Embedding auxetic structures in composite substrate layer for enhancing performance of stretchable strain sensors

• An auxetic layer is embedded in the composite substrate to enhance the strain sensor functionality. • A theoretical design routine programs bidirectional sensitivity via strain transfer. • Synergistic deformation dynamically regulates lateral contraction in auxetic sensing substrate. The mechanical coupling between the sensing and substrate layers is critical for stretchable strain-sensing devices in wearable electronics. This study proposes a facile composite substrate design by embedding auxetic structures directly into a polybutylene adipate terephthalate (PBAT) film. Using direct ink writing, we fabricate highly ordered 3D sinusoidal (polydimethylsiloxane) PDMS filaments within the PBAT matrix, achieving exceptional auxetic behavior. By tuning the sinusoidal structure, the transverse contraction of the composite substrate can be precisely controlled under longitudinal stretching. When serpentine-shaped sensing materials are deposited onto the substrate, the composite strain sensor exhibits high and stable sensing performance owing to reduced transverse contraction enabled by the coupled deformation of the sensing layer and the substrate. These findings demonstrate the potential of embedded auxetic architectures for developing multifunctional composite materials.