Development of experimental microfluidic device and methodology for assessing microrheological properties of blood.

BACKGROUND AND OBJECTIVE: Microfluidics is a useful tool for investigating blood microrheology. The study aimed to present the development of a microfluidic device for assessing the microrheological properties of blood cells' suspensions and its application in patients with diabetes mellitus type 2 (T2DM). METHODS: A new microfluidic device was elaborated, connected to a system, including a microscope with a digital camera, a pump with a manometer and a computer with specially developed software. Blood cells' suspensions were investigated in a microchamber between two parallel optical slides within a 100µm distance. The motion of the blood cells in the microchamber was observed by the microscope and it was recorded and visualized by a digital camera. A method for evaluating the deformability of blood cells and a device for its implementation were used [1]. RESULTS: The pressure and flow rate ranges in the microfluidic device were specified by model suspensions of beta-ferroxy-hydroxide and red blood cells (RBC) suspensions. The pressure changes, realized by a pump (micropipette), connected to a manometer were established and the corresponding shear rates in the microfluidic device were determined. Data about the blood microrheological properties like RBC aggregation and deformability, leukocyte adhesion from a group of healthy volunteers and from patients with T2DM were obtained. CONCLUSIONS: The developed device and experimental system is a promising tool for the study of blood microrheology.

Smart Complex Fluids Based on Two-Antennary Oligoglycines.

Antennary oligoglycines are synthetic products, obtained as a result of preliminary molecular design. Equal-length antennae are built of glycine residues joined through the C end to an oligoamine branching core with an amine group at the N terminus exposed outside. The results of systematic research on the properties of aqueous solutions containing two-antennary oligoglycine with four glycine portions are reported. The central feature is the competition between amphiphilic self-assembly and formation of polyglycine II motifs. A combined procedure is developed to characterize bulk and interfacial structures and coatings. It includes registration of bulk aggregates, examination of interfacial layers at solution/air and solution/solid boundaries, drainage, and stability of liquid films. The obtained results provide new insight into the structure-property relationships in these smart fluids and give essential hints about key factors allied to possible applications in medicine, pharmaceuticals, and environmental protection.

Combined Sum Frequency Generation and Thin Liquid Film Study of the Specific Effect of Monovalent Cations on the Interfacial Water Structure.

Some salts have been recently shown to decrease the sum frequency generation (SFG) intensity of the hydrogen-bonded water molecules, but a quantitative explanation is still awaited. Here, we report a similar trend for the chloride salts of monovalent cations, that is, LiCl, NaCl, and CsCl, at low concentrations. Specifically, we revealed not only the specific adsorption of cations at the water surface but also the concentration-dependent effect of ions on the SFG response of the interfacial water molecules. Our thin-film pressure balance (TFPB) measurements (stabilized by 10 mM of methyl isobutyl carbinol) enabled the determination of the surface potential that governs the surface electric field affecting interfacial water dipoles. The use of the special alcohol also enabled us to identify a remarkable specific screening effect of cations on the surface potential. We explained the concentration dependency by considering the direct ion-water interactions and water reorientation under the influence of surface electric field as the two main contributors to the overall SFG signal of the hydrogen-bonded water molecules. Although the former was dominant only at the low-concentration range, the effect of the latter intensified with increasing salt concentration, leading to the recovery of the band intensity at medium concentrations. We discussed the likelihood of a correlation between the effect of ions on reorientation dynamics of water molecules and the broad-band intensity drop in the SFG spectra of salt solutions. We proposed a mechanism for the cation-specific effect through the formation of an ionic capacitance at the solution surface. It explains how cations could impart the ion specificity while they are traditionally believed to be repelled from the interfacial region. The electrical potential of this capacitance varies with the charge separation and ion density at the interface. The charge separation being controlled by the polarizability difference between anions and cations was identified using the SFG response of the interfacial water molecules as an indirect probe. The ion density being affected by the absolute polarizability of ions was tracked through the measurement of the surface potentials and Debye-Hückel lengths using the TFPB technique.

Foams and foam films stabilized by CnTAB: influence of the chain length and of impurities.

Quantitative comparison of foam films and the corresponding foams is very demanding. One problem is the fact that investigations of foam films are usually performed at constant capillary pressures P, whereas in foams P is a function of the height of the foam column. A way out of this dilemma is to examine films and foams at the same P. The method of choice for the foam films is the thin film pressure balance (TFPB), whereas the corresponding investigation of foams is based on the foam pressure drop technique (FPDT). An extensive TFPB study on foam films stabilized by the cationic alkyltrimethylammonium bromides C(n)TAB with n=10, 12, 14, and 16 was performed by Bergeron. For this series a steep increase of the foam film stability was observed when the chain length was increased from n=12 to n=14. Moreover, the influence of impurities was found to be limited to the films stabilized by C(12)TAB. In order to study the correlation between the properties of films and foams, the present study deals with the respective foam properties investigated with the FPDT. It was found that both the steep increase in the film stability and the influence of impurities are also reflected in the properties of the foam.