Theoretical study of rectangular pulse electrical stimulation(RPES) on skin cells (in vivo) under conforming electrodes

Our previous in vivo experimental results have shown RPES can enhance skin wound healing by using conforming electrodes. Based on an equation of polarization transmembrane voltage, two equations were derived to describe the peak RPES intensity on skin cells in vivo: (1) U = 1.5 a J/σ, (2) J(m) = 1.5 a (J/σ) (C(m)/τ). Where U: polarization transmembrane voltage. a: radius (R) for spherical cells or semi-length (L) for long fibers parallel to the electrical field. J: external imposed pulse current density under the electrode. σ: average conductivity of skin tissue. J(m): transmembrane displacement current density. C(m): membrane capacitance per unit area and τ: time constant. Calculations indicated that the sensory fibers (SF) would receive the strongest stimulation compared to other cells in skin since generally LSF ≥ 100 R. The sensitivity of SF to the stimulation could enhance skin wound healing as well as protect normal skin cells from harmful electroporation. From these theoretical calculations, we proposed a theoretical range of the pulse current density as: U₁ σ/(1.5 L) ≤ J ≤ U₂ σ/(1.5 L), where U₁ and U₂ are the excitation threshold voltage (about 0.01 V) and polarization electroporation voltage (about 0.1 V) for a SF respectively, for RPES to enhance skin wound healing.