ABS 017: Thin Film Electrodes Produce Robust Signal to Advance Musculoskeletal Research

Tia Gandhi ¹, Timauri-Lee Carby ², Alessa Elkareh ², Mateo Gonzales ³ , Daniel Gutierrez ¹, Thomas Xie ³ , Yifan Zhou ⁴ , Dr. Scott Keene ³

¹ Rice University Department of Bioengineering
² Rice University Department of Electrical Engineering
³ Rice University Department of Materials Science and NanoEngineering
⁴ Rice University Department of Chemical and Biomolecular Engineering

The Van Wickle Journal (2026) Volume 2, ABS017

Introduction: Musculoskeletal conditions, including arthritis, are the leading cause of disability in the United States and require accurate characterization of fine muscle activity for applications in rehabilitation, disease monitoring, prosthetics, and kinematic analysis. Conventional surface electromyography (sEMG) electrodes rely on rigid structures that suffer from poor biological interfacing, discomfort during movement, and motion artifacts that compromise signal fidelity. To address these limitations, Team Flex Transistor developed the Flex Electrode, a bendable organic electrochemical transistor (OECT)-inspired sEMG device integrating material science, electrical engineering, and bioengineering principles. The system combines a bendable polyimide (PI) substrate, gold electrodes, and the conductive polymer PEDOT:PSS [poly(2,3-dihydrothieno-1,4-dioxin) - poly(styrenesulfonate)] to create a conformal skin interface capable of capturing fine muscle activity with improved signal-to-noise ratio (SNR). The Flex Electrode interfaces with a custom printed circuit board (PCB) that performs current-to-voltage conversion, amplification, filtering, and scaling for compatibility with standard data acquisition systems.

Each independently addressable OECT channel was fabricated on a glass slide using patterned gold electrodes, thermal evaporation of titanium and gold layers, and spin-coated PEDOT:PSS bridging. The transistor-like geometry amplified weak ionic biopotentials into stronger electronic outputs prior to downstream processing. Benchtop validation used a source measurement unit (SMU) to characterize device behavior. Current-voltage sweeps demonstrated curved saturation and linear regions consistent with transistor-like operation and ohmic contact formation. Human testing with fist-closing and index-pointing tasks through the Flex Electrode, PCB, and data acquisition unit (DAQ) demonstrated an average SNR of approximately 10 dB after digital post-processing, exceeding the approximately 8 dB performance of standard electrodes, indicating capability for both gross and fine motor signal acquisition. The Flex Ecosystem provides a compact, biocompatible, and motion-adaptive alternative to conventional sEMG technologies with broad applications in musculoskeletal research and clinical monitoring.

Methods: The Flex Electrode was fabricated on a 75.0 × 27.3 mm glass slide using polyimide (PI) substrate, patterned gold, and PEDOT:PSS conductive channels. Electrode patterns were created using Cricut-produced PI masking tapes, followed by thermal evaporation of a 5 nm titanium adhesion layer and 100 nm gold layer. PEDOT:PSS was spin-coated between electrode pairs to form independently addressable OECT channels with a width-to-length ratio of 2.9 to promote transconductance. EMG saline gel was the interface between the device and skin after electrodes were peeled from glass and cut to separate pairs. Signals were routed through zero insertion force (ZIF) connectors to a custom PCB designed for current-to-voltage conversion, amplification, bandpass filtering (19.42–159.24 Hz), and scaling to ±5 mV for DAQ compatibility. Benchtop testing utilized a SMU to sweep gate-source voltage using phosphate-buffered saline, followed by EMG file-input and human testing with Python post-processing.

Results: Electrical characterization demonstrated transistor behavior consistent with OECT operation, including distinct linear and saturation regions during gate-source voltage sweeps. These responses supported effective semiconductor-metal interfacing between PEDOT:PSS and the gold electrodes. Signal conditioning through the PCB amplified and filtered biologically relevant EMG frequencies while maintaining DAQ compatibility. Testing with prerecorded EMG signals followed by digital post-processing produced an average SNR of approximately 10 dB, exceeding the approximately 8 dB measured using conventional electrodes. Human testing further demonstrated stable signal acquisition during fist-closing and index-finger pointing tasks, supporting the ability to capture both gross and fine motor activity during motion.

Discussion: The Flex Electrode demonstrates the potential of bendable bioelectronics to improve sEMG acquisition in applications requiring precise muscle characterization. By combining bendable substrates, conductive polymers, and signal-processing electronics, the system addresses limitations associated with rigid electrodes, particularly motion-related noise and limited adaptability to skin. The reduced interelectrode spacing and conformal design improves measurements from dense muscle regions that are difficult to isolate using standard systems. Benchtop and human testing suggest the platform can support robust acquisition during movement. Future work will focus on expanded human validation, wearability studies, and integration with machine learning tools for musculoskeletal research.