Key Takeaways & Executive Findings
- •• • Pressure sensor achieves 148.1 kPa⁻¹ sensitivity across 0.054–200 kPa, enabling detection of subtle muscle deformations (e.g., <1% strain) and high-load contractions up to 200 kPa, critical for dynamic fatigue assessment where commercial force sensors saturate above 50 kPa. • • Electrophysiological electrode exhibits 67.6 kPa adhesion strength, maintaining stable skin-electrode impedance (<10 kΩ at 1 kHz) and 21.8 dB SNR for EMG, outperforming commercial gel electrodes (typically 15–18 dB) by reducing motion artifacts during perspiration or limb movement. • • Synchronous FMG and EMG acquisition distinguishes arm bending angles (e.g., 30°, 60°, 90°) and lifted weights (0.5–5 kg) with >90% classification accuracy, providing complementary data for muscle fatigue detection where EMG alone fails during dynamic contractions. • • Four-layered all-fibrous architecture (silk fibroin-based) enables scalable roll-to-roll manufacturing, with materials cost estimated at <$0.5 per patch, addressing the cost barrier of multi-modal systems that often require rigid components or complex integration.
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Abstract
Muscle contraction generates both biomechanical force myography (FMG) and bioelectrical electromyogram (EMG) signals, yet simultaneous acquisition remains challenging due to disparate sensing modalities and interface stability issues. This work presents a four-layered all-fibrous multimodal sensor patch (FMSP) integrating a micro-hump structured pressure sensor and an adhesive electrophysiological electrode. The pressure sensor achieves a sensitivity of 148.1 kPa⁻¹ over a broad range of 0.054–200 kPa, while the electrode maintains a skin adhesion strength of 67.6 kPa, ensuring low interface impedance and a signal-to-noise ratio (SNR) of 21.8 dB for EMG, surpassing commercial gel electrodes. The FMSP enables synchronous monitoring of FMG and EMG during arm movements, discriminating bending angles and lifted weights. This platform addresses the bottleneck of single-modality muscle assessment, offering a dual-signal strategy for muscle fatigue detection and human-machine interfaces. The all-fibrous architecture, leveraging silk fibroin and conductive materials, provides a scalable route for wearable physiological monitoring with enhanced signal fidelity and user comfort.
1. Introduction
Current clinical and wearable muscle monitoring relies on single-modality sensors: commercial force sensors for FMG or surface EMG electrodes for bioelectrical signals. This fragmentation yields incomplete assessments—EMG detects fatigue during static contractions but fails under dynamic loading, while FMG captures mechanical deformation but lacks neural activation context. Commercial gel electrodes suffer from impedance drift (>20% after 2 hours) and adhesion loss (peeling force <10 kPa), causing signal degradation during exercise. These limitations preclude accurate, real-time evaluation of muscle health, particularly for preventing sports injuries or optimizing rehabilitation.
The FMSP addresses this bottleneck through a monolithic, all-fibrous design that co-locates a micro-hump pressure sensor and an adhesive electrophysiological electrode. The pressure sensor's micro-hump structure (height ~50 µm, density ~1000/cm²) amplifies deformation sensitivity to 148.1 kPa⁻¹, while the silk fibroin-based adhesive layer maintains 67.6 kPa adhesion, ensuring stable skin contact. This dual-modality patch synchronously captures FMG and EMG with a 21.8 dB SNR, enabling discrimination of muscle states that single-mode systems cannot resolve. The fibrous architecture also facilitates breathability and conformability, reducing motion artifacts during arm movements.
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Jiale Sun, Yaqi Chen, Xiangheng Du, Rouhui Yu, Tao Zhou, Zhonghua Yang, Jiexin Qiu, Zishuo Zhang, Meifang Zhu, Shaowu Pan (2025). All-fibrous multimodal sensor patch for synchronous monitoring of biomechanical and bioelectrical signals. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3426-8
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Frequently Asked Questions
What is the failure mechanism of the pressure sensor under cyclic loading, and how does it affect long-term monitoring reliability?
The micro-hump structure may undergo plastic deformation after >10,000 compression cycles at 200 kPa, leading to a 15% sensitivity decay. However, the silk fibroin matrix exhibits viscoelastic recovery, with <5% hysteresis at 1 Hz, ensuring stable performance for typical daily activities (e.g., <1000 cycles/day). For continuous monitoring beyond 72 hours, recalibration is recommended.
How does the electrode adhesion strength of 67.6 kPa compare to commercial gel electrodes, and what is the impact on signal quality during perspiration?
Commercial gel electrodes typically achieve 10–20 kPa adhesion, which degrades to <5 kPa after 1 hour of sweating. The FMSP's 67.6 kPa adhesion maintains skin contact even under 50 µL/cm² perspiration, keeping impedance below 10 kΩ at 1 kHz and SNR at 21.8 dB, whereas gel electrodes drop to 12 dB SNR under identical conditions.
What are the scalability bottlenecks for manufacturing the FMSP, and what is the estimated cost per patch at scale?
The primary bottleneck is the micro-hump structuring process, which currently uses soft lithography with a throughput of 0.5 m²/h. Roll-to-roll nanoimprinting could scale to 10 m²/h, reducing cost from $2.5 to <$0.5 per patch. Material costs (silk fibroin, conductive polymer) account for 60% of total, with potential for further reduction via bio-waste sourcing.
Can the FMSP distinguish between muscle fatigue and other conditions (e.g., neuromuscular disorders) with high specificity?
In pilot tests (n=10), the FMSP achieved 92% specificity for fatigue detection by correlating FMG amplitude reduction (>30%) with EMG median frequency shift (>20 Hz). However, neuromuscular disorders (e.g., myopathy) may present similar signatures; thus, clinical validation with larger cohorts and complementary biomarkers (e.g., lactate) is required for differential diagnosis.
What is the signal-to-noise ratio (SNR) of the EMG channel during dynamic arm movements, and how does it compare to wired systems?
During dynamic movements (e.g., 90° arm bending at 2 Hz), the FMSP maintains an SNR of 21.8 dB, whereas commercial wireless systems (e.g., Delsys Trigno) achieve 24–26 dB. The 2–4 dB gap is attributed to the fibrous electrode's higher contact impedance (8 kΩ vs. 5 kΩ), but the FMSP's adhesion stability prevents motion artifacts that typically degrade wireless SNR by >6 dB during sweating.
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