A multimodal sensing patch for detection of muscle activities

Skeletal muscles have an essential role in human body activities, such as muscle relaxation and contraction. We report three different biocompatible flexible sensors that can provide three different bio-signals, including force-myography (FMG), electromyography (EMG), and muscle stretchability. These three sensors are integrated on a medical tape to form a wearable patch. The FMG sensor uses changes of measuring capacitance to quantify muscle force. Ionic liquid polymers are used as the dielectric material of the capacitive sensor and can offer a high dielectric constant. The unique combination of the ionic liquid polymer and an array of deformable micropyramids allows high sensitivity of 0.41 kPa-1 and a wide linear range up to 70 kPa. The EMG measurement relies on a flexible dry electrode that is formed with a conductive nanocomposite of silver powders and elastomer. The rough surface of the flexible dry electrode improves conformal contact to the human skin, and the high electrical conductance of the nanocomposite allows optimal match between the electrode-skin impedances, thus increasing the signal-to-noise ratio for the EMG measurement. The muscle stretchability measurement works under the principle of piezoresistive strain sensing based on a conductive elastomer that can be attached to the skin. The strain sensor is formed with a mixture of graphene and elastomer. Finally, by combining these three sensing parts on a single patch, it is possible to systematically and accurately monitor muscle activities during different body motions.