A new 3D printing technique has been developed by a team at Virginia Tech that could be used to develop intelligent materials and self-adaptive infrastructures and transducers. [Zheng, X. et al., Nature Mater. (2019); DOI: 10.1038/s41563-018-0268-1]

Xiaoyu 'Rayne' Zheng and his team can now 3D print piezoelectric materials that could be exploited in a wide range of devices for converting movement, impact and stress from any direction into an electrical signal, or indeed an electrical energy supply. Piezoelectric materials were notoriously available only in a few defined shapes and are commonly brittle, crystalline ceramics. Printable piezoelectric materials have none of those limitations and can also be "activated" offering the possibility of tactile sensing, impact and vibration monitoring, energy harvesting, and various other applications. Moreover, the 3D printer approach avoids the need for clean-room facilities.

Zheng's team developed a model that allowed them to manipulate and design arbitrary piezoelectric constants. In contrast to conventional piezoelectric materials in which electric charge movements are prescribed by the intrinsic crystals, the new materials can be programmed to a specific voltage response and this can be magnified, reversed or suppressed in any direction.

"We have developed a design method and printing platform to freely design the sensitivity and operational modes of piezoelectric materials," Zheng explains. "By programming the 3D active topology, you can achieve pretty much any combination of piezoelectric coefficients within a material, and use them as transducers and sensors that are not only flexible and strong, but also respond to pressure, vibrations and impacts via electric signals that tell the location, magnitude and direction of the impacts within any location of these materials."

Fundamentally, Zheng's team has produced a substitute for conventional piezoelectric materials that mimics the crystal structure but allows for the lattice orientation to be altered by design. "We have synthesized a class of highly sensitive [perovskite-based] piezoelectric [nanocomposite] inks that can be sculpted into complex three-dimensional features with ultraviolet light," Zheng adds. "The inks contain highly concentrated piezoelectric nanocrystals bonded with UV-sensitive gels, which form a solution that we print with a high-resolution digital light 3D printer."

The team adds that there are other benefits to their approach, saying that these electromechanical metamaterials "achieve high specific piezoelectric constants and have tailorable flexibility using only a fraction of their parent materials."