Researchers develop paper fabricated pressure sensors for use in healthcare for precise pressure measurement

The Indian Institute of Science (IISc) researchers from the Centre for Nano Science and Engineering (CeNSE) have developed fabricated pressure sensors that use paper as the medium which find applications in healthcare. This is because medical treatments depend considerably on accurate and precise measurement of pressure.

Now flexible and wearable pressure sensors are typically fabricated using petroleum-based polymers. The solid waste generated from using such non-biodegradable plastics is harmful for the environment. To combat this, researchers fabricated pressure sensors that use paper as the medium.

A pressure sensor detects physical pressure and converts it into an electrical signal that is displayed in the form of a number indicative of its magnitude. Nowadays, paper-based electronic devices are gaining greater attention owing to their natural biodegradability, excellent flexibility, porous fibrous structure, light weight, and low cost. However, paper-based sensors developed so far have certain disadvantages. The research findings have been published in ACS Sustainable Chemistry & Engineering, 2022.

“In any sensor, there is always a trade-off between sensitivity and dynamic range. We want to have high sensitivity. Sensitivity is essentially a measure of the smallest entity (amount of pressure) that we can detect. And we want to sense that quantity over an extensive range,” says Navakanta Bhat, Professor at the Centre for Nano Science and Engineering (CeNSE) and corresponding author of the paper.

It was Prof Bhat’s team which proposed a design for the paper sensor that, by feature of its structure and multi layering aspects, achieves high sensitivity and can detect a broad range of pressures calculated as 0-120 kPa with a response time of 1 millisecond.

According to Neha Sakhuja, a former PhD student at CeNSE and the first author of the paper, the sensor is made of plain and corrugated cellulose papers coated with tin-monosulfide (SnS) stacked alternatively to form a multi-layered architecture. SnS is a semiconductor that conducts electricity under specific conditions. Paper in itself is an insulator.

The major challenge was choosing an appropriate 3D device structure and material to give conductive properties to paper. Now this can be used as wearable paper pressure sensor, she added.

“When pressure is applied on the sensor’s surface, the air gaps between the paper layers decrease, increasing the contact area between these layers. Higher contact area leads to better electrical conductivity. On releasing the pressure, the air gaps increase again, thus decreasing the electrical conduction. This modulation of the electrical conductivity drives the sensing mechanism of the paper sensor. Our key contribution is the simplicity of the device. It is like creating paper origami,” stated Prof. Bhat.

The sensor shows promise in being developed into a flexible and wearable electronic device, especially in the healthcare sector. For example, the research team mounted it onto a human cheek to investigate the motion involved in chewing, strapped it to an arm to monitor muscle contraction, and around fingers to track their tapping. The team even designed a numeric, foldable keypad constructed using the in-house paper-based pressure sensor to demonstrate the device’s usability, he noted.

“The future applications of this device are limited only by our imagination. We would also like to work on increasing the stability and durability of these sensors and possibly collaborate with industries to manufacture them in large numbers, said Prof. Bhat.

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