Biodegradable porous Zn@ZnO scaffolds with core-shell structure fabricated by direct ink writing and high-temperature...

Direct ink writing (DIW) followed by debinding and sintering processes offers unique advantages for fabricating biodegradable porous metallic scaffolds while avoiding several key issues associated with powder bed fusion additive manufacturing. Although DIW has been successfully applied to Mg, Fe, and their alloys, Zn-based scaffolds fabricated by DIW remain largely unexplored. Here, we fabricated, for the first time, porous Zn-based scaffolds with a Zn@ZnO core-shell structure using DIW printing combined with debinding and high-temperature oxidation. Their microstructure, degradation behavior, electrochemical response, evolution of mechanical properties, and in vitro biocompatibility were systematically evaluated. Furthermore, the sintering and corrosion mechanisms of the scaffolds were analyzed. High-temperature oxidation produced ZnO shells with thicknesses of 0.5-9.2 μm and induced the formation of needle- or flake-like ZnO, enabling stable bonding among Zn@ZnO spheres. Specimens prepared at oxidation temperatures between 500 °C and 650 °C exhibited similar yield strength and elastic modulus, while the compressive strength increased significantly with higher oxidation temperatures. Throughout the 28 days of in vitro biodegradation, the mechanical properties of the scaffolds remained within the range of cancellous bone, with mass losses between 2.8% and 7.4%. During the 7-day direct culture, all specimens exhibited good cytocompatibility, as indicated by cell viabilities above 75% and elevated alkaline phosphatase (ALP) activity. Overall, this study demonstrates the great potential of DIW-fabricated Zn@ZnO scaffolds for biodegradable bone-substituting biomaterials. STATEMENT OF SIGNIFICANCE: Direct ink writing (DIW) has emerged as a promising technique for fabricating porous biodegradable metallic scaffolds due to its low energy consumption and broad material compatibility. However, the application of DIW to biodegradable Zn-based bone implants remains largely unexplored. In this study, a fabrication strategy combining DIW with high-temperature oxidation is proposed to produce porous Zn-based scaffolds with a unique Zn@ZnO core-shell architecture. Controlled oxidation enables the formation of a multiscale hierarchical pore structure and allows effective regulation of degradation behavior, mechanical performance, and cytocompatibility. This work provides insights into the DIW processing of Zn-based biodegradable metals and highlights the potential of Zn@ZnO scaffolds for biofunctional bone substitute applications.