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
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