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The potential of wearable sensors is finally beginning to be realized with recent advancements in computing technology and the miniaturization of electronic components. The continuous measurements captured by wearable sensors are expected to bring big changes to applications ranging from medical diagnostics and personal fitness to gaming and entertainment. However, the most obvious location to place a wearable sensor — on articles of clothing — is noticeably neglected by devices presently on the market. Wristwatches, patches, and arm bands work well for many use cases, but these options are just not as transparent to our daily routines as is wearing a shirt or pair of pants.

A major roadblock preventing the adoption of textile-based sensors is the lack of suitable options in conductive threads. An ideal conductive thread for this purpose would be compatible with the computerized embroidery used in the modern textile industry, and would also be highly conductive, mechanically robust, and inexpensive. Unfortunately, the presently available options just do not check all of these boxes, hence the dearth of clothing-based sensors on the market. A new conductive thread developed by researchers at Imperial College London may soon change all this and open the door to a new world of sensing technologies. Their thread can be incorporated into mass produced textiles using traditional manufacturing methods, is inexpensive, highly conductive, and holds up well to wear and even machine washing.

The team developed a low-cost poly(3,4-ethylenedioxythiophene) polystyrene sulfonate-modified cotton conductive thread that they call PECOTEX. The thread was given its mechanical strength by exploiting a crosslinking reaction using divinyl sulfone. Additionally, the material was found to be more conductive than the silver-based conductive threads that are currently available commercially. With the cost to produce a meter of this thread sitting at about fifteen cents, it is well within range for the mass production of sensor-laden textiles.

This novel material has some very desirable traits, but to prove that it could be useful in real world wearable sensors, the team had to conduct some experiments to put it through its paces. They first created a face mask using traditional, computerized embroidery techniques that contained electrodes made from their conductive thread. These electrodes were designed to monitor the respiration of the wearer. It was found that the mask was capable of identifying several types of breathing patterns, and with very low levels of noise. Of course the team’s innovation is just the novel conductive thread, so there was still a need for external electronic and computing resources to capture and interpret the signals acquired by the embroidered electrodes. A thread alone that is capable of performing all of these tasks has not yet arrived.

A similar experiment was conducted in which the researchers developed a t-shirt with embedded electrodes for measuring heart activity. Characteristic waveforms such as Q, R, and S were clearly identifiable, but the caveat still applies that external equipment was required to obtain these measurements (an ECG machine, in this case), and it was also necessary to apply a conductive gel between the skin and electrode, which eliminates much of the convenience of designing such a sensor into a t-shirt in the first place.

The work done by the team at Imperial College London is an important first step towards the mass production of textile-based sensors. But as the experiments made clear, it is just a first step. Further technological advancements are needed before substantial, obtrusive supporting hardware can be eliminated from these wearable devices, which would then render them wearable in real-world situations.

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