Ultra-linear flexible pressure sensors via skin-inspired gradient engineering

Flexible pressure sensors face an irreconcilable trade-off among linearity, sensitivity, and signal stability due to viscoelastic creep. Inspired by the gradient modulus characteristics of human skin, this study employs electrospinning to construct a heterogeneous structure composed of a high-modulus nanofiber network embedded in a low-modulus ionic gel. This structure mimics epidermal rigidity (high-modulus nanofiber layer), dermal viscoelasticity (fiber-gel hybrid), and hypodermal compliance (soft ionic matrix) to synergistically redistribute stress and suppress ion migration. The sensor achieves breakthrough performance: a wide linear range (1 MPa) with near-perfect linearity (R² = 0.999) and ultrahigh sensitivity (81.3 kPa⁻¹), yielding a record linear sensing factor (LSF, 81,300). Simultaneously, it exhibits ultralow creep (1.76 % signal drift under sustained loading)—96.8 % lower than non-structured iongels—enabled by nanofiber-restricted ion pathways. Theoretical modeling reveals a dynamic compensation mechanism where pressure-induced changes in dielectric properties, contact area expansion, and electric double-layer thinning interact linearly. Laboratory validation demonstrates high-fidelity plantar pressure monitoring during gait cycles and machine learning-based prediction of vertical ground reaction forces with exceptional accuracy (R² > 0.95). This work establishes a new design paradigm for high-precision flexible sensing by fundamentally resolving long-standing material limitations.