Hybrid FFF-DIW System for 3D-Printed Reactive Unit Cells

Additive manufacturing has enabled low cost production of three-dimensional solids for a wide range of applications. However, most of these printed articles are static structures that lack the capacity to do work. In this study, we describe a general methodology for 3D printing polymer structures with embedded chemical reactants. A hybrid fused fabrication (FFF) and direct ink write (DIW) printer has been built to create structures with enclosed chemical reactants that can be released and mixed upon mechanical actuation to activate a chemical process. Simplified unit cell structures have been designed and fabricated to activate under tension, compression, or bending, with mixing and reaction initiated at a designed trigger force. The structural materials chosen for this work are thermoplastic polyurethane (TPU) and polylactic acid (PLA). TPU is selected for its relatively high elongation strain compared to PLA, enabling strain-induced failure of an enclosed PLA septum while maintaining the integrity of a TPU outer shell. Different designs were modeled and fabricated to demonstrate control of the activation force required to initiate the reaction. Furthermore, various reactants were used to show compatibility with multiple chemical functions. Lastly, we developed a structure composed of multiple reactive unit cells throughout its body, to show how the reactive unit cell concept combined with additive manufacturing can enable complex mechano-chemical behaviors.