Cells in New Light Ion Concentration, Voltage, and Pressure Gradients across a Hydrogel Membrane

" We show that the gel barrier is able to maintain a stable separation of ionic solutions of different ionic strengths and chemical compositions without any pumping activity. For the Na+/K+ concentration gradient sustained across the barrier, a negative electric potential develops within the K+ -rich side. The situation is reminiscent of that in the cell. Furthermore, also the advective flow of water molecules across the gel barrier is restricted, despite the gel’s large pores and the osmotic or hydrostatic pressure gradients across it. This feature has important implications for osmoregulation." {Credits 1}

" The existence of such solute-free water layers has been observed next to many hydrophilic surfaces and, thanks to its properties, was given a generic name of exclusion zone (EZ)[29−33]. We were able to confirm the presence of an ion-depleted EZ water layer adjacent to the alginate hydrogel in experiments in which crystal precipitation was induced in situ in a solution containing the alginate gel." {Credits 1}

" Due to the charge separation across the EZ layer (positive ions within the gel and their negative counterions at the EZ/bulk solution boundary), an electric force is created that opposes the chemical force driven by the concentration gradient." {Credits 1}

" Very notably, this is the situation analogous to that existing in a cell, where different ionic compositions between inside and outside, with the electric potential difference, are expressed across the cell membrane. The intrinsic properties of a permselective hydrogel are thus sufficient prerequisites to express these features, without the energy expenditure required in the case of membrane pumps." {Credits 1}

" In our experiments, voltage emerges across the porous gel network separating the two solutions. It has been previously shown that an electric field applied to a nanochannel can enhance the alignment of water molecules inside the channel, forming a liquid-crystalline phase [36]. Weak electric fields, of the strength comparable to that acting across the cell membrane, have been demonstrated to restrict water flow within a nanochannel due to this increased water structuring [36]. Water structure, resembling the liquid-crystalline state, has been previously suggested to exist next to many hydrophilic surfaces, termed the EZ water layer." {Credits 1}

{Credits 1} 🎪 Kowacz, M., & Pollack, G. H. (2020). Cells in New Light: Ion Concentration, Voltage, and Pressure Gradients across a Hydrogel Membrane. ACS Omega. https://doi.org/10.1021/acsomega.0c02595. © 2020 American Chemical Society. This is an open access article published under an ACS AuthorChoice License.