Direct ink writing of nickel nanowires/hexagonal boron nitride based capacitive pressure sensors using a water-based ink

The advancement of next-generation flexible electronics relies on the development of high-performance components that are lightweight, conformable, and compatible with scalable additive manufacturing processes. Here, we report a fully 3D-printed capacitive pressure sensor featuring a novel dielectric composite ink composed of nickel nanowires (NiNWs), hexagonal boron nitride (h-BN), and polyethylene oxide (PEO). This eco-friendly, water-based ink was engineered for direct ink writing (DIW), enabling the fabrication of printed planar capacitive sensors, with dimensions of 1.5 cm x 0.6 cm, comprised of interdigitated silver electrodes topped with composite dielectric layer on flexible, polyimide substrates. The composite dielectric ink included: h-BN, a 2-D nanomaterial which served as a charge storing nanomaterial with low dielectric loss, and a PEO binder, which stabilized the nanosheets and provided to the necessary viscoelastic properties for print fidelity and structural stability. Adding a small concentration of NiNWs to the hBN/PEO composite enhanced the dielectric properties due to an increase in interfacial polarization. The printed capacitive sensors incorporating an hBN/PEO/NiNW dielectric layer exhibited reliable pressure-responsive behavior across a wide sensing range (0–466 kPa), with sensitivities of 0.024 and 0.008 kPa⁻¹ in low - medium, and high-pressure regimes, respectively; these sensitivities were 7 – 8 times higher than for similar devices with hBN/PEO dielectric layers without NiNWs. Sensors demonstrated fast response times, low hysteresis, mechanical durability over cyclic loading, and high signal fidelity under dynamic pressure. Furthermore, the sensors enabled real-time monitoring of physiological signals including pulse, voice, and motion, underscoring their applicability in wearable health diagnostics and soft human–machine interfaces.