Wearable mask allows vegetative patients to communicate by breathing

Engineers have devised a wearable mask that exploits static electricity and carbon nanotubes to enable patients in intensive care units, in vegetative states or those who otherwise have lost their ability of speech and physical movement to communicate with others via morse code.

A paper describing the device was published in the journal of Nano Research on May 05 at DOI:https://doi.org/10.1007/s12274-022-4339-x.

A range of devices from mobile phones to computer tablets acting as human-machine interfaces (HMIs) have been a godsend for patients who suffer from aphasia—an illness that causes them to lose their language ability—and others who have had their speaking ability curtailed. But most of these involve the replacement of speech with some form of physical movement such as pointing or pressing keys. For those who have not just lost their speech ability but also capacity for physical movement, these devices are not much help.

In recent years however, triboelectric nanogenerators, or “TENGs”, in HMI applications. Triboelectricity occurs when certain materials become electrically charges when they come into contact with another material. Giving a comb a static electric charge when drawing it through hair or rubbing a balloon until it attracts bits of paper are both common examples of the triboelectric effect.

In HMIs, TENGs act as sensors that are self-powered (by this same triboelectricity) extremely light weight, low cost and are easy to fabricate. They can convert biomechanical energy from various types of human motion into electricity. Of particular interest have been TENGs made of materials that generate electric outputs when driven by breathing air flow.

These breath-driven TENGs have so far been deployed for breathing monitoring, as cardiac arrest or sleep apnoea alarms, and to control electrical appliances.

“We wondered if breath-driven TENGs could do something even more impressive,” said Yanchao Mao—one of the authors of the paper and a researcher with the School of Physics and Microelectronics at Zhengzhou University—describing what attracted them to the technology.

“Even vegetative patients often still have the ability to breath on their own,” he added. “So could the diverse characteristics of breathing airflow such as intensity, length, frequency, and rhythm could be used to carry subjective language information of a human?”

The engineers constructed a breath-driven TENG that acts as a HMI sensor for language expression through human breathing, and that is integrated in a mask. The device is also fabricated via 3D printing resin and makes use of very thin paper (just 120 microns) printed with carbon nanotubes (CNT). The CNT-printed paper is fixed in middle of a channel by a tiny copper wire, allowing its another end to freely oscillate. When a person is wearing the mask and airflow from breathing flows crosses this channel, the CNT-printed paper oscillates like a flag in the breeze. The oscillation generates periodic contact and then separation with the resin channel wall. Triboelectric charges are produced by this contact and separation owing to different electron attracting abilities between the CNTs and resin.

“The triboelectric charges act as signals that can encode human subjective information in much the same way that electric telegraphs transmitted Morse code in the 19th Century,” added Dr Mao. “In fact, in exactly the same way.”

The researchers integrated the TENG-mask device with a voltage comparator, a wireless transmitter, a processor, and terminal displays to constitute a breathing-based language expressing system.  By using Morse code as the language expressing protocol, this system can extract subjective information from human breathing behaviors and output corresponding language text on a screen that is then readable by others.   

The voltage achieved by the TENG and the length of time of a particular electric signal constrain the letter that is communicated. But too high a voltage threshold would require users to breath too hard, reducing comfort, while too low a voltage introduces potential error in recognition of the letter attempting to be expressed. The time threshold involves a similar challenge: a long-time interval obviously slows down communication, but too short a time interval forces patients to breath too quickly. An optimal time interval and voltage for a patient thus involves a compromise between breathing comfort and accuracy.

But thankfully, the necessary effort in terms of time interval and voltage varies depending on the patient involved (as everyone breaths slightly differently). And so the engineers are able to make personalized adjustments to the threshold values to maximise comfort while permitting communications accuracy. In tests, they hit a 93.33 percent accuracy rate, which is enough to realize fluent language expression.

Having proven the viability of the device and communications technique, the engineers now want to fine-tune it and take next steps toward commercial viability.

The paper is also available on SciOpen (https://www.sciopen.com/home) by Tsinghua University Press.

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About Nano Research 

Nano Research is a peer-reviewed, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society. It offers readers an attractive mix of authoritative and comprehensive reviews and original cutting-edge research papers. After more than 10 years of development, it has become one of the most influential academic journals in the nano field. Rapid review to ensure quick publication is a key feature of Nano Research. In 2020 InCites Journal Citation Reports, Nano Research has an Impact Factor of 8.897 (8.696, 5 years), the total cites reached 23150, and the number of highly cited papers reached 129, ranked among the top 2.5% of over 9000 academic journals, ranking first in China’s international academic journals.

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