Optical 3D μ-printing of PVDF-based flexible microstructural auxetic metamaterials and 3D microgrid pyramid arrays for wearable electronics

Piezoelectric auxetic metamaterials with microstructures hold significant promise for the design of force and tactile sensors. Here, a maskless ultraviolet (UV) lithography-based optical 3D μ-printing with high-resolution, rapid prototyping, and customized fabrication is reported to prepare polyvinylidene difluoride (PVDF)-based flexible piezoelectric sensors. With customized crosslinking for the mixture of PVDF solutions, acrylate resins, and additives, these sensors feature 2D negative Poisson’s ratio (2D-NPR) metamaterial networks and 3D microgrid structures on flexible substrates, offering optimized mechanical and electrical properties. Initially, the 2D-NPR metamaterial networks demonstrate a sensitivity of 2.09 mV/°, and a signal-to-noise ratio (SNR) of 30.87 dB for detecting bending behaviors. Additionally, further mechanical designs on 3D arrayed pyramid-shaped (AP-S) sensors with microgrid structures and electronic code locks composed of this sensor array significantly enhance their versatility in detecting vector loads and gesture codes. Notably, compared to planar PVDF sensors, the performance of this 3D microgrid structure sensor has been significantly improved by 1.53-fold, with a 4.25-fold enhancement for the limits of detection. Moreover, the proposed 2D and 3D sensors provide exceptional temperature stability and hysteresis characteristics. Leveraging machine learning algorithms, these flexible piezoelectric sensors can accurately detect human rehabilitation states, marking significant progress in advanced wearable electronics.