The goal of the proposed research is to develop a wearable device that can directly stimulate sweat secretion and rapidly quantify the concentration of insulin in sweat. In stark contrast to a blood draw and subsequent insulin quantification in a clinical lab, the envisioned wearable sweat sensor can noninvasively and rapidly quantify insulin at any desired time at home. This study will validate the performance of the wearable devices for in situ quantification of insulin in sweat and determine the concentration correlation between sweat, dermal interstitial fluid, and blood.
The study will take place at the research facility of the Center for Translational Research on Aging and Longevity (CTRAL), Texas A\&M University located in the Human Clinical Research Building) affiliated with Texas A\&M University. Some study procedures (e.g., body composition) may be skipped if completed within the past 3 months at CTRAL. All data will be recorded in Case Report Form and stored in the Research Electronic Data Capturing (REDCap) System.
Subjects will be asked to arrive in the fasted state on all study days. Fasting prior to screening is not required. On the screening day, body weight, height, and body composition by Dualenergy X-ray absorptiometry (DXA) will be measured. In addition, The SixMinute Walk Test (6MWT) and skeletal muscle function tests will be assessed at the end of each screening visit. Questionnaires about your overall health and well-being will also be completed. The study visit will begin with vital signs. Before administration of the feeding or the tracer solution, baseline blood will be collected for measurement of the natural enrichment of metabolites. The research nurse will place a catheter (small, flexible, plastic tube) in a vein of the arm or hand. The hand will be placed in a warmed box to increase blood flow. There will be a device with electrodes used to generate and collect sweat on your forearm. Once sweat collection is started, we will also apply a microneedle patch to the forearm of the subject for 5-30 minutes duration. Microneedle patches (sensors) are small flexible sticker-like devices. They will be applied to the skin using a small spring loaded applicator to measure the chemical analytes in the dermal interstitial fluids. After 2 hours of baseline biological samples of sweat, dermal interstitial fluid, and blood have been collected, we will provide a standardized meal as a liquid drink consisting of whey, maltodextrin and sunflower oil, flavored using vanilla sugar-free instant pudding. Biological sampling will continue to occur for the following 5 hours.
