Development of wearable dual-mode piezoresistive and piezoelectric sensor for muscle activity monitoring

In 2019, musculoskeletal disorders affected approximately 1.71 billion individuals globally, underscoring the essential role of accurate muscle activity monitoring in diagnosing conditions, guiding rehabilitation, and evaluating treatment effectiveness. The market for muscle activity monitoring, dominated by electromyography (EMG) technologies, was valued at $786.0 million in 2021 and is projected to rise to $1,648.7 million by 2031. Despite EMG’s prominence in capturing detailed neuromuscular data, its vulnerability to interference and demanding electrode placement and skin preparation requirements present notable challenges. Mechanomyography (MMG), which registers muscle contractions' mechanical vibrations, emerges as a less invasive and user-friendly alternative. Low-frequency MMG signals are critical for appraising muscle strength and endurance, while high-frequency signals yield insights into muscle reactivity and contraction dynamics. MMG uniquely measures muscle deformation, providing an avenue to quantify electromechanical delay in muscle activities, and its resistance to electrical noise makes it advantageous for assessing electrically evoked contractions. Yet, MMG’s broader application in clinical and everyday monitoring is impeded by the rigidity, bulkiness, and discomfort associated with current sensors. Traditional MMG technologies, including accelerometers, microphones, and piezoelectric ceramics, struggle with inconsistent placement and capturing a comprehensive frequency range. Consequently, there is a compelling need for MMG sensor innovation to enable ongoing, practical muscle activity monitoring. Our preliminary work indicates that piezoresistive liquid metal composites, which alter resistance under mechanical stress, and piezoelectric polymers that generate electrical charges in response to such stress, are ideally suited for sensing muscle vibration across a spectrum of frequencies. Leveraging our expertise in additive manufacturing, we aim to develop groundbreaking, all-printed, flexible, and wireless MMG sensors that accurately detect human muscle movements across their entire frequency spectrum. This project will unite piezoresistive and piezoelectric materials with advanced flexible electronics, positing that our dual-mode, 3D-printed sensor system will outshine existing MMG technologies in accuracy, sensitivity, and adaptability. The anticipated outcome is the creation of cutting-edge, customizable, wearable MMG devices that can reliably monitor muscle activity, facilitating at-home health management and potentially reducing the economic burden of musculoskeletal care. This aligns with the projected market growth and represents a transformative step in non-invasive muscle function assessment.