In a recent article published in Microsystems & Nanoengineering, researchers discussed developing and applying multichannel microneedle dry electrode patches for minimally invasive transdermal recording of electrophysiological signals.
These patches offer a novel approach to acquiring physiological electrical signals from various tissue regions, providing valuable spatiotemporal information for organ electrophysiology reconstruction.
a Position of the MMA electrode on a rabbit model when used to record the ECG signal in differential acquisition mode. b ECG signal fragments from 4 channels. c Overlay of ECG signals detected by 31 channels. d PSD plot of the recorded ECG signals. e The changes in the amplitude of the ECG signal at each stage were analyzed. (× indicates that no electrophysiological signal was detected.) f Position of the MMA electrode on a rabbit model when used to record the EMG signal in differential acquisition mode. g EMG signal fragments from 4 channels. h Overlay of EMG signals detected by 31 channels. i PSD plot of the recorded EMG signals. j Changes in the amplitude of the EMG signal at each stage were analyzed (× indicates that no electrophysiological signal was detected). Image Credit: https://www.nature.com/articles/s41378-024-00702-8
Background
Advancements in multichannel electro-physiological signal acquisition technology have enabled the fabrication of microelectrode patterns on planar substrates, allowing for the collection of detailed physiological electrical signals.
The benefits of multichannel signal acquisition are highlighted, particularly in the context of neuromuscular control research and clinical diagnosis of neuromuscular diseases. Single-electrode approaches are limited in capturing the complexity of muscle activation, underscoring the importance of multichannel systems for analyzing activity across individual and multiple muscle groups.
The Current Study
The multichannel microneedle dry electrode patches were fabricated using a dimensionality reduction approach. A flexible circuit board served as the device's substrate, enabling the integration of 32 independent channels on a single patch. Individual electrode functionalization and assembly techniques were employed to ensure the proper functioning of each microneedle for electrophysiological signal sensing.
The microneedles were designed to penetrate the stratum corneum (SC) layer of the skin, allowing direct contact with the interstitial space to reduce skin-electrode impedance and enhance signal acquisition efficiency.
A custom circuit system was developed to support the operation of the multichannel microneedle dry electrode patches. This system facilitated multichannel and high-frequency potentiometric signal acquisition, enabling the collection, storage, and display of electrophysiological signals recorded by the device.
The performance of the multichannel microneedle dry electrode patches was evaluated through experimental studies on a rabbit model. Electrocardiogram (ECG), electromyogram (EMG), and electroencephalogram (EEG) signals were recorded using the patches to assess their signal quality and spatial distribution capabilities. Comparative analyses were conducted to evaluate the efficacy of the patches in recording electrophysiological signals in a minimally invasive manner.
The recorded electrophysiological signals were analyzed using signal processing techniques, including power spectral density analysis and spatial distribution profiling.
The data obtained from the multichannel microneedle dry electrode patches were compared with signals recorded by conventional flat dry electrode arrays to assess signal quality and impedance characteristics. The analysis aimed to demonstrate the superiority of the microneedle array device in transcutaneous signal recording and impedance reduction.
Furthermore, electrical theoretical modeling, COMSOL mechanical simulation, and in vitro, transdermal impedance testing experiments were conducted to validate the beneficial effects of microneedle transdermal penetration on reducing electrode-skin impedance and enhancing the amplitude of collected subcutaneous electrophysiological signals.
Results and Discussion
The multichannel microneedle dry electrode patches successfully recorded high-quality electrophysiological signals, including ECG, EMG, and EEG signals. The recorded signals exhibited distinct characteristic peaks and signal magnitudes comparable to those obtained using conventional flat dry electrode arrays.
Power spectral density analysis of the recorded signals revealed energy distribution predominantly in the lower-frequency range. The multichannel microneedle dry electrode patches demonstrated the capability to capture and analyze signal components across different frequency bands, providing valuable insights into the frequency characteristics of physiological electrical signals. The spectral analysis highlighted the device's ability to accurately capture and represent the temporal features of electrophysiological activities.
Spatial distribution assessments of ECG signals across different electrode channels showcased the synchronous nature of signals recorded by the multichannel patches. Minor variations in signal amplitude and morphology were observed among electrode channels, attributed to differences in electrode attachment and skin contact.
The spatial distribution analysis underscored the uniformity and consistency of signal acquisition across multiple channels, validating the device's ability to capture electrophysiological signals with high spatial resolution.
Continuous monitoring of ECG signals over an extended period demonstrated the stability and reliability of the multichannel microneedle dry electrode patches.
The patches maintained consistent signal quality and amplitude throughout the monitoring duration, indicating their robust performance in long-term signal recording applications. The high mechanical stability of the microneedle structure ensured secure electrode attachment to the skin, minimizing signal instability caused by electrode movement or displacement.
Conclusion
In conclusion, the multichannel microneedle dry electrode patches proved to be effective in transdermal recording of electrophysiological signals, offering a minimally invasive and reliable method for physiological signal acquisition.
The study's findings support the utility of these patches in clinical applications and scientific research, emphasizing their potential for enhancing diagnostic accuracy and providing detailed temporal and spatial information for organ electrophysiology studies.
Journal Reference
Liu, Z., Xu, X., Huang, S. et al. (2024). Multichannel microneedle dry electrode patches for minimally invasive transdermal recording of electrophysiological signals. Microsystems & Nanoengineering 10, 72. https://doi.org/10.1038/s41378-024-00702-8, https://www.nature.com/articles/s41378-024-00702-8