Decoupling Gauge Factor and Baseline Resistance Through Crack-Percolation Hybrid Design for Flexible Multimodal...

Flexible strain sensors for wearable systems, soft robotics, and distributed electronics exhibit a coupling between gauge factor (GF) and baseline resistance (R₀), as both depend on a structural parameter, limiting independent control of sensitivity and electrical characteristics. Here, a single-walled carbon nanotubes (SWNT)/SU-8/cracked-polydimethyl-siloxane (PDMS) (SSC) platform is introduced to decouple GF and R₀ through two independent fabrication parameters. Pre-strain (0-4%) defines closable cracks in a SU-8/PDMS bilayer, setting GF (0.1-100), while the spray volume of a 0.1 wt% SWNT dispersion (1-3 mL) controls R₀ from ∼10 kΩ to >1 MΩ through network percolation. Finite-element and Monte Carlo analyses indicate that the large GF originates from stochastic changes in conductive pathways within sparse SWNT networks bridging dynamically closing cracks, rather than from crack geometry alone. The platform is demonstrated in IGZO thin-film transistor-based strain-to-frequency converters (0.67-1.9 MHz over 0-3% strain), μ-LED modulation, broadband vibration sensing (82.4-329.6 Hz), and wearable bio-logging modules. As an application, the system detects ultra-slow respiration in anesthetized large mammals (lynx: 22-23 BPM; tiger: 2-3 BPM), where conventional monitors show limited sensitivity. These results define a new framework for strain sensing with independent control of electrical and mechanical responses, with broad implications for flexible and bio-integrated electronic systems.