An auxetic cellular structure as a universal design for enhanced piezoresistive sensitivity

Existing piezoresistive pressure sensors are limited because of the low sensitivity of conventional piezoresistive porous materials, which have positive Poisson’s ratio (PPR) values. Here, we propose a universally applicable strategy for fabricating piezoresistive metamaterials with an auxetic cellular structure, negative Poisson’s ratio (NPR), and enhanced pressure sensitivity. This hyperbolic and re-entrant microstructure enables porous, conductive metamaterials (e.g., titanium carbide [MXene], graphene, carbon nanotubes, silver nanowire, poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) [PEDOT:PSS]) to produce significant macroscopic transverse contraction under longitudinal compression with minimum NPR values below −0.45. This auxetic effect significantly increases the number of cellular wall-to-wall contact points and conductive pathway formations in the porous metamaterials under compression, significantly reducing electrical resistance. Sensitivity is markedly improved in this design compared with the traditional structure. The substantially enhanced mechanical elasticity and durability induced by the NPR effect gives piezoresistive metamaterials excellent sensing stability and reliability even under repeated episodes of significant compressive deformation.