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Newly developed bioactive glass-ceramic composite toughened by tetragonal zirconia
Clinical Materials 4 (1989) 285-294
Composi Newly Developed Bioactive Glass-Ceramic Toughened by Tetragonal Zirconia Toshihiro Hoya Corporation,
Kasuga
& Kiichi Nakajima
Materials Research Laboratory, Tokyo, 196 Japan
(Received 5 January
3-3-l Musashino,
Akishima-shi,
1989; sent for revision 11 May 1989; accepted 28 June 1989)
ABSTRACT A new type of bioactive glass-ceramic toughened by the dispersion of tetragonal zirconia polycrystal (TZP) grains was developed. This bioceramic exhibited high bending strength (500-800 MPa) and toughness. The high strength and toughness can be attributed to the inhibition of the crack propagation by deflection, branching and pinning, and the wastage of the fracture energy in propagating through TZP grains. It was shown that in composites containing TZP (especially up to 50 %vol.) a new apatite layer could form on the surface after immersion in simulated body fluid.
1 INTRODUCTION such as Bioglass@‘l and sintered apatite’ show good ility and bioactivity. However, their clinical application as hard tissue replacements is limited because their mechanical str are not sufficiently high. Apatite- and wollastonite-containing a ceramic (glass-ceramic A-W)%’ exhibits good biocompatibility high bioactivity for forming tight chemical bonding with bone tiss glass-ceramic A-W shows relatively high mechanical strength 300 MPa in three-point bending), its applications in dental implant artificial bone, etc., are expected, and clinical tests have been Carrie out. However, some artificial hard tissues (for example, dental imp1 for front teeth, artificial joints, etc.) require even higher strength. 285 Clinical
Materials
0267-6605/89/$03.50
England.
Printed in Northern
Ireland
@
1989
Elsevier
Science
Publishers
Ltd,
286
Toshihiro Kasuga, Kiichi Nakajima
the other hand, tetragonal zirconia polycrystal (TZP) is a very strong and tough ceramic? and, furthermore, shows good biocompatibility.7,8 A bioactive and mechanically tough ceramic will be widely applicable to many other tissue replacements. In this study, a new type of bioactive glass-ceramic composite toughened by tetragonal zirconia will be proposed.
2 EXPERIMENTAL 2.1 Preparation of 47.7Ca0-6.5P,O,-43+SiO,In this study, the composition l.SMgO-OmSCaF, (%wt) was selected as the base glass for matrices of the composite. Apatite and /3-wollastonite crystals are precipitated in the glass by the appropriate heat treatment. Their contents are 15 and 70 %wt, respectively. After implanting in the lower jaw of a dog, this glass-ceramic was found to form chemical bonds with bone tissues (Hoya Corporation, unpublished data). The preparation process for the composite material is shown in Fig. 1. A batch mixture of the composition described above was melted in a platinum crucible at 1500 “C, and then quenched into water to form the glass. The resultant glass was pulverized into powder of 2-3 pm mean particle diameter. The zirconia powder used in this study (Nippon Shokubai Kagaku Kogyo Co. Ltd, NS-3YS) contained 3 %mol Y,O, and was prepared by
Fig. 1.
Preparation process of composites.
Newly developed bioactive glass-ceramic
composite
287
the co-precipitation method. TZP shows high strength and toughness by stress-induced phase transformation. It has been reported,9 however, that the phase transformation of TZP from tetragonal to monoclinic in wet environments takes place at lower temperatures and at a higher rate than in a dry environment. This transformation is accompanied cracking and sometimes caused the degradation of mechanical pr0perties.l’ The phase transformation of zirconia in the glass-cera composites could be restricted by using dense TZP consisting of v fine crystal grains. l1 In order to prepare tough and stable TZP, T grains sintered at 1150-1300°C were used in this study. The TZP for fabrication of the composite consisted of particles of 2-3 pm mean particle diameter and a grain size of 0.2-0.3 pm. The relative densities of the TZP particles was 97%. The glass powder was mixed with the TZP by ball-milling with ethanol. The blended powder was hot-pressed uniaxially in vacuu (~10~~ Pa) at 1150 “C under 25-30 MPa pressure. 2.2 Physical properties and microstructure od specimens (4-5 mm@), ground with No. 400 diamond, were broken in three-point bending (the length of supported span: 15-20mm) at a crosshead speed of O-5 mmmin-’ with an Instron testing machine in air at room temperature. For each sample, measurements were made. The three-point bending strength (a,> calculated using the following equation: 8PL a, = ZD3 where P, L and D are the load to failure, the length of supported s and the diameter of specimen, respectively. The chevron-notched beam specimens were used to measure the fracture toughness (K,,) as shown in Fig. 2. The crosshead rate and the length of supported span were 0.05 mm min-l and 15 mm mm-l, respectively. The Kr, was calculated using the following equation: P 3.08 + 5.00($) BW0.5 (
Krc=---
+ 8.33($~)(;)[~~;~
~o~~w]
where a, is the initial crack length (distance from line of loa application to tip of chevron), a, is the length of the chevron note the specimen surface (distance from line of load application to poi chevron emergence at specimen surface), and P and 5’are the lo failure and the length of supported span, respectively. Five measurements were made for each sample.
Toshihiro Kasuga, Kiichi Nakajima
288
P
Fig. 2.
The specimen with a chevron notch for fracture toughness measurement. a,, Initial crack length (distance from line of load application to tip of chevron); a,, length of chevron notch at specimen surface (distance from line of load application to point of chevron emergence at specimen surface); B, specimen thickness ( = 3-O mm); P, load; S, length of supported span; W, specimen width ( = 4-O mm); W,, notch width ( = 0.15 - 0.20 mm).
Densities of the composites were determined by liquid displacement. Theoretical densities of the composites were estimated from the densities of the glass-ceramic and TZP using 2.98 and 6.10 g cm-3, respectively. The crystalline phases in the composites thus obtained were determined by X-ray diffraction (XRD) analysis. Polished surfaces of the composites were observed using scanning electron microscopy (SEM). 2.3 Estimation of bioactivity The in-vitro test in the simulated body fluid (SBF) is a good method to determine whether the material has the ability of forming chemical bonds to living b0ne.l’ When the bioactive materials are immersed in SBF containing the ions shown in Table 1, a new apatite layer may form on the surface.13 It is assumed that apatite layer formation is closely related to the bonding ability of materials to living bone. The TABLE
Ion Concentrations
1
in Human Plasma and Simulated Body Fluid Ion concentration (mbf)
Human plasma SBF
Na+
K+
MgZf
Ca’
Cl-
142.0 142.0
5.0 5.0
1.5 1.5
2.5 2.5
103.0 148.8
HCO;
13.5 4.2
HPO:-
1.0 1.0
Newly developed bioactive glass-ceramic
composite
289
composites were soaked in SBF at 37 “C for 10 and 30 days and t examined by XRD and/or SEM to see whether an apatite layer formed on their surfaces.
3 RESULTS .l Microstructure
AND DISCUSSION
and mechanical
properties
Figure 3 is an SEM photograph of the composite containing 30% vol. TZP, Observed using the backscattered electron imaging mode. The glass-ceramic matrix appears dark and the TZP grains bright due to their different atomic numbers. It was observed that the grains of t TZP were dispersed in the glass-ceramic matrix without intense agglomeration. Figure 4 shows the relation between the bending strength of composites in air and the volume fraction (Vf) of TZP. The stren increased with increasing V, up to 60%, while it decreased abruptly increasing V, over 70%. For example, the bending strength of composite containing V, 30% was 500-650 MPa (the mean value and the standard deviation are 581 and 53 MPa, respectively). This va about 2-3 times higher than that of the matrix materials and as h that of well-sintered alumina ceramics. Moreover, it is higher than that
Fig. 3.
SEM photograph
of polished
surface of the composite TZP.
containing
30% voi
290
Toshihiro Kasuga, Kiichi Nakajima
O------J
Fig. 4.
0
Relation between sintered TZP content (V,) and bending strength of the composite.
20
40
GO
TZP content
80
103
(~01%)
of the glass-ceramic composites prepared by using TZP-containing alumina (mean values of 440-460 MPa) .14,15 TZP particles agglomerated in composites containing over 70% TZP. Therefore, it was very hard to fabricate the dense composites because TZP did not sinter very well at 1150 ‘Cl6 As a result, the strength and toughness of the composites containing over 70 %vol TZP were very low. Figure 5 shows the relation between the V, and the fracture toughness (K,,). The K,, value of the composite containing 30% TZP was 3.16 MPa m”-5 (standard deviation, O-14), about twice as high as the matrix material. The KIc increased with increasing V, up to 60%, while it decreased abruptly with increasing V, over 70%, which is similar to the profile of the relation between the bending strength and V,. Generally, the bending strength of brittle materials is related to the fracture toughness as follows:17
where
Y is a parameter
which depends
on the specimen
s; 2
6
Q5B 4-
_E 3-
7
al’2 i :
Y 3 2 _d /’ k?! 3 lFig. 5. Relation TZP (V,) and fracture (K,,) of content toughnessbetween the composite
measured by chevron-notched
beam method.
$
and crack
Oo, ,
\ \ 1
I I 20
TZP cor&t
I /
1 I I I 60 80
(~01%)
Newly developed bioactive glass-ceramic
composite
291
ometry, and C is the critical flaw size in the material Therefore, it is ggested that the increase in strength is attributed to the increase in fracture toughness. Figure 6 shows the crack profile of a Vickers indentation introduce in the composite (V,30) at a load of 9.8 N. The crack propagate through the crystallized glass matrix, as well as the TZP particles. It seems that the propagation through the TZP grain absorbs an especially large fracture energy. Finally, the crack was pin-stopped. It appears that the fracture toughness and the strength is modified by the presence of TZP particles in the composite. .2. Estimation
of bioactivity
The X-ray intensities of the (300) reflection of apatite, before and after soaking the composites, in SBF, are plotted in Fig. 7. New apatite crystals were actively formed on the surface of the composites containing up to 40% TZP. However, for the composites containing over 50% TZP, the (300) intensities of apatite in XRD were almost buried in the background because of the small content of crystallize
Fig. 6.
Crack profile of Vickers indentation introduced load of 9.8 N.
in the composite
(V,30%) at a
Toshihiro Kasuga, Kiichi Nakajima
292
?? L. 30d Fig. 7. Relation between TZP content (V,) and XRD peak height of apatite at the surface of the composite after soaking in SBF at 37°C. The XRD peak height is the X-ray (CuK,, 40 KV 20 mA) diffraction intensity of the (300) reflection of apatite. 0, Before soaking in SBF; 0, after soaking in SBF for 10 days; 0, after soaking in SBF for 30 days.
f I 10 g x 0
I
I
0
I
20
I
I
I
I
I
40
60
TZP
content
8
80
0
10 0
(~01%)
glass matrix. Consequently, it is difficult to estimate their bioactivity by this method. Figure 8 is an SEM photograph of the surface of the composite containing 30% TZP after 30 days’ soaking. The surface of the composite was covered with a new apatite layer. An apatite layer grew not only on the glass-ceramic matrix but also on the TZP grains. 4
CONCLUSIONS
A new type of glass-ceramic composite zirconia polycrystal was fabricated.
Fig. 8.
SEIM photograph
toughened
by tetragonal
of apatite formed on the composite (Vr30%) after soaki w in SBF at 37 “C for 30 days.
Newly developed bioactive glass-ceramic
1.
2.
composite
293
The bending strength and the fracture toughness of the Compaqites were twice or three times higher than those of the glassceramic matrix material. After immersing the composite in simulated body fluid, a new apatite layer was formed on the surface. Therefore, it was suggested that this composite has bioactivity.
As mentioned above, this composite has a high potentiality for iomaterial uses such as dental implants or artificial bones. Evaluation of this composite
by implantation
in bone is now in progress.
REFERENCES 1. Hench, L. L., Splinter, R. J., Allen, W. C. & Greenlee, T. K., Bonding mechanism at the interface of ceramic prosthetic materials. J. Biomed. Muter. Res., Symposium No. 2 (1971) 117-41. 2. Jarco, M., Kay, J. F., Gumaer, K. I., Doremus, R. H. & Drobeck, Tissue, cellular and subcellular events at a bone-ceramic hydroxyl interface. J. Bioeng., 1 (1977) 79-92. 3. Kobubo, T. et al., Apatite- and wollastonite-containing glass-ceramics for
prosthetic application. Bull. Inst. Chem. Res., 60 (1982) 260-8. 4. Nakamura,
T., Yamamuro, T., Higashi, S., Kokubo, T. & Its, S., A new glass-ceramic for bone replacement; Evaluation of its bonding to bone tissue. J. Biomed. Mater. Res., 19 (1985) 685-98. 5. Yamamuro, T. et al., Artificial bone for use as a bone pros In Progress in Artificial Organs, Vol. 2, ed. K. Atsumi et al. ISA0 No. 204, Cleveland, 1984, pp. 810-14. 6. Masaki, T., Mechanical properties of toughened ZrOz-YzO, ceramics. ;P.
Am. Cerum. Sot., 69 (1986) 638-40. 7. Garvie, R. C., Urbani, C., Kennedy,
Biocompatibility
of magnesia-partially
D. R. & McNeuer, J. C., stabilized zirconia ceramics. J.
Mater. Sci., 19 (1984) 3224-8. 8. Cranin, A. N., Schnitmen, P. A., Rabkin,
and zirconia
coated
vitallium
M. & Denissen, T., Alumina oral endosteal implants in Beagles. J.
Biomed. Mater. Res., 6 (1975) 257-62. 9. Nakajima, K., Kobayashi, K. & Murata, Y., Phase stability of Y-TZ aqueous solutions. In Advances in Ceramics, ed. N. Ciaussen, M. Ruhle &
A. H. Heuer. The American Ceramic Society, Columbus, OH, 1985, pp~ 399-407. 10. Kobayashi, K., Kuwajima, H. & Masaki, T., Phase change and mechanical properties of ZrO,-Yz03 solid electrolyte after aging. Solid State Ion., $4 (1981) 489-93. Il.
Kasuga, T., Nakajima, N. & Nakagawa, H., Phase transformation of TZP in bioactive glass-ceramic composite. J. Ceram. Sot. Jpn, 97 (1989) 322-7. 12. Kushitani, H., Kokubo, T., Sakka, S. & Yamamuro, T., Effect of co-existing ions in a solution on formation of apatite on glass-ceramics for artificial bone. Jpn. Ceram. Sot. Meeting, 1987, pp. 933- 4.
294
Toshihiro
Kasuga,
Kiichi Nakajima
13. Kokubo, T. et al., Surface structure of a load-bearable bioactive glass-ceramic A-W. In Ceramics in Clinical Applications, ed. P. Vincenzini. Elsevier, Amsterdam, 1987, pp, 175-84. 14. Kasuga, T., Uno, T., Yoshida, M. & Nakajima, K., Bioactive glassceramic composite toughened by tetragonal zirconia. Transactions of 3rd World Biomaterials Congress, 1988, p. 72. 15. Kasuga, T., Yoshida, M., Uno, T. & Nakajima, K., Preparation of zirconia-toughened bioactive glass-ceramics. J. Mater. Sci., 23 (1988) 2255-8. bioactive glass-ceramics. 16. Nakajima, K. & Kasuga, T., Zirconia-toughened J. Cerum. Sot. Jpn, 97 (1989) 256-61. 17. Irwin, G. R. & Paris, P. C., Fracture: An Advanced Treatise, Vol. 3, Engineering Fundamentals and Environmental Effects, ed. H. Liebowitz.
Academic Press Inc., New York, 1971, p. 9.
Composi Newly Developed Bioactive Glass-Ceramic Toughened by Tetragonal Zirconia Toshihiro Hoya Corporation,
Kasuga
& Kiichi Nakajima
Materials Research Laboratory, Tokyo, 196 Japan
(Received 5 January
3-3-l Musashino,
Akishima-shi,
1989; sent for revision 11 May 1989; accepted 28 June 1989)
ABSTRACT A new type of bioactive glass-ceramic toughened by the dispersion of tetragonal zirconia polycrystal (TZP) grains was developed. This bioceramic exhibited high bending strength (500-800 MPa) and toughness. The high strength and toughness can be attributed to the inhibition of the crack propagation by deflection, branching and pinning, and the wastage of the fracture energy in propagating through TZP grains. It was shown that in composites containing TZP (especially up to 50 %vol.) a new apatite layer could form on the surface after immersion in simulated body fluid.
1 INTRODUCTION such as Bioglass@‘l and sintered apatite’ show good ility and bioactivity. However, their clinical application as hard tissue replacements is limited because their mechanical str are not sufficiently high. Apatite- and wollastonite-containing a ceramic (glass-ceramic A-W)%’ exhibits good biocompatibility high bioactivity for forming tight chemical bonding with bone tiss glass-ceramic A-W shows relatively high mechanical strength 300 MPa in three-point bending), its applications in dental implant artificial bone, etc., are expected, and clinical tests have been Carrie out. However, some artificial hard tissues (for example, dental imp1 for front teeth, artificial joints, etc.) require even higher strength. 285 Clinical
Materials
0267-6605/89/$03.50
England.
Printed in Northern
Ireland
@
1989
Elsevier
Science
Publishers
Ltd,
286
Toshihiro Kasuga, Kiichi Nakajima
the other hand, tetragonal zirconia polycrystal (TZP) is a very strong and tough ceramic? and, furthermore, shows good biocompatibility.7,8 A bioactive and mechanically tough ceramic will be widely applicable to many other tissue replacements. In this study, a new type of bioactive glass-ceramic composite toughened by tetragonal zirconia will be proposed.
2 EXPERIMENTAL 2.1 Preparation of 47.7Ca0-6.5P,O,-43+SiO,In this study, the composition l.SMgO-OmSCaF, (%wt) was selected as the base glass for matrices of the composite. Apatite and /3-wollastonite crystals are precipitated in the glass by the appropriate heat treatment. Their contents are 15 and 70 %wt, respectively. After implanting in the lower jaw of a dog, this glass-ceramic was found to form chemical bonds with bone tissues (Hoya Corporation, unpublished data). The preparation process for the composite material is shown in Fig. 1. A batch mixture of the composition described above was melted in a platinum crucible at 1500 “C, and then quenched into water to form the glass. The resultant glass was pulverized into powder of 2-3 pm mean particle diameter. The zirconia powder used in this study (Nippon Shokubai Kagaku Kogyo Co. Ltd, NS-3YS) contained 3 %mol Y,O, and was prepared by
Fig. 1.
Preparation process of composites.
Newly developed bioactive glass-ceramic
composite
287
the co-precipitation method. TZP shows high strength and toughness by stress-induced phase transformation. It has been reported,9 however, that the phase transformation of TZP from tetragonal to monoclinic in wet environments takes place at lower temperatures and at a higher rate than in a dry environment. This transformation is accompanied cracking and sometimes caused the degradation of mechanical pr0perties.l’ The phase transformation of zirconia in the glass-cera composites could be restricted by using dense TZP consisting of v fine crystal grains. l1 In order to prepare tough and stable TZP, T grains sintered at 1150-1300°C were used in this study. The TZP for fabrication of the composite consisted of particles of 2-3 pm mean particle diameter and a grain size of 0.2-0.3 pm. The relative densities of the TZP particles was 97%. The glass powder was mixed with the TZP by ball-milling with ethanol. The blended powder was hot-pressed uniaxially in vacuu (~10~~ Pa) at 1150 “C under 25-30 MPa pressure. 2.2 Physical properties and microstructure od specimens (4-5 mm@), ground with No. 400 diamond, were broken in three-point bending (the length of supported span: 15-20mm) at a crosshead speed of O-5 mmmin-’ with an Instron testing machine in air at room temperature. For each sample, measurements were made. The three-point bending strength (a,> calculated using the following equation: 8PL a, = ZD3 where P, L and D are the load to failure, the length of supported s and the diameter of specimen, respectively. The chevron-notched beam specimens were used to measure the fracture toughness (K,,) as shown in Fig. 2. The crosshead rate and the length of supported span were 0.05 mm min-l and 15 mm mm-l, respectively. The Kr, was calculated using the following equation: P 3.08 + 5.00($) BW0.5 (
Krc=---
+ 8.33($~)(;)[~~;~
~o~~w]
where a, is the initial crack length (distance from line of loa application to tip of chevron), a, is the length of the chevron note the specimen surface (distance from line of load application to poi chevron emergence at specimen surface), and P and 5’are the lo failure and the length of supported span, respectively. Five measurements were made for each sample.
Toshihiro Kasuga, Kiichi Nakajima
288
P
Fig. 2.
The specimen with a chevron notch for fracture toughness measurement. a,, Initial crack length (distance from line of load application to tip of chevron); a,, length of chevron notch at specimen surface (distance from line of load application to point of chevron emergence at specimen surface); B, specimen thickness ( = 3-O mm); P, load; S, length of supported span; W, specimen width ( = 4-O mm); W,, notch width ( = 0.15 - 0.20 mm).
Densities of the composites were determined by liquid displacement. Theoretical densities of the composites were estimated from the densities of the glass-ceramic and TZP using 2.98 and 6.10 g cm-3, respectively. The crystalline phases in the composites thus obtained were determined by X-ray diffraction (XRD) analysis. Polished surfaces of the composites were observed using scanning electron microscopy (SEM). 2.3 Estimation of bioactivity The in-vitro test in the simulated body fluid (SBF) is a good method to determine whether the material has the ability of forming chemical bonds to living b0ne.l’ When the bioactive materials are immersed in SBF containing the ions shown in Table 1, a new apatite layer may form on the surface.13 It is assumed that apatite layer formation is closely related to the bonding ability of materials to living bone. The TABLE
Ion Concentrations
1
in Human Plasma and Simulated Body Fluid Ion concentration (mbf)
Human plasma SBF
Na+
K+
MgZf
Ca’
Cl-
142.0 142.0
5.0 5.0
1.5 1.5
2.5 2.5
103.0 148.8
HCO;
13.5 4.2
HPO:-
1.0 1.0
Newly developed bioactive glass-ceramic
composite
289
composites were soaked in SBF at 37 “C for 10 and 30 days and t examined by XRD and/or SEM to see whether an apatite layer formed on their surfaces.
3 RESULTS .l Microstructure
AND DISCUSSION
and mechanical
properties
Figure 3 is an SEM photograph of the composite containing 30% vol. TZP, Observed using the backscattered electron imaging mode. The glass-ceramic matrix appears dark and the TZP grains bright due to their different atomic numbers. It was observed that the grains of t TZP were dispersed in the glass-ceramic matrix without intense agglomeration. Figure 4 shows the relation between the bending strength of composites in air and the volume fraction (Vf) of TZP. The stren increased with increasing V, up to 60%, while it decreased abruptly increasing V, over 70%. For example, the bending strength of composite containing V, 30% was 500-650 MPa (the mean value and the standard deviation are 581 and 53 MPa, respectively). This va about 2-3 times higher than that of the matrix materials and as h that of well-sintered alumina ceramics. Moreover, it is higher than that
Fig. 3.
SEM photograph
of polished
surface of the composite TZP.
containing
30% voi
290
Toshihiro Kasuga, Kiichi Nakajima
O------J
Fig. 4.
0
Relation between sintered TZP content (V,) and bending strength of the composite.
20
40
GO
TZP content
80
103
(~01%)
of the glass-ceramic composites prepared by using TZP-containing alumina (mean values of 440-460 MPa) .14,15 TZP particles agglomerated in composites containing over 70% TZP. Therefore, it was very hard to fabricate the dense composites because TZP did not sinter very well at 1150 ‘Cl6 As a result, the strength and toughness of the composites containing over 70 %vol TZP were very low. Figure 5 shows the relation between the V, and the fracture toughness (K,,). The K,, value of the composite containing 30% TZP was 3.16 MPa m”-5 (standard deviation, O-14), about twice as high as the matrix material. The KIc increased with increasing V, up to 60%, while it decreased abruptly with increasing V, over 70%, which is similar to the profile of the relation between the bending strength and V,. Generally, the bending strength of brittle materials is related to the fracture toughness as follows:17
where
Y is a parameter
which depends
on the specimen
s; 2
6
Q5B 4-
_E 3-
7
al’2 i :
Y 3 2 _d /’ k?! 3 lFig. 5. Relation TZP (V,) and fracture (K,,) of content toughnessbetween the composite
measured by chevron-notched
beam method.
$
and crack
Oo, ,
\ \ 1
I I 20
TZP cor&t
I /
1 I I I 60 80
(~01%)
Newly developed bioactive glass-ceramic
composite
291
ometry, and C is the critical flaw size in the material Therefore, it is ggested that the increase in strength is attributed to the increase in fracture toughness. Figure 6 shows the crack profile of a Vickers indentation introduce in the composite (V,30) at a load of 9.8 N. The crack propagate through the crystallized glass matrix, as well as the TZP particles. It seems that the propagation through the TZP grain absorbs an especially large fracture energy. Finally, the crack was pin-stopped. It appears that the fracture toughness and the strength is modified by the presence of TZP particles in the composite. .2. Estimation
of bioactivity
The X-ray intensities of the (300) reflection of apatite, before and after soaking the composites, in SBF, are plotted in Fig. 7. New apatite crystals were actively formed on the surface of the composites containing up to 40% TZP. However, for the composites containing over 50% TZP, the (300) intensities of apatite in XRD were almost buried in the background because of the small content of crystallize
Fig. 6.
Crack profile of Vickers indentation introduced load of 9.8 N.
in the composite
(V,30%) at a
Toshihiro Kasuga, Kiichi Nakajima
292
?? L. 30d Fig. 7. Relation between TZP content (V,) and XRD peak height of apatite at the surface of the composite after soaking in SBF at 37°C. The XRD peak height is the X-ray (CuK,, 40 KV 20 mA) diffraction intensity of the (300) reflection of apatite. 0, Before soaking in SBF; 0, after soaking in SBF for 10 days; 0, after soaking in SBF for 30 days.
f I 10 g x 0
I
I
0
I
20
I
I
I
I
I
40
60
TZP
content
8
80
0
10 0
(~01%)
glass matrix. Consequently, it is difficult to estimate their bioactivity by this method. Figure 8 is an SEM photograph of the surface of the composite containing 30% TZP after 30 days’ soaking. The surface of the composite was covered with a new apatite layer. An apatite layer grew not only on the glass-ceramic matrix but also on the TZP grains. 4
CONCLUSIONS
A new type of glass-ceramic composite zirconia polycrystal was fabricated.
Fig. 8.
SEIM photograph
toughened
by tetragonal
of apatite formed on the composite (Vr30%) after soaki w in SBF at 37 “C for 30 days.
Newly developed bioactive glass-ceramic
1.
2.
composite
293
The bending strength and the fracture toughness of the Compaqites were twice or three times higher than those of the glassceramic matrix material. After immersing the composite in simulated body fluid, a new apatite layer was formed on the surface. Therefore, it was suggested that this composite has bioactivity.
As mentioned above, this composite has a high potentiality for iomaterial uses such as dental implants or artificial bones. Evaluation of this composite
by implantation
in bone is now in progress.
REFERENCES 1. Hench, L. L., Splinter, R. J., Allen, W. C. & Greenlee, T. K., Bonding mechanism at the interface of ceramic prosthetic materials. J. Biomed. Muter. Res., Symposium No. 2 (1971) 117-41. 2. Jarco, M., Kay, J. F., Gumaer, K. I., Doremus, R. H. & Drobeck, Tissue, cellular and subcellular events at a bone-ceramic hydroxyl interface. J. Bioeng., 1 (1977) 79-92. 3. Kobubo, T. et al., Apatite- and wollastonite-containing glass-ceramics for
prosthetic application. Bull. Inst. Chem. Res., 60 (1982) 260-8. 4. Nakamura,
T., Yamamuro, T., Higashi, S., Kokubo, T. & Its, S., A new glass-ceramic for bone replacement; Evaluation of its bonding to bone tissue. J. Biomed. Mater. Res., 19 (1985) 685-98. 5. Yamamuro, T. et al., Artificial bone for use as a bone pros In Progress in Artificial Organs, Vol. 2, ed. K. Atsumi et al. ISA0 No. 204, Cleveland, 1984, pp. 810-14. 6. Masaki, T., Mechanical properties of toughened ZrOz-YzO, ceramics. ;P.
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