122
The Body Electric
Wolffs-law
reorganization
occurs
because
something
stimulates
the
periosteum to grow new bone at a surface where there's compressional
stress, while dissolving bone where there's tensional stress. Again, the
question for researchers is: What turns on the periosteal cells?
After I'd finished giving my paper on the salamander's current of in-
jury at the orthopedic meeting early in 1961, several people came up to
the stage to ask questions. Among them was Andy Bassett, a young
orthopedic surgeon who was doing research at Columbia. In our conver-
sation we came up with an angle for investigating Wolff's law—piezo-
electricity. Simply put, this is the ability of some materials to transform
mechanical stress into electrical energy. For example, if you bend a
piezoelectric crystal hard enough to deform it slightly, there'll be a pulse
of current through it. In effect, the squeeze pops electrons out of their
places in the crystal lattice. They migrate toward the compression, so
the charge on the inside curve of a bent crystal is negative. The potential
quickly disappears if you sustain the stress, bur when you release it, an
equal and opposite positive pulse appears as the electrons rebound before
settling back into place.
Since I'd shown that a stronger-than-normal negative current preceded
regeneration, Bassett suggested that maybe bone was iezoelectric and