Multi-material fused filament fabrication of flexible 3D piezoelectric nanocomposite lattices for pressure sensing and energy harvesting applications

Flexible three-dimensional (3D) piezoelectric sensors and energy harvesters are in great demand for wireless and low power consumption human health monitors, artificial skins and soft robots. In this work, a multi-material fused filament fabrication (FFF) 3D printing technique is used to fabricate 3D piezoelectric and flexible nanocomposite structures with integrated electrodes by utilizing a developed piezoelectric nanocomposite filament and a commercially available conductive nanocomposite filament. The developed piezoelectric nanocomposite filament consists of flexible polyurethane (TPU) matrix and 30 vol% (maximum allowable content) of piezoelectric ceramic lead zirconate titanate (PZT) nanoparticle fillers. The fabricated and poled TPU/30vol%PZT piezoelectric nanocomposite has an elongation at break strain ∼56% and a d33 value 6.8 pC/N. Four types of 3D piezoelectric nanocomposite lattices including simple cubic, body-centered cubic, cuboctahedron and octet truss are fabricated and tested along with a fully dense solid counterepart. Under the same maximum applied compressive force, the octet truss piezoelectric nanocomposite lattice generates two times higher voltage output than the fully dense solid counterpart. As a demonstration for the potential applications, a multi-material 3D printed flexible piezoelectric nanocomposite shoe sole made of the octet truss infill pattern can generate a peak-to-peak voltage (Vpp) ∼20 V through a typical human stomp. Our approach can open a new avenue for design and manufacturing of flexible piezoelectric devices for sensing and energy harvesting applications.