Mesh-Structured Multi-Carbon Composite for Flexible Strain Sensors: High-Sensitivity Strain Detection Across Wide Temperature Ranges and Underwater Environments.

The development of flexible strain sensors has evolved significantly in recent years, with research priorities progressively shifting toward fabrication accessibility, performance optimization, and functional versatility to address increasingly complex application requirements in ambient intelligence and human-machine interface technologies. For human biomechanical and physiological monitoring applications, environmental robustness represents a critical design consideration, as sensors must maintain consistent performance characteristics despite exposure to thermal fluctuations, varying humidity levels, and potential liquid immersion during perspiration or aquatic activities. This work addresses these challenges through the implementation of a hierarchical nanocomposite sensing architecture incorporating three kinds of carbon allotropes─carbon black, graphene, and multiwalled carbon nanotubes─to form a strain-responsive conductive network. The functional composite was integrated with a microstructured silicone elastomer substrate (Ecoflex 00-30) featuring engineered surface topography to enhance interfacial adhesion and strain transfer efficiency. A conformal encapsulation layer of the same elastomer provides environmental isolation while preserving mechanical compliance. The nanocomposite sensing layer is realized by depositing the composite nanoconductive material on the elastomer substrate by screen printing, spraying, and drip coating. These three simple, convenient and low-cost processing methods make the nanocomposite sensing layer firmly adhere to the microstructure surface of the elastic substrate to form our flexible strain sensor. The resultant sensors exhibited exceptional performance metrics, including low strain detection threshold, broad measurement range, high gauge factor in the large-strain regime, rapid response time, and environmental stability. These characteristics enabled diverse applications spanning physiological signal monitoring (cardiovascular and musculoskeletal), acoustic transduction, submerged operation, and consistent performance across a 60 °C thermal range. The demonstrated combination of performance, environmental robustness, and fabrication accessibility positions this sensing platform for potential translation into emerging application domains, including continuous health monitoring in complex environments, next-generation prosthetic interfaces with enhanced proprioceptive feedback, soft robotics with distributed strain mapping capabilities, and human-machine interfaces for extended reality systems.