Directly-Printed Soft Three-Dimensional Electrodes for High-Density Electromyography Recording for Long Term Monitoring of Ischemia and Volumetric Muscle Loss in Murine Models

In modern electromyography (EMG) recording, conventional surface electrodes are commonly used. These electrodes tend to be rigid and do not conformally attach with skin surfaces. Modern research focuses developing electrodes on flexible substrate that have good surface adhesion with biological interfaces. These devices are still limited as the sensing electrodes as they do not conformally contact with the body. Also, the flexible substrates tend to be bulky in size which limits seamless in-situ electrode deployment. The recording signal obtained by surface electrodes are weaker than needle-based electrode that penetrates the epidermis layer of the skin, removing signal resistance. That said, these needle-based electrodes are highly intrusive and cause inflammations when used for a prolong duration. For long-term EMG monitoring of patients with muscular disability, clinical approach favors using surface electrodes which are skin-compatible but lacks signal quality. Herein, we present a substrate-less device that is made of biocompatible soft electrodes for high-density EMG recording. These electrodes are directly printed to form three-dimensional (3D) structure on water-soluble thin film. These electrodes are injected into the skin to remove signal interfaces from epidermis layer, producing high-quality EMG signals that modern surface electrodes fail to capture. Furthermore, the simple and easily manipulatable printing technique allows printing of array of 3D soft electrodes for high-density EMG recording to monitor complex musculoskeletal movement. Furthermore, the soft electrodes have self-repairing property that provides mechanical durability for more advanced and intense movements. Due to its non-invasive property, we are able to detect and monitor the rehabilitative effect of muscle extracellular drugs in murine models of ischemia and volumetric muscle loss. The long-term recording of EMG signal shows the extensiveness of muscle-rehabilitative drugs to treat muscle trauma, providing new possibility for drug screening. The seamless method of device implementation and the significant quality of EMG signals provides interesting prospect for advanced clinical study or human-robot interfaces.