Ca‐ and/or B‐modified silicon oxycarbides were synthesized via pyrolysis of suitable polysilsesquioxane‐based single‐source precursors. Their polymer‐to‐ceramic transformation was investigated with thermogravimetric analysis, coupled with in situ evolved gas analysis. The prepared silicon oxycarbides were investigated with respect to their crystallization behavior, network architecture, and chemical compositions. The network connectivity in silicon oxycarbides can be affected/tuned upon using two different “tools”: (a) first, the use of network modifiers, such as Ca in our study, leads to a slight depolymerization of the network via generation of a small amount of Q3 sites; (b) second, the modification of silicon oxycarbide with B/Ca leads to a decrease of the carbon content in the network and thus to a significant decrease of its connectivity. Using these two different effects, the network connectivity in silicon oxycarbides can be finely tuned.
The
bioactivity of Ca and/or B modified silicon oxycarbides has
been assessed in vitro upon immersion in SBF (simulated
body fluid). In the context of the present work, bioactivity refers
to the likeliness of hydroxyapatite crystallization (biomineralization)
on the surface of a material when in contact with physiological fluids.
The incorporation of Ca and B into the silicon oxycarbide glass network
is found to increase its bioactivity, which seems to scale with the
content of Ca; thus, SiOC glass with a relatively large
Ca/Si molar ratio (i.e., 0.12) is shown to exhibit bioactive characteristics
similar to those of the benchmark silicate bioactive glass of 45S5 composition. The release kinetics of the SiOC glasses modified with Ca and/or B during the SBF test was studied
by inductively coupled plasma-optical emission spectroscopy. It has
been observed that the Si release kinetics can be correlated with
the Ca content in the SiOC glasses: SiOC based glasses modified with Ca exhibited low Si release activation
energies (i.e., 0.07 eV), being comparable to that of 45S5 bioactive glass (i.e., 0.04 eV); whereas silicon oxycarbides without
Ca modification showed higher activation energies for Si release (i.e.,
0.27 eV).
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