The study addresses the phenomenon of mechanoelectrical transduction in the polyelectrolyte hydrogels and, in particular, the search of driving force for the change of gel electrical potential under 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 counterion and gel networking density. The rectangular samples (~10 mm in length and 2x2 mm in cross-section) of gel-based sensors underwent the dynamic axial deformation, and simultaneous monitoring of their geometrical dimensions and the electrical potential was performed. Sensor elongation resulted in the overall increase of gel volume, and it always was accompanied by the change of gel potential toward the depolarization (diminishing of the negative values). Theoretical model based on the assumption of total electrical charge constancy in the course of filament dynamic deformation was proposed to describe the dependence of gel potential on its volume. Good agreement between the model predictions and the experimental trend was shown. The proposed mechanism of mechanoelectrical transduction based on the stretch-dependant volume change of polyelectrolyte hydrogels might be useful to understand the nature of mechanical sensing in much more complex biological gels like the cell cytoskeleton.

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Ferrogels (FG) are magnetic composites that are widely used in the area of biomedical engineering and biosensing. In this work, ferrogels with different concentrations of magnetic nanoparticles (MNPs) were synthesized by the radical polymerization of acrylamide in stabilized aqueous ferrofluid. FG samples were prepared in various shapes that are suitable for different characterization techniques. Thin cylindrical samples were used to simulate the case of targeted drug delivery test through blood vessels. Samples of larger size that were in the shape of cylindrical plates were used for the evaluation of the FG applicability as substitutes for damaged structures, such as bone or cartilage tissues. Regardless of the shape of the samples and the conditions of their location, the boundaries of FG were confidently visualized over the entire range of concentrations of MNPs while using medical ultrasound. The amplitude of the reflected echo signal was higher for the higher concentration of MNPs in the gel. This result was not related to the influence of the MNPs on the intensity of the reflected echo signal directly, since the wavelength of the ultrasonic effect used is much larger than the particle size. Qualitative theoretical model for the understanding of the experimental results was proposed while taking into account the concept that at the acoustic oscillations of the hydrogel, the macromolecular net, and water in the gel porous structure experience the viscous Stocks-like interaction.

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