Wearable pressure sensors have demonstrated great potential in detecting pulse pressure waves on the skin for the noninvasive and continuous diagnosis of cardiac conditions. However, difficulties lie in positioning conventional single-point sensors on an invisible arterial line, thereby preventing the detection of adequate signal amplitude for accurate pulse wave analysis. Herein, we introduce the spatiotemporal measurements of arterial pulse waves using wearable active-matrix pressure sensors to obtain optimal pulse waveforms. We fabricate thin-film transistor (TFT) arrays with high yield and uniformity using inkjet printing where array sizes can be customizable and integrate them with highly sensitive piezoresistive sheets. We maximize the pressure sensitivity (16.8 kPa −1 ) and achieve low power consumption (10 1 nW) simultaneously by strategically modulating the TFT operation voltage. The sensor array creates a spatiotemporal pulse wave map on the wrist. The map presents the positional dependence of pulse amplitudes, which allows the positioning of the arterial line to accurately extract the augmentation index, a parameter for assessing arterial stiffness. The device overcomes the positional inaccuracy of conventional single-point sensors, and therefore, it can be used for medical applications such as arterial catheter injection or the diagnosis of cardiovascular disease in daily life.
A flexible, patch-type strain sensor is described for continuous monitoring of pulse waves. The proposed sensor exploits the piezo-resistivity of the conductive polymer, polyaniline (PANI), to detect dynamic volume changes in blood vessels owing to pulse waves. The proposed PANI film was fabricated through electrodeposition, which is considered as a suitable low-cost technique for mass production in the sensor manufacturing industry. Thus, it is prospective for a disposable wearable sensing system solution in remote healthcare applications. Besides, a flexible sensor packaging can be achieved by laminating the PANI films and an ECOFLEX elastomer to the film bandage. The proposed PANI sensor has high sensitivity (gauge factor of 74.28) and linearity (R 2 = 0.99). It also showed a high correlation with commercially available photoplethysmography (PPG) sensor with the small bias and confidence interval to the PPG sensor: bias < 0.1% and confidence interval < 3% for all subjects. Moreover, the proposed PANI sensor was tested for prospective circulatory system-related applications such as measuring heart rate, stiffness index, and pulse transit time. Finally, the proposed study suggests that the proposed PANI sensor is a promising candidate for continuous, long-term, unobtrusive pulse wave monitoring, which can provide real-time insights into an individual's health status.
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