V. M. Podgaetsky

Nonlinear absorption in pyran dyes

The paper represents the results of nonlinear absorption study for solutions of deciaminomethylenepyran dyes DCM 627 and DCM-684 (yuloidine) at wavelength of 532 nm with 350 ps pulse duration obtained with the use of z-scan technique. It is shown that the induced absorption detected is due to two-photon absorption. Nonlinear and two-photon coefficients of absorption are evaluated. The results of numerical simulation are presented.

The tensile strength characteristics study of the laser welds of biological tissue using the nanocomposite solder

Laser welding device for biological tissue has been developed. The main device parts are the radiation system and adaptive thermal stabilization system of welding area. Adaptive thermal stabilization system provided the relation between the laser radiation intensity and the weld temperature. Using atomic force microscopy the structure of composite which is formed by the radiation of laser solder based on aqua- albuminous dispersion of multi-walled carbon nanotubes was investigated. AFM topograms nanocomposite solder are mainly defined by the presence of pores in the samples. In generally, the surface structure of composite is influenced by the time, laser radiation power and MWCNT concentration. Average size of backbone nanoelements not exceeded 500 nm. Bulk density of nanoelements was in the range 106-108 sm-3. The data of welding temperature maintained during the laser welding process and the corresponding tensile strength values were obtained. Maximum tensile strength of the suture was reached in the range 50-55°C. This temperature and the pointwise laser welding technology (point area ~ 2.5mm) allows avoiding thermal necrosis of healthy section of biological tissue and provided reliable bonding construction of weld join. In despite of the fact that tensile strength values of the samples are in the range of 15% in comparison with unbroken strips of pigskin leather. This situation corresponds to the initial stage of the dissected tissue connection with a view to further increasing of the joint strength of tissues with the recovery of tissue structure; thereby achieved ratio is enough for a medical practice in certain cases.

Investigation of cell proliferative activity on the surface of the nanocomposite material produced by laser radiation

A new method for the formation of composite nanomaterials based on multi-walled and single-walled carbon nanotubes (CNT) on a silicon substrate has been developed. Formation is carried out by ultrasound coating of a silicon substrate by homogenous dispersion of CNTs in the albumin matrix and further irradiation with the continuous laser beam with a wavelength of 810 nm and power of 5.5 watts. The high electrical conductivity of CNTs provides its structuring under the influence of the laser radiation electric field. The result is a scaffold that provides high mechanical strength of nanocomposite material (250 MPa). For in vitro studies of materials biocompatibility a method of cell growth microscopic analysis was developed. Human embryonic fibroblasts (EPP) were used as biological cells. Investigation of the interaction between nanocomposite material and cells was carried out by optical and atomic force microscopy depending on the time of cells incubation. The study showed that after 3 hours incubation EPP were fixed on the substrate surface, avoiding the surface of the composite material. However, after 24 hours of incubation EPP fix on the sample surface and then begin to grow and divide. After 72 hours of incubation, the cells completely fill the sample surface of nanocomposite material. Thus, a nanocomposite material based on CNTs in albumin matrix does not inhibit cell growth on its surface, and favours their growth. The nanocomposite material can be used for creating soft tissue implants

Laser structuring of carbon nanotubes in the albumin matrix for the creation of composite biostructures

Abstract. This paper presents the composite biostructures created by laser structuring of the single-walled carbon nanotubes (SWCNTs) in an albumin matrix. Under the exposure of femtosecond laser radiation, the heating of the albumin aqueous solution causes liquid water to evaporate. As a result, we obtained a solid-state composite in the bulk or film form. Using the molecular dynamic method, we showed the formation of a framework from SWCNTs by the example of splicing of the open end of one nanotube with the defect region of another nanotube under the action of the laser heating. Laser heating of SWCNTs up to a temperature of 80°C to 100°C causes the C─C bond formation. Raman spectra measured for the composite biostructures allowed us to describe the binding of oxygen atoms of amino acid residues of the albumin with the carbon atoms of the SWCNTs. It is found that the interaction energy of the nanotube atoms and albumin atoms amounts up to 580  kJ/mol. We used atomic force microscopy to investigate the surface of the composite biostructures. The pore size is in the range of 30 to 120 nm. It is proved that the proliferation of the fibroblasts occurred on the surface of the composite biostructures during 72 h of incubation.

The method of laser forming of nanocarbon biocompatible coatings for implants

The work is devoted to laser method of biocompatible coatings forming to create implants of the human body ligaments. Coating is a carbon nanotubes scaffold formed in the water-protein dispersion by the electric field of the laser radiation. Study has been conducted on the structure and properties of carbon nanotubes coatings and proliferative activity of biological cells on its surface.

Laser-limiting materials for medical use

The important problem of modern laser medicine is the decrease of an exposure of biological tissues outside of an operational field and can be solved by optical radiation limiting. Organic dyes with reversibly darkening can be placed onto surfaces of irradiated tissues or can be introduced in solder for laser welding of vessels. The limiting properties of a set of nontoxic organic compounds were investigated. Nonlinear optical properties of dyes having reverse saturable absorption (pyran styryl derivatives, cyanine and porphyrine compounds) were studied under XeCl and YAG:Nd (II harmonics) lasers excitation. The effect of attenuation of a visible laser radiation is obtained for ethanol solutions of cyanines: radiation attenuation coefficient ( AC) = 25-35 at N/S = 100-250 MW/cm2. In water solutions of such compounds in UV spectrum range AC ≈ 10. The spectral characteristics of compounds appeared expedient enough to operational use in laser limiters (broad passband in visible range of a spectrum). Under the data of Z-scanning (the scheme F/10) value AC ≈ 70 was reached. The limiting of power laser radiation in visible (λ = 532 nm) and UV- (λ = 308 nm) spectral region and nanosecond pulse duration (7 -13 ns) across porphyrine solutions and their complexes with some metals (13 compounds) was investigated too. The comparative study of optical limiting dependence on intensity of laser radiation, solvent type and concentration of solutions was carried out for selecte wavelength. There was shown a possible use of pyran styryl derivatives DCM as limiters of visual laser radiation. To understand a mechanism of laser radiation limitation the light induced processes were experimentally and theoretically studied in organic molecules. The quantum-chemical investigation of one cyanine compound was carried out. There were noted the perspectives of laser radiation limiting by application of inverted schemes of traditional laser shutters. Usage of phenomena of light -induced opalescence in one-component liquids and spinodal decay in stratifying liquid solutions is proposed.

Synthesis of new sulfonated mono- and diphthalocyanines d- and f-elements and perspectives of their application for plastic surgery

We carried out the synthesis of the new compounds -- sulfonated mono- and diphthalocyanines of d- and f-elements (sPcM, sPc2M). The unusual geometry of these compounds leads to the appearance of new properties -- they are highly water soluble, non- toxic and in contrast to porphyrines they strongly absorb clinically useful light. Suitable methods for synthesis of unknown before water soluble Ga, In and Ti phthalocyanines have been developed. Our investigations show that these compounds are prospects for plastic surgery.

Nonlinear threshold effect in the Z-scan method of characterizing limiters for high-intensity laser light

A threshold model is described which permits one to determine the properties of limiters for high-powered laser light. It takes into account the threshold characteristics of the nonlinear optical interaction between the laser beam and the limiter working material. The traditional non-threshold model is a particular case of the threshold model when the limiting threshold is zero. The nonlinear characteristics of carbon nanotubes in liquid and solid media are obtained from experimental Z-scan data. Specifically, the nonlinear threshold effect was observed for aqueous dispersions of nanotubes, but not for nanotubes in solid polymethylmethacrylate. The threshold model fits the experimental Z-scan data better than the non-threshold model. Output characteristics were obtained that integrally describe the nonlinear properties of the optical limiters.

Research on limiting of high power laser radiation in nonlinear nanomaterials

Dispersive and composite nanomaterials based on multi-walled and single-walled carbon nanotubes and its conjugates with dye of zinc phthalocyanine were produced. The composition and the structure of dispersive and composite materials were investigated using analytical methods of spectroscopy and microscopy. Nonlinear characteristic of nanomaterials of limiters by direct nonlinear scanning and Z-scan method were investigated. Studies suggest the possibility of using such nanomaterials in laser intensity limiters. Proposed threshold model characterizing limiters of powerful laser radiation takes into account the threshold nature of nonlinear interaction of irradiation with the nonlinear material. Threshold effect of nonlinear interaction of laser irradiation with several nonlinear material based on multi-walled and single-walled carbon nanotubes was experimentally found. It was shown that threshold model fit better with experimental data of Z-scan.

Picosecond streak camera application in experiments on optical tomography of biological media

There are some difficulties in the use of a well-known X-ray computer tomography technique due to the strong light scattering in biological tissues. We propose to analyze the whole light scattering picture for the development of novel processing algorithms in tomographical imaging. Time-resolved experiments on the forward scattering of IR-light from a model of biological media illuminated by a picosecond YAG-laser with 10 ps pulse duration have been performed. The scattering radiation was recorded by a streak camera having 1.5 ps time resolution. From these results and theoretical considerations the analytic expression for intensity against time distribution of the laser radiation passed through the media has been obtained. The expression can be used as the basis for tomographical reconstruction.