Development of a 3D printable material system possessing inherent piezoelectric properties to fabricate integrable sensors in a single-step printing process without poling is of importance to the creation of a wide variety of smart structures. Here, we study the effect of addition of barium titanate nanoparticles in nucleating piezoelectric β-polymorph in 3D printable polyvinylidene fluoride (PVDF) and fabrication of the layer-by-layer and self-supporting piezoelectric structures on a micro- to millimeter scale by solvent evaporation-assisted 3D printing at room temperature. The nanocomposite formulation obtained after a comprehensive investigation of composition and processing techniques possesses a piezoelectric coefficient, d, of 18 pC N, which is comparable to that of typical poled and stretched commercial PVDF film sensors. A 3D contact sensor that generates up to 4 V upon gentle finger taps demonstrates the efficacy of the fabrication technique. Our one-step 3D printing of piezoelectric nanocomposites can form ready-to-use, complex-shaped, flexible, and lightweight piezoelectric devices. When combined with other 3D printable materials, they could serve as stand-alone or embedded sensors in aerospace, biomedicine, and robotic applications.

Although soft robotics promises a new generation of robust, versatile machines capable of complex functions and seamless integration with biology, the fabrication of such soft, three dimensional (3D) hierarchical structures remains a significant challenge.

Given the ever-increasing demand for customization and miniaturization, in situ three-dimensional (3D) printing of piezoelectric polymers comes as an efficient means to cater to smart structures via multimaterial printing. Applying our hybrid printing technique to polyvinylidene-fluoride–barium-titanate (PVDF–BaTiO3) nanocomposites, to combine the fabrication and high-voltage poling steps, shrinks the manufacturing time, overcomes the disadvantages of adherence in nonconformal piezoelectric films or fabrics, and increases the sensitivity and scope for on-demand applications. A remarkable 300% improvement in piezoelectric charge output is achieved upon the addition of 10 wt % BaTiO3 nanoparticles and application of an electric field of 1 MV m–1, compared with printed unpoled neat PVDF. We demonstrate the application of the in situ poling process in the form of sensors printed directly on a shoe insole for gait analysis. The sensors fabricated in this work effectively distinguish between walking and stamping as both portable in-shoe sensor as well as sensors attached to the ground.

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