Soft Device for Simultaneous Measurements of Contractility and Electrophysiology of Neuromuscular Tissue

Biological tissues serve as rich sources of electrical and mechanical signals that offer valuable insights into their function, disease conditions, and metabolic activity. However, certain neuromuscular tissues, such as those in the gastrointestinal (GI) tract, can undergo significant conformational changes when physiologically active. These tissues have received limited research attention due to challenges faced by rigid probes in conforming to their dynamic surface, which can experience strain levels of up to 40%. Conventional inextensible devices cannot capture the relationship between electrophysiological and mechanical responses of these tissues. This hinders the acquisition of crucial neuromechanical information in the gastrointestinal system, essential for understanding GI homeostasis and the connections between the enteric and central nervous systems.<br/>To address these challenges, this study introduces bimodal electrodes made from poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and polydimethylsiloxane (PDMS) that enable simultaneous monitoring of electrical and mechanical responses of gut tissue. PEDOT:PSS demonstrates long-term stability and outperforms metal electrodes that delaminate, crack, and degrade over time. PDMS, used as a substrate and insulation material, shows promise due to its superior intrinsic strain properties surpassing popular polymers like polyimide and parylene C.<br/>In contrast to traditional electrode fabrication methods, this work utilizes shadow masks and solution-processable spin coating techniques, resulting in a faster and simpler fabrication process. To optimize the spin coating of PEDOT:PSS on PDMS, Capstone FS-300 was added for stability and film homogeneity. Polyethylene glycol (PEG) was incorporated to maintain electrical conductivity during stretch, enabling mechanical monitoring. The PEG concentration can be adjusted to tune the device's electrical sensitivity to strain changes. A low PEG concentration improves sensitivity to smaller strains for measuring spontaneous contractions, while a higher concentration makes the device strain insensitive for pure electrophysiology data. The PDMS-PEDOT:PSS-PDMS devices exhibit reduced delamination and cracking during accelerated aging compared to metal-based and parylene C devices.<br/>The device was validated on <i>ex vivo</i> mouse and human gastrointestinal tissues. The device successfully monitored muscle electrical activity and motility. During induced propulsive movements through the mouse small intestine, the device recorded electrophysiological voltage amplitude changes ranging from 2.1 to 3.5 times, corresponding to the strength of the contraction. These voltage changes were temporally correlated with resistance variations resulting from mechanical propulsion. The signals observed from the human stomach were similar in nature to those observed when monitoring the mouse small intestine, highlighting the variety of <i>ex vivo</i> applications of the devices and ability to detect signals in relatively thick (human) and thin (mouse) tissues. Furthermore, the ability to wrap the electrode system around a small diameter tissue as well as affixing it to a flat surface demonstrates the adaptability of device. <br/>In conclusion, the presented bimodal tissue monitoring device integrates soft, flexible, and stretchable electrodes using thin PDMS and PEDOT:PSS layers doped with PEG and Capstone. Its electrical sensitivity to strain can be finely tuned for specific applications by adjusting the dopants in the PEDOT:PSS. The device's flexibility and stretchability make it suitable for monitoring gastrointestinal function, including motility and electrical activity, as demonstrated on mouse small intestine and human stomach tissue. It has the potential to provide clinical insights into complex disorders like irritable bowel syndrome and gastroparesis.