Skin insertion mechanisms of microneedle-based dry electrodes for physiological signal monitoring

This paper assesses the skin penetration mechanisms and insertion forces of a microneedle-based dry electrode for physiological signal monitoring. Using force-displacement measurements, it is shown that these ultrasharp microneedles, fabricated using a bulk micromachining process and which have tip radii as low as 50 nm, penetrate in-vivo human skin smoothly and without a measurable rupturing action. Skin staining techniques have been used to demonstrate that 95% penetration is achieved at just 20 mN per needle. These very low penetration forces facilitate the design of safe microneedle arrays and remove the requirement for applicator devices. Wearable electrode prototypes have been assembled using these arrays, and electrocardiography (ECG) recordings have been carried out to verify the functionality of the technique.