V.G. Andreev

Composition of PLGA and PEI/DNA nanoparticles improves ultrasound-mediated gene delivery in solid tumors in vivo

The goal of this study was to enhance gene delivery and tumor cell transfection in vivo by using a combination of ultrasonication with complex nanoparticles consisting of two types of nanoparticles: PEI/DNA beta-gal plasmid with highly positive zeta-potential and air-filled poly (lactic-co-glycolic acid) (PLGA) particles (with negative zeta-potential) manufactured in our laboratory. The PLGA/PEI/DNA nanoparticles were a colloid with positive zeta-potential and injected i.v. in nude mice with DU145 human prostate tumors. We found that the combination of PLGA/PEI/DNA nanoparticles with ultrasonication substantially enhanced tumor cell transfection in vivo. The overexpression of beta-gal gene was evaluated histochemically and by Western blot analysis. At least an 8-fold increase of the cell transfection efficacy was obtained in irradiated tumors compared to non-irradiated controls, while little to no cell death was produced by ultrasonication.

Porous silicon nanoparticles as sensitizers for ultrasonic hyperthermia

Aqueous suspensions of porous silicon nanoparticles (NPs) with average size ∼100 nm and concentration ∼1 g/L undergo significant heating as compared with pure water under therapeutic ultrasonic (US) irradiation with frequencies of 1–2.5 MHz and intensities of 1–20 W/cm2. This effect is explained by taking into account the efficient absorption of US energy by NPs. The observed US-induced heating of biodegradable NPs is promising for applications in ultrasonic hyperthermia of tumors.

A thermoacoustic sensor for recording high-power nanosecond microwave pulses

The operating principle and design of an uncooled noise-immune high-power microwave pulse sensor is described. The sensor operation is based on the effect of acoustic signal generation when microwave pulses are absorbed in a layer structure, in which a thin metal nanometer-thick film is used as an absorber. The sensor is placed in a free space and intended to detect microwave pulses with ∼10- to 100-ns durations in a 10- to 300-GHz frequency band with a pulse repetition rate of up to 5 kHz. For 10-ns-long pulses, the sensor sensitivity is 0.5 V/mJ.

Measurement of shear elasticity and viscosity of rubberlike materials

The method and results of measuring the shear elastic modulus of a rubberlike polymer by the deformation of a plane elastic layer are described. For shear deformations not exceeding 0.5 of the layer thickness, the shear modulus is constant and its value is in agreement with the value determined by pressing a rigid ball against the polymer layer. For deformations exceeding 0.5 of the layer thickness, the stress-strain dependence becomes nonlinear. The coefficient of shear viscosity is determined from the shear wave form generated by focused ultrasound in a homogeneous polymer sample.

Motion of a group of microparticles in a viscoelastic medium under the action of acoustic radiation force

We theoretically and experimentally substantiate the method of detecting microcalcifications in mammary gland tissue. Calcium salts accumulate in soft tissues, primarily forming clusters of individual microparticles. We study the motion of solid microparticles distributed in a viscoelastic medium. Displacement of particles is caused by the radiation force occurring as a consequence of energy scattering and absorption of an ultrasound beam focused in the particle region. The radiation force acts over the course of 200 μs, after which the medium with distributed particles relaxes to the initial state. Motion of the medium is tracked by the cross-correlation method with short probing pulses following at a frequency of 5 kHz. The presence of solid microparticles leads to a change in the character of motion of the medium after pulsed ultrasound action. The amplitude and duration of displacements increases in comparison to the homogeneous medium, and the motion character itself becomes significantly complicated.

Shear standing waves in a resonator with a rubberlike inhomogeneous medium

A modification of the finite-element method is proposed for calculating shear standing waves in a resonator filled with an incompressible elastic medium with allowance for the finite dimensions of the resonator and inhomogeneities of the shear modulus. Resonance curves are calculated for resonators with inhomogeneities in the form of cavities and elastic inclusions. Numerical calculations are compared with experimental data.

Spectral characteristics of nanometer-thick chromium films in terahertz frequency range

The spectral characteristics (reflection, transmission, and absorption coefficients) of thin chromium films on silica substrates have been measured using a pulsed source of terahertz radiation. The spectra of optical coefficients were obtained in a frequency range of 0.25–1.1 THz. Dependences of the optical coefficients on the metal film thickness at 1 THz were constructed. The maximum absorption coefficient (43%) was observed at a film thickness of 10 nm.

Shear wave excitation in a rubberlike medium by focused shock pulse

Ultrasonic excitation of shear waves is important for elasticity imaging of biological tissue. In the shear wave elasticity imaging shear strain is remotely induced in tissue by the radiation force of focused modulated ultrasound. Previous study has shown that tone bursts of millisecond duration at megahertz frequencies with intensities and exposures typical for diagnostic ultrasound may induce bulk radiation force of the order of 0.01 N/cm3 and shear displacements of the order of 10 μ. In this work, new nonlinear mechanisms are discussed that provide detectable shear displacements by means of single submicrosecond pulses. Two new possibilities are discussed. Significantly enhanced radiation force and greater shear displacement can be produced in tissue by single acoustic videopulse with nonzero momentum. Another possibility is based on the enhanced nonlinear absorption which occurs after the shock is formed in the temporal profile of the pulse. Nonlinear mathematical models describing the process of gene...

Excitation of shear waves inside of rubberlike material by focused ultrasound

It is known that the difference in shear modulus for normal tissues and for pathological ones can reach two or three orders. This is the basis for the development of a very sensitive medical diagnostics method. Shear stresses inside of tissue can be excited by a focused ultrasound. The efficiency of this process is the main problem. The phenomenon of shear wave excitation by a focused acoustical beam has been studied experimentally and theoretically. In the experiment a shear wave has been excited in rubberlike material (transparent polymer) by powerful focused ultrasonic beam in a pulsed regime. The registration of the shear deformation has been performed by means of an optical beam, which was focused at a target in the thickness of polymer sample. Temporal profiles of a shear wave have been registered at different distances from the focal region. The measured value of shear wave velocity was in a good agreement with its theoretical prediction. A theoretical model of shear wave generation by a beam of a ...

Motion of spherical microparticles in a viscoelastic medium under the action of acoustic radiation force

The motion of spherical microparticles with sizes (50–250 μm) less than or comparable to the wavelength of ultrasound (300 μm) in a gel-like medium is studied. Particle displacement is defined by the acoustic radiation force and the motion of the medium. It is shown that a specific feature of microparticle motion is their complete deceleration for a time of about 1 ms after switching off the ultrasound, and their subsequent displacement is determined entirely by the medium’s relaxation. The aim of the work is to develop ultrasonic means of detecting microcalcifications in breast tissues.