(K-437) Soft device for simultaneous measurements of contractility and electrophysiology of neuromuscular tissue

Friday, October 13, 2023

9:30 AM – 10:30 AM PDT

Location: Exhibit Hall - Row K - Poster # 437

Presenting Author(s)

PO

Poppy Oldroyd

PhD Student
Electrical Engineering Division, Department of Engineering, University of Cambridge
Cambridge, England, United Kingdom

Co-Author(s)

SO

Sophie Oldroyd

PhD Student
Department of Chemical Engineering and Biotechnology, Philippa Fawcett Drive, University of Cambridge, United States

Primary Investigator(s)

GM

George Malliaras

Professor
Electrical Engineering Division, Department of Engineering, University of Cambridge, United States

Last Author(s)

RO

Róisín Owens

Professor
Department of Chemical Engineering and Biotechnology, Philippa Fawcett Drive, University of Cambridge, United States

Introduction:: 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 tract, can undergo significant conformational changes when physiologically active. Conventional inextensible devices cannot capture the dynamic relationship between electrophysiological and mechanical responses on these tissues. This study introduces electrodes made from poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and polydimethylsiloxane (PDMS) that enable simultaneous monitoring of electrical and mechanical responses. The PDMS substrate and insulation layers conform to tissue surfaces while maintaining contact during muscle contractions and relaxations associated with propulsive movements within the gastrointestinal tract. Thus, the presented PEDOT:PSS composition allows for accurate recording of electrical activity while exhibiting sensitivity to mechanical changes. In contrast to traditional electrodes requiring cleanroom facilities and lithographic techniques, this work utilizes shadow masks and solution-processable spin coating techniques, offering a faster and simpler fabrication process. Tested on ex vivo mouse and human gastrointestinal tissues, which can experience up to 40% strain, the device successfully monitored muscle electrical activity and motility. These stretchable bimodal devices hold great potential for studying correlations between electrophysiological and mechanical responses, thereby significantly contributing to neurology, gastroenterology, and pharmacology research.

Materials and Methods::

Electrodes were fabricated using spin coating techniques with 20 µm layers of PDMS as the substrate and insulation. Macro-scale conductive PEDOT:PSS tracks were deposited between the PDMS layers using a laser cut shadow mask (Figure 1A). Additives, including 4 wt% PEG, 1 wt% Capstone, and 5 wt% GOPS, were incorporated with PEDOT:PSS to optimize deposition, conductivity, and stability. The PDMS was oxygen treated before deposition. The mechanical and electrical properties of the device were characterized by strain and force curves, as well as current measurements under a constant chronoamperometric voltage, converted to resistance (Figure 1C-D). A strain gauge layout (Figure 1A) with tunable PEG concentration allowed for sensitivity adjustments to specific tissues (Figure 1B). Ex vivo experiments were conducted using an organ bath setup (Figure 2A), where the device was applied to mouse small intestine or human stomach tissue. Resistance changes during forced movements were recorded using a potentiostat, and calibration curves were used to translate resistances into strain measurements (Figure 2B). The accuracy of resistance data was confirmed by correlating it with measurements from an internal pressure transducer. For simultaneous electrical and mechanical recordings, the PDMS insulation layer covering the electrodes was removed, enabling direct contact with the outer muscularis layer of the small intestine. An electrophysiological system was connected in parallel to the potentiostat, and the electrophysiology signal associated with forced contraction was isolated by subtracting the strain gauge-induced resistance change.

Results, Conclusions, and Discussions::

During induced propulsive movements through the mouse small intestine, the device recorded electrophysiological voltage amplitude changes of 2.1 to 3.5 times, depending on the strength of the contraction (Figure 2C). As well as resistance changes due to mechanical propulsion. To confirm that the signal was not a result of movement artifacts, a non-living tissue segment was subjected to forced distension, which did not elicit any electrical signal related to electrophysiology. These findings demonstrate the device's capability to effectively monitor electrical and mechanical activity during contractions. Further validation of the device was conducted using explanted human stomach tissue. The device was securely pinned onto the muscle layer after removing the mucosal layer, allowing the tissue to undergo spontaneous contractions. The device successfully recorded electrophysiological voltage changes associated with these contractions, as depicted by peaks in voltage magnitude (Figure 2D). The observed signals from the human stomach exhibited similar characteristics to those observed when monitoring the mouse small intestine, highlighting the variety of ex vivo applications of the devices and ability to detect signals in relatively thick (human) and thin (mouse) tissues.

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. The simple fabrication method enables the production of conformable electrodes that maintain good contact with tissues and organs during large contraction cycles. The device's ability to detect small strain changes and record large-scale muscle signals makes it an excellent tool for monitoring tissue health and biological activity. 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 insights into complex disorders like irritable bowel syndrome and gastroparesis. Furthermore, this device has broad applications, offering an opportunity to correlate electrophysiological activity with mechanical responses.

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