Dry electrodes offer an accessible continuous acquisition of biopotential signals as part of current in-home monitoring systems but often face challenges of high-contact impedance that results in poor signal quality. The performance of dry electrodes could be affected by electrode material and skin hydration. Herein, we investigate these dependencies using a circuit skin-electrode interface model, varying material and hydration in controlled benchtop experiments on a biomimetic skin phantom simulating dry and hydrated skin. Results of the model demonstrate the contribution of the individual components in the circuit to total impedance and assist in understanding the role of electrode material in the mechanistic principle of dry electrodes. Validation was performed by conducting in vivo skin-electrode contact impedance measurements across ten normative human subjects. Further, the impact of the electrode on biopotential signal quality was evaluated by demonstrating an ability to capture clinically relevant electrocardiogram signals by using dry electrodes integrated into a toilet seat cardiovascular monitoring system. Titanium electrodes resulted in better signal quality than stainless steel electrodes. Results suggest that relative permittivity of native oxide of electrode material come into contact with the skin contributes to the interface impedance, and can lead to enhancement in the capacitive coupling of biopotential signals, especially in dry skin individuals.
Here we present a 3D-printed, wirelessly controlled microsystem for drug delivery, comprising a refillable microreservoir and a phase-change peristaltic micropump. The micropump structure was inkjet-printed on the back of a printed circuit board around a catheter microtubing. The enclosure of the microsystem was fabricated using stereolithography 3D printing, with an embedded microreservoir structure and integrated micropump. In one configuration, the microsystem was optimized for murine inner ear drug delivery with an overall size of 19 × 13 × 3 mm3. Benchtop results confirmed the performance of the device for reliable drug delivery. The suitability of the device for long-term subcutaneous implantation was confirmed with favorable results of implantation of a microsystem in a mouse for six months. The drug delivery was evaluated in vivo by implanting four different microsystems in four mice, while the outlet microtubing was implanted into the round window membrane niche for infusion of a known ototoxic compound (sodium salicylate) at 50 nL/min for 20 min. Real-time shifts in distortion product otoacoustic emission thresholds and amplitudes were measured during the infusion, demonstrating similar results with syringe pump infusion. Although demonstrated for one application, this low-cost design and fabrication methodology is scalable for use in larger animals and humans for different clinical applications/delivery sites.
In-home physiological monitoring devices enable the monitoring of vital health parameters and can facilitate health recovery. The current state of the art is inclined towards non-invasive technologies such as wearable mobile devices and patch-based sensors. In this chapter, we provide an overview of progress made in the field of dry electrodes for biopotential acquisition, based on their mechanistic principles, materials, testing methods, and effectiveness in a real-world setting. Important parameters affecting the dry electrode performance such as the area, material, applied pressure and skin hydration are discussed. Traditionally, the development and testing of these wearable electrodes are conducted empirically, in vivo on human skin. However, due to the inter- and intra-subject variability in human skin properties, reliability, repeatability, and the efficacy of the device under investigation cannot be evaluated. Thus a review is presented about the skin phantoms used to simulate the electrical properties of the skin, which has the potential to serve as a robust method to test the functionality of current and future electrodes. This retrospective overview provides researchers with an understanding of the mechanistic principle of biopotential electrodes and the crucial factors that affect electrode performance, thus facilitating wearable electrode development.
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