One of the trickiest things in the field of robotic engineering is getting the manipulators right. Look down at your hand: you probably have five digits, four fingers and a thumb which are articulated and largely independent of one another (modulo a bit of funny business with the ring and little fingers but, as with many things natural variation comes into play here). Each finger folds and rotates in ways that the science of engineering hasn't quite gotten the hang of replicating. Then a group of scientists discovered an insanely simple design: a small sack full of granules and a …