength measurement was carried out using a four point bending method with a span length of 10 mm and crosshead speed of 0.1 mm/min, using a universal testing machine (UnitechTM, R&B, Korea). The hardness
Fig. 1 shows the SEM micrograph (a) and particle size distribution (b) of PMMA powder, which was used as the pore-forming agent. Most of the PMMA powder particles were spherical-shaped, with a range of about 150–200 lm in diameter, as shown in the particle size distribution. However, some of them were less than 100 lm in diameter and some were very large, at about 300 lm in diameter. Fig. 2 shows thermogravimetric (TG) and differential thermal analysis (DTA) profiles of PMMA powder. In the TG profile, the percentage of weight loss of PMMA
Fig. 2. TG and DTA profiles of PMMA powder.
Fig. 1. (a) SEM micrograph and (b) particle size distribution of PMMA powder.
A.K. Gain et al. / Scripta Materialia 54 (2006) 2081–2085
powder decreased as the temperature increased to 340 C. However, at over 425 C, the PMMA powder was completely removed. On the other hand, in the DTA profile, an endothermic reaction occurred around 380 C due to the decomposition of the PMMA powder. This result indicates that the PMMA powder can be used as a pore-forming agent for the fabrication of porous ceramics. Fig. 3 shows FTIR profiles of (a) raw t-ZrO2, (b) PMMA powder, (c) the mixture of powders of (a) and (b), and (d) burned-out sample. In the FTIR spectra (a, b), the main band peaks of the starting t-ZrO2 and PMMA powders at 1627 cm 1 and 1720 cm 1, respectively, were clearly observed. In the case of the mixture of powders (c), mixed
Fig. 3. FTIR profiles of (a) raw t-ZrO2, (b) PMMA powder, (c) mixture of powders of (a) and (b), (d) after burnout of green body.
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t-ZrO2 and PMMA powders band peaks were detected. However, after burning-out at 700 C in an air atmosphere (d), only t-ZrO2 band peaks were found, the same as the starting t-ZrO2 powder shown in Fig. 3(a). Thus, we confirmed that the PMMA powder as a pore forming agent was successfully removed during the burning-out process. Fig. 4 shows the SEM micrographs of porous t-ZrO2 bodies depending on the PMMA content. After the burning-out and sintering processes, the pore forming agent (PMMA) was successfully removed and porous t-ZrO2 bodies without processing bulk defects, such as large size shrinkage and cracks, were the result. The spherical-shaped pores were homogeneously dispersed in the t-ZrO2 matrix. The pore size ranged from about 120 to 170 lm in diameter, although a small number of fine pores less than 50 lm in diameter were clearly observed. This observation means that the pore size in the porous body was slightly different from the size of the starting pore forming agent due to the densification of compact bodies during the sintering process. As the PMMA content increased, the number of pores significantly increased, as shown in Fig. 4(a)–(d). However, in the case of 80 vol.% PMMA contents, network-type porous t-ZrO2 bodies were found, due to the necking of the pore-forming agent PMMA. Bucholz et al. [12] reported that the pore size, shape and connectivity were important factors in improving osteoconductivity and also enhancing the ingrowth of bone tissue. Fig. 5 shows the SEM fracture surfaces of 30 vol.% PMMA content porous t-ZrO2 bodies. In the low magnification image (a), it was confirmed that many sphericalshaped pores were well dispersed on the fracture surface. The rough fracture surface was clearly observed. In an enlarged image of the pore frame region (b), the typical
Fig. 4. SEM micrographs of porous t-ZrO2 bodies depending on PMMA content: (a) 20 vol.%, (b) 40 vol.%, (c) 60 vol.% and (d) 80 vol.% PMMA.
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Fig. 5. SEM fracture surface of (a) porous t-ZrO2 body containing 30 vol.% PMMA and (b), (c) enlarged images of pore frame and pore regions.
intergranular fracture mode was observed with a rough surface, although a few grains showed a transgranular fracture mode. The average t-ZrO2 grain size was about 1 lm in diameter. In the enlarged spherical pore region (c), many sharp grains were clearly observed. Fig. 6 shows the relative density and elastic modulus of porous t-ZrO2 bodies depending on PMMA content. The values of relative density and elastic modulus of porous t-ZrO2 bodies containing 10 vol.% PMMA were about 89% and 178 GPa, respectively. However, as the PMMA content increased, their values decreased due to an increase of pores. In the sample which contained 60 vol.% PMMA, the values of relative density and elastic modulus were about 43% and 40 GPa, respectively. From this measurement, it was clear that the elastic modulus of porous t-ZrO2 bodies containing 60 vol.% PMMA was almost the same as human cortical bone. Fig. 7 shows the bending strength and hardness of porous t-ZrO2 bodies depending on PMMA content. The values of bending strength and hardness of porous t-ZrO2 bodies which contained 10 vol.% PMMA were about 570 MPa and 902 Hv, respectively. As the PMMA content increased, the bending strength and hardness values dramatically decreased due to a remarkable increase in the number of pores. The values of bending strength and hardness of porous t-ZrO2 bodies that contained 60 vol.% PMMA were about 170 MPa and 248 Hv, respectively.
Fig. 7. Bending strength and hardness of porous t-ZrO2 bodies depending on PMMA content.
In general, for the application of bio-implant materials in load bearing parts, the elastic modulus and bending strength as well as the biocompatibility are especially important parameters. As much as possible, their material properties should be similar to those of natural bone. However, most bioceramics have a high elastic modulus and bending strength compared with human bone. So after implantation, bone absorption phenomena have been reported due to the stress shield effect during their longterm application [13]. Consequently, to control the elastic modulus and bending strength, to be similar to human bone, as well as to improve the biocompatibility, porous t-ZrO2 bodies were fabricated. From this study, it was clear that the values of the elastic modulus and bending strength of porous t-ZrO2 bodies containing 60 vol.% PMMA exhibit almost the same material properties as human bone. 4. Conclusion
Fig. 6. Relative density and elastic modulus of porous t-ZrO2 bodies depending on PMMA content.
Porous t-ZrO2 bodies were successfully fabricated using commercial t-ZrO2 and different volume percentages (10–80%) of PMMA powders. As the volume percentage of the PMMA powder as a pore-forming agent increased, the number of pores increased remarkably. In the case of 80 vol.% PMMA contents, network-type porous t-ZrO2 bodies were formed, due to the necking of the pore-forming agent PMMA. The spherical-shaped pores ranged from
A.K. Gain et al. / Scripta Materialia 54 (2006) 2081–2085
about 120 to 170 lm in diameter. The material properties such as relative density, elastic modulus, bending strength and hardness decreased as the volume percentage of the PMMA content increased. The values of elastic modulus and bending strength of porous t-ZrO2 bodies containing 60 vol.% PMMA were about 40 GPa and 170 MPa, respectively, almost the same as human bone. Acknowledgement This work was supported by the NRL research program of the Korean Ministry of Science and Technology. References [1] Biasini V, Parasporo M, Bellosi A. Thin Solid Film 1997;297:207. [2] Maca K, Dobsak P, Boccaccini AR. Ceram Int 2001;27:577.
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[3] Heisel MC, Silva MM, Schmalzried MTP. J Bone Jt Surg 2003;85: 1366. [4] Agli GD, Esposito S, Mascolo G, Mascolo MC, Pagliuca C. J Eur Ceram Soc 2005;25:2017. [5] Feder A, Anglada M. J Eur Ceram Soc 2005;25:3117. [6] Suchanek W, Yashima M, Kakihana M, Yoshimura M. Biomaterials 1997;18:923. [7] Lee BT, Kang IC, Cho SH, Song HY. J Am Ceram Soc 2005;88:2262. [8] Werner J, Krcmar BL, Friess W, Greil P. Biomaterials 2002;23: 4285. [9] Berndt CC, Haddad GN, Farmer AJD, Gross KA. Mater Forum 1990;14:161. [10] Reilly DT, Burstein AH. J Biomech 1975;8:393. [11] Ishizaki K, Komarneni S, Nanki M. Porous materials process technology and applications. Dordrecht: Kluwer Academic Publishers; 1998 [Chapter 2]. [12] Bucholz RW, Carlton A, Holmes RE. Orthop Clin North Am 1987;18:323. [13] Goto T, Yasunaga Y, Takahashi K, Ochi M. Arch Orthop Trauma Surg 2004;124:357.
Microstructure and mechanical properties of porous yttria stabilized zirconia ceramic using poly methyl methacrylate powder Asit Kumar Gain a, Ho-Yeon Song b, Byong-Taek Lee b
a,*
a School of Advanced Materials Engineering, Kongju National University, 182 Shinkwan-dong, Kongju City, Chungnam 314-701, South Korea Department of Microbiology, School of Medicine, Soonchunhyang University, 366-1, Ssangyoung-dong, Cheonan-city, Chungnam, 330-090, Korea
Received 26 January 2006; received in revised form 28 February 2006; accepted 3 March 2006 Available online 3 April 2006
Abstract Porous t-ZrO2 ceramic was fabricated by pressureless sintering, using commercial t-ZrO2 and different volume percentages of poly methyl methacrylate (PMMA) powders (20–80%). The spherical pores ranged from about 120 to 170 lm in diameter. By increasing the PMMA content, the number of pores, material properties and pore morphology were changed dramatically. The values of relative density, elastic modulus, bending strength and hardness of the 60 vol.% PMMA content sample, sintered at 1550 C, were about 43%, 40 GPa, 170 MPa and 248 Hv, respectively. 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Porous t-ZrO2 ceramic; Microstructure; Material properties
1. Introduction The interest in porous ceramics has significantly increased due to their wide application, e.g., as environmental filters, gas/liquid separators, lightweight structural materials, biomaterials, thermal insulators, and sensors [1,2]. Recently, yttria stabilized zirconia (t-ZrO2) and Al2O3 have been widely used for implants, such as total hip prostheses and dental materials, due to their excellent biocompatibility, as well as their desirable material properties such as strength, chemical stability and wear resistance [3,4]. The mechanical properties of zirconia ceramics are better than those of monolithic Al2O3 ceramics. In particular, t-ZrO2 ceramic showed excellent fracture toughness of about 4–15 MPa.m1/2, as compared with 2– 12 MPa.m1/2 for human bone [5,6], due to the presence of a phase transformation toughening mechanism. The most important factors when considering the application of
*
Corresponding author. Tel.: +82 41 850 8677; fax: +82 41 858 2939. E-mail address: [email protected] (B.-T. Lee).
bioceramics, are their biocompatibility and reasonable mechanical properties. The osteoconduction in porous materials is closely related to the size, shape, connectivity, and porosity of the pores because of their cell attachment, growth behavior and bond strength between the tissue and the artificial implant in the human body [7]. For the fast bone ingrowth of porous materials, it has been reported that the optimum pore size diameter is in the range 150– 250 lm [8]. Another important factor is the fracture strength and elastic modulus, which are inversely dependent on the porosity. Generally, the elastic modulus of dense t-ZrO2 is about 200 GPa, compared with human cortical bone which is only 7–30 GPa [9], and the longitudinal tensile strength of bovine plexiform bone which is about 167 MPa [10]. Recently, many researchers have focused on the fabrication of porous ceramics. It has been recognized that porous ceramics can be fabricated with the following approaches: (1) controlling the particle size of starting ceramic powders to maintain constant pores among particles; (2) reducing the processing parameters such as forming pressure and/ or sintering temperature; (3) mixing the ceramic powders
1359-6462/$ - see front matter 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2006.03.009
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A.K. Gain et al. / Scripta Materialia 54 (2006) 2081–2085
with a bubble former where the large, homogenous pores can be introduced; and (4) mixing ceramic powders with additional organic particles, which burn out at relatively low temperatures and form small, homogenous pores [11]. In this work, porous t-ZrO2 bodies were fabricated using different volume percentages of PMMA powder as a pore-forming agent and by controlling the pore size and shape. This paper also focuses on the relationship between the microstructure and material properties, as well as the elastic modulus, of porous t-ZrO2 bodies, which is compared with that of human bone.
was measured using a Vickers hardness tester (HV-112, Akashi, Japan) by indenting with a load of 2.5 kg (15 points/sample). Some discs of 25 mm in diameter were prepared for the measurement of the elastic modulus with an ultrasonic technique at 5 MHz (pulse receiver 5055PR and Oscilloscope 93354CM, LeCoroy Co., USA). The chemical analysis was performed using Fourier transform infrared spectroscopy (FTIR). The pore size and microstructure of the porous t-ZrO2 bodies were examined by scanning electron microscopy (SEM, JSM-635F, Jeol) with a Pt coating technique.
2. Experimental procedure
3. Results and discussion
The starting materials were yttria stabilized zirconia (3 mol% Y2O3 doped, t-ZrO2) powder (Tosoh Corporation, Nanyo manufacturing complex, Japan) with a particle size averaging about 70 nm and poly methyl methacrylate (PMMA, LG Chemical Company, Korea) powder with a particle size of about 150–200 lm in diameter, used as the pore-forming agent. First, yttria stabilized zirconia and different volume percentages (10–80%) of PMMA powders were mixed for 24 h by a ball mill using Al2O3 balls as the milling media. Then, the mixture of powders was separated from the milling media and compacted by a uniaxial compaction machine into pellets. Finally, the green pellets were heat treated in two steps. First, the pore-forming agent, PMMA powder, was burned out in air at 700 C in an electrically heated furnace. The heating rate was limited to 30 C/h to allow the volatile components to evaporate and prevent bulk defects such as cracks and swelling. Second, the burnout samples were sintered for 2 h at 1550 C in an air atmosphere. Densities of the sintered samples were measured by the Archimedes method. For bending strength measurement, the samples were cut to dimensions of 4 · 3 · 35 mm3 and then each bar was polished with diamond paste to 3 lm. The bending strength measurement was carried out using a four point bending method with a span length of 10 mm and crosshead speed of 0.1 mm/min, using a universal testing machine (UnitechTM, R&B, Korea). The hardness
Fig. 1 shows the SEM micrograph (a) and particle size distribution (b) of PMMA powder, which was used as the pore-forming agent. Most of the PMMA powder particles were spherical-shaped, with a range of about 150–200 lm in diameter, as shown in the particle size distribution. However, some of them were less than 100 lm in diameter and some were very large, at about 300 lm in diameter. Fig. 2 shows thermogravimetric (TG) and differential thermal analysis (DTA) profiles of PMMA powder. In the TG profile, the percentage of weight loss of PMMA
Fig. 2. TG and DTA profiles of PMMA powder.
Fig. 1. (a) SEM micrograph and (b) particle size distribution of PMMA powder.
A.K. Gain et al. / Scripta Materialia 54 (2006) 2081–2085
powder decreased as the temperature increased to 340 C. However, at over 425 C, the PMMA powder was completely removed. On the other hand, in the DTA profile, an endothermic reaction occurred around 380 C due to the decomposition of the PMMA powder. This result indicates that the PMMA powder can be used as a pore-forming agent for the fabrication of porous ceramics. Fig. 3 shows FTIR profiles of (a) raw t-ZrO2, (b) PMMA powder, (c) the mixture of powders of (a) and (b), and (d) burned-out sample. In the FTIR spectra (a, b), the main band peaks of the starting t-ZrO2 and PMMA powders at 1627 cm 1 and 1720 cm 1, respectively, were clearly observed. In the case of the mixture of powders (c), mixed
Fig. 3. FTIR profiles of (a) raw t-ZrO2, (b) PMMA powder, (c) mixture of powders of (a) and (b), (d) after burnout of green body.
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t-ZrO2 and PMMA powders band peaks were detected. However, after burning-out at 700 C in an air atmosphere (d), only t-ZrO2 band peaks were found, the same as the starting t-ZrO2 powder shown in Fig. 3(a). Thus, we confirmed that the PMMA powder as a pore forming agent was successfully removed during the burning-out process. Fig. 4 shows the SEM micrographs of porous t-ZrO2 bodies depending on the PMMA content. After the burning-out and sintering processes, the pore forming agent (PMMA) was successfully removed and porous t-ZrO2 bodies without processing bulk defects, such as large size shrinkage and cracks, were the result. The spherical-shaped pores were homogeneously dispersed in the t-ZrO2 matrix. The pore size ranged from about 120 to 170 lm in diameter, although a small number of fine pores less than 50 lm in diameter were clearly observed. This observation means that the pore size in the porous body was slightly different from the size of the starting pore forming agent due to the densification of compact bodies during the sintering process. As the PMMA content increased, the number of pores significantly increased, as shown in Fig. 4(a)–(d). However, in the case of 80 vol.% PMMA contents, network-type porous t-ZrO2 bodies were found, due to the necking of the pore-forming agent PMMA. Bucholz et al. [12] reported that the pore size, shape and connectivity were important factors in improving osteoconductivity and also enhancing the ingrowth of bone tissue. Fig. 5 shows the SEM fracture surfaces of 30 vol.% PMMA content porous t-ZrO2 bodies. In the low magnification image (a), it was confirmed that many sphericalshaped pores were well dispersed on the fracture surface. The rough fracture surface was clearly observed. In an enlarged image of the pore frame region (b), the typical
Fig. 4. SEM micrographs of porous t-ZrO2 bodies depending on PMMA content: (a) 20 vol.%, (b) 40 vol.%, (c) 60 vol.% and (d) 80 vol.% PMMA.
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Fig. 5. SEM fracture surface of (a) porous t-ZrO2 body containing 30 vol.% PMMA and (b), (c) enlarged images of pore frame and pore regions.
intergranular fracture mode was observed with a rough surface, although a few grains showed a transgranular fracture mode. The average t-ZrO2 grain size was about 1 lm in diameter. In the enlarged spherical pore region (c), many sharp grains were clearly observed. Fig. 6 shows the relative density and elastic modulus of porous t-ZrO2 bodies depending on PMMA content. The values of relative density and elastic modulus of porous t-ZrO2 bodies containing 10 vol.% PMMA were about 89% and 178 GPa, respectively. However, as the PMMA content increased, their values decreased due to an increase of pores. In the sample which contained 60 vol.% PMMA, the values of relative density and elastic modulus were about 43% and 40 GPa, respectively. From this measurement, it was clear that the elastic modulus of porous t-ZrO2 bodies containing 60 vol.% PMMA was almost the same as human cortical bone. Fig. 7 shows the bending strength and hardness of porous t-ZrO2 bodies depending on PMMA content. The values of bending strength and hardness of porous t-ZrO2 bodies which contained 10 vol.% PMMA were about 570 MPa and 902 Hv, respectively. As the PMMA content increased, the bending strength and hardness values dramatically decreased due to a remarkable increase in the number of pores. The values of bending strength and hardness of porous t-ZrO2 bodies that contained 60 vol.% PMMA were about 170 MPa and 248 Hv, respectively.
Fig. 7. Bending strength and hardness of porous t-ZrO2 bodies depending on PMMA content.
In general, for the application of bio-implant materials in load bearing parts, the elastic modulus and bending strength as well as the biocompatibility are especially important parameters. As much as possible, their material properties should be similar to those of natural bone. However, most bioceramics have a high elastic modulus and bending strength compared with human bone. So after implantation, bone absorption phenomena have been reported due to the stress shield effect during their longterm application [13]. Consequently, to control the elastic modulus and bending strength, to be similar to human bone, as well as to improve the biocompatibility, porous t-ZrO2 bodies were fabricated. From this study, it was clear that the values of the elastic modulus and bending strength of porous t-ZrO2 bodies containing 60 vol.% PMMA exhibit almost the same material properties as human bone. 4. Conclusion
Fig. 6. Relative density and elastic modulus of porous t-ZrO2 bodies depending on PMMA content.
Porous t-ZrO2 bodies were successfully fabricated using commercial t-ZrO2 and different volume percentages (10–80%) of PMMA powders. As the volume percentage of the PMMA powder as a pore-forming agent increased, the number of pores increased remarkably. In the case of 80 vol.% PMMA contents, network-type porous t-ZrO2 bodies were formed, due to the necking of the pore-forming agent PMMA. The spherical-shaped pores ranged from
A.K. Gain et al. / Scripta Materialia 54 (2006) 2081–2085
about 120 to 170 lm in diameter. The material properties such as relative density, elastic modulus, bending strength and hardness decreased as the volume percentage of the PMMA content increased. The values of elastic modulus and bending strength of porous t-ZrO2 bodies containing 60 vol.% PMMA were about 40 GPa and 170 MPa, respectively, almost the same as human bone. Acknowledgement This work was supported by the NRL research program of the Korean Ministry of Science and Technology. References [1] Biasini V, Parasporo M, Bellosi A. Thin Solid Film 1997;297:207. [2] Maca K, Dobsak P, Boccaccini AR. Ceram Int 2001;27:577.
2085
[3] Heisel MC, Silva MM, Schmalzried MTP. J Bone Jt Surg 2003;85: 1366. [4] Agli GD, Esposito S, Mascolo G, Mascolo MC, Pagliuca C. J Eur Ceram Soc 2005;25:2017. [5] Feder A, Anglada M. J Eur Ceram Soc 2005;25:3117. [6] Suchanek W, Yashima M, Kakihana M, Yoshimura M. Biomaterials 1997;18:923. [7] Lee BT, Kang IC, Cho SH, Song HY. J Am Ceram Soc 2005;88:2262. [8] Werner J, Krcmar BL, Friess W, Greil P. Biomaterials 2002;23: 4285. [9] Berndt CC, Haddad GN, Farmer AJD, Gross KA. Mater Forum 1990;14:161. [10] Reilly DT, Burstein AH. J Biomech 1975;8:393. [11] Ishizaki K, Komarneni S, Nanki M. Porous materials process technology and applications. Dordrecht: Kluwer Academic Publishers; 1998 [Chapter 2]. [12] Bucholz RW, Carlton A, Holmes RE. Orthop Clin North Am 1987;18:323. [13] Goto T, Yasunaga Y, Takahashi K, Ochi M. Arch Orthop Trauma Surg 2004;124:357.