Micro- and nano-scale additive manufacturing technologies: fabrication methods, aerospace applications, and future directions

Additive manufacturing at micro and nano-scale is currently a revolutionary technology in making complex and high-resolution structures with features that are in the range of tens and hundreds of manometers down to micrometres in diameter. It is critically reviewed state-of-the-art publication on micro and nano-scale additive technologies in regard to their fabrication principles, capabilities, limitations, and future applications in biomedical contexts, MEMS, photonic, electronic, defence and aerospace. The methods include Two-Photon Polymerisation (2PP), Inkjet-printing, Electrohydrodynamic Jet printing (EHD), Direct ink-writing (DIW), Micro-stereolithography (µ-SLA) and Focused Electron Beam Induced Deposition (FEBID). Micro-stereolithography, being compromise technique in terms of resolution and throughput, is one of the techniques evaluated. Two-Photon Polymerisation in comparison has best resolution amongst the examined procedures with feature sizes being less than 100 nanometres, and as such is well suited to creating nanoscale parts, where precision is essential. These results highlight the disruptive nature of the µ-AM and n-AM technologies in facilitating next generation high-performance, miniaturised systems in industrial applications. However, despite their remarkable capabilities, several manufacturing challenges limit their widespread industrial implementation. Overcoming these problems will be the key to changing the status of micro and nano-scale additive manufacturing as a laboratory innovation in various fields of manufacturing application.