Significant Environmental Factors in the Drift of Electrical Properties in Conductive Nano-Composite Sensors for Biomechanical Motion-Tracking

Wearable nanocomposite stretch sensors are an exciting new development in biomaterials for biomechanical motion-tracking technology, with applications in the treatment of low back pain, knee rehabilitation, fetal movement tracking, and other fields. When strained, the resistance of the low-cost sensors is reduced, enabling human motion to be monitored using a suitable sensor array. However, current sensor technologies have exhibited significant drift, in the form of increased electrical resistance, if left stored in typical room conditions. The purpose of the present work was to evaluate the influence of several environmental factors, including temperature, humidity, oxygen levels, and light exposure, that could impact the change in electrical properties of these sensors. These physiological conditions are present during use of the sensors on human subjects as well as during sensor storage, making it vital to understand their effects on sensor properties. The electromechanical performance of the sensors stored under a range of conditions was monitored over a period of several weeks. The observations obtained indicate that the presence of oxygen and humidity in the environment where the sensors are stored is the primary contributor to drift in the sensor response. Sensors that are kept in de-oxygenated or desiccated environments do not display an increase in electrical resistance over time. This understanding allows for long-term storage of the sensors without degradation. It also assists in identifying the internal processes at work within the nanoparticle-polymer matrix that cause changes in electrical properties.