(312a) Invited: Wearable Fabric Sensor for Determination of Sodium Ions in Sweat

A study done on college athletes showed only 34% were properly hydrated. Failure to keep the body properly hydrated can lead to a variety of health complications, including ulcers, high blood pressure, and kidney disease. In addition to health hazards, improper hydration can significantly hinder athlete performance. The majority of endurance athletes interviewed listed hydration as one of their top concerns during a race. Currently available monitors such as Garmin, Fitbit, and the Apple Watch log miles/pace/calories burned by measuring heart rate at the wrist, and some add-on devices track heart rate. However, in order to obtain physiological information, such as dehydration or lactic acid levels, athletes must use point-of-care devices (e.g. Lactate Plus) that often require a finger prick blood draw from the athlete. The trend of monitoring fitness and physiological statistics via smart apparel and accessories has seen a steady growth over the past decade and is predicted to continue to increase.

We have developed flexible, lightweight fabric materials that can selectively determine physiological information from sweat forming on the surface of the skin. The technology is the first lightweight fabric sensor to provide real-time information regarding hydration levels during exercise or training through selective determination of sodium ion levels. As sodium ion levels in the sweat increase, athletes must replace these electrolytes to remain hydrated. These dehydration patterns are unique and vary based on diet, weather conditions, and human physiological cycles. Therefore, there is not a “one size fits all” hydration program. The ability to monitor an individual’s hydration parameters is unique to the our sensor and gives it a competitive advantage over “sweat monitors” that monitor water lost or “water timers” that remind the athlete to drink water every 20 minutes.

In spite of advances made towards the detection of biomarkers in sweat, there is no sensor capable of long-term detection in constricted or load-bearing applications where other flexible plastic sensors might cause discomfort. We have developed a flexible mat sensor made of multiwall functionalized nylon-6 material. The material is also functionalized with a molecule that reacts with sodium ions. As the sensor reacts with sodium ions in sweat, a complex-molecule forms which impedes the flow of an electrical current. This change in the current flow can allow the sensor to quantify the amount of sodium present. The proposed sensor will be measure overall sodium ion concentration and changes in sodium ion concentration, so that all wearers will be able to determine if they are suffering from an electrolyte imbalance, regardless of starting point.

In this talk, we will discuss the ability of our sensor to withstand stress, strain, and bending. Uniaxial and biaxial tensile testing was performed on both neat nylon and the functionalized sensor material. Preliminary results show that the addition of nanotubes into the nylon matrix increase strength, without sacrificing stretch. Subject testing of our prototype sensor on 30-50 participants will also be discussed.