V. I. Yusupov

Laser-induced hydrodynamics in water-saturated biotissues. 1. Generation of bubbles in liquid

The hydrodynamic effects that are induced in water by the moderate-power (1–5 W) CW laser radiation delivered via an optical fiber are investigated. The effective hydrodynamic processes in water are related to the explosive boiling in the vicinity of the heated end surface of the fiber. The resulting bubbles with sizes ranging from several to several tens of microns have velocities of up to 100 mm/s in the vicinity of the end surface. The generation of bubbles in a capillary gives rise to the stable circulation of liquid with the period ranging from 0.2 to 1.0 s. The hydrodynamic effects under study can be employed in the surgical and regenerative procedures in biotissues.

Laser-induced hydrodynamics in water-saturated biotissues: 2. Effect on delivery fiber

The degradation of the end surface of the delivery fiber due to the laser-induced hydrodynamic processes caused by the irradiation of the water-saturated tissue by CW laser with a wavelength of 970 nm and moderate power (1–10 W) is analyzed. It is demonstrated that the temperature in the vicinity of the end surface can be up to several thousand degrees at a laser intensity of about 104 W/cm2. Relatively high temperatures and pressures that are reached upon the collapse of the cavitation microbubbles lead to the formation of the nanosized diamond-phase particles and supercritical water, which also facilitates the degradation of fiber.

Laser-induced hydrodynamics in water-saturated tissue: III. Optoacoustic effects

Studied in this work are specific features of acoustic vibrations generated at the hot blackened tip of an optical fiber (the so-called hot tip) delivering moderate-power (1?10?W) CW laser radiation in contact with water or a water-saturated biotissue. Generated upon such contact is a wideband acoustic signal whose characteristics largely depend on the object exposed and treatment scheme. Placing the hot tip in an acoustic resonator is demonstrated to cause distinct amplitude modulation of the acoustic noise. The formation of laser channels in an intervertebral disc or the intramedullary cavity of a bovine thighbone gives rise to the emission of a quasiperiodic train of pulses associated with the explosive growth and collapse of steam-gas bubbles in the hot-tip-to-biotissue contact region. The resultant pressure pulses, 20???15?MPa in amplitude, cause damage to the adjacent tissue and facilitate the production of a laser channel at a rate of some 0.4?5?mm?s?1. During the course of laser treatment the biotissue gradually gets saturated with steam-gas bubbles, which results in the development of low-frequency pressure oscillations in the range 0.1?10?Hz and a gradual pressure rise to around 200?kPa, leading to reduction of the natural frequencies of the resonance modes of the biotissue. The possible effect of these acoustic vibrations on the biotissue is discussed.

Effects of laser-induced quenching and restoration of photoluminescence in hybrid Si/SiOx nanoparticles

We studied the processes of pulsed and continuous-wave (CW) laser excitation of photoluminescence (PL) in nc-Si/SiOx nanoparticles. CW laser irradiation of the nc-Si/SiOx sol in dimethylsulfoxide (DMSO) and in a thin film was found to quench PL with an essentially nonexponential dynamics. The laser-induced variation of the Rayleigh scattering signal from the nc-Si/SiOx sol in DMSO was found to replicate that of the PL quenching. The IR and Raman spectra of the laser-exposed nc-Si/SiOx exhibited no new bands that could be evidence of their chemical transformations. There were also no perceptible effects pointing to laser-induced aggregation of the nc-Si/SiOx particles in the sol. 355xa0nm pulse-periodic laser irradiation of the nc-Si/SiOx particles preliminarily exposed to a 405xa0nm CW laser (which causes a strong PL quenching effect) was found to result in a rapid restoration of the original PL signal, which means that the effect of laser quenching of PL can be entirely reversible. We considered a mechanism of the reversible photosensitivity of nc-Si/SiOx, based on the processes of ionization of the photoluminescent oxygen-deficient centers in their suboxide shell and electron capture by traps, followed by their laser-assisted photorecombination.

Synthesis of photoluminescent Si/SiO x core/shell nanoparticles by thermal disproportionation of SiO: structural and spectral characterization

Core/shell Si/SiOx nanoparticles (Si/SiOx-NP) having bright red-infrared photoluminescence were obtained by a three-stage synthesis based on the thermal disproportionation of microdispersed SiO. Transformation patterns of structure and spectroscopic properties of the material during passage through all process stages (starting from initial SiO microparticles and up to the Si/SiOx-NP sols) have been revealed by using Raman, photoluminescence and ESR spectroscopy, XPS, XRD, and electron microscopy. Thermal annealing of SiO microparticles (stage I) results in formation of amorphous-crystalline Si nanophase in the matrix of SiO2, as well as generation of paramagnetic Pb centres with the concentration up to 4xa0×xa01018xa0particles/g. At the annealing temperature, Tanxa0>xa0900xa0°C, a rapid growth of nanocrystal sizes takes place, and, simultaneously, a rapid growth of paramagnetic Pb centre concentration occurs. Elimination of SiO2 from the annealed sample by etching in HF (stage II) stimulates further crystallization of amorphous-crystalline core, caused by stress relaxation inside the Si core when removing SiO2 matrix. Functionalization of nanoparticle surface (stage III) allows obtaining core/shell Si/SiOx-NP with a bright red-infrared photoluminescence and their sols. Average size of the crystalline Si core increases from 4.7 to 11.1xa0nm when Tan at the stage I rises from 350 to 1100xa0°C. At relatively low Tanxa0=xa0350xa0°C, the nanoparticles with monocrystalline Si cores are mainly formed, while at Tanxa0>xa01100xa0°C, a large number of polycrystalline Si nanoparticles are also observed. Our TEM images have revealed the existence of monocrystalline Si nanoparticles having significantly different contrast even at comparable nanoparticle sizes. We attribute that to the formation of both bulk (with a high TEM contrast) and flat (2D) Si nanocrystals (with a low TEM contrast) in the course of SiO annealing.

Trapping of nanoparticles in a liquid by laser-induced microbubbles

Nanoparticles a few nanometers in diameter contained in a colloidal solution can be captured by the surface of a microbubble produced by a well-focused beam of a continuous wave visible laser. The concentration of the nanoparticles on the surface of the microbubble is found to gradually increase during the course of irradiation. The mechanism of such a trapping is associated with the laser-induced Marangoni convection developing in the vicinity of the microbubble as a result of the temperature gradient obtained at its surface.

[Influence of low-dose-rate red and near-infrared radiations on the level of reactive oxygen species, the genetic apparatus and the tumor growth in mice in vivo].

The effect of low-dose-rate red and near-infrared radiations from the matrix of light emitted diode (650 nm and 850 nm) and a He-Ne laser (633 nm) on activation of the reserve of a natural defense system in the mice exposed to radiation in vivo was studied by the level of reactive oxygen species (ROS) production in blood cells, the induction of cytogenetic adaptive response in bone marrow cells, thymus and spleen, and the rate of Ehrlich ascites carcinoma growth in a solid form. As a positive control animals were irradiated with X-rays by the scheme of the radiation-induced adaptive response (0.1 Gy + 1.5 Gy). The levels of ROS production was assessed in whole blood by luminol-dependent chemiluminescence, of cytogenetic damage — by the “micronucleus test” in the bone marrow, the weight of the thymus and spleen — by index of organ, and the rate of tumor growth — according to its size for 30 days after inoculation. Adaptogenic and anticarcinogenic effects of studied radiations were revealed. The values of these effects were not different from those in animals pre-irradiated with the X-rays. The relationship between the level of ROS production and adaptive response induction in the mice under the influence of non-ionizing radiation was first ascertained. The experimental data obtained may indicate a similar mechanism of induction of protective responses to ionizing and non-ionizing radiations in mice in vivo.

Induction of the Adaptive Response in Mice Exposed to He-Ne Laser and X-Ray Radiation

We studied the dose-dependent induction of in vivo adaptive response in the bone marrow and blood of mice exposed to low-intensity radiation of He-Ne laser (633 nm) and X-ray radiation by the severity of cytogenetic injury and intensity of ROS production, respectively. Induction of the adaptive response in mice preexposed to He-Ne laser and X-ray radiation depended on the adaptive dose and the interval between the adaptive and main doses and correlated with changes in ROS generation. The adaptive response after exposure to low-intensity ionizing and non-ionizing radiation was observed in the same dose range, which attests to similar mechanisms of its induction.

Dynamics of a photothermal self-assembly of plasmon structures in polymer films containing gold and silver precursors

This work is devoted to considering mechanisms that form silver and gold nanoparticles (NPs) in thin (200 μm) cross-linked oligourethane methacrylate (OUM) polymer films impregnated with different precursors of these metals. The investigations are connected with recording the kinetics of variation in the transmission of films under the action of continuous laser radiation with wavelengths of 405 and 532 nm, resulting in the photolysis of precursor molecules. Precursor molecules were introduced into the matrix by the diffusion saturation of films in an ethanol medium or in supercritical carbon dioxide. It was established that the time dependences are determined by the metal type, wavelength, and laser radiation power, as well as by way of precursor impregnation. Two effects connected with laser action on such films were found. One of them corresponds to a jumplike change in transmission of samples with the gold precursor; the second is caused by the formation of dense NP structures in the form of films on the sample surface.

Influence of low-intensity red diode and laser radiation on the locomotor activity of sea urchin sperm

146 Monochromatic (laser) and quasimonochromatic light in the range 600–900 nm can stimulate metabolic processes in eukaryotes [1–4]. Despite the fact that this phenomenon has already been successfully used for decades in medical practice (low intensity laser therapy), the range of possible applications of this type of radiation is still expanding, and the cellular mecha nisms of interaction of the laser beam with cells are investigated.