Mechanoelectrical transduction in the hydrogel-based biomimetic sensors

• Like living cells, polyelectrolyte gels exhibit mechanoelectrical transduction.
• Gel sensor swells under stretch and its negative electrical potential diminishes.
• Counter-ion concentration in gel decreases upon stretch-dependent swelling.
• Theoretical model attributes the depolarization to the gel charge density decrease.

The study addresses the phenomenon of mechanoelectrical transduction in polyelectrolyte hydrogels and, in particular, the search of the driving force for the change of the electrical potential of a gel under the applied mechanical stretch. Polyelectrolyte gels of calcium and magnesium salts of polymethacrylic acid were synthesized by the radical polymerization in water solution. Their electrical potential measured by microcapillary electrodes was negative and fall within 100–140 mV range depending on the nature of a counterion and the networking density of a gel. The rectangular samples (∼10 mm in length and 2 × 2 mm in cross-section) of gel-based sensors underwent the dynamic axial deformation, and the simultaneous monitoring of their geometrical dimensions and the electrical potential was performed. Sensor elongation resulted in the overall increase of gel volume, and it was always accompanied by the gel potential change toward the depolarization (diminishing of the negative values). Theoretical model based on the assumption of the total electrical charge conservation in the course of the dynamic deformation of a filament was proposed to describe the dependence of the electrical potential of a gel on its volume. Good agreement between the predictions of the model and the experimental trend was shown. The proposed mechanism of mechanoelectrical transduction based on the stretch-dependant volume changes in polyelectrolyte hydrogels might be useful to understand the nature of mechanical sensing in much more complex biological gels like the cell cytoskeleton.