One way round this problem would be to find an alternative source of nerve cells.

ECONOMIST: Something new in mind

It causes the cells to lose oxygen very easily, turning them from round shapes to crescent shapes that cause painful episodes known as pain crises.

CNN: Sickle cell patient refuses to let disease define her

The brain cells have been taught how to control the robot's movements so it can steer round obstacles and the next step, say its creators, is to get it to recognise its surroundings.

BBC: Rat-brain robot aids memory study

Cancer cells can differ hugely within a tumour - it helps them develop ways to resist drugs and spread round the body.

BBC: Thriving cancer's 'chaos' explained