This text is based on the information presented in the "Dr. Karl and the Naked Scientist" BBC radio programme

Robotic prosthetic arms controlled by nerve impulses of the stump of the amputated limb have been around for quite a while. 

Though they are still very expensive, many people can afford them and use them on more or less regular basis, which improved quality of life of those without an arm and made them less dependent on help of other people.

However, a serious issue with such prostheses is lack of feedback. 

This is especially important when people use their prosthetic arms for handling fragile or soft things. 

They often apply too much force and break a glass with water or juice they wanted to drink or crumple a box of pills or chocolates, of which they wanted to take one, or crumple letters, newspapers, books and important documents.

A team of researchers from Switzerland and Italy designed a robotic arm, which can provide such a feedback using various sensors of pressure and touch built into its fingers and palm and electrical processing of their signals in such a way that they could be fed into remaining nerves of the stump of the arm. This allows the users of such prostheses to detect the shape and texture of the object, as well as how hard they are gripping it, and adjust the force of the grip.

Scientists invited a person named Denis for testing this idea. Denis lost his arm 9 years ago, but had never used robotic prostheses before. Researchers implanted electrodes into nerves of his stump. They worried that nerves that had not been in use for 9 years would not conduct the feedback signals properly.

However, after a week of training it appeared that the nerves work well enough. With more training, practice and experience Denis was able to detect the shape, hardness and roughness of the surface of an object by touching it with the hand of his prosthetic arm, even without seeing it, and could control the strength of his grip in wide range, making it harder or softer when required.

So far this prosthesis is an experimental device. It is too big and heavy to be used on the daily basis without assistance, much heavier than existing robotic prostheses without the feedback sensors. However, this research has shown that this approach is workable, and development of prostheses with feedback makes sense and can substantially improve conditions of people who lost their arms.