THE ELECTROMECHANICAL PROPERTIES OF FLUID-FILLED BONE - A NEW DIMENSION

The current understanding of electromechanical effects in fully hydrated bone is that they are electrokinetic (streaming potential) in nature. The presence of a second competing mechanism, piezoelectricity, which dominates in dry conditions, has been denied in conditions of full hydration based on the absence of a piezoelectric response from wet collagen. Since the mineralized collagenous matrix of bone can only absorb 26 wt% water (Relative Humidity (RH) = 60%), there seems no reason to dismiss a piezoelectric component entirely and experimental evidence was sought using a new measuring technique. A comprehensive analysis has been developed to relate both mechanisms to bone structure at different levels of hydration. Our results indicate the presence of both mechanisms at full hydration, with the piezoelectric effect leading streaming potential in the time domain. The immediate implication of this finding is that it is the piezoelectric effect which determines the characteristics of the generated electrical signal and may subsequently influence bone generation and remodelling.