Direct Ink Writing Additive Manufacturing of Polyimide Aerogels.

Polyimide aerogels (PAs) are ideal for applications in thermal protection, lightweight electronics, and energy devices due to their excellent mechanical properties, ultra-low density, extremely low thermal conductivity, and high thermal-oxidative stability. Conventional PA manufacturing involves a sol-gel process followed by post-processing (drying and imidization). However, PAs fabricated using this method are geometrically limited by the mold shape and are fragile, have poor sample machinability, and are prone to shrinkage and deformation. Direct ink writing (DIW) additive manufacturing (AM) overcomes these limitations of conventional manufacturing processes by extruding ink to construct architectural lattices with high dimensional fidelity, enabling the fabrication of complex, conformal, and multi-scale structures. DIW AM can produce PA components that are thermally and electrically stable, as well as geometric freedom, thus supporting high-precision and functional hierarchical design. This review provides the first overview of DIW AM of PAs. By summarizing printable ink formulations, printing parameters, drying routes and thermal/chemical imidization processes, as well as applications of printed samples, it comprehensively describes the current state of the art in DIW additive manufacturing of PAs and highlights key technical bottlenecks (printability vs. porosity trade-off, economic and environmental, etc.). It also outlines possible future research directions.