Ambiguity in the interpretation of the low-frequency dielectric properties of biological tissues

Zimmermann, Július; Rienen, Ursula van

doi:10.1016/j.bioelechem.2021.107773

Cited by 25 publications

(25 citation statements)

References 48 publications

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“…However, this approach is not feasible anymore if there is no suitable prior knowledge available. This could be, for example, the case for hydrogels with dielectric properties changing over time ( Mawad et al, 2016 ) or biological tissues with highly uncertain dielectric properties ( Zimmermann and van Rienen, 2021 ). Then, the recorded voltage and current could be used to infer these dielectric properties.…”

Section: Discussionmentioning

confidence: 99%

Using a Digital Twin of an Electrical Stimulation Device to Monitor and Control the Electrical Stimulation of Cells in vitro

Zimmermann

Budde

Arbeiter

et al. 2021

Front. Bioeng. Biotechnol.

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Electrical stimulation for application in tissue engineering and regenerative medicine has received increasing attention in recent years. A variety of stimulation methods, waveforms and amplitudes have been studied. However, a clear choice of optimal stimulation parameters is still not available and is complicated by ambiguous reporting standards. In order to understand underlying cellular mechanisms affected by the electrical stimulation, the knowledge of the actual prevailing field strength or current density is required. Here, we present a comprehensive digital representation, a digital twin, of a basic electrical stimulation device for the electrical stimulation of cells in vitro. The effect of electrochemical processes at the electrode surface was experimentally characterised and integrated into a numerical model of the electrical stimulation. Uncertainty quantification techniques were used to identify the influence of model uncertainties on relevant observables. Different stimulation protocols were compared and it was assessed if the information contained in the monitored stimulation pulses could be related to the stimulation model. We found that our approach permits to model and simulate the recorded rectangular waveforms such that local electric field strengths become accessible. Moreover, we could predict stimulation voltages and currents reliably. This enabled us to define a controlled stimulation setting and to identify significant temperature changes of the cell culture in the monitored voltage data. Eventually, we give an outlook on how the presented methods can be applied in more complex situations such as the stimulation of hydrogels or tissue in vivo.

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Section: Discussionmentioning

confidence: 99%

Using a Digital Twin of an Electrical Stimulation Device to Monitor and Control the Electrical Stimulation of Cells in vitro

Zimmermann

Budde

Arbeiter

et al. 2021

Front. Bioeng. Biotechnol.

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“…This study addressed the question of the approximation for tCS electric field modeling in the case of a realistic head model with the main five tissues used in the literature. The use of the Cole-Cole model can be criticized, since deviations in conductivity have been identified at low frequencies (¡ 1 MHz) [41], which could be attributed to electrode-electrolyte interface during measurements [29], [58]. This issue was recently addressed by compensating this electrode-electrolyte interface impedance [58], which opens the possibility to use corrected values.…”

Section: Discussionmentioning

confidence: 99%

“…The use of the Cole-Cole model can be criticized, since deviations in conductivity have been identified at low frequencies (¡ 1 MHz) [41], which could be attributed to electrode-electrolyte interface during measurements [29], [58]. This issue was recently addressed by compensating this electrode-electrolyte interface impedance [58], which opens the possibility to use corrected values. However, another study reported similar range of values for relative permittivity but higher conductivities than the initial measurements, in mice tissues [30] and is physically plausible.…”

Section: Discussionmentioning

confidence: 99%

Quasi-Static Approximation Error of Electric Field Analysis for Transcranial Current Stimulation

Gaugain,

Quéguiner,

Bikson

et al. 2022

Preprint

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Numerical modeling of electric fields induced by transcranial alternating current stimulation (tACS) is currently a part of the standard procedure to predict and understand neural response. Quasi-static approximation for electric field calculations is generally applied to reduce the computational cost. This study aims to analyze and quantify the validity of the approximation over a broad frequency range. Methods: We performed electromagnetic modeling studies using an anatomical head models. We considered approximations assuming either a purely ohmic medium (i.e., static formulation) or a lossy dielectric medium (quasi-static formulation). The results were compared with the solution of Maxwell's equations for the cases of harmonic and pulsed signals. Finally, we analyzed the effect of electrode positioning on these errors. Results: Our findings demonstrate that the quasi-static approximation is valid and produces a relative error below 1% up to 1.43 MHz. The largest error is introduced in the static case, where the error is over 1% across the entire considered spectrum and as high as 20% in the brain at 10 Hz. Finally, we highlight the special importance of considering the capacitive effect of tissues for pulsed waveforms, which allows to avoid significant signal distortion induced by the purely ohmic approximation. Conclusion: Quasi-static approximation remains valid in the frequency range currently used for tACS. However, neglecting the permittivity introduces significant error for both harmonic and non-harmonic signals. Significance: The results point out that reliable low frequency dielectric data are needed for tCS numerical modeling. Quasi-static approximation should be favoured over the static one given the low additional computational cost.

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“…Isotropic conductivity values for grey and white matter were evaluated in the frequency domain based on ( Gabriel et al, 1996 ), but omitting

-dispersion as proposed in Zimmermann and van Rienen (2021) and additionally upscaled. The conductivity

of non-dispersive cerebrospinal fluid was fixed to 2.0 S/m.…”

Section: Methodsmentioning

confidence: 99%

Linking profiles of pathway activation with clinical motor improvements – A retrospective computational study

Butenko

Neudorfer

et al. 2022

NeuroImage: Clinical

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Ambiguity in the interpretation of the low-frequency dielectric properties of biological tissues

Cited by 25 publications

References 48 publications

Using a Digital Twin of an Electrical Stimulation Device to Monitor and Control the Electrical Stimulation of Cells in vitro

Using a Digital Twin of an Electrical Stimulation Device to Monitor and Control the Electrical Stimulation of Cells in vitro

Quasi-Static Approximation Error of Electric Field Analysis for Transcranial Current Stimulation

Linking profiles of pathway activation with clinical motor improvements – A retrospective computational study

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