Tissue and Cell Nonlinearity

Nonlinear behavior in suspensions has been smdied, for example. Block and Hayes (1970) and Jones (1979) for electroporation, see Section 10.11.1 for defibrillation, see Section 10.9.1. Memristive elements are described in Section 9.2.11. 

At a sufficiently low volume power density, every biomaterial is linear. At a sufficiently high volume power density, every biomaterial is nonlinear. Many applications make use of the nonlinear region, where the principle of superposition no longer is valid. The nonlinearity may be a property of the biomaterial, or of the electrode/electroljrtic systems used. 

At the atomic and molecular levels, some of the charge displacements will reach saturation at high E-field strength levels (Section 8.4.1). The alignment of dipoles in a polar dielectric will reach a maximum when the field energy is of the same order of magnitude as the Boltzmann factor kT. 

At the cellular level, the cell membranes of polarized cells are of the order of 10 kV/mm, and additional field strengths may easily bring the membrane into a nonlinear region even without cell excitation. Cell excitation, the opening of membrane channels, and the creation of an action potential are the result of nonlinear processes. Electroporation and electrofusion of cells in vitro (Section 10.11) are also processes in the nonlinear region. 

In human skin, Yamamoto et al. (1981) found the upper limit of linearity to be about 10 pA/cm at 10 Hz and 100 pA/cm at 100 Hz. Ionic flow through human skin in vivo is 

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