Arterial Pulse Signal Amplification by Adding a Uniform PDMS Layer to a Pyrex-based Microfluidic Tactile Sensor

Various flexible tactile sensors based on micro/nano-fabrication technology have been developed to amplify a measured pulse signal for accuracy. Yet, these sensors suffer from complicated configurations and fabrication complexity. This work is aimed to investigate the feasibility of amplifying a measured pulse signal by adding a uniform polydimethylsiloxane (PDMS) layer to a Pyrex-based microfluidic tactile sensor. The amplifying mechanism of the proposed approach is revealed by theories on sensor-artery interaction. The pulse signals at the radial artery (RA) deep under the skin and the superficial temporal artery (STA) near the skin of one subject are measured by the sensor first with no uniform layer and then with a set of uniform layers with different mixing ratios of PDMS and thickness. Arterial parameters: elasticity, viscosity and radius, are estimated from the measured pulse signals. As compared to those measured with no uniform layer, a uniform layer generates a pulse signal at transmural pressure ( $\text{P}_{\text {T}}$ ) near zero, greatly amplifies the measured pulse signal at both arteries, causes a moderate increase in estimated arterial elasticity, and has negligible effect on estimated arterial viscosity and radius. Due to their anatomical difference, pulse signal amplification is attributed to improved pulse transmission at tissue-sensor interface at the RA and alleviated suppression of the true pulse signal at the STA. The effect of overlying tissue and a uniform layer on estimated arterial parameters is further discussed. The proposed solution offers a low-cost solution to acquiring an amplified pulse signal at $\text{P}_{\text {T}}$ near zero for CV health assessment.