Tapping the Vein

But I thought computers were already powered by tears.

When it comes to energy-rich bodily fluids, blood is hard to beat. Plasma, the liquid component of blood, is constantly suffused with dissolved glucose, our cells' primary source of energy. Most enzymatic biofuel cells that have been developed to date target this molecule. [...] When this was implanted into a rat's abdomen, it generated around 40 microwatts of power, which the team actually used to operate both an LED and a digital thermometer. [...]

Human sweat is rich in a compound called lactate, which can also be used to generate electricity using EFCs, replacing their glucose fuel. Since sweat is so much easier to access, researchers have already been able to test perspiration-powered EFCs on humans with encouraging results. [...] Emphatic proof came the year after, when another group from UC San Diego came up with a wearable, textile-based EFC that could be integrated into sweat bands. A volunteer wore one of these while riding an exercise bike and, as with the tattoo-based devices, the cyclist's sweat allowed the fuel cells to generate electricity. This time, however, the sweat produced enough power to run an electronic device -- either an LED or a digital watch -- for a few tens of seconds at a time. [...]

At first glance, tears might seem like an even more unreliable source of fuel than sweat. But whatever our emotional state, we're always a little dewy-eyed. The cornea is continually kept moist by a film of what are called "basal" tears (as opposed to the "psychic" tears that well up when we cry). These mostly serve to lubricate and nourish the eye, but they're also full of energy. Among other chemicals, basal tears contain glucose, lactate, and ascorbate (a compound similar to vitamin C), any of which are an excellent fuel source for EFCs. [...] The Utah researchers have just developed the first-ever contact lens with an integrated EFC, allowing it to generate electricity from human tears alone.

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