Strings made from a magnetic suitable (electric bass needs magnetism with pups, unless your doing lightwave bass, which may not need that), but anyway, strings made from the metal of another planet with properties combining the best of steal and nickel and elements unknown on earth. By furry bear looking critters who want that special sound of electric bass to accompany their drum circles. Lol.
See, somebody's thinking outside the box!
Actually, with the huge numbers of ways you can sense vibration besides magnetism, no metal really is needed. But it's always been the go-to, because all strings have metal in them. That's because pickups sense metal strings which we already have, because of pickups......