Theres a common problem with health-tracking devices like smartwatches: theyre not really attached to you, which leaves you relying on a short-lived battery and a wireless connection. Even a self-powered patch has its limits. Thats where Harvard and MIT think they can help: theyve developed smart tattoos that effectively place health sensors in your skin, no power or wireless link required. The ink in the tattoos reacts to the chemical composition of your interstitial fluid, wh…<...Read more