A kinetic model for magnetostriction of a ferrogel with physical networking.

Kinetics of magnetostriction of ferrogel with physical networking based on natural polysaccharide guar gum with embedded strontium hexaferrite magnetic particles were studied in the uniform magnetic field 420 mT. An ellipsoidal sample was elongated by 37% along the applied field and contracted by 15% in the transverse direction, while its volume was kept constant. The characteristic time of magnetostriction was 440 s. Dynamic mechanical analysis in an oscillatory mode showed that the deformation of ferrogel is mostly elastic rather than viscous. Its storage modulus was almost constant in a frequency range of 0.1-100 Hz and by at least an order of magnitude larger than the loss modulus. Meanwhile, a developed theoretical model based on the elasto-viscous behaviour of the ferrogel failed to estimate correctly the experimental value of its magnetostriction. Calculated values of the elongation of ferrogel in the field were several orders of magnitude lower than those observed in the experiment for the ferrogel with physical networking. Consistency between the experiment and the theory was achieved using the alternative consideration based on the deformation of a liquid droplet of ferrofluid. The applicability of such an approach was discussed concerning structural relaxation properties of the ferrogel with physical networking. This article is part of the theme issue 'Transport phenomena in complex systems (part 1)'.

Modelling of magnetoimpedance response of thin film sensitive element in the presence of ferrogel: Next step toward development of biosensor for in-tissue embedded magnetic nanoparticles detection.

In-tissue embedded magnetic nanoparticle (MNPs) detection is one of the most interesting cases for cancer research. In order to understand the origin, the limits and the way of improvement of magnetic biosensor sensitivity for the detection of 3D mezoscopic distributions of MNPs, we have developed a magnetoimpedance biosensor prototype with a [Cu (3 nm)/FeNi(100 nm)]5/Cu(500 nm)/[FeNi(100 nm)/Cu(3 nm)]5 rectangular sensitive element. Magnetoimpedance (MI) responses were measured with and without polyacrylamide ferrogel layer mimicking natural tissue in order to evaluate stray fields of embedded MNPs of γ-Fe2O3 iron oxide. A model for MI response based on a solution of Maxwell equations with Landau-Lifshitz equation was developed in order to understand the origin of the prototype sensitivity which reached 1.3% of ΔZ/Z per 1% of MNPs concentration by weight. To make this promising technique useful for magnetically labeled tissue detection, a synthesis of composite gels with MNPs agglomerates compactly located inside pure gel and their MI testing are still necessary.

Features of silicon- and titanium-polyethylene glycol precursors in sol-gel synthesis of new hydrogels.

The formation of organic/inorganic hydrogels based on silicon and titanium polyethylene glycolates, new biocompatible water-soluble precursors in sol-gel processing, was investigated. The influence of different factors on the gelation process, such as excess of PEG, water molar content, pH of medium, electrolyte additives, was investigated in comparison with silicon- and titanium-glycerol precursors. The specific features of gelation for each type of precursor were revealed. It has been determined that titanium polyethylene glycolates synthesized and used in the excess of PEG formed transparent polymeric hydrogels resistant to syneresis under certain conditions. The titanium polyethylene glycolates synthesized without excess of PEG formed turbid heterogeneous colloidal gels. In the case of silicon polyethylene glycolates the hydrogels obtained were polymeric. Dynamic light scattering was used to confirm the polymeric or colloidal type of gelation. The solid and liquid phases of polymeric silicon- and titanium-polyethylene glycol hydrogels were separated by exhaustive extraction. The solid phase was characterized by combined thermal analysis with simultaneous quadruple mass spectrometry, XRD, IR spectroscopy, and liquid phase-atomic emission spectroscopy. The structural features of polymeric gels were investigated by SEM and TEM methods. The cross-linking density of polymeric hydrogels was evaluated using Flory-Rehner theory based on the mechanical properties of swollen networks of flexible polymeric chains.

Carbon deposition from aromatic solvents onto active intact 3d metal surface at ambient conditions.

The process of carbon deposition onto 3d metal surface immersed in aromatic solvents (benzene, toluene, xylene) at ambient conditions was studied for as-prepared magnetic nanoparticles (MNPs) and Fe-based films by thermal analysis, mass spectrometry, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, electron microscopy, and energy-dispersive X-ray spectroscopy. The mechanism of the deposition at the interface is likely the heterogeneous Scholl oxidation of the aromatic hydrocarbons, which is the cationic polymerization of the aryl rings. It results in the formation of polycyclic aromatic hydrocarbons (PAH) chemically bonded to the surface of a MNP or thin metallic film. The benzene rings in the polycyclic deposit do not maintain planar aligned structures and do not provide delocalization of the π-electrons in the zone structure. Contrary to the dense graphite layers, the polycyclic layers, although chemically bonded, are not attached tightly to the surface. Such "hairlike" structure of the carboneous deposit might be especially favorable for the applications that imply the enhanced interaction at the surfaces incorporated in the functional matrices (polymeric composites or biosensors). The aromatic chemical nature of the deposit provides strong interaction with most polymers, while its loose structure favors conformational mobility of macromolecular chains at the interface.

[Mechanical characteristics of synthetic polyelectrolyte gel as a physical model of the cytoskeleton].

A physical model of the cytoskeleton based on synthetic polyelectrolyte hydrogel of polymethacrylic acid has been proposed. From the physicochemical point of view, the structures of polyelectrolyte gel and the cytoskeleton show a high degree of similarity. It was shown that polyelectrolyte gel can shorten and produce mechanical stress in response to changes in the composition of the surrounding solution. The mechanical properties of the model gel were evaluated: Young modulus (2-6 kPa), stress relaxation time (0.1-1 s), and apparent viscosity (0.3-3 kPa x s). The viscoelastic properties of the gel depend on the degree of its swelling. It has been demonstrated that the mechanical properties of gels of polymethacrylic acid are close to those of biological objects.

[Mechanoelectric potentials in synthetic hydrogels: possible relation to cytoskeleton].

Mechanical and electrical properties of a synthetic polyelectrolyte hydrogel considered as a model of the cytoskeletal gel were studied. Hydrogels were synthesized from polymethacrylic acid by radical polymerization in aqueous solution. The electrical charge was introduced into the gel network by partial neutralization of monomer acids with magnesium (hydro)oxides. Through the use of a motor, triangular longitudinal (axial) deformations were applied to gel samples. Simultaneously, the electrochemical (Donnan) potential of the gel was measured using conventional microelectrodes. We found that: (1) the Young modulus of the gel was 0.53 kPa; (2) at a given deformation velocity, the extent of gel deformation closely correlates with the gel potential; and (3) at the same level of gel deformation, the lower the deformation velocity, the higher the relative change of gel potential. These findings show a striking similarity to the data obtained in living cells, particularly in cardiac myocytes. A hypothesis involving the deformation-induced solvent migration from the gel to the surrounding solution is considered. It is concluded that the physicochemical features of the cytoskeletal gel may play a role in determining the mechanoelectric properties of excited cells.

[The relationship between the mechanical and electrical properties of a synthetic hydrogel chosen as an experimental model of cytoskeleton].

A correlation between the electrochemical (Donnan) potential and volume swelling has been studied for synthetic polyelectrolyte hydrogels considered as models of cytoskeleton gel-forming biopolymers. Hydrogels based on polyacrylic and polymethacrylic acids with varying network density have been synthesized by radical polymerization in water solution. Electric charge was introduced into the gel network by partial neutralization of acidic monomers by alkali and alkali-earth (hydr)oxides. The electrochemical (Donnan) potential of synthetic gels was measured by a conventional microelectrode technique used in studies of cell potential. It was shown that the negative electric potential became lower as the equilibrium swelling degree decreased for a large number of anionic gels with varying electric charge and network density, i.e., the content of water in the gel decreased. It was shown that the abrupt phase transition of hydrogel structure from a swollen to a contracted state under the influence of K+/Ca2+ ionic exchange is accompanied by a similar decrease in absolute values of the Donnan potential of the gel. A kinetic study showed that volume changes went prior to the decrease in electric potential. This suggests that the volume phase transition in gel structure is the major cause for the electric response. A similarity was shown between the swelling/collapse phase transition in the gel and volume changes in cytoskeleton beneath the cell membrane. Based on the universal properties of synthetic and biopolymer hydrogels, a possible swelling-induced mechanism of cell electrical potential regulation is proposed.