Architecting Co-continuous PVDF Composites via Multi-material 3D Parallel Printing for Enhanced Piezoelectricity and Wearable Sensing.

Flexible piezoelectric composites have attracted considerable attention for self-powered sensing; however, achieving efficient electromechanical response while maintaining structural integrity under repeated deformation remains challenging. Herein, a structure-driven multi-material 3D parallel printing strategy is developed to construct polyvinylidene fluoride (PVDF)-based piezoelectric composites with a co-continuous dual-phase architecture. In this design, ionic liquid (IL)-modified PVDF serves as the piezoelectric phase, where the IL promotes β-phase formation and dipole orientation, while carbon nanotubes (CNTs)-reinforced PVDF provides a conductive phase for electrical signal collection. Unlike conventional stacked configurations, the parallel-printed architecture enables continuous integration of the piezoelectric and conductive phases, providing intimate interfacial contact and a mechanically interconnected structure. The resulting structural continuity facilitates stress transfer during mechanical deformation and contributes to a stable electromechanical response. Kelvin probe force microscopy measurements further reveal an interfacial potential difference of 85.6 mV, indicating distinct interfacial electrical characteristics between the two phases. The optimized sensor delivers an output voltage of 0.55 V at 5 N, a sensitivity of 439.77 mV/N in the low-force regime, and a response time of 28 ms, together with excellent mechanical stability. Finite element analysis and experimental results demonstrate that the enhanced piezoelectric response is closely associated with the continuous deformation and effective stress transfer enabled by the parallel architecture. The sensor further exhibits reliable performance in human-motion monitoring and human-machine interaction. This work establishes multi-material 3D parallel printing as a structure-engineering approach for integrating piezoelectric and conductive phases and provides a versatile route toward high-performance flexible piezoelectric sensing devices.