A robot arm can mimic the movements of a human one, thanks to a device that measures muscle activity.

Muscle sensors are typically embedded in the tissue, but the flexible device created by Ifor Samuel and his colleagues at the University of St Andrews, UK, is worn on the operator's arm. An organic light-emitting diode in the sensor emits red light, which penetrates skin, bounces off muscle tissue and is detected by light-sensitive polymers in the device.

The sensor, unlike those that measure muscle electrical activity, can distinguish between types of muscle contraction, because light is scattered differently from muscle fibres when a person is lifting or pushing.

The team showed how the sensor could be used to control a robot arm, and hope that the device will one day be able to control prosthetic limbs using residual muscle.

Adv. Mater. http://doi.org/f2wpnh (2014)