Layered structures in nature, such as seashells and human bones containing varying chemical compositions or physical architectures provide high mechanical robustness or versatile functions that have inspired many man-made systems like honeycomb aerospace structures. However, conventional processing involving multiple materials has challenges in assembly, especially with manual pick-and-place that are impossible to conduct at the micro or nanoscale. 3D printing is a layer-by-layer addition process with high design flexibility and a made-on-demand procedure. The cloud-based operation with minimum dependence on a supply chain has shown its advantages over casting or molding, with broad applications in automotive, biomedical, electronics, robotics, and architectural industries. However, current manufacturing has been limited by its ability to manipulate multiple materials, especially tuning their submicron characteristics when showing non-compatible chemical or physical features. For example, the deposition and patterning of nanoparticles with different dimensions have seen little success, except in highly precise and slow 3D printing (eg., Aerojet). Thus, we have designed and developed a new 3D printing mechanism, Multiphase Direct Ink Writing (MDIW). The MDIW, built on a multi-material extrusion-based platform, is capable of simultaneously manufacturing layered and sub-layered microstructures benefiting the organization and assembly of submicron features (e.g., polymer crystal engineering, nanoparticle morphologies) for structural and functional behaviors. The unique design of the printhead allows multiple feedstocks to be rearranged and multiplied within individual printing lines, with a resolution control at unit micrometers at a speed of 20cm/s. This research will demonstrate different material systems with control over material types, interfacial interactions, and printing parameters (i) The polyvinyl alcohol (PVA) and PVA/multiwalled carbon nanotube (MWNTs) suspensions as feedstocks will exhibit PVA crystallization tunability and MWNTs dispersion/alignment control within microlayers for enhanced mechanical robustness. (ii) Thermoplastic polyurethane (TPU) with different thermoplastic (polycaprolactone) and metal nanoparticle (iron oxide) compositions to tune stimuli-responsiveness.

Novel additive manufacturing mechanism for layered composites

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