Wouldn't it be great if, before you went for a jog or hit the gym, you didn't have to worry if your iPhone or portable Bluetooth radio was fully charged? A team of engineers from the UC San Diego Jacobs School of Engineering has announced a breakthrough invention that could fix this issue - stretchable biofuel cells which extract energy from human sweat and can power wearable electronics, like Bluetooth radios and LEDs. It works because the cells have an enzyme that oxidizes lactic acid in sweat and generates current. The team built a stretchable electric foundation by using screen-printing, lithography and 3D printing to create carbon nanotube-based cathode and anode arrays. Read more at 3DPrint.com: http://3dprint.com/185109/sweat-powers-wearables/