Facile Preparative Access to Bioactive Silicon Oxycarbides with Tunable Porosity

Abstract

In the present work, Ca-containing silicon oxycarbides (SiCaOC) with varying Ca content have been synthesized via sol-gel processing and thermal treatment in inert gas atmosphere (pyrolysis). It has been shown that the as-prepared SiCaOC materials with low Ca loadings (Ca/Si molar ratios = 0.05 or 0.12) were X-ray amorphous; their glassy network contains Q3 sites, indicating the presence of Ca2+ at non-bridging-oxygen sites. SiCaOC with high Ca content (i.e., Ca/Si molar ratio = 0.50) exhibits the presence of crystalline calcium silicate (mainly pseudowollastonite). Furthermore, it has been shown that the incorporation of Ca into the SiOC glassy network has a significant effect on its porosity and specific surface area. Thus, the as-prepared Ca-free SiOC material is shown to be non-porous and having a specific surface area (SSA) of 22.5 m2/g; whereas SiCaOC with Ca/Si molar ratio of 0.05 exhibits mesoporosity and a SSA value of 123.4 m2/g. The further increase of Ca content leads to a decrease of the SSA and the generation of macroporosity in SiCaOC; thus, SiCaOC with Ca/Si molar ratio of 0.12 is macroporous and exhibits a SSA value of 39.5 m2/g. Bioactivity assessment in simulated body fluid (SBF) confirms the hydroxyapatite formation on all SiCaOC samples after seven days soaking, unlike the relatively inert ternary silicon oxycarbide reference. In particular, SiCaOC with a Ca/Si molar ratio of 0.05 shows an increased apatite forming ability compared to that of SiCaOC with Ca/Si molar ratio of 0.12; this difference is considered to be a direct consequence of the significantly higher SSA of the sample with the Ca/Si ratio of 0.05. The present work indicates two effects of Ca incorporation into the silicon oxycarbide glassy network on its bioactivity: Firstly, Ca2+ is shown to contribute to the slight depolymerization of the network, which clearly triggers the hydroxyapatite formation (compare the bioactive behavior of SiOC to that of SiCaOC with Ca/Si molar ratio 0.12 upon SBF exposure); secondly, the Ca2+ incorporation seems to strongly affect the porosity and SSA in the prepared SiCaOC materials. There is an optimum of Ca loading into the silicon oxycarbide glassy network (at a Ca/Si molar ration of 0.05), which provides mesoporosity and reaches maximum SSA, both highly beneficial for the bioactive behavior of the materials. An increase of the Ca loading leads, in addition to the crystallization of calcium silicates, to a coarsening of the pores (i.e., macroporosity) and a significant decrease of the SSA, both negatively affecting the bioactivity.

Effect of the Content and Ordering of the sp2 Free Carbon Phase on the Charge Carrier Transport in Polymer-Derived Silicon Oxycarbides

“…The glassy network of silicon oxycarbides can be easily altered via incorporating additional network formers (i.e., boron) [ 8 ] or modifiers (e.g., Li, Ca, Mg, etc.) [ 3 , 5 , 6 , 9 , 10 ], thus structural properties such as network connectivity and polymerization can be finely tuned [ 6 ]. This allows for providing finely adjustable properties in silicon-oxycarbide-based materials.…”

Radiological evaluations of low cost wollastonite nano‐ceramics graft doped with iron oxide in the treatment of induced defects in canine mandible

“…The Si concentrations was increased with increasing soaking time (coming out from the wollastonite dissolution), which possess a great role in the biomineralization process in most of silicate-based materials. [25][26][27] The release of iron in SBF was increased in the beginning of the soaking period, which confirms iron leaching from the wollastonite nano-ceramics (for those contain iron). This was followed by great decrease in the iron concentrations in SBF solutions, which could be explained by the fact that iron is involved in precipitated apatite layer, these results are in line with early reported studies.…”

“…The behaviors of measured Ca and P ions in the SBF after samples submersion are inversely proportional to each other (Figure 6(a),(b) Ca release was increased (coming out from the wollastonite dissolution) and P concentrations decreased in the SBF solutions suggesting that Ca concentrations increases the precipitation of P ions from the SBF onto the samples surfaces (carbonated apatite layers). The Si concentrations was increased with increasing soaking time (coming out from the wollastonite dissolution), which possess a great role in the biomineralization process in most of silicate‐based materials 25‐27 . The release of iron in SBF was increased in the beginning of the soaking period, which confirms iron leaching from the wollastonite nano‐ceramics (for those contain iron).…”

Polymer-Derived Biosilicate®-like Glass-Ceramics: Engineering of Formulations and Additive Manufacturing of Three-Dimensional Scaffolds

“…Preceramic polymers [ 1 ], especially in the form of polysiloxanes, known also as ‘silicones’, have been recently recognized as raw materials for a new generation of bioceramics, such as Ca-, Ca-/Mg- and Ca-/Zn- silicates [ 2 , 3 , 4 , 5 , 6 , 7 ]. In particular, silicone resins, embedding micro- and nano-sized fillers, consisting of carbonates, hydroxides or simple oxides may yield the desired silicate with excellent purity, at a generally lower temperature (900–1100 °C), offering interesting shaping possibilities [ 8 , 9 , 10 , 11 , 12 , 13 ].…”