Engineers from Germany's Saarland University, however, have taken a different approach with their hand. It moves its fingers via shape-memory nickel-titanium alloy wires, bundled together to perform intricate tasks by working like natural muscle fibers.

The individual wires are so thin that even when a number of them are wound together, the resulting bundle is still only about as thick as a cotton thread – but it has the tensile strength of a much thicker metal wire.

When the nickel-titanium alloy wire bundles are heated by conducting a supplied electrical current, the lattice-like internal structure of the alloy responds by contracting, causing the wires themselves to get shorter. Once they cool down, the wires return to their original relaxed state. That's why bundles of tiny wires were used, instead of single larger wires – the increased surface area of the bundles allows the wires to cool rapidly, once the electrical current is shut off.