An Inorganic Water‐Glass‐Based Hydrogel for Processing Hierarchically Porous 3D Structures by Combined Robocasting and Direct Foaming

Abstract

Bioinspired, graded structures with hierarchical porosity, combining high surface area with low density, are attractive for a wide range of applications. Local adaptation of properties makes it possible to fine‐tune their strength and degradation kinetics over time. Production of such structures is, however, still scientifically and technically challenging. A versatile approach for fabricating hierarchical, porous structures from water‐glass (WG), exploiting its inherent foaming ability in conjunction with robocasting, for applications such as, bone‐replacement scaffolds, is presented. The unique processing route that is proposed uses a purely inorganic, mouldable sodium silicate hydrogel based on WG as ink for robocasting, which makes it cost‐effective and highly environmentally friendly. The WG‐based hydrogels can be used in a pure state, and also as carrier systems, e.g., for tricalcium phosphate. Following heat treatment at a relatively low temperature of 450 °C, the robocast parts develop hierarchical porosities. Multi‐microscale porosity is created due to foaming during heating, in addition to the macroscale porosity designed during robocasting. The suggested process opens up a powerful alternative to fabrication routes presently available for hierarchically porous structures.