Development of optimal scaffolds for bone tissue regeneration is still a challenge. The present work deals with the preparation and characterization of SiO₂-CaO and SiO₂-CaO-P₂O₅ sol-gel derived monoliths, with potential application as glass scaffolds for bone regeneration. The aim was to achieve a hierarchical dual pore structure including pores of both ~100’s of micrometers and a few to 10’s of nanometers in size, leading to a coral-like morphology with interconnected macropores, based on polymerization-induced (spinodal-type) phase separation made to occur in parallel with the sol-gel transition, by adding a water soluble polymer to the sol-gel solution. The SiO₂ content was varied between 60 – 77 mol% and different processing strategies have been tested, namely by varying the Si alkoxide (TEOS or TMOS), the CaO precursor (Ca nitrate or acetate), the type and concentration of polymer (PEO or PEG) and the temperature/time schedule during sol processing and gel drying and heat treatment.

The morphological and textural characterization of the scaffold materials, performed by field emission SEM, nitrogen adsorption and mercury intrusion porosimetry, confirmed the presence of a dual pore structure including interconnected macropores (~ 10 - 200 μm) plus the inherent nanopore (~ 5 - 40 nm) structure tailored by solvent exchange procedures. Scaffold bioactivity has been demonstrated by the precipitation of hydroxyapatite after immersion in simulated body fluid, by means of SEM and infrared (IR) spectroscopy. The effect of the non-bridging/bridging oxygen ratio of the gel derived glass was also investigated and it was verified by IR and Raman spectroscopies, combined with EDX analysis, that the net amount of Ca²⁺ incorporated into the glass network tended to be lower than the nominal batch concentration and it depended on the CaO precursor and the processing conditions. The influence of these factors on the scaffold bioactivity is discussed in detail.

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