3D Aerosol Jet® printing for microstructuring: Advantages and limitations

Aerosol Jet® printing (AJ®P) is a direct writing printing technology that deposits functional aerosolized solutions on free-form substrates. Its potential has been widely adopted for two-dimensional (2D) microscale constructs in printed electronics (PE), and it is rapidly growing toward surface structuring and biological interfaces. However, limited research has been devoted to its exploitation as a three-dimensional (3D) printing technique. In this study, we investigated AJ®P capabilities for 3D microstructuring of three inks, as well as their advantages and limitations by employing three proposed 3D AJ®P strategies (continuous jet deposition, layer-by-layer, and point-wise). In particular, 3D microstructures of increasing complexity based on silver nanoparticle (AgNPs)-, poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT:PSS)-, and collagen-based inks were investigated at various aspect ratios and resolutions. Biocompatibility assays were also performed to evaluate inks cytotoxicity effects on selected cellular lineages, including neuronal and osteoblast cell lines. Results show the possibility to print not only arrays of micropillars of different aspect ratios (AgNPs-ARs ~ 20, PEDOT:PSS-ARs ~ 4.5, collagen-ARs ~ 2.5), but also dense and complex (yet low reproducible) leaf- or flake-like structures (especially with the AgNPs-based ink), and lattice units (collagen-based ink). Specifically, this study demonstrates that the fabrication of 3D AJ®-printed microstructures is possible only with a specific set of printing parameters, and firmly depends on the ink (co-)solvents fast-drying phenomena during the printing process. Furthermore, the data concerning inks biocompatibility revealed high cytotoxicity levels for the AgNPs-based ink, while low ones for the PEDOT:PSS and the collagen-based inks. In conclusion, the paper provides general guidelines with respect to ink development and print strategies for 3D AJ®P microstructuring, opening its adoption in a vast range of applications in life science (tissue engineering, bioelectronic interfaces), electronics, and micromanufacturing.