Temporal and thermal effects on deformation potentials in bone

There were 44 freshly excised adult rat femora subjected to mechanical deformation in a 4-point bending jig while the load/deformation curves and the electrical potentials generated were recorded simultaneously. Serial testing was repeated after storage of specimens up to 30 days at 25 degrees C and -15 degrees, and after heating for 1 h at 70 degrees, 80 degrees, and 85 degrees C. The amplitude of the potential decreased shortly after the femora had been excised until, by 4-7 days, it reached a plateau which was 10-20% of the initial value. In some cases polarity reversal occurred. These changes were not prevented by freezing or drying nor were they accompanied by increased stiffness. It is presumed that they are related to more subtle changes in the mechanical properties of bone or to alterations in the generating or conducting mechanisms. Heating caused a significant increase in potential without a change in the waveform. A corresponding increase in the deformation occurred due to softening of the bone which could, in itself, be responsible for the increased potential without a basic alteration in the transducer mechanism.