Liquid Metal Strain Sensors For Pediatric Patients

• Claudia McCormick, Biomedical Engineering, University of Delaware

• Nathan Lazarus, Electrical and Computer Engineering, University of Delaware

Juvenile Arthritis (JIA) affects 1 in every 1,000 children in the US. Current medical devices for JIA patients’ are largely designed for and tested on adults, with slight modifications for pediatrics. These devices fail to adapt to a child’s anatomy, which can lead to misdiagnosis. Stretchable sensors are a common wearable device in biomechanics, used to measure volume expansion and motion changes in patients’ joints. These sensors can be used longitudinally as a child’s body develops. This project aims to understand how scaling down a stretchable strain sensor affects its properties. In this design, four stretchable strain sensors were developed that include an embedded channel of non-toxic liquid metal, eutectic gallium indium (EGaIn). The channel length of these sensors are 50 mm, 40 mm, 30 mm, and 20 mm. To understand how to scale down the sensors, we must understand how different sized channels vary during longitudinal studies. Therefore, the resistance values during loading were recorded up to 120% strain. Scaling down the channels reduced the resistance in each sensor; the 50 mm channel has a resistance of 2.593 ohms and the 20 mm channel has a resistance of 1.455 ohms at 120%. The sensitivity changes during scaling were also analyzed, which is done by calculating the rate of change in resistance of the channel sizes. These calculations showed a noticeable difference; the 40 mm channel had the greatest rate of change in resistance followed by the 50 mm channel, 30 mm channel, and lastly the 20 mm channel. Overall, for the sensors to be used longitudinally, it is important to understand how the properties of the sensor change when it is scaled. Based on these results, we can customize these sensors for a broad range of sizes to adapt to a child’s anatomy.