Stretchable knee-wear wearable offers insights into improving e-textiles for healthcare – ScienceDaily

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This continuous and long-term monitoring is possible thanks to analysis systems that are portable or non-portable. Non-portable systems are reliable, but require a laboratory environment and trained individuals, and are therefore not practical for daily use. On the other hand, portable systems are portable, cheaper, and much easier to use. Unfortunately, typical wearable sensors tend to be inflexible and bulky.

A relatively new player in the field of wearable systems are wearable devices made of conductive fabric (CF), which are soft, lightweight, malleable, and non-invasive. These sensors are comfortable and suitable for long-term monitoring. However, most CF-based wearables become error-prone if they are displaced from their intended location and rely on external components that restrict the sensors’ sensitivity and working range.

To overcome these limitations, a research team created a wearable device with a high degree of design and functional freedom. Associate Professor Low Hong Yee and colleagues from the Singapore University of Technology and Design (SUTD) collaborated with Dr. Tan Ngiap Chuan of SingHealth Polyclinics and published their research paper, ‘All-knitted and integrated soft wearable with high elasticity and sensitivity for continuous monitoring of human joint movement’ in Advanced Sanitary Materials.

According to Associate Professor Low, his key considerations when designing the wearable were the accuracy and reliability of the sensor data and making the sensor dependent on as few external components as possible. The result was a highly elastic, fully functional sensing circuit made from a single fabric. Because the knee joint is important for lower extremity mobility, the portable device was designed for the knee.

To develop this single-fabric circuit, the team mechanically coupled an electrically conductive thread with a highly elastic dielectric thread in various stitch patterns. Dimensions were customized according to the subject’s leg. The functional components—sensors, interconnects, and resistors—formed a stretchable circuitry in the fully woven wearable that enabled real-time data collection.

However, it is difficult to unite sensors, interconnects, and resistors into a single stretchable fabric. Associate Professor Low mentioned that “synergizing yarns with different electrical and mechanical properties to achieve high signal sensitivity and high stretchability” was challenging, as the desired properties for each component were very different.

Sensors need to produce a large change in resistance to improve sensitivity, while interconnects and resistors need fixed resistances of the highest and lowest values, respectively. As such, the researchers optimized the yarn composition and stitch type for each component before connecting the functional circuitry to a circuit board contained in a pocket of the handheld device, enabling real-time wireless data transmission.

With a soft knee wearable developed, its components functional and data transmission possible, it was time to test the performance of the wearable. The team tested the wearable device through extension-flexion activities, walking, jogging, and stair climbing. Subjects wore the knee along with reflective markers that were detected by a motion capture system, allowing comparison between sensor data and actual joint movement.

Sensor response time was less than 90 milliseconds for step input, which is fast enough to monitor human movements included in the study. Furthermore, the smallest change in joint angle that the sensors could detect was 0.12 degrees. The sensor data showed a strong correlation with the joint movement data acquired from the motion capture system, demonstrating the reliability of the sensor data.

The potential impact of such a device in the medical field is enormous. Continuous long-term monitoring of joint movement is important to keep track of mobility-related conditions. Often people ignore the first signs of decreased mobility as they are not considered severe enough to seek help. Wearable technology solves this problem by evaluating a user’s mobility directly in real time.

Embedding easy-to-use sensor circuitry in soft, comfortable fabric can increase public adoption of wearable technology, especially among athletes and the elderly. Data can be collected in real time and translated into indicators that can detect decreased mobility. When signs of decreased mobility are found, preventive care, prognosis, and management of the medical condition can be provided.

Building on this work, the team intends to study the effect of sweat and humidity on sensor signals and expand the research to include subjects from both healthy and unhealthy populations in the future. “We have started work to extend the wearable device to special user groups and to monitor other joints in the body, such as the shoulder,” said Associate Professor Low. “We are also looking to secure an incubation fund to explore the commercialization potential of the wearable device.”

Video: https://youtu.be/KPlSPtDVs2k