Stability and Thrombogenicity Analysis of Collagen/Carbon Nanotube Nanocomposite Coatings Using a Reversible Microfluidic Device.

Currently, the development of stable and antithrombogenic coatings for cardiovascular implants is socially important. This is especially important for coatings exposed to high shear stress from flowing blood, such as those on ventricular assist devices. A method of layer-by-layer formation of nanocomposite coatings based on multi-walled carbon nanotubes (MWCNT) in a collagen matrix is proposed. A reversible microfluidic device with a wide range of flow shear stresses has been developed for hemodynamic experiments. The dependence of the resistance on the presence of a cross-linking agent for collagen chains in the composition of the coating was demonstrated. Optical profilometry determined that collagen/c-MWCNT and collagen/c-MWCNT/glutaraldehyde coatings obtained sufficiently high resistance to high shear stress flow. However, the collagen/c-MWCNT/glutaraldehyde coating was almost twice as resistant to a phosphate-buffered solution flow. A reversible microfluidic device made it possible to assess the level of thrombogenicity of the coatings by the level of blood albumin protein adhesion to the coatings. Raman spectroscopy demonstrated that the adhesion of albumin to collagen/c-MWCNT and collagen/c-MWCNT/glutaraldehyde coatings is 1.7 and 1.4 times lower than the adhesion of protein to a titanium surface, widely used for ventricular assist devices. Scanning electron microscopy and energy dispersive spectroscopy determined that blood protein was least detected on the collagen/c-MWCNT coating, which contained no cross-linking agent, including in comparison with the titanium surface. Thus, a reversible microfluidic device is suitable for preliminary testing of the resistance and thrombogenicity of various coatings and membranes, and nanocomposite coatings based on collagen and c-MWCNT are suitable candidates for the development of cardiovascular devices.

Spectral analysis combined with nonlinear optical measurement of laser printed biopolymer composites comprising chitosan/SWCNT.

Biopolymer composites based on two types of chitosan (chitosan succinate and low-molecular weight chitosan) with single-walled carbon nanotubes (SWCNT) were created by laser printing. SWCNT have good dispersibility in chitosan solutions and therefore, can form relatively homogeneous films that was shown in scanning electron microscopy images. For the studies film composites were formed under the action of laser radiation on aqueous dispersion media. Study of the nonlinear optical process during the interaction of laser radiation with a disperse media has shown that low-molecular chitosan has a large nonlinear absorption coefficient of 17 cm/GW, while the addition of SWCNT lead to a significant increase up to 902 cm/GW. The threshold intensity for these samples was 5.5 MW/cm2 with nanotubes. If intensity exceeds the threshold value, nonlinear effects occur, which, in turn, lead to the transformation of a liquid into a solid phase. Characterization of films by FTIR and Raman spectroscopy indicated arising molecular interactions between chitosan and SWCNT detected as a small frequency shift and a change in the shape of radial breathing mode (RBM). The results indicate the possibility using aqueous dispersion media based on chitosan and SWCNT to create three-dimensional films and scaffolds for tissue engineering by laser printing.

The study of the interaction mechanism between bovine serum albumin and single-walled carbon nanotubes depending on their diameter and concentration in solid nanocomposites by vibrational spectroscopy.

The results of the study of composites based on bovine serum albumin (BSA) and single-walled carbon nanotubes (SWCNT) are presented. Nanocomposites were created by evaporation of the water-albumin dispersion with nanotubes using diode laser with temperature control. Two types of nanotubes were used. SWCNT I were synthesized using the electric arc method, SWCNT II were synthesized using the gas phase method. SWCNT I had a diameter and length less than SWCNT II. The mechanism of interaction between BSA and SWCNT in solid nanocomposites is considered. An experimental and theoretical studies of the interaction between aspartic (Asp) and glutamic (Glu) amino acids located on the outer surface of BSA and nanotubes using of vibrational spectroscopy (Fourier-transform infrared (FTIR) and Raman spectroscopy) was carried out. The possibility of nanotubes functionalization by oxygen atoms of negative amino acid residues Asp and Glu, which are on the outer surface of BSA, is shown by molecular modeling. The formation of covalent bonds between BSA and SWCNT in nanocomposites with different concentrations of nanotubes (0.01, 0.1 and 1 g/l) was confirmed by vibrational spectra. The covalent interaction between BSA with SWCNT under the laser irradiation leads to the conformational changes in the secondary and tertiary structures of albumin. This is confirmed by a significant decrease in the intensity of the absorption bands in the high-frequency region. The calculation of the vibrational spectra of the three Glycine:Glycine, Glutamic acid:Threonine and Aspartic acid:Lysine complexes, which take into account hydrogen, ion-dipole and ion-ion bonds, showed that a disturbance in the intermolecular interaction between amino acid residues led to significant decrease in the intensity of absorption bands in the region of stretching vibrations bonds OH and NH. From the Raman spectra, it was found that a significant number of defects in SWCNT is caused by the covalent attachment of oxygen atoms to the graphene surface of nanotubes. An increase in the diameter of nanotubes (4 nm) has practically no effect on the absorption spectrum of nanocomposite, while measuring the concentration of SWCNT affects the FTIR spectra. This confirmed the hydrophobic interaction between BSA and SWCNT. Thus, it was shown that BSA solid nanocomposites with CNTs can interact either with the help of hydrophobic forces or with the formation of covalent bonds, which depends on the diameter of the used nanotubes. The viability of connective fibroblast tissue cells on nanocomposites with both types of SWCNT was demonstrated. It was found that nanocomposites based on SWCNT I provide slightly better compatibility of their structure with fibroblasts. It allows to achieve better cell adhesion to the nanocomposite surface. These criteria make extensive use of scaffold nanocomposites in biomedicine, depending on the requirements for their quality and application.

Ionic and tautomeric composition of cytosine in aqueous solution: resonance and non-resonance Raman spectroscopy study.

A complex experimental and theoretical study of the structural composition of cytosine in water was performed. Raman and resonance Raman spectra of cytosine in acidic, neutral, and alkaline water solutions (pH = 3, 7, and 10, respectively) were recorded at excitation wavelengths of 514, 266, 218, and 200 nm. The temperature dependence of the frequencies and intensities of the resonance Raman bands was obtained in the temperature interval of 4-80 °C. To interpret the experimental Raman and resonance Raman spectra and to determine the structural composition of the water solution of cytosine, the spectra of cytosine and its cation, anion, oxoimine, and hydroxoamine forms were calculated at the B3LYP/6-311++G(d,p) level using the SCRF method. The electronic spectra and geometric parameters of the cytosine and its molecular forms in the excited electronic states close to the excitation wavelengths of the resonance Raman spectra were calculated using the DFT method. The cation exists in the acidic solution together with cytosine and its oxoimine and hydroxoamine tautomeric forms. Cytosine with a small amount of anion dominates in the alkaline medium. The structural composition of the water solution of cytosine is confirmed by the results of quantum-mechanical calculations of the intensity distribution in the resonance Raman spectra.

Raman spectroscopic study of the tautomeric composition of adenine in water.

An experimental and theoretical study of the tautomeric composition of adenine (Ade) in water using Raman spectroscopy is reported. Experimental resonance Raman spectra of adenine at excitation wavelengths of 200, 218, and 266 nm were compared with quantum-mechanical calculations of N(9)H- and N(7)H-adenine tautomers and their cations. Both theoretical and experimental studies of nonresonance Raman spectra (457 nm excitation) of adenine were also performed for comparison. A satisfactory agreement of the calculated results with the experimental data was obtained. The Raman spectra are interpreted, and the basic regularities of the Raman intensity distribution are explained. On the basis of the analysis performed, the tautomeric composition of adenine in water is revealed. It is shown that the Ade-N(9),N(1)H(+) cation is the predominant form and that some neutral forms of Ade-N(9)H and Ade-N(7)H tautomers exist in water at pH 3.