Enhancing glucose flux into sweat by increasing paracellular permeability of the sweat gland

<div><p>Non-invasive wearable biosensors provide real-time, continuous, and actionable health information. However, difficulties detecting diluted biomarkers in excreted biofluids limit practical applications. Most biomarkers of interest are transported paracellularly into excreted biofluids from biomarker-rich blood and interstitial fluid during normal modulation of cellular tight junctions. Calcium chelators are reversible tight junction modulators that have been shown to increase absorption across the intestinal epithelium. However, calcium chelators have not yet been shown to improve the extraction of biomarkers. Here we show that for glucose, a paracellularly transported biomarker, the flux into sweat can be increased by >10x using citrate, a calcium chelator, in combination with electroosmosis. Our results demonstrate a method of increasing glucose flux through the sweat gland epithelium, thereby increasing the concentration in sweat. Future work should examine if this method enhances flux for other paracellularly transported biomarkers to make it possible to detect more biomarkers with currently available biosensors.</p></div

Glucose flux under normal conditions.

<p>Sweat glucose concentration and sweat rates measured at various time points following artificial sweat stimulation. Sweat glucose concentration is inversely proportional to sweat rate. The average glucose flux for all participants is roughly 100 fmol/(min-gland) (<i>n</i> = 6).</p

Glucose flux under electroosmotic flow and paracellular permeability enhancement with electroosmotic flow.

<p>Total glucose flux measured before, during, and after treatments: iontophoresis of either acetate (black) which should induce only electroosmosis, or citrate (blue) which should induce both paracellular permeability enhancement and electroosmosis (<i>n</i> = 4).</p

Oxide-Free Actuation of Gallium Liquid Metal Alloys Enabled by Novel Acidified Siloxane Oils

Electrowetting and electrocapillarity of liquid metals have a long history, and a recent explosion of renewed interest. Liquid metals have electromagnetic properties and surface tensions (>500 mN/m) that enable new forms of reconfigurable devices. However, the only nontoxic option, gallium alloys, suffer from immediate formation of a semirigid surface oxide. Although acids or electrochemical reduction can remove this oxide, these approaches surround the gallium alloy in a fluid that is also electrically conducting, diminishing electromagnetic effectiveness and precluding electrowetting actuation. Reported here are acidified siloxanes that remove and prevent oxide formation. Importantly, the siloxane oil associatively incorporates hydrochloric or hydrobromic acids, is electrically insulating, is chemically stable, removes etching byproducts (including water), and allows robust electrowetting. This work opens up new opportunities for liquid metal reconfiguration, and is of fundamental interest due to the unexpected chemical stability of the acidified siloxanes and their application to other materials and surfaces