A Stretchable Microneedle Electrode Array for Stimulating and Measuring Intramuscular Electromyographic Activity.

Area of Science:

• Biomedical Engineering
• Neuroscience
• Materials Science

Background:

• Accurate muscle electrical activity measurement is crucial for diagnostics and prosthetics.
• Existing electrodes often lack the flexibility and resolution for dynamic, large-area tissue monitoring.
• Need for advanced wearable sensors capable of in vivo stimulation and recording.

Purpose of the Study:

• To develop and characterize a stretchable microneedle electrode array (sMEA) for multi-site muscle stimulation and electrophysiological recording.
• To evaluate the sMEA's performance under physiological strain and its biocompatibility in vivo.
• To demonstrate the sMEA's utility in measuring electromyographic (EMG) signals and stimulating muscle.

Main Methods:

• Fabrication of sMEA using a polydimethylsiloxane (PDMS) substrate, conductive-PDMS traces, and stainless-steel microneedles.
• Mechanical testing to assess resistance under tensile strain (~63%).
• In vivo implantation in feline muscle to evaluate biocompatibility, EMG signal acquisition, and stimulation capabilities.

Main Results:

• The sMEA maintained low resistance (<10 $\Omega$) even at ~63% strain, accommodating full physiological motion.
• The device demonstrated excellent cytocompatibility for at least 28 days in vivo.
• Clear compound motor unit action potentials were recorded, and stable electrical stimulation was achieved in moving muscle.

Conclusions:

• The developed sMEA offers high signal fidelity and spatial resolution comparable to intramuscular electrodes over a large area.
• The stretchable and biocompatible nature of the sMEA enables stable, long-term in vivo muscle monitoring and stimulation.
• This technology holds significant potential for wearable sensors, neuroprostheses, and advanced electrophysiological studies in both animals and humans.