Synthesis of ceramics in MOn/2-SiO2 systems through sol-gel processing under coexistence of polyethylene glycol and in vitro evaluation of their bioactivity

Abstract

Sol-gel processing from tetraethoxysilane (TEOS) under coexistence of polyethylene glycol (PEG) allows controlled morphology of the formed silica because of the phase separation during the poly condensation of the hydrated sol. The presence of PEG controlled the morphology effective in preparation of the ceramics, even in the CaO-SiO2 binary system, starting from TEOS and Ca (NO3)2. In the present study, some ceramics were prepared using the MOn/2-SiO2 binary systems, where M is given as Na+ (n = 1), Mg2+ (n = 2) and Al3+ (n = 3), through sol-gel processing in the presence of PEG, to compare the compositional changes in the morphology of the ceramics. In the case of NaO 1/2-SiO2, the framework size increased remarkably with increasing amounts of Na+ in the starting compositions up to 30 mol%, while continuous pores of approximately 10 μm were observed at 5 mol% of Na+. In the case of MgO-SiO2, the framework size increased with increasing amounts of Mg2+ up to 20 mol% in the starting composition. Aggregation of particles with approximately 3μm in size was observed at 25 mol% and more. The trend in morphological change with addition of Mg2+ was quite similar to that with Ca2+. With AlO 3/2-SiO2, particles were obtained when the starting composition was more than 10 mol % Al3+. The size of the particles appeared to decrease with increasing amounts of Al3+. The morphology and phase separation behavior are strongly affected by the charge value of the metal ions, because the number of non-bridging oxygens coordinated to the metal ion increased with increasing charge value in the sol-gel processing. A specimen prepared with starting composition 20NaO1/2 ·80SiO 2 and heated at 600°C formed hydroxyapatite on the particle surfaces within 7 d after soaking in a simulated body fluid (SBF), suggesting a potential for bioactivity on application of bone repair.