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Wavy Nanofiber Yarn Bends and Stretches to Track Muscle Motion

Elastic yarn-type strain sensors provide unparalleled benefits for use in wearable electronics, including fitness and health trackers, human-computer interfaces, and pliable machines.

Wavy Nanofiber Yarn Bends and Stretches to Track Muscle Motion

​​​​​​​Study: Polypyrrole-Coated Graphene Oxide-Doped Polyacrylonitrile Nanofibers for Stretchable Strain Sensors. Image Credit: whitehoune/

In a study published in ACS Applied Nano Materials, a new elastic substrate was developed and used to create a remarkably elastic yarn-type strain detector. The device was made of graphene oxide-loaded polyacrylonitrile nanofilament-covered hybrid yarn, with an on-site polymerized polypyrrole conducting polymer added to the nanofilament surface.

Growing Interest in Flexible Strain Sensors

Elastic wearable resistance strain sensors (RSS) have piqued the attention of many researchers owing to their promising applications in fitness and health tracking, speech identification, human movement capturing, human-computer interactions, and flexible robots.

In principle, an elastic wearable RSS belongs to a class of wearable electronics that can convert a variation in force to a corresponding change in resistance when worn. Wearability is an essential feature of elastic RSS'. Generally, the fabric is a common wearable commodity utilized in the construction of wearable RSS' because of its wearability, elasticity, and comfort.

Bringing the Best Out of Yarn-type Strain Sensors

Compared with fabric strain sensors (FSS), yarn strain sensors (YSS) are readily incorporated into different wearable devices or interwoven into the fabric. Still, FSS created by fabric post-treatment is better suited for standalone usage. As a result, YSSs have substantial benefits for use in wearable technologies.

Given the requirements for the detector's practical usage, it is critical that yarn strain sensors be able to monitor substantial deformations and have outstanding sensory qualities like responsiveness, steady cycling, low hysteresis, and robustness.

Depending on the RSS's detection method, the collective impact of a highly flexible substrate, prudent architectural layout, and strong connection between the flexible substrate and the conducting substance may result in significant deformations and good detection qualities.

Maximizing the Stretchability of a YSS

Buckling processes are beneficial for fabricating flexible equipment from non-flexible substances because imposed tensile stresses can be successfully absorbed by full extension of flexural wrinkles or waves. Application areas for highly flexible strain gauges are broadened as a result.

A straightforward, inexpensive spinning approach for producing a very flexible nanofilament-covered hybrid yarn with a consistent curved architecture and tensile extension of as much as 532 percent has recently been reported.

The flexible fiber in the heart and a significant amount of nanoscale filaments on the flexible fiber exterior make up the super flexible nanofilament-covered hybrid yarn. Flexibility and enhanced nanofilament architecture are advantageous in developing a yarn-type strain sensor with a broad tracking range, great responsiveness, and minimal hysteresis.

When stress is applied, high flexibility gives a wide detection range. A nanofilament architecture with a compact specific size and bigger specific areas may allow substantial contact resistance change.

Existing Research on the Subject

In a previous study, conducting (PVA-co-PE) nanofibrous arrangements were used to create a highly responsive piezoresistive detector with a sensitivity of 2.79 kPa-1, a response latency of 3 ms, and a recovering duration of 10 ms.

Another study described a wearable fabric detector made from sophisticated nanofilament sensing yarns; the detector had a large GFs of 114-720 throughout a huge elongation range of 0.1-220 percent, a wide detection range of around 0.001-5 N, and great endurance over as much as 10,000 cycles.

Based on these studies, it was estimated that an elastic wearable RSS based on a nanofilament-covered hybrid yarn with a curved architecture could have great potential.

Important Findings of the Study

A super flexible yarn-type strain gauge was developed using a graphene oxide loaded polyacrylonitrile (PAN) nanofilament-covered hybrid yarn with a wavy structure as the flexible substrate.

The wavy yarn architecture provided outstanding bendability and stretch sensing characteristics to the yarn-type strain gauge. During stretching, the highest resistance change was found to be 173, and the tracking range reached up to 500 percent. Furthermore, the yarn-type strain gauge demonstrated remarkable bending-detection characteristics, with a resistance change value of 16.6 for a bending degree was 4 cm.

The yarn-type strain gauge demonstrated steady cyclic stability, with just a minor rate of resistance loss detected after 10,000 bending and stretching cycles. 

Notably, the developed yarn-type strain gauge can detect human muscular vibrations and motion, indicating promising applications in wearable electronics.


Zhou, Y., Liao, H. et al. (2022). Polypyrrole-Coated Graphene Oxide-Doped Polyacrylonitrile Nanofibers for Stretchable Strain Sensors. ACS Applied Nano Materials. Available at:

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Shaheer Rehan

Written by

Shaheer Rehan

Shaheer is a graduate of Aerospace Engineering from the Institute of Space Technology, Islamabad. He has carried out research on a wide range of subjects including Aerospace Instruments and Sensors, Computational Dynamics, Aerospace Structures and Materials, Optimization Techniques, Robotics, and Clean Energy. He has been working as a freelance consultant in Aerospace Engineering for the past year. Technical Writing has always been a strong suit of Shaheer's. He has excelled at whatever he has attempted, from winning accolades on the international stage in match competitions to winning local writing competitions. Shaheer loves cars. From following Formula 1 and reading up on automotive journalism to racing in go-karts himself, his life revolves around cars. He is passionate about his sports and makes sure to always spare time for them. Squash, football, cricket, tennis, and racing are the hobbies he loves to spend his time in.


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