Mikhail S. Savelyev

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.

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.

Threshold effect in optical limiters based on conjugates J-type phthalocyanine dimers Zn and Mg with single-walled carbon nanotubes

Laser radiation limiters can be made on the basis of working substances, which have strong nonlinear effects after reaching a certain critical value (threshold limiting). Thus, it becomes possible to obtain a high transmission for a safe beam and a sharply reduced transmission for a hazardous beam. To determine the nonlinear and linear optical properties of these materials there were carried out comprehensive spectroscopic studies, experiments by Z-scan methods with an open aperture and a fixed location of the limiter. Working substances was developed which is suspension of conjugates J-type phthalocyanine dimers Zn or Mg with single-walled carbon nanotubes (SWCNTs) in water. Created conjugates can be used not only for protecting eyes and light-sensitivity elements, but for forming three-dimensional tissueengineered structures. Using conjugates J-type phthalocyanine dimers Zn and Mg with SWCNTs will increase the optical absorption in the wavelength range of laser processing by reducing the thermal effect on other substances in the composition of this structure. The Nd:YAG laser was used as the laser radiation source for generating pulses of 16 ns duration at a wavelength of 532 nm with the linearly polarized laser beam in the horizontal plane and a shape of Gaussian type. The threshold of limiting, linear and nonlinear absorption coefficients were determined by output characteristic, that was obtained by fixed location of the limiter. Created working substances have values of the following order: linear absorption coefficient ~ 3 cm-1 for layer of 0.2 cm thickness, low limiting threshold ~ 1 MW·cm-2 and high value of the nonlinear absorption coefficient ~ 550 cm GW-1 . Knowing the nonlinear optical parameters, Z-scan data with an open aperture can be calculated for comparison with experimental data.

Laser nanocomposites based on proteins and carbon nanotubes for restoration of biological tissues

The study of structural properties of nanocomposites, based on different types of single walled carbon nanotubes (SWCNTs) and proteins (albumin, collagen), was carried out. The binding of protein molecules to the carbon component was described by Raman spectroscopy. Complex analysis of the structure and microporosity of nanocomposites was performed by the X-ray microtomography. The nanoporosity study was carried out using the low-temperature nitrogen porosimetry method. Samples based on SWCNTs with smaller size had the most homogeneity. With an increase in the concentration from 0.01 to 0.1 %, the mean micropore size increased from 45 to 93 μm, porosity in general increased from 16 to 28 %. The percentage of open pores was the same for all samples and was 0.02. As it was shown by Raman spectroscopy the protein component in nanocomposites has undergone irreversible denaturation and can act as a biocompatible binder and serve as a source of amino acids for biological tissues. These nanocomposites are bioresorbable and can be used to repair cartilage and bone tissue. This is especially important in the treatment of diseases of hyaline cartilage and subchondral bone.

Threshold effect in properties of limiters for high-intensity laser radiation

Creation of limiters for intensive laser radiation requires the development of effective methods for testing materials to determine the nonlinear optical parameters characterizing their properties. The limiting threshold, linear and nonlinear absorption coefficients can be determined not only from data of Z-scan with open aperture, but also with the help of a fixed location of the limiter. The use of this method makes it possible to determine the output characteristic of the studied material from which nonlinear optical parameters can be calculated. Characteristics of carbon nanotubes and graphene oxide in water were obtained with the fixed location of the limiter. The experiments were performed using an Nd:YAG laser that generates pulses of 16 ns duration at a wavelength of 532 nm with the linearly polarized laser beam in the horizontal plane and a shape closed to Gaussian type. Theoretical curves for method of fixed location of the sample according to threshold model was calculated and compared with the experimental data. Normalized weakening coefficients, limiting threshold, linear and nonlinear absorption coefficients were found for studied dispersions and calculation of Z-scan with open aperture was made. The value of normalized weakening coefficient was higher in dispersed medium of SWСNTs with water (Knorm≈20) in comparison with oxide graphene in water (Knorm≈14). The dependences of normalized weakening coefficient bias input energy were approximately linear in both cases.

Laser structuring of carbon nanoframe in a protein matrix for the creation of 3D composite materials and coatings for applications in tissue engineering

The results of experimental creation of nanocomposites using femtosecond laser are presented. We have theoretically proved the formation of a carbon nanotube frame in a protein matrix during laser structuring of single-walled carbon nanotubes. We have selected the technological parameters of synthesis of nanocomposites, which provide the proliferation of living cells.

Creation of advanced optical limiters based on J-type phthalocyanine dimers and their conjugates with single-walled carbon nanotubes

Creation of effective means of protection from laser radiation of high power requires the development of optical materials (working substance), with their transparence being decreased sharply above a certain critical value of the laser intensity due to the appearance of non-linear optical properties (limiting threshold). Based on the threshold model, the working substance of the optical limiter was characterized. Experimental data of z-scan with open aperture are used to determine the nonlinear optical parameters of solutions of dimeric phthalocyanine complexes of Mg and Zn of J-type in tetrahydrofuran (THF) and thin films of their conjugates with single-walled carbon nanotubes (SWCNTs). The output characteristic (output (peak) fluence vs input (peak) fluence), that describes the basic properties of optical limiters, was obtained with the fixed location of the optical limiter. Dimeric phthalocyanine complexes were found to have low limiting threshold ~ 2 MW·cm-2 and high value of the nonlinear absorption coefficient ~ 330 and 370 cm GW-1, respectively. Conjugates of these dimeric phthalocyanines with SWCNTs have been produced for the improving of the limiting parameters and increasing of the optical nonlinearity. Size of J-type dimeric phthalocyanine complexes of Mg and Zn were determined by the scanning electron microscopy (SEM). The atomic force microscopy (AFM) allowed to determine the dimensions of nanotubes. The structure parameters, such as diameter and defects as well as the strength of aggregates were estimated with the Raman spectroscopy. For our experiments, the lens with a focal length of 20 cm was used. As the laser radiation source, the Nd:YAG laser was used to generate pulses of 16 ns duration at a wavelength of 532 nm with the linearly polarized laser beam in the horizontal plane and a shape closed to Gaussian type.

Investigation of laser limiters based on disperse and composite nanomaterials

Work is devoted to the search new materials of laser irradiation limiter. Were created nanomaterials (dispersion and composites) for limiters based on multiwalled and single-walled carbon nanotubes. Were carried out studies of the structure of nanomaterials by atomic force microscopy. Investigated the thermal and photo-stability of the samples. Measured and calculated nonlinear optical properties of nanomaterials by direct scanning and Z-scan. A comparison of theoretical and practical nonlinear optical characteristics. And also investigated the electrical conductivity of liquid and solid nanomaterials.

Investigation of limiting properties of nonlinear materials

Definition of nonlinear optical characteristics of substances of laser radiation limiters (LRL) was considered. Nanocomposite and disperse optical materials based on single-walled carbon nanotubes (SWCNT) of semiconducting and metal types with a high perfection of the crystal structure were investigated. The amount of semiconducting SWCNTs outnumbered metal several times Most SWCNTs were presented in clusters as separate loose fibers. It indicated a high degree of its dispersion. In the dispersion of carboxylated SWCNTs in tetrahydrofuran laser attenuation coefficient AC ~ 13 at a linear transmission T0 ≈ 75 %. In the dispersion of SWCNT functionalized zinc phthalocyanine derivatives, AC = 13-14 at T0 = 55-75%. Nanocomposites based on polymethylmethacrylate with functionalized SWCNTs AC ~ 8 at T0 ≈ 70%. A new method of simultaneous calculation of the beam waist radius and nonlinear absorption coefficient from the Z_scan data is proposed. The value of nonlinear optical characteristics of ZnSe, porphyrin-graphene (Graphene-TPP), fullerene-graphene (Graphene-60), polyethylene oxide containing multilayer carbon nanotubes (PEO/MWNT), along with polymethine dyes PD-792 and PD-7098 and dicyanomethylene pyran dyes DCM-627 and DCM-684, are obtained.