Abstract
In this paper, we present a disposable, colorimetric, user-friendly and mass-customizable dermal patch for chronological collection and discrete real-time in situ measurement of sweat secretion over a small area of skin. The patch consists of a laminated filter paper patterned into radially arranged channels/fingers with water-activated dyes at their tips. As channels are filled during perspiration, their tips change color once fully saturated, providing easily identifiable levels of water loss which in turn can be mapped to personal dehydration levels. The patch can be manufactured at low cost in a variety of sizes to allow hydration monitoring for individuals participating in activities under different conditions (intensity, temperature, humidity, etc.). Furthermore, we describe an analytical model that enables mass customization of such a flexible wearable system accommodating a broad range of sweat rates and volumes to generate patch designs that are personalized to an individual’s sweat rate, desired time of usage, and the temporal resolution of the required feedback. As a proof-of-concept demonstration, we characterized laser-fabricated patches that cover (7 cm × 5 cm) area of skin having various wicking materials, thicknesses (180–540 µm), and pore sizes (3–11 µm). Tests were conducted at various flow rates simulating different sweating intensities in the range of 1.5–15 mg/cm2/min. Experimental results for the case of a half-marathon runner targeting 90 min of usage and sweating at a rate of 1.5 mg/cm2/min indicated measurement accuracy of 98.3% when the patch is completely filled.
Highlights
Hydration is a delicate physiological parameter with even small deviations of 2% from normal levels negatively affecting a person’s cognitive and physical performance by over 30%1
Qualitative inspection and mechanical assessment Prototypes of the patches corresponding to the three use cases of the office resting person, half marathon runner, and the ultramarathon runner were fabricated and are shown in Fig. 3a (i−iv)
In Case 2, the central circular region corresponds to 324 mL of total body sweat loss; the second strip being filled (Fig. 4b (ii)) corresponds to 401 mL of sweat loss; the ninth strip (Fig. 4b (iii)) corresponds to 1.484 L of sweat loss; and the filling of the entire patch (Fig. 4b (iv)) corresponds to 2.33 L of whole-body sweat loss
Summary
Hydration is a delicate physiological parameter with even small deviations of 2% from normal levels negatively affecting a person’s cognitive and physical performance by over 30%1. Studies have shown that more than half of all marathon runners have experienced a major decrease in running performance due to being dehydrated, and at least onethird of all marathon runners have suffered heat-related illness symptoms (e.g., severe muscle or stomach cramping, light-headedness, dizziness, nausea, or loss of ability to think clearly) during a run due to being dehydrated[4]. In these kinds of sporting activities, the most common cause of dehydration is sweat loss required for thermoregulation[5]. Monitoring of hydration and sweat loss are very important during physically strenuous activities such as in sports; in addition to avoiding medical emergencies, it can
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