Biomedical Engineering Reference
In-Depth Information
0.0011
0.0010
0.0009
0.0008
0.0007
0.0006
0
5
TiO
2
content in the glass (mol%)
10
Figure 4.15
Dissolved P
2
O
5
relative to total amount of P
2
O
5
versus TiO
2
content
in an invert phosphate glass of the composition P
2
O
5
-CaO-MgO-Na
2
O(P
2
O
5
content constant at 37 mol%).
and differentiation compared to a TiO
2
-free control, an effect that can be
explained by lower degradation rates and less pronounced pH changes
for increasing TiO
2
content (glasses gave slightly acidic pH values, with
a decreasing TiO
2
content corresponding to a decrease in pH) [9].
Replacing calcium with strontium in TiO
2
-containing metaphosphate
glasses did not have any marked effects on cell proliferation over up to
seven days [11]. Although strontium is known to stimulate osteoblasts
and to inhibit osteoclasts
in vitro
[12], and it is also the basis of
a drug (Protelos
®
, Servier) for treating osteoporosis, the increase in
solubility (due to the larger ionic radius of Sr
2
+
compared to Ca
2
+
)and
the subsequent pH decrease apparently overcame the beneficial effects
of strontium.
Zinc-containing metaphosphate glasses (P
2
O
5
-CaO-Na
2
O-ZnO,
with ZnO contents between 1 and 20 mol%) showed attachment of
osteoblast-like cells, but cells maintained a round morphology and did
not spread on the glasses, indicating that the cells were not happy on
the surface [13]. These findings can be explained by potentially negative
effects of zinc: while zinc was shown to have a stimulatory action on
bone formation, higher than optimum levels of zinc were shown to be