A Case for Sweat
Despite its importance, sweat sensing has not become a broadly adopted bodily measurement due to challenges associated with small flow rates and lack of easily worn sweat sensors. This is compounded by the variability of sweating between persons, and the inability to build personalized baselines. We developed a prototype to use hydrogels + optical sensing + computation to enable sweat measurement in a novel, low-cost, and unobtrusive manner.
Our concept:
- Use the capabilities of hydrogels to sense moisture and specific particles, but avoid the limits of low levels of moisture by using the optical properties of expanded hydrogels.
- Optical sensors are increasingly prevalent in wearables (in cameras, heart rate monitors, and ambient light sensors). The hydrogel film acts as an amplification of the presence of sweat useful for the optical sensors.
- In addition, the presence of computation abilities on the device allows the development of baselines with longitudinal sweat data. The device also knows environmental conditions (such as weather), activities (such as whether you are working out), and other context (heart rate, GPS, calendar etc.).
Why add hydrogels to optical sensing? Sweat accumulates on the skin at different times and positions on the skin. Hydrogel provides an amplification layer by increasing the surface area in which to absorb sweat from different points on the skin and bounce light for the optical sensors that would otherwise find it difficult to detect reflectivity off an unknown surface.Optical sensors can’t directly measure specific contents in sweat, such as glucose or ions. Custom hydrogels provide an additional sensor to turn molecular changes into a larger changes that can be detected by optical sensors.
