Biomedical Engineering Reference
In-Depth Information
interfacial thicknesses of the hard tissue-bioactive
glasses are shown in Fig. 3.2.10-2 for several composi-
tions.
The
thickness
decreases
as
the
bone-bonding
boundary is approached.
Gross et al. (1988) and Gross and Strunz (1985) have
shown that a range of low-alkali (0 to 5 wt.%) bioactive
silica glass-ceramics (Ceravital) also bond to bone. They
found that small additions of Al 2 O 3 ,Ta 2 O 5 ,TiO 2 ,
Sb 2 O 3 , or ZrO 2 inhibit bone bonding ( Table 3.2.10-5 ,
Fig. 3.2.10-1 ). A two-phase silica-phosphate glass-
ceramic composed of apatite [Ca 10 (PO 4 ) 6 (OH 1 F 2 )] and
wollastonite [CaO, SiO 2 ] crystals and a residual silica
glassy matrix, termed A-W glass-ceramic (A-WGC)
(Nakamura et al., 1985; Yamamuro et al., 1990; Kokubo,
1993), also bonds with bone. The addition of Al 2 O 3 or
TiO 2 to the A-W glass-ceramic also inhibits bone bond-
ing, whereas incorporation of a second phosphate phase,
B-whitlockite (3CaO, P 2 O 5 ), does not.
Another multiphase bioactive phosphosilicate
containing phlogopite (Na, K) Mg 3 [AlSi 3 O 10 ]F 2 and ap-
atite crystals bonds to bone even though Al is present in
the composition (H¨hland and Vogel, 1993). However,
the Al 3 þ ions are incorporated within the crystal phase and
do not alter the surface reaction kinetics of the material.
The compositions of these various bioactive glasses and
glass-ceramics are compared in Table 3.2.10-5 .
Fig. 3.2.10-5 Compositional dependence (in wt.%) of bone
bonding and soft tissue bonding of bioactive glasses and glass-
ceramics. All compositions in region A have a constant 6 wt.%
of P 2 O 5 . A-W glass ceramic has higher P 2 O 5 content
(see Table 3.2.10-5 for details). I B , Index of bioactivity.
(e.g., window or bottle glass, or microscope slides) behave
as nearly inert materials and elicit a fibrous capsule at the
implant-tissue interface. Glasses within region C are
resorbable and disappear within 10 to 30 days of im-
plantation. Glasses within region D are not technically
practical and therefore have not been tested as implants.
The collagenous constituent of soft tissues can
strongly adhere to the bioactive silicate glasses that lie
within the dashed line region in Fig. 3.2.10-5 . The
Table 3.2.10-5 Composition of bioactive glasses and glass-ceramics (in weight percent)
45S5
45S5F
45S5.4F 40S5B5
52S4.6
55S4.3
KGC
KGS
KGy213
A-W GC MB GC
Bioglass Bioglass Bioglass Bioglass Bioglass Bioglass Ceravital Ceravital Ceravital
SiO 2
45
45
45
40
52
55
46.2
46
38
34.2
19-52
P 2 O 5
6
6
6
6
6
6
16.3
4-24
CaO
24.5
12.25
14.7
24.5
21
19.5
20.2
33
31
44.9
9-3
Ca(PO 3 ) 2
25.5
16
13.5
CaF 2
12.25
9.8
0.5
MgO
2.9
4.6
5-15
MgF 2
Na 2 O
24.5
24.5
24.5
24.5
21
19.5
4.8
5
4
3-5
K 2 O
0.4
3-5
Al 2 O 3
7
12-33
B 2 O 3
5
Ta 2 O 5 /TiO 2
6.5
Structure
Glass
Glass
Glass
Glass
Glass
Glass-
ceramic
Glass-
ceramic
Glass-
ceramic
Glass-
ceramic
Reference
Hench
et al.
Hench
et al.
Hench
et al.
Hench
et al.
Hench
et al.
Hench
et al.
Gross
et al.
Gross
et al.
Nakamura
et al.
H ¨ hland
and Vogel
(1972)
(1972)
(1972)
(1972)
(1972)
(1972)
(1988)
(1988)
(1985)
(1993)
Search WWH ::




Custom Search