Mechanoelectric transduction in bone

Abstract

The cells in living bone are embedded in a charged, organic-inorganic solid permeated by ionic fluids flowing through a complex network of channels (diameter ∼10−1–102μm). The solid matrix, which has a high degree of composite material organization beginning at the macromolecular level, has even finer pores of diameter ≳10−3μm containing extracellular fluids. Since bone cells are thus bathed in fluid environments of varying ionic composition and concentration, it is likely that the physiology of bone depends on its electrical and electromechanical properties. This hypothesis is supported by the known effects of externally applied mechanical and electrical signals on physiological functions. Contrary to the earlier perception of bone as an insulating material, it is now recognized that the fluid content of bone endows it with physiologically significant conductivity. Mechanoelectric transduction in bone, at low frequencies, is most likely an electrokinetic process associated with the solid-fluid interfaces in bone. Electromechanical properties of bone have been determined experimentally by measurements of stress-generated potentials and streaming potentials in wet bone specimens and electrophoretic mobility of bone particles. Interpretation of results has been difficult due to the complexity of the solid-fluid interfaces in bone and the often undefinable alterations of the pores and interfaces due to specimen preparation. This paper is a review of the present state of knowledge of mechanoelectric transduction in bone and its physiological significance.