In this study, porous silica structures were 3D-printed through the layer-by-layer deposition of sodium alginate (SA) and polyvinyl alcohol (PVA) gel-inks followed by freeze-casting consolidation allowed fabricate components with customized design in terms of pore-microstructure and porosity to overcome the challenges of tissue engineering for bone regeneration. The rheological properties of the gel-inks were optimized by the addition of methylcellulose (MC) a viscosity modifier and a thixotropic agent. PVA and SA gel-inks with 41 and 56 vol% of nanosilica-coated microsilica (NMS) based powders exhibiting a pseudo-plastic behavior with yield stresses above ∼10 and 30 Pa, respectively, were extruded through a nozzle of 1.11 mm with pressure controlled up to 2 bar and constant printing speed of 10 mm/s. The printed structures were carefully dried by two different procedures: room temperature or freeze drying for a period of 24 h, and then fired at 1200 °C at 5 °C/min for 2 h. The microstructural evaluation of silica structures exhibiting highly porous microstructures ranging from 69 up to 76%, depending on the gelling agent, suggest that freeze-dried samples, which possess unidirectionally aligned porosities are suitable for tissue engineering applications.
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