Applications of biocompatible micro-pyramid array dry electrodes in bioelectric potentials measurement in wearable healthcare devices

Abstract

Thin dry electrodes are promising components in wearable healthcare devices. Assessing the condition of the human body by monitoring biopotentials facilitates the early diagnosis of diseases as well as their prevention, treatment, and therapy. Existing clinical-use electrodes have limited wearable-device usage because they use gels, require preparation steps, and are uncomfortable to wear. While dry electrodes can improve these issues and have demonstrated performance on par with gel-based electrodes, providing advantages in mobile and wearable applications

the materials and fabrication methods used are not yet at the level of disposable gel electrodes for low-cost mass manufacturing and wide adoption. The market for wearable medical devices has thrived in the last few years, providing people a convenient way to monitor their health condition or track their physical activity. Elevated blood pressure (BP) affects a large amount of the adult population worldwide, and it is a risk factor for cardiovascular complications, which are among the leading causes of death in recent years. BP measurement has become one of the most anticipated functions on wearable devices, but it is difficult to integrate in the devices due to the need for inflatable cuffs that would hinder the search for a small size in wearable devices. In clinical environments, arterial lines are used to monitor blood pressure of patients in critical care. However, such devices involve risk of complications such as ischemia and infection. The placement of these devices is also challenging in very small or very ill patients, such as in neonatal or pediatric intensive care units. Here, a low-cost manufacturing process for thin dry electrodes with a conductive micro-pyramidal array is presented for large-scale on-skin wearable applications. The electrode is fabricated using micromolding techniques in conjunction with solution processes in order to guarantee ease of fabrication, high device yield, and the possibility of mass production compatible with current semiconductor production processes. Fabricated using a conductive paste and an epoxy resin that are both biocompatible, the developed micro-pyramidal array electrode operates in a conformal, non-invasive manner, with low skin irritation, which ensures improved comfort for brief or extended use. The operation of the developed electrode was examined by analyzing electrode-skin-electrode impedance, electroencephalography, electrocardiography, and electromyography signals and comparing them with those measured simultaneously using gel electrodes. The second part of this thesis report further advancements in the context of BP and other cardiovascular measurements. Cuff-less BP measurement is commonly based on the measurement of pulse transit time (PTT) between an electrocardiogram (ECG) and a photoplethysmogram (PPG) in order to acquire proximal and peripheral blood pulse signals. First, a small low-power circuit is presented, able to acquire ECG and Red/IR PPG at an extremely low-power consumption. This component is able to measure the biosignals for extended periods of time on a small sized battery, in a small space. The last part of the thesis focuses on the algorithms used to calculate the derived values (such as heart rate, oxygen saturation or blood pressure) from measured ECG and PPG signals. These calculations are done on a smart device connected wirelessly to the sensor, and able to show all the monitored values in real time.