Abstract
The interaction of osseous tissue with electric fields is an important subject. The electrical stimulation of bone promotes osteogenesis, while bone impedance has been proposed as a measure of osteoporosis, to follow fracture healing, or as a method to improve safety of surgical procedures. However, a deeper understanding of the electrical properties of bone and their relation to the architecture of osseous tissue is required to extend the range of use of electrical measurements to clinical studies. In this paper we apply electrical impedance spectroscopy to study the conductivity of fresh bovine tibia and we correlate the measured conductivities with its structural properties. Impedance was measured using a custom-made cell and a potentiostat. Bone conductivity was determined at 100 kHz, where the phase shift was negligible. A good agreement (R2 = 0.83) was found between the measured conductivity and the bone volume fraction, determined on microCT images. Based on this relationship, an equivalent circuit model was created for bone samples. The results of this ex-vivo study are comparable to previous in-vivo observations reporting bone resistivity as a function of bone density. This information can be used to construct a map of the tissue resistivity directly derived from clinical images.
Highlights
The electrical stimulation of bone has been applied for more than a decade to stimulate bone growth in the case of nonunion[1,2] or after spinal fusion[3,4]
We focused on the measurement of the resistive component of the bone impedance; that is, we used impedances measured at frequencies where the phase angle was minimal, and we subsequently correlated these impedances to morphometric parameters
Following the idea previously presented by Wyss-Balmer et al.22. namely that bone is a perfect resistor and that the frequency dependence is due to the double-layer interface at the point of electrode contact, we determined bone impedance at about 100 kHz, where the phase shift was approximately zero
Summary
The electrical stimulation of bone has been applied for more than a decade to stimulate bone growth in the case of nonunion[1,2] or after spinal fusion[3,4]. Over the past four decades, several investigations have been performed in order to determine the electrical properties of osseous tissue – mostly conductivity and permittivity – across a broad range of frequencies[11,12,13,14,15,16,17] These studies all suffer from limitations that are due to the (mostly capacitive) response of the metal/bone interface. Relationships were established for the electrical permittivity and loss factor but not for the electrical conductivity, which the authors associated with the density and water content of trabecular bone[6] Their interpretation, relies on the assignment of measured phase shifts to the bulk properties of the studied conductive medium (osseous tissue), and surface effects are not taken into account. Special electrodes were designed to reduce stray capacitance and the conductivity of bone was determined at frequencies corresponding to a minimal phase shift
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