Phosphorus Research Bulletin Vol. 29 (2015) pp.021-030
Memorial Review for the Science Award 2012
CONTROL OF BETA-TRICALCIUM PHOSPHATE BIOMATERIAL PROPERTIES BY METAL-ION-SUBSTITUTION Kazuaki Hashimoto1*, Naoyuki Matsumoto2, Hirobumi Shibata1 (*Corresponding author email:
[email protected]) 1
Department of Life and Environmental Sciences, Faculty of Engineering, Chiba Institute of Technology: 2-17-1, Tsudanuma, Narashino, Chiba 275-0016, Japan
2
Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST) : 1-1-1, Higashi, Tsukuba, Ibaraki 305-8565, Japan
Keywords: β-Tricalcium phosphate, Ceramic biomaterials, Solid solutions substitution, Property control Abstract: β-tricalcium phosphate (β-TCP) has a fast rate of bioabsorption, and has been used clinically as bioabsorbant ceramics that is absorbed in vivo and gradually replaced by newly formed bone. Here, we focus on various metal ions with regards to their solid solution substitution in β-TCP, and explain the effects of ion substitution in β-TCP on properties such as structural stability and solubility from a crystal chemistry viewpoint. We also discuss the possibility of metal-ion-subsituted β-TCP materials as hard tissue replacements. (Received Dec. 30, 2014; Accepted Feb. 21, 2015)
greater mechanical properties to the patient's hard tissue
INTRODUCTION
are required. However, it is difficult to produce sintered In recent years, the ratio of the population over the
bodies that have the same mechanical properties as the
age of 65 in Japan has been higher than that in the United
autologous bone using β-TCP alone. Additionally, the rate
States and various European countries, and the declining
of absorption of β-TCP in vivo is faster than the rate of
1
birth-rate and population ageing are rapidly worsening .
new bone formation, which may risk causing additional
As the ageing of society progresses, the number of
fractures that accompany inflammatory reactions upon
patients
osteoporosis
embedding and sudden loss of mechanical strength. Thus,
increases because of the reduction in bone density caused
regulation of the solubility of bioabsorbant hard tissue
by ageing. Owing to this, the importance of hard tissue
replacements has been emphasised, and complexes
substitutes, which are used in repairing and filling the
consisting of compounds with different solubilities, such
emerging
with
fractures
and
2
defective part of the bone, is increasing . Of these,
as the two-phase ceramic mixture of HAp and β-TCP,
β-tricalcium phosphate (β-TCP) has a very fast rate of
have been investigated. These investigations have led to
bioabsorption, and has been used clinically as a
numerous reports focusing on the preparation and
bioabsorbant ceramic that is absorbed in vivo, and
sinterability of two-phase ceramic mixtures of varying
3
ratios4.
gradually replaced by newly formed bone . Where this clinical application takes place, the rate of
In this review, we focus on various metal ions with
in vivo absorption is matched to the rate of new bone
regards to their solid solution substitution into β-TCP, and
formation. Because bone repair materials are used in
explain the effects of positive ion substitution in β-TCP on
places subject to loads in vivo, materials with the same or
properties such as structural stability and solubility from a
-
21 -
materials science viewpoint. We also discuss the
typical bond length for a 6-coordinated Ca. Additionally,
possibility of metal-ion-subsituted β-TCP materials as hard tissue replacements. 1. THE CRYSTAL STRUCTURE OF TRICALCIUM PHOSPHATE Tricalcium phosphate (Ca3(PO4)2:TCP) may exist as three polymorphisms: β5,6, α, and α'. β-TCP (theoretical density: 3.07 g/cm3), which is stable at low temperatures, undergoes a phase transition at 1150-1180°C to α-TCP (theoretical density: 2.86 g/cm3), which is stable at high temperatures. Additionally, α-TCP undergoes a phase transition
at
temperatures
above
1430°C
to
(a)
the
high-temperature meta-stable α'-TCP state. β-TCP belongs to the rhombohedral crystal system, and has a space group (S.G.) and lattice packing of R3c (No.161) and Z = 21, respectively. Additionally, the lattice constants for a hexagonal lattice are a = b = 1.04352 nm, c = 3.74029 nm, α = β = 90°, and γ = 120°5. Figure 1 shows the symmetry operation of (001) plane of space group No.1617, and the schematic of the
A column
unit cell produced from the crystal structure of β-TCP reported
by
Yashima
et
al.5
There
are
two
B column
crystallographically independent columns, A and B, that exist along the c axis. Column A exists on a 3-fold axis composed
of
(b)
[–P(1)–Ca(4)–Ca(5)–P(1)–□
(vacancy)–Ca(5)–], while column B is composed of [–P(3)–Ca(1)–Ca(3)–Ca(2)– P(2)–], with Ca not aligned linearly but along a kinked line. The crystal structure of β-TCP, with column A at the centre of the rotational axis, has 6 B columns with a spiral rotation that forms a tunnel structure extending in the [001] direction. Vacancy
Table 1 shows the site occupancies, atomic positions, and coordination numbers for the Ca and P sites for each column within the unit cell of β-TCP reported by Yashima et al5). The Ca(4) in column A is a specific Ca site with a coordination number of 3 and a site occupancy of 0.43
A column
(theoretical occupancy is 0.5). In other words, a vacancy (□) exists at Ca(4), and because the Ca-O bond is long, it
B column
(c)
is weak compared to the Ca–O bond at other Ca sites, as well as having a low bond valence sum (BVS) of 0.65 (theoretical value is 1.0). Meanwhile, the Ca-O bond length at Ca(5) has a considerably smaller value than the -
Figure 1 Schematic of the β-TCP unit cell. (a) Symmetry operation of (001) plane of space group(S.G.) No.1617, (b) structure as viewed down the [001] axis, and (c) structure as viewed down the [100] axis5.
22 -
Table 1 The atomic position, site occupancy, coordination number (c.n.), BVS, and the ratio of atoms at each position, for each atom in the unit cell of β-TCP5 . atom Ca(1) Ca(2) Ca(3) Ca(4) Ca(5) P(1) P(2) P(3)
position site occupancy 18b 18b 18b 6a 6a 6a 18b 18b
1.0 1.0 1.0 0.43 1.0 1.0 1.0 1.0
atomic position x -0.2741 -0.3812 -0.2734 0.0 0.0 0.0 -0.3128 -0.3470
the BVS for Ca(5) is 2.7 (theoretical value is 2.0), which is a higher value than the other Ca positions. In this way, Ca(4) and Ca(5) exist in column
A of β-TCP
(β-Ca21□(PO4)14) with crystallographic specificity.
y -0.1382 -0.1745 -0.1486 0.0 0.0 0.0 -0.1394 -0.1536
z 0.1663 -0.0332 0.0611 -0.0851 -0.2664 0.0 -0.1315 -0.2332
c.n.
BVS
ratio/ %
7 8 8 3 6 4 4 4
2.0 2.1 1.8 0.65 2.7 4.9 5.0 5.0
27.3 27.3 27.3 9.1 9.1 14.2 42.9 42.9
occurs in column A as 3Ca+□ = 3MⅡ+□). The metal ion molar fraction is expressed as MⅡ = MⅡ/(Ca+MⅡ+□). After dry blending of the samples, a solid phase reaction was
2. PREPARATION AND PROPERTIES OF SOLID
achieved in atmospheric conditions followed by sintering
SOLUTIONS OF METAL-ION-SUBSTITUTED TCP
at temperatures in the range of 800-1200°C for 1-24 h; generally, sintering was performed at 1100°C for 24 h.
1) Formation of bivalent metal-ion-substituted TCP solid solutions There are numerous reports of bivalent metal-ionsubstitution into solid solutions of β-TCP. Lazoryak et al. have reported the crystal structures of a series of compounds such as Ca9M(PO4)7 (M=Fe,Co,Cu)8. In addition, the thermal stability and sinterability of these compounds due to substitution has been reported9,10. First, substitution with bivalent metal ions with ionic radii less than that of Ca (Mg, Zn, etc.) will be explained. The preparation of materials and method of synthesis for forming a solid solution by the substitution of bivalent metal ions (MⅡ) into β-TCP will be discussed. Calcium carbonate, calcium hydrogen-phosphate, and an oxide containing the bivalent metal ion are used as starting materials, which are combined to produce a (Ca+M Ⅱ+□)/P
Figure 2 The X-ray diffraction patterns of the sintered bodies obtained by Mg ion-substitution.
molar ratio = 1.571 (the "□" in the structure is assumed to
Figure 2 shows the X-ray diffraction patterns of the
exist at a molar percentage of 4.6mol%). Furthermore, for
sintered bodies obtained by Mg ion-substitution. The
bivalent metal ions, the Ca ion and the bivalent metal ion
patterns had a β -TCP crystal structure until a total
are combined under the assumption that they will
amount of 13.64mol% and these peaks shifted to higher
substitute at a 1:1 ratio (it is assumed that substitution -
angle.
23 -
group: R3m). The Sr ions corroborate the formation of partially substituted β-TCP solid solutions. Additionally, the value of 81.8mol% is in agreement with the total of the percentages of Ca(1), Ca(2), and Ca(3) at each of the positions of the positive ions shown in Table 1. Owing to this, the chemical formula of the product at the solubility limit is Sr18Ca3□(PO4)14. In this way, the mechanism of solid solution substitution differs among bivalent metal ions due to differences in their ionic radii.
Mg ion molar percent /mol%
Figure 3 Changes in lattice constants of Mg-β-TCP by varying Mg molar percent10.
S.G. R3c
S.G. R3m
Figure 3 shows the change in the lattice constants for Mg-β-TCP obtained by changing the Mg molar percentage. From the changes in the lattice constants, an increase in the Mg molar percent leads to a contraction along the a axis until 13.6mol%. The length along the c axis reduces linearly until 9.1mol% Mg and then increases linearly
Sr ion molar percent /mol%
Figure 4 Changes in lattice constants of Sr-β-TCP by varying Sr molar percent11.
again until 13.6mol% Mg. Bivalent positive ions with a small ionic radius preferentially substitute with Ca(5) of column A until an ion molar percentage of 9.1mol%, and
2) Formation of monovalent metal-ion-substituted TCP
then substitute only 4.6mol% into Ca(4) for a total amount
solid solutions
of 13.6mol%. The chemical formulae of the product at
Because research into solid solution substitution of
9.1mol% and 13.6mol% are Ca19Mg2□(PO4)14, and
metal ions into β-TCP has mainly centred on bivalent
Ca18Mg3□(PO4)14, respectively10.
metal ions, there is not as much research on the formation
Next, substitution with bivalent metal ions with ionic
of solid solutions by substitution with monovalent ions. Of
radii greater than that of Ca will be explained. The
the published work, the research by Ando et al. into the
production of solid solutions using exchange by Sr ions to
two
component
solid-phase
reaction
of
13
11
Ca3(PO4)2-CaNaPO4 is well-known . Additionally, the
blend in a similar way to Mg ions was investigated . Figure 4 shows the change in the lattice constants for
authors have reported the formation of solid solutions of
the sample obtained by changing the Sr molar percent.
β-TCP using the monovalent ions Li, Na, and K and the
From the figure, increases in the Sr molar percent led to
thermal stability14 and solubility15 of these sol id solutions.
linear elongations on both the a and c axes until 81.8mol%
When forming a solid solution substitution using monovalent
was reached, with a plateau afterwards, and a change to a
metal ions, in addition to calcium phosphate, an alkali carbonate
new, different diffraction pattern; that of Sr 3(PO4)2 (space
is used as the starting material and combined to produce a
-
24 -
(Ca+MⅠ+□)/P molar ratio of 1.571. In this case, the mixture assumes that the monovalent positive ions will substitute with
3)
same solid phase reaction as that previously described for the
of
hybrid
mono-
and
bivalent
metal-ion-substituted TCP solid solutions Because the Ca positions differ for substitution into
both the calcium ions and the vacant position. The molar ratio is expressed as MⅠ = MⅠ / (Ca+MⅠ+□). The synthesis method has the
Formation
β-TCP by monovalent metal ions and bivalent metal ions, the simultaneous solid solution substitution of both monovalent and bivalent metal ions was investigated. When monovalent metal ions (MI) and bivalent metal
bivalent metal ions. Figure 5 shows the change in the lattice constants for the sample
ions (MII) are substituted simultaneously to produce a
obtained by changing the Na or K molar percent. As seen in the
solid solution, an alkali carbonate and an oxide that
changes of the lattice constants, there were linear changes in
contains bivalent metal ions are used as the starting
each case with an accompanying increase in the molar percent of
materials and combined to produce a (Ca+MI+ MII+□)/P
up to 9.1 mol%. This observation corroborates the formation of
molar ratio of 1.571. Furthermore, blending is performed
partially substituted solid solutions. When substituting with Na
on the assumption that monovalent metal ions substitute
ions, there was no change in the length along the a axis of the
with Ca(4) and bivalent positive ions substitute with Ca(5).
solid solution; however, there was some contraction along the c
The molar percentage of each metal ion is expressed by M
axis. On the other hand, for K ions, there was elongation of the a
= M/(Ca+M+□).
axis of the solid solution and even greater contraction on the c
Figure 6 shows the changes in the lattice constants of
axis than with Na ions. Monovalent ion substitution forms solid
NaMg-β-TCP by varying Na molar percent, while
solutions whereby the vacancy and Ca(4) of column A are
maintaining a Mg molar percent of 9.1mol%. From the
substituted with the form 2MⅠ＝Ca ion+□, at a solubility limit of
figure, increases in the Na molar percent cause no change along the a axis; however, there is a linear contraction
9.1mol%. This value of 9.1mol% is in agreement with the ratio
along the c axis until 9.1mol%, supporting the
of Ca(4) at each of the positions of the positive ions shown in
simultaneous substitution of Na and Mg ions to form a
Table 1. The chemical formula of the product at the solubility
solid solution. Two Na ions substitute for the vacancy and the calcium ion at Ca(4), causing the contraction along the
limit is Ca20MⅠ2(PO4)14 (MⅠ:Na,K)16,17.
c axis.
Na ions contents /mol%
Monovalent ion molar percent /mol%
Figure 5 The lattice constants of Na-β-TCP and K-β-TCP obtained by different Na and K molar percentages10. -
Figure 6 Changes in lattice constants of NaMg-β-TCP by varying Na molar percent, maintaining a Mg molar percent of 9.1mol%.
25 -
The monovalent metal ion substitutes for Ca(4) of column A, and the bivalent metal ion for Ca(5), which shows that they undergo simultaneous solid solution substitution up to 9.1mol%. The chemical formula at this solubility limit was shown to be Ca18Mg2Na2(PO4)14, with the same structure as β-TCP (space group (S.G.): R3c)18. 4) Crystal structure of metal-ion-substituted TCP solid solutions Figure 7 shows the atom sequences and interatomic distances along column A on the c axis for each sample. Figure 8 shows the relationship between coordination number (c.n.) of each positive ion and the average M-O bond length for each sample. Furthermore, the straight lines on Figure 8 represent the M-O bond lengths calculated from the coordination number of each ion. The coordination number of Ca(1) in β-TCP is 7, with an average Ca(1)-O distance of 0.2435 nm. For Ca(2) and Ca(3), the coordination number is 8, with an average Ca(2)-O distance of 0.2486 nm and an average Ca(3)-O distance of 0.2544 nm. From Fig. 8, a correlation was found between the coordination number and average Ca-O
Figure 8 The relationship between coordination number and M-O bond lengths for each sample of positive ions. (●:Ca(1), Ca(2), Ca(3), Ca(4) and Ca(5) at β-TCP, ■:Mg of Ca(4) site and Mg of Ca(5) site at Mg-β-TCP; ▲:Na of Ca(4) site at Na-β-TCP; ▼:K of Ca(4) site at K-β-TCP)
bond lengths. However, Ca(4) has a coordination number of 3 and an average Ca(4)-O bond length of 0.2538 nm,
If each type of metal ion is substituted into β-TCP,
leading to a larger value than that calculated for the Ca-O
they are mainly placed into Ca(5) and Ca(4), with the
bond length for a coordination number of 3. Additionally,
coordination numbers and bond lengths of Ca(1), Ca(2),
Ca(5) has a coordination number of 6 and an average
and Ca(3) remaining mostly unchanged. If an Mg ion is
Ca(5)-O bond length of 0.2263 nm, leading to a smaller
substituted, the lattice constants of Mg-β-TCP become a =
value than that calculated for the Ca-O bond length for a
b = 1.03293 nm, and c = 3.72191 nm. In particular, the
5,6
coordination number of 6 .
6-coordinated Mg-O bond length of Ca(5) becomes 0.2150 nm, which is roughly in agreement with the calculated bond length. However, while a strained 6-coordinated bond is formed for the Mg-O bond at Ca(4), the average Mg-O distance is 0.2675 nm, which differs from the calculated bond length. This results from the Mg-O bond being weak because of its site occupancy of 0.5. Regarding structural changes due to substitution of an Mg ion, the contraction of the 6-coordinated Mg-O bond length of the Ca(5) position causes contraction along the a and c axes for solid solutions substituted by 0-9.1mol%. If additional Mg ions are substituted, Mg ions enter the Ca(4) position, moving along in the direction of P(1) and
Figure 7 The atomic sequences and inter-atomic distances
elongating the MgCa(4)-MgCa(5) bond length, forming a
within column A along the c axis. -
26 -
strained 6-coordinated bond with the oxide ions that
across
the
entire
crystal.
However,
because
the
coordinate with P(1). The elongation along the c axis of
electrostatic energy of the substituted M-O bond is
the substituted solid solution between 9.1 and 13.6mol% is
proportional to 1/r (where r is the radius of the ion), if the
consistent with elongation of the bond lengths of
M-O bond length contracts, as in Mg ion substitution, the
MgCa(4)-MgCa(5) and MgCa(5)-P(1).
electrostatic bond strengthens and the internal energy of
If Na ions are substituted, the lattice constants of
the crystal (U) is reduced. Additionally, substituting with
Na-β-TCP become a = b = 1.04391 nm and c = 3.73096
Mg ions increases the bond entropy (S) at the Ca positions.
nm. Na substitution occurs at the Ca(4) position. The
In other
average Na-O bond length at Ca(4) is 0.2655 nm, which is
S(Mg-β-TCP) > S(β-TCP). If this is considered with the
larger than the calculated value for a 6-coordinated Na-O
introduction of the Helmholtz energy (F) equation F = U -
bond length. As shown in Fig. 8, at position Ca(4) in
TS, then F(β-TCP) > F(Mg-β-TCP), confirming that
Na-β-TCP, where the Na ions substitute into, there are two
Mg-β-TCP is a thermodynamically stable product.
words,
U(Mg-β-TCP) < U(β-TCP), and
substitution sites (Na (site occupancy: 0.8) and Na' (site
From these thermodynamic considerations, the
occupancy: 0.2)) that slightly perturb the direction of the c
thermal stabilities of β-TCP and metal-ion-substituted
16,17
axis
β-TCP solid solutions were evaluated14. Isothermal
.
The lattice constants of K-β-TCP, where a K ion is
transformation curves were produced for β-TCP and
are a = b = 1.04729 nm and c =
metal-ion-substituted solid solutions of β-TCP at fixed
3.72787 nm. The average K-O bond length was closer to
temperatures, and the results were analysed using the
the bond length of the calculated value of a 9-coordinated
Johnson-Mehl-Avrami equation to find the rate of the β-α
bond (K-O: 0.2933 nm), rather than the value for a
transition reaction.
6-coordinated
the
the β-α transition of β-TCP and the metal-ion-substituted
coordination number differed from that of the Na ion.
β-TCP solid solutions. When compared at 1200°C, there is
Additionally, contraction of the c axis in the monovalent
an ordered decline in the rate constant: β-TCP > solid
metal-ion-substituted samples corresponded with the
solutions of monovalent metal ions > solid solutions of
substituted into Ca(4),
bond
(K-O:
0.2795
reduction in Ca(5)-P(1) bond length
16,17
nm),
and
.
Figure 8 shows the rate constants for
bivalent metal ions. While this shows a remarkable
The lattice constants of NaMg-β-TCP, where Na and
dependence upon the amount of ions used to produce the
Mg ions are simultaneously substituted, are a = b =
solid solution and the Ca position substituted by the ions,
1.03397 nm and c = 3.7029 nm. As per the other samples,
as long as the valence remains the same, these are
there is little difference in the coordination of the Ca-O
independent of the type of metal ion used.
bond at Ca(1)-Ca(3). The Mg ion is placed at Ca(5) to form a 6-coordinated bond (Mg-O: 0.2092 nm), and the
Table 2 The rate constants for the β-α transition of β-TCP
Na ion is placed at Ca(4), also forming a 6-coordinated
and each metal-ion-substituted β-TCP. Rate constants for the β-α transition / min-1
bond (Na-O: 0.2615 nm). Contraction of the c axis' lattice
Sample β-TCP
constant suggests that NaMg-β-TCP has a stable crystal structure18). 5) Thermodynamic behaviour of metal-ion-substituted TCP solid solutions We also focused on the thermodynamic behaviour of
Sample Li-β-TCP Na-β-TCP K-β-TCP Mg-β-TCP
1130℃ 0.348
1150℃ 0.515
Additive 0.05mol% 1200℃ 0.068 0.083 0.107 0.028
1250℃ 0.626 0.679 0.754 0.167
1300℃ 2.080 2.282 2.860 0.655
1170℃ 1.033
1200℃ 1.548
Additive 0.20mol% 1200℃ 0.033 0.046 0.049 0.017
1250℃ 0.224 0.242 0.064 0.064
1300℃ 0.891 0.988 1.234 0.320
the ions substituted into the β-TCP structure. Because the substituted ions are sufficiently isolated from the other
6) Solubility of metal-ion-substituted TCP solid solutions
positive ions in the crystal, as long as the charge of the
The solubility of inorganic compounds (solubility
substituted ion is the same the non-electrostatic repulsion
product: Ksp) depends upon ΔG ﾟ = RT ln Ksp. This means
of the M-O and M-M bonds will be roughly the same -
that if the thermal stability of the β-TCP structure is high,
27 -
the solubility will be low, and vice versa. In other words,
progress well; cavities remained in the microstructure and
from the evaluation of the thermal stability in β-α
densification did not occur. In β-TCP, it seems this is
transitions of metal-ion-substituted β-TCP, the solubility
because a considerable shrinkage of volume occurs before
can also be estimated.
the cavities can discharge to the external surface, which causes sintering to continue while the cavities remain. In Mg-β-TCP, the diffusional reaction was suppressed even under sintering conditions of 1150°C for 24 h, owing to the increased thermal stability of the crystal structure. Grain growth was suppressed in the Mg-β-TCP, leading to sintered particles with small diameters. Additionally, because of suppression of volume shrinkage in the early stage of sintering β-TCP, the cavities remained inside the sintered bodies without being expelled to the surface. Diffusion occurs more readily for Na-β-TCP, which has a Ca(4) vacancy suppressed by Na ions, thus promoting grain growth and leading to a larger grain radius. Additionally, perhaps because the rate of volume shrinkage is slowed, inner cavities are expelled, thus promoting densification. Because of the coupling of the
Figure 9 Evaluation of the solubility of solid solutions of each metal-ion-substituted β-TCP in acetic acid-sodium acetate buffer solution.
sinterabilities of the monovalent and bivalent metal ions in MgNa-β-TCP,
well-balanced
sintering
occurs.
Densification of the sintered bodies and micronization of Thus, a fixed amount of a powdered sample was
the sintered grains occurs simultaneously; therefore, the
suspended in 0.08 M acetic acid-sodium acetate buffer
size of the sintered grains is very small and there are very
3
solution (0.10 g powder per 30 cm solution) with a pH of
few inner cavities. The inner cavities of these sintered
5.5, and its solubility evaluated using a calcium
bodies also appear to affect the flexural strength, as the
electrode15). The results showed that the solubility for each
reduced open porosity increases the density, which in turn
metal-ion-substituted solid solution decreased in the order
augments the flexural strength (Figure 11).
of:
β-TCP
>
bivalent
(Ca(1)-(3)
substitution)
>
monovalent (Ca(4) substitution) > HAp > bivalent (Ca(5) substitution) (Figure 9). Additionally, solubility decreased proportionally with increasing amounts of substitution. The
solubility
corresponds
with
crystallographically,
of the the
solid
solutions
thermal structural
of
β-TCP
stability stability
and, of
the
6-coordinated Ca(5) contributes to this thermal stability. 7) Sinterability of metal-ion-substituted TCP solid solutions Figure 10 shows SEM images of the representative microstructure of sintered β-TCP and the sintered solid solutions of each metal-ion-substituted β-TCP. Even under sintering conditions at 1100°C for 24 h, which does not cause the α transformation, sintering of β-TCP did not -
28
Figure 10 Microscopic structure of the sintered β-TCP and each metal-ion-substituted β-TCP. (β-TCP: 24 h at 1100°C-, others: 24 h at 1150°C ) -
3. SUMMARY In the present report, the crystal structure of β-TCP and the substitution mechanism of mono- and bivalent ions, as well as their altered properties, have been clarified. Substituted β-TCP solid solutions influence the solubility and sinterability of the substituted solid solution depending on the positions and the amount of substituted atoms in the structure. Additionally, this has an impact on its bioabsorbability and its mechanical characteristics as a biomaterial. Regarding the substitution of various metal ions Figure 11 The bending strengths of the sintered bodies of NaMg-β-TCP by varying Na molar percent, maintaining a Mg molar percent of 9.1mol%.
into
β-TCP,
substitution
using
ions
with
pharmacological action, and the evaluation of such, will be important challenges in the future.
8) The effect of substituting metal ions into TCP-like ACKNOWLEDGEMENTS
biomaterials The effects of ion substitution are important in the control of properties of TCP-like biomaterials such as
This study was supported in part by grants in aid
solubility and sinterability of the solid solutions.
(No.25350554) from the Ministry of Education, Science,
Meanwhile, there are essential elements in vivo that
Sports, and Culture of Japan.
preserve homoeostasis, and allow for normal metabolism. References
In particular, the pharmacological action of elements ion
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essential
for
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motivated
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21
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22
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Zn
(1
wt%
or
less)
had
bone
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29 -
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