Rational Design of Purely Inorganic Self-Healing Colloidal Hydrogels To Enable “Green” 3D Printing of Bioglass-Based Bone Substitutes

3D printing of ceramics or glass typically requires sacrificial organic plasticizers and high-temperature sintering, which is time- and cost-consuming, potentially cytotoxic, and may compromise the bioactivity and functionality of the inorganic components. We herein developed purely inorganic self-healing colloidal gels, consisting of electrostatically attractive silica-based hard nanospheres, to enable 3D printing of highly strong inorganic constructs via additive-free and low temperature sintering (LTS) processing. Through cross-scale analysis of the structural and mechanical features, we quantitatively described the constitutive relationship of attractive colloidal gels based on the integration of colloidal assembly theory with experimental characterizations. This mechanistic understanding further allowed us to develop considerably strong colloidal gels (maximal compressive modulus ∼2.3 MPa) without compromising the self-healing ability. We further demonstrated the excellent printability, shape-fidelity, and reprocessability of the inorganic gels, thereby facilitating additive-free inorganic 3D printing followed by LTS treatment at ∼700 °C. This "green" inorganic 3D-printing strategy enabled cost-efficient and bioactivity-preserved fabrication of bioglass-based bone substitutes, which led to improved in vivo osteogenesis and osteointegrity. In general, this work emphasizes the significance of rationale design and mechanistic understanding of self-healing colloidal gels with outstanding performances as printable inks and provides an avenue for customized fabrication of functional inorganic 3D structures toward applications in biomedical, machinery, energy, and chemical industries.