Analytical methods to determine electrochemical factors in electrotaxis setups and their implications for experimental design

Abstract

Direct current (DC) stimulation can be used to influence the orientation and migratory behavior of cells and results in cellular electrotaxis. Experimental work on such phenomena commonly relies on electrochemical dissolution of silver:silver-chloride (Ag:AgCl) electrodes to provide the stimulation via salt bridges. The strong ionic flow can be expected to influence the cell culture environment. In order to shed more light on which effects that must be considered, and possibly counter balanced, we here characterize a typical DC stimulation system. Silver migration speed was determined by stripping voltammetry. pH variability with stimulation was measured by ratiometric image analysis and conductivity alterations were quantified via two electrode impedance spectroscopy. It could be concluded that pH shifts towards more acidic values, in a linear manner with applied charge, after the buffering capability of the culture medium is exceeded. In contrast, the influence on conductivity was of negligible magnitude. Silver ions could enter the culture chamber at low concentrations long before a clear effect on the viability of the cultured cells could be observed. A design rule of 1cm salt bridge per C of stimulation charge transferred was however sufficient to ensure separation between cells and silver at all times.

SCHEEPDOG: programming electric cues to dynamically herd large-scale cell migration

“…Further, the silver foil electrodes were chloridized electrochemically (Methods, Huang et al 2013;Vulto et al 2009) to improve electrode longevity over traditional bleachbased methods. Since cytotoxic electrochemical byproducts are produced at each electrode-electrolyte interface, most electrotaxis systems integrate a salt-bridge diffusion barrier to these byproducts (Schopf et al, 2016), while some use continuous media perfusion across the cells to minimize their concentration (Cole and Gagnon, 2019). SCHEEPDOG integrated both structured agarose bridges (Hou et al, 2014;Huang et al, 2013;Song et al, 2013;Wu et al, 2015) and continuous culture media perfusion to keep tissues oxygenated and free of any electrochemical byproducts (Methods).…”

Bioelectric Control of Metastasis in Solid Tumors

“…174 Electrical impedance spectroscopy, which measures TEP through the skin, is inexpensive and easily implemented clinically as it is already used for applications such as cardiac cycle imaging, gastrointestinal function monitoring, and skin cancer detection. [185][186][187] Understanding the significance and role of bioelectric changes at the cellular and tissue level can be used to further the development of this technology to detect changes in the breast tissue using electric potential, both earlier and with greater accuracy than current methods.…”

Come together: bioelectric healing-on-a-chip

“…After the tissues have grown, the stencils are removed, and the device is clamped over the cells, aligned such that that the central slit electrode is in the gap between cells (Fig. 1E) (20,36,37). Because the current used in our device is moderate (~6-10 mA) and the 1.5 mm gap between tissues is relatively large, the central cathode must be able to sink current for an extended period to induce tissue convergence, ideally 12 hours or more.…”