Bioactive glass sol-gel foam scaffolds:evolution of nanoporosity during processing and in situ monitoring of apatite layer formation using small- and wide-angle X-ray scattering

Recent work has highlighted the potential of sol-gel-derived calcium silicate glasses for the regeneration or replacement of damaged bone tissue. The work presented herein provides new insight into the processing of bioactive calcia-silica sol-gel foams, and the reaction mechanisms associated with them when immersed in vitro in a simulated body fluid (SBF). Small-angle X-ray scattering and wide-angle X-ray scattering (diffraction) have been used to study the stabilization of these foams via heat treatment, with analogous in situ time-resolved data being gathered for a foam immersed in SBF. During thermal processing, pore sizes have been identified in the range of 16.5-62.0 nm and are only present once foams have been heated to 400 degrees C and above. Calcium nitrate crystallites were present until foams were heated to 600 degrees C; the crystallite size varied from 75 to 145 nm and increased in size with heat treatment up to 300 degrees C, then decreased in size down to 95 rim at 400 degrees C. The in situ time-resolved data show that the average pore diameter decreases as a function of immersion time in SBF, as calcium phosphates grow on the glass surfaces. Over the same time, Bragg peaks indicative of tricalcium phosphate were evident after only 1-h immersion time, and later, hydroxycarbonate apatite was also seen. The hydroxycarbonate apatite appears to have preferred orientation in the (h,k,0) direction.

Probing crystallisation of a fluoro-apatite - mullite system using neutron diffraction

Real-time small angle neutron scattering and wide angle neutron scattering studies were undertaken concurrently on a glass ionomer of nominal composition 4.5(SiO2)-3(Al2O3)-1.5(P2O5)-3(CaO)-2(CaF2). Neutron studies were conducted as a function of temperature to investigate the crystallisation process. No amorphous phase separation was observed at room temperature and the onset of crystallisation was found to occur at 650°C, which is 90°C lower than previously reported. The first crystalline phase observed corresponded to fluorapatite; it was only upon further heating was the mullite phase became present. The crystallite size at 650°C was found to be ~115Å and the result was consistent across all measurements.