Good-bye charging cords and batteries. Wearable electronics such as the Apple Watch might soon power themselves with a clean, portable energy source: human motion.

If cutting-edge nano science pans out, limited battery life may no longer be the bugaboo of everyday technology. At universities worldwide, researchers are finding new ways to produce power from walking, typing, and other basic activities.

Their progress, documented in at least 146 scientific papers in the last three years, holds promise not only for wearable devices but also for keyboards, smartphones, laptops, and biomedical applications such as robotic skins.

"Self-powered electronics will play a critical role in the Internet of Things," in which people and devices are seamlessly connected, says Zhong Lin Wang, a leading researcher in