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The structure and property of a new, biologically active glass-ceramics used as articifial bones
Journal of Non-CrystallineSolids North-Holland, Amsterdam
95 & 96 (1987)
1087 - 1094
1087
THE STRUCTURE AND PROPERTY OF A NEW, BIOLOGICALLYACTIVE GLASS-CERAMICS USED AS ARTIFICIAL BONES LIAO Yunmao and HUANGZhangje Institute of Optics and Electronics, Academia Sinica, P.O.Box 355, Chengdu, P.R. China CHEN Anyu West China University of Medical Sciences, Chengdu, P.R.China Bioactive glass-ceramic reported in this paper is a new material which can be used as a kind of a r t i f i c i a l bone. Its crystallization behaviour, l a t t i c e parameter, surface structure, interfacial action and physicochemical properties are presented. I . INTRODUCTION |n the middle of 1970s, Hench studied the surface-active glass, "Bioglass ''I. Since then, some bioactive glass-ceramics have been developed. One of them is Ceravital 2.
Kokubo et al. reported their successful study on the Apatite/
Wollastonite(A/W) ceramics (MgO-CaO-SiO2-P205)3.
In this paper, we present a
new bioactive glass-ceramic (BGC). After a large number of animal experiments, in which 52 dogs and 150 rabbits were tested at West China University of Medical Sciences, the a r t i f i c i a l bones made from BGC have been used in clinic for more than two years. Acceptancein the clinic of the university is more than 450 patients and the success probability is approximately I00%. 2. EXPERIMENTAL RESULTS AND DISCUSSION 2.1 Chemical composition The composition range of the bioactive glass-ceramics was studied.
The
basic composition is MgO-CaO-SiO2-P205 with the addition of B203, Al203, Na20 and some other components. They are shown in Table l and Fig. I.
The
experimental results show that when B203. Al203, Na20 and other minor elements are added to the base composition, the melting point decreases and the thermal and chemical s t a b i l i t i e s are improved; especially the bioactivity is increased. The authors found from animal experiments that the bioactivity of the glassceramics with fine grains is better than those with large grains. indicates that some nucleation reagents should be introduced. 0022-3093/87/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
This
Liao Yunmao et al. / Glass-ceramics used as artificial bones
1088
Table I. Composition of BGC Component content (wt%) MgO CaO
0-7.2 33.4-60.1
SiO2
21.6-41,5
P205 B203 Al203 , Na20 others*
10.9-19.7 I-3 0-2.5 1.5-3 0.5-I.5
*: CaF2, TiO2
MgSiO3
7
/
100p . . . . . 0 CaI0(P04)60
~
,~cfi~.~0 50 100 CaSi03
Fig. l The formation region of the bioactive glass-ceramics in wt%. 2.2 Crystallization There are three exothermal peaks in the DTA curve of the glass (Fig. 2). A peak at 895°C is that for the crystallization of apatite (AP), one at 935°C is that for the crystallization of parawollastonite (PW) and the other at lO00°C is related to the transition from PW to pseudowollastonite (PSW). At ll50°C AP phase begins to disappear. The crystalline phase related to B203, Al203 or Na20 is not found during the crystallization process. The wollastonite also appears in different phases. The wollastonite phase crystallized at low temperatures is monoclinic or t r i c l i n i c wollastonite. Both of them have chain structure. Althoughtheir XRD spectra are nearly the same, a
AP
A Pw (PW)
800
900 1000 Temperature (oC)
i l l l l l l l l l
ill
20 Fig. 2 DTA curve of BGC (sample 15°C/min.).
iii
il
ill
Ii
30
i aill
Ii
II
111 i , , ,
iI
i ii
ii,
40 28 Ou K=t
Fig. 3 XRD patterns of the glass-ceramics.
1089
Liao Yunmao et al. / Glass-ceramics used as artificial bones
lower angle d i f f r a c t i o n line which is near d=3.83A can be used to distinguish between them4.
In the resulting glass-ceramics, the wollastonite is monoclinic
parawollastonite (PW).
As the other metallic ions enter the lattice, i t s
d i f f r a c t i o n lines s h i f t towards a higher angle side.
As the chemical
composition of the bioglass changes, the amount of crystals and crystallization temperature also change. The results are shown in Tables 2 and 3.
WhenMgO is
introduced into the base glass composition, the c r y s t a l l i z a t i o n temperatures of PW and AP increase.
The glass-ceramics system has a eutectic point at the PW-
rich side. Table 2. C r y s t a l l i z a t i o n properties (4.5 wt% MgO)
Sample
Composition
Crystallization
Quantities of the
ratio(AP/PW)
temperature(°C)
crystallized phase(%)
AP
PW
AP
PW
No.l
0.37
900
929
20.3
31.3
No.2
0.59
895
935
26.2
35.1
No.3
0.90
872 "
970
34.4
14.9
Table 3. Crystallization properties (AP/PW=O.52) Sample
MgO
Crystallization
(wt%)
temperature(°C)
Quantities of the crystallized phase (%)
AP
PW
AP
PW
No.4
6
905
940
22.8
28.9
No.5
0
885
900
24.2
32.9
In the course of glass-ceramic preparation, AP is segregated more easily than PW.
In order to describe i t quantitatively, the authors adopted
Kissinger's formula to obtain the activation energy of c r y s t a l l i z a t i o n for sample No.2 using the DTA data. AP PW The difference is evident.
The results are shown below:
81 Kcal./mol I15 Kcal./mol Main glass network formers in both glasses are
[Si04] and [P04] tetrahedra, respectively.
In PW, [Si04] tetrahedra are in
chain structure, but in AP, [P04] tetrahedral can not be formed. This would
1090
Liao Yanmao et al. / Glass-ceramics ttsed as artificial bones
explain the difference in case in c r y s t a l l i z a t i o n . 2.3 Physicochemical
properties
The glass-ceramics obtained have the following physical and chemical properties. Compressive strength:
1400 Kg/cm2
Elastic modulus
95.5xi04 Kg/cm2 640 Kg/cm2
Hardness ,
6100 Kg/cm2
Bending strength
Water-resistance*
:
0.6 ~g/mm2
Acid-resistance**
:
30 pg/mm2
Thermal expansion c o e f f i c i e n t :
91.5xlO-7/K (20-120°C)
*" In d i s t i l l e d water at 98°C f o r 1 hour **" In O. OIN HCI solution f o r 1 hour 2.4 Lattice parameters MgSiO3 or the s i m i l a r phase could not be found, even i f the content of MgO in the base glass increased to 7 wt%.
Mg2+ ions are dissolved in PW and AP and
form isomorphic solid solutions, which have varying l a t t i c e parameters.
The
l a t t i c e parameters taken by the r o t a t i o n XRD instrument, using Cu-Ke X-ray, carbon bent crystal monochromater and Si-powder as an internal standard, are shown in Table 4.
I t is seen t h a t the l a t t i c e parameters of AP change l i n e a r l y
with MgO content, and that the change of a-axis is larger than t h a t of c-axis. In PW, the changes of a-axis and c-axis are larger than that of b-axis.
PW
phase transforms from monoclinic towards orthorombic, which improves the crystal symmetry. parameters.
and 3% for PW. ion (I.06~).
The c e l l volumes also change with the change o f the l a t t i c e
When the MgO content is 4.5 wt%, the shrinkages are 0.07% f o r AP The radius of Mg2+ ion is 0.78A which is less than that of Ca2+
Therefore, Mg2+ ions tend to arrange themselves along the
d i r e c t i o n of a-axis and c-axis.
Table 4. The l a t t i c e parameters (A) of AP and PW MgO
(wt%)
AP a
PW c
a
b
c
0
9.452
6.962
15.33
7.28
7.07
95°20'
4.5
9.421
6.950
15.13
7.22
6.98
90o20'
7.2
9.408
6.946
/
/
/
/
Liao Yunmao et al. / Glass-ceramics used as artificial bones
1091
2.5 Surface morphology and structure as well as interfacial action For a long time, stomatologists have been suspecting whether the sucsessful implantation depends upon the interracial action or not.
Therefore, i t is
important to study the surface morphology and surface structure of the materials to be implanted.
(a)
(b)
(c)
(d)
Fig. 4a. Morphology at the fractured face of the compact material Fig. 4b, The microscopic structure of BGC material after HF erosion. white: Apatite phase grey : parawollastonite phase other: glass phase Fig. 4c. Surface morphology of porous material. Fig. 4d. Surface morphology of granules.
There are two crystalline phases in the glass-ceramics. about 60%. The grains are fibrous-shaped. for all the glass-ceramics.
The total amount is
The average grain size is 0.5 pm
The glass-ceramics has a large amount of pores
with diameters ranging from lO to 20 pm.
The porosity is about 3%. The
increase in porosity will reduce the mechanical performance of the material,
Liao Yunmao et aL / Glass.ceramics ztsed as artificial bones
1092
but i t w i l l be useful for the formation of osteogenet tissue (Fig. 4). The materials implanted to animal body are exposed to a complex chemical surrounding and the interface may be subjected to changes. SEM observation shows that the particles are produced on the surface of the implanted material and grow gradually both in number and size.
The change of relative content of
chemical elements on surface with time was observed by fluorescent X-ray analysis. The result shows that the content of P increases and that of Ca nearly remains unchanged. The contents of Mg and Si decrease with time. The reason is that the implanted material is selectively corroded (Fig. 5).
l
1~ 0 / +~2.
~
4~ ~Io5 ~4
BGC
~0,5
l
0
l
200
b
~
•
400 600 Time (h)
Fig. 5 Change of relative content of various elements on the surface with time,
Fig. 6 Osteal combination photograph of bio-active glass-ceramics after 46 days.
In 46-day specimens (Fig. 6), the narrow spaces between the implants and bones are f u l l of net-shaped bones. New bones are formed between surfaces of implants and the primary bones, and no boundary of f~brous connective tissue is found there. In IB6-day specimens, the implants are perfectly surrounded by mature plate-like bones and the interfaces are osteal combination. At present very l i t t l e is known about the mechanism of bonding, as stated by Hench that "the bonding mechanisms of surface-active glass and glass-ceramics involve a complex combination of physicochemical and ultrastructural phenomena''5.
Liao Yunmao et al.
Glass-ceramics used as artificial bones
1093
3. CONCLUSION I. The glass formation region in the MgSiO3-CaSiO3-Calo(P04)60 system to obtain good bioactive glass-ceramics (BGC) having good physicochemical properties and a good b i o a c t i v i t y has been investigated. 2. In the BGC there are two c r y s t a l l i n e phases, AP and PW. dissolves into PW.
Mg2+ ions mainly
As a r e s u l t the l a t t i c e parameters vary with the content of
MgO. 3. The a c t i v a t i o n energy f o r the c r y s t a l l i z a t i o n of PW is larger than t h a t for AP. 4. In the interface between the implanted material and osteoid tissue, osteal connection w i l l grow up a h a lf year l a t e r . REFERENCES I ) L.L. Hench, Proc. Xth Intern. Congr. Glass, No. 9, 30 (1974). 2) H. Bromer, K. Deutsher, B. Blencke, E. P f e il and V. Strunz, "Science of Ceramics", Vol.9 (1979) p. 219. 3) T. Kokubo et a l . , In Biomaterials 84, Transcations, Second World Congress on Biomaterials, ed. J.M. Anderson (Society for Biomaterials, Washington, D.C., 1984) p. 351. 4) X-ray D i f f r a c t i o n Card JCPDS, 10-489 and 19-249. 5) L.L. Hench and J. Wilson, Surface-Active Biomaterials Science, Voi.226 (1984) 630-636.
95 & 96 (1987)
1087 - 1094
1087
THE STRUCTURE AND PROPERTY OF A NEW, BIOLOGICALLYACTIVE GLASS-CERAMICS USED AS ARTIFICIAL BONES LIAO Yunmao and HUANGZhangje Institute of Optics and Electronics, Academia Sinica, P.O.Box 355, Chengdu, P.R. China CHEN Anyu West China University of Medical Sciences, Chengdu, P.R.China Bioactive glass-ceramic reported in this paper is a new material which can be used as a kind of a r t i f i c i a l bone. Its crystallization behaviour, l a t t i c e parameter, surface structure, interfacial action and physicochemical properties are presented. I . INTRODUCTION |n the middle of 1970s, Hench studied the surface-active glass, "Bioglass ''I. Since then, some bioactive glass-ceramics have been developed. One of them is Ceravital 2.
Kokubo et al. reported their successful study on the Apatite/
Wollastonite(A/W) ceramics (MgO-CaO-SiO2-P205)3.
In this paper, we present a
new bioactive glass-ceramic (BGC). After a large number of animal experiments, in which 52 dogs and 150 rabbits were tested at West China University of Medical Sciences, the a r t i f i c i a l bones made from BGC have been used in clinic for more than two years. Acceptancein the clinic of the university is more than 450 patients and the success probability is approximately I00%. 2. EXPERIMENTAL RESULTS AND DISCUSSION 2.1 Chemical composition The composition range of the bioactive glass-ceramics was studied.
The
basic composition is MgO-CaO-SiO2-P205 with the addition of B203, Al203, Na20 and some other components. They are shown in Table l and Fig. I.
The
experimental results show that when B203. Al203, Na20 and other minor elements are added to the base composition, the melting point decreases and the thermal and chemical s t a b i l i t i e s are improved; especially the bioactivity is increased. The authors found from animal experiments that the bioactivity of the glassceramics with fine grains is better than those with large grains. indicates that some nucleation reagents should be introduced. 0022-3093/87/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
This
Liao Yunmao et al. / Glass-ceramics used as artificial bones
1088
Table I. Composition of BGC Component content (wt%) MgO CaO
0-7.2 33.4-60.1
SiO2
21.6-41,5
P205 B203 Al203 , Na20 others*
10.9-19.7 I-3 0-2.5 1.5-3 0.5-I.5
*: CaF2, TiO2
MgSiO3
7
/
100p . . . . . 0 CaI0(P04)60
~
,~cfi~.~0 50 100 CaSi03
Fig. l The formation region of the bioactive glass-ceramics in wt%. 2.2 Crystallization There are three exothermal peaks in the DTA curve of the glass (Fig. 2). A peak at 895°C is that for the crystallization of apatite (AP), one at 935°C is that for the crystallization of parawollastonite (PW) and the other at lO00°C is related to the transition from PW to pseudowollastonite (PSW). At ll50°C AP phase begins to disappear. The crystalline phase related to B203, Al203 or Na20 is not found during the crystallization process. The wollastonite also appears in different phases. The wollastonite phase crystallized at low temperatures is monoclinic or t r i c l i n i c wollastonite. Both of them have chain structure. Althoughtheir XRD spectra are nearly the same, a
AP
A Pw (PW)
800
900 1000 Temperature (oC)
i l l l l l l l l l
ill
20 Fig. 2 DTA curve of BGC (sample 15°C/min.).
iii
il
ill
Ii
30
i aill
Ii
II
111 i , , ,
iI
i ii
ii,
40 28 Ou K=t
Fig. 3 XRD patterns of the glass-ceramics.
1089
Liao Yunmao et al. / Glass-ceramics used as artificial bones
lower angle d i f f r a c t i o n line which is near d=3.83A can be used to distinguish between them4.
In the resulting glass-ceramics, the wollastonite is monoclinic
parawollastonite (PW).
As the other metallic ions enter the lattice, i t s
d i f f r a c t i o n lines s h i f t towards a higher angle side.
As the chemical
composition of the bioglass changes, the amount of crystals and crystallization temperature also change. The results are shown in Tables 2 and 3.
WhenMgO is
introduced into the base glass composition, the c r y s t a l l i z a t i o n temperatures of PW and AP increase.
The glass-ceramics system has a eutectic point at the PW-
rich side. Table 2. C r y s t a l l i z a t i o n properties (4.5 wt% MgO)
Sample
Composition
Crystallization
Quantities of the
ratio(AP/PW)
temperature(°C)
crystallized phase(%)
AP
PW
AP
PW
No.l
0.37
900
929
20.3
31.3
No.2
0.59
895
935
26.2
35.1
No.3
0.90
872 "
970
34.4
14.9
Table 3. Crystallization properties (AP/PW=O.52) Sample
MgO
Crystallization
(wt%)
temperature(°C)
Quantities of the crystallized phase (%)
AP
PW
AP
PW
No.4
6
905
940
22.8
28.9
No.5
0
885
900
24.2
32.9
In the course of glass-ceramic preparation, AP is segregated more easily than PW.
In order to describe i t quantitatively, the authors adopted
Kissinger's formula to obtain the activation energy of c r y s t a l l i z a t i o n for sample No.2 using the DTA data. AP PW The difference is evident.
The results are shown below:
81 Kcal./mol I15 Kcal./mol Main glass network formers in both glasses are
[Si04] and [P04] tetrahedra, respectively.
In PW, [Si04] tetrahedra are in
chain structure, but in AP, [P04] tetrahedral can not be formed. This would
1090
Liao Yanmao et al. / Glass-ceramics ttsed as artificial bones
explain the difference in case in c r y s t a l l i z a t i o n . 2.3 Physicochemical
properties
The glass-ceramics obtained have the following physical and chemical properties. Compressive strength:
1400 Kg/cm2
Elastic modulus
95.5xi04 Kg/cm2 640 Kg/cm2
Hardness ,
6100 Kg/cm2
Bending strength
Water-resistance*
:
0.6 ~g/mm2
Acid-resistance**
:
30 pg/mm2
Thermal expansion c o e f f i c i e n t :
91.5xlO-7/K (20-120°C)
*" In d i s t i l l e d water at 98°C f o r 1 hour **" In O. OIN HCI solution f o r 1 hour 2.4 Lattice parameters MgSiO3 or the s i m i l a r phase could not be found, even i f the content of MgO in the base glass increased to 7 wt%.
Mg2+ ions are dissolved in PW and AP and
form isomorphic solid solutions, which have varying l a t t i c e parameters.
The
l a t t i c e parameters taken by the r o t a t i o n XRD instrument, using Cu-Ke X-ray, carbon bent crystal monochromater and Si-powder as an internal standard, are shown in Table 4.
I t is seen t h a t the l a t t i c e parameters of AP change l i n e a r l y
with MgO content, and that the change of a-axis is larger than t h a t of c-axis. In PW, the changes of a-axis and c-axis are larger than that of b-axis.
PW
phase transforms from monoclinic towards orthorombic, which improves the crystal symmetry. parameters.
and 3% for PW. ion (I.06~).
The c e l l volumes also change with the change o f the l a t t i c e
When the MgO content is 4.5 wt%, the shrinkages are 0.07% f o r AP The radius of Mg2+ ion is 0.78A which is less than that of Ca2+
Therefore, Mg2+ ions tend to arrange themselves along the
d i r e c t i o n of a-axis and c-axis.
Table 4. The l a t t i c e parameters (A) of AP and PW MgO
(wt%)
AP a
PW c
a
b
c
0
9.452
6.962
15.33
7.28
7.07
95°20'
4.5
9.421
6.950
15.13
7.22
6.98
90o20'
7.2
9.408
6.946
/
/
/
/
Liao Yunmao et al. / Glass-ceramics used as artificial bones
1091
2.5 Surface morphology and structure as well as interfacial action For a long time, stomatologists have been suspecting whether the sucsessful implantation depends upon the interracial action or not.
Therefore, i t is
important to study the surface morphology and surface structure of the materials to be implanted.
(a)
(b)
(c)
(d)
Fig. 4a. Morphology at the fractured face of the compact material Fig. 4b, The microscopic structure of BGC material after HF erosion. white: Apatite phase grey : parawollastonite phase other: glass phase Fig. 4c. Surface morphology of porous material. Fig. 4d. Surface morphology of granules.
There are two crystalline phases in the glass-ceramics. about 60%. The grains are fibrous-shaped. for all the glass-ceramics.
The total amount is
The average grain size is 0.5 pm
The glass-ceramics has a large amount of pores
with diameters ranging from lO to 20 pm.
The porosity is about 3%. The
increase in porosity will reduce the mechanical performance of the material,
Liao Yunmao et aL / Glass.ceramics ztsed as artificial bones
1092
but i t w i l l be useful for the formation of osteogenet tissue (Fig. 4). The materials implanted to animal body are exposed to a complex chemical surrounding and the interface may be subjected to changes. SEM observation shows that the particles are produced on the surface of the implanted material and grow gradually both in number and size.
The change of relative content of
chemical elements on surface with time was observed by fluorescent X-ray analysis. The result shows that the content of P increases and that of Ca nearly remains unchanged. The contents of Mg and Si decrease with time. The reason is that the implanted material is selectively corroded (Fig. 5).
l
1~ 0 / +~2.
~
4~ ~Io5 ~4
BGC
~0,5
l
0
l
200
b
~
•
400 600 Time (h)
Fig. 5 Change of relative content of various elements on the surface with time,
Fig. 6 Osteal combination photograph of bio-active glass-ceramics after 46 days.
In 46-day specimens (Fig. 6), the narrow spaces between the implants and bones are f u l l of net-shaped bones. New bones are formed between surfaces of implants and the primary bones, and no boundary of f~brous connective tissue is found there. In IB6-day specimens, the implants are perfectly surrounded by mature plate-like bones and the interfaces are osteal combination. At present very l i t t l e is known about the mechanism of bonding, as stated by Hench that "the bonding mechanisms of surface-active glass and glass-ceramics involve a complex combination of physicochemical and ultrastructural phenomena''5.
Liao Yunmao et al.
Glass-ceramics used as artificial bones
1093
3. CONCLUSION I. The glass formation region in the MgSiO3-CaSiO3-Calo(P04)60 system to obtain good bioactive glass-ceramics (BGC) having good physicochemical properties and a good b i o a c t i v i t y has been investigated. 2. In the BGC there are two c r y s t a l l i n e phases, AP and PW. dissolves into PW.
Mg2+ ions mainly
As a r e s u l t the l a t t i c e parameters vary with the content of
MgO. 3. The a c t i v a t i o n energy f o r the c r y s t a l l i z a t i o n of PW is larger than t h a t for AP. 4. In the interface between the implanted material and osteoid tissue, osteal connection w i l l grow up a h a lf year l a t e r . REFERENCES I ) L.L. Hench, Proc. Xth Intern. Congr. Glass, No. 9, 30 (1974). 2) H. Bromer, K. Deutsher, B. Blencke, E. P f e il and V. Strunz, "Science of Ceramics", Vol.9 (1979) p. 219. 3) T. Kokubo et a l . , In Biomaterials 84, Transcations, Second World Congress on Biomaterials, ed. J.M. Anderson (Society for Biomaterials, Washington, D.C., 1984) p. 351. 4) X-ray D i f f r a c t i o n Card JCPDS, 10-489 and 19-249. 5) L.L. Hench and J. Wilson, Surface-Active Biomaterials Science, Voi.226 (1984) 630-636.