Alexander P. Safronov

Laser Target Evaporation Fe 2 O 3 Nanoparticles for Water-Based Ferrofluids for Biomedical Applications

Maghemite spherical magnetic nanoparticles (MNPs) were prepared by laser target evaporation. X-ray diffraction, transmission electron microscopy, specific surface area, and dynamic light scattering studies were performed. For water-based suspensions prepared on the basis of obtained MNPs, the zeta potential was measured. Magnetic and microwave measurements were performed both for MNPs and ferrofluids. To estimate the inductive magnetic heating of electrostatically self-stabilized or electrostatically stabilized by adsorbed citrate ions ferrofluids, magneto-inductive heating experiments were performed that showed heating efficiency. For the study of cytotoxicity and maghemite MNPs accumulation process, two non-pathogenic Exophiala nigrum (black) and its mutant strain (red) yeasts were studied. In both cases, no significant alterations of cell morphology were observed.

Effect of cytoskeletal elastic properties on the mechanoelectrical transduction in excitable cells.

This paper addresses the possible mechanism of stretch on cell electrochemical potential change, based on the physicochemical properties of cytoskeletal network. Synthetic polyelectrolyte gel was used as an experimental model of the cytoskeleton. Gel samples with different density of network cross linking were studied. Triangular axial deformations of samples were applied. Simultaneously, the electrochemical (Donnan) potential of the gel was measured between a micropipette electrode pinned into the swollen gel, and a reference electrode in the outer solution. We found that axial deformation shifts the gel potential toward depolarization. The extent of gel depolarization showed a close negative correlation with the Young modulus of the gel. We suggest that the underlying mechanism is likely to be a universal process of counterion adsorption on charged polymer filaments due to the decrease of distance between polymer filaments owing to gel elongation.

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 hydroxide. 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 is 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.

Polyacrylamide Ferrogels with Magnetite or Strontium Hexaferrite: Next Step in the Development of Soft Biomimetic Matter for Biosensor Applications

Magnetic biosensors are an important part of biomedical applications of magnetic materials. As the living tissue is basically a “soft matter.” this study addresses the development of ferrogels (FG) with micron sized magnetic particles of magnetite and strontium hexaferrite mimicking the living tissue. The basic composition of the FG comprised the polymeric network of polyacrylamide, synthesized by free radical polymerization of monomeric acrylamide (AAm) in water solution at three levels of concentration (1.1 M, 0.85 M and 0.58 M) to provide the FG with varying elasticity. To improve FG biocompatibility and to prevent the precipitation of the particles, polysaccharide thickeners—guar gum or xanthan gum were used. The content of magnetic particles in FG varied up to 5.2 wt % depending on the FG composition. The mechanical properties of FG and their deformation in a uniform magnetic field were comparatively analyzed. FG filled with strontium hexaferrite particles have larger Young’s modulus value than FG filled with magnetite particles, most likely due to the specific features of the adhesion of the network’s polymeric subchains on the surface of the particles. FG networks with xanthan are stronger and have higher modulus than the FG with guar. FG based on magnetite, contract in a magnetic field 0.42 T, whereas some FG based on strontium hexaferrite swell. Weak FG with the lowest concentration of AAm shows a much stronger response to a field, as the concentration of AAm governs the Young’s modulus of ferrogel. A small magnetic field magnetoimpedance sensor prototype with Co68.6Fe3.9Mo3.0Si12.0B12.5 rapidly quenched amorphous ribbon based element was designed aiming to develop a sensor working with a disposable stripe sensitive element. The proposed protocol allowed measurements of the concentration dependence of magnetic particles in gels using magnetoimpedance responses in the presence of magnetite and strontium hexaferrite ferrogels with xanthan. We have discussed the importance of magnetic history for the detection process and demonstrated the importance of remnant magnetization in the case of the gels with large magnetic particles.

Mechanical, Electrical and Magnetic Properties of Ferrogels with Embedded Iron Oxide Nanoparticles Obtained by Laser Target Evaporation: Focus on Multifunctional Biosensor Applications

Hydrogels are biomimetic materials widely used in the area of biomedical engineering and biosensing. Ferrogels (FG) are magnetic composites capable of functioning as magnetic field sensitive transformers and field assisted drug deliverers. FG can be prepared by incorporating magnetic nanoparticles (MNPs) into chemically crosslinked hydrogels. The properties of biomimetic ferrogels for multifunctional biosensor applications can be set up by synthesis. The properties of these biomimetic ferrogels can be thoroughly controlled in a physical experiment environment which is much less demanding than biotests. Two series of ferrogels (soft and dense) based on polyacrylamide (PAAm) with different chemical network densities were synthesized by free-radical polymerization in aqueous solution with N,N’-methylene-diacrylamide as a cross-linker and maghemite Fe2O3 MNPs fabricated by laser target evaporation as a filler. Their mechanical, electrical and magnetic properties were comparatively analyzed. We developed a giant magnetoimpedance (MI) sensor prototype with multilayered FeNi-based sensitive elements deposited onto glass or polymer substrates adapted for FG studies. The MI measurements in the initial state and in the presence of FG with different concentrations of MNPs at a frequency range of 1–300 MHz allowed a precise characterization of the stray fields of the MNPs present in the FG. We proposed an electrodynamic model to describe the MI in multilayered film with a FG layer based on the solution of linearized Maxwell equations for the electromagnetic fields coupled with the Landau-Lifshitz equation for the magnetization dynamics.

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 has been 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 have been evaluated: Young modulus (2–6 kPa), stress relaxation time (0.1–1 s), and apparent viscosity (0.3–3 kPa 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.

Magneto-inductive heating of water-based iron oxide ferrofluids

Spherical magnetic nanoparticles (MNPs) of iron oxide were fabricated by laser target evaporation technique. Water-based ferrofluids were prepared on the basis of obtained MNPs. Their structure and magnetic properties were studied by a number of methods including transmission electron microscopy, X-ray diffraction, SQUID-magnetometry and magnetic relaxation losses measurements. Magneto-inductive heating experiment showed the specific power loss value of 2 W/g for 1.8 kA/m alternating magnetic field of 214 kHz frequency. These parameters indicate that LTE MNPs are perspective materials for biomedical applications such as hyperthermia.

Effect of a magnetic field on the rheological properties of magnetic liquids based on iron oxides

The concentration dependence of the effect a static magnetic field has on the viscosity of aqueous and water-glycerol magnetic liquids based on Fe2.8O4 iron oxide is studied. The viscosity of aqueous and water-glycerol magnetic liquids are found to grow by factors of 2.5 and 20, respectively, as the concentration of magnetic particles and the field intensity grow. The concentration dependence of the magnetic field effect passes through a maximum.

Flory-Huggins parameters for weakly crosslinked hydrogels of poly(acrylic acid) and poly(methacrylic acid) with various degrees of ionization

The interaction of poly(acrylic acid) and poly(methacrylic acid) polyelectrolyte networks with water in relation to their degrees of ionization is studied via the methods of isothermal equilibrium sorption and microcalorimetry. On the basis of these data, the integral Flory-Huggins parameters and their enthalpy and entropy components are calculated. It is shown that, at all degrees of ionization, water is a good solvent for poly(acrylic acid) gels and a poor solvent for poly(methacrylic acid) gels. At low degrees of ionization of networks, the thermodynamic quality of the swelling medium worsens for both gel series relative to that of the uncharged network. As the degree of ionization of the poly(acrylic acid) gel is increased above 10%, the quality of the solvent improves, and, at high degrees of ionization, the Flory-Huggins parameter becomes close to zero. For PMAA gels, the quality of the solvent improves when the degree of ionization is above 40%. An analysis of the enthalpy and entropy components of the binary interaction parameter shows that the observed tendencies are primarily related to the loss of entropy as a result of structuring processes in poly(acrylic acid) and poly(methacrylic acid) hydrogels. For poly(methacrylic acid) gels, an increase in the degree of ionization leads to increases in the negative values of the noncombinatorial entropy and the positive values of the entropy interaction parameter. This phenomenon is probably associated with the development of hydrophobic association processes. For hydrophilic poly(acrylic acid) gels, the entropy interaction parameter monotonically declines to zero with an increase in the degree of ionization, thereby ensuring improvement in the thermodynamic quality of the medium.

Interaction of aerosil nanoparticles with networks of polyacrylamide, poly(acrylic acid), and poly(methacrylic acid) hydrogels

For hydrogels based on rarely crosslinked matrices of polyacrylamide, poly(acrylic acid), and poly(methacrylic acid) filled with aerosil, the equilibrium degrees of swelling are measured as functions of the filler contents. The differences in the behaviors of gels are analyzed in terms of the competitive intermolecular interaction in three-component systems. For this purpose, the enthalpies of swelling for preliminarily dried and partially hydrated gels are measured via isothermal microcalorimetry. On the basis of concentration dependences of the enthalpy of swelling, the values of the enthalpy Flory-Huggins parameter for polymer matrices filled and unfilled with water, the parameters of structural changes in the polymers in filled hydrogels, and the enthalpies of adhesion and adsorption interactions of polymer matrixes with the surface area of aerosil are estimated. It is shown that there is a linear correlation between the change in the Flory-Huggins parameter and the enthalpy of adsorption of subchains on the surface of aerosil particles that assumes negative values in the case of poly(acrylic acid) and positive values in the case of poly(methacrylic acid) and polyacrylamide.