Roumen Todorov

Effect of Rhamnolipids on Pulmonary Surfactant Foam Films

The effect of a rhamnolipid biosurfactant on pulmonary surfactant is studied employing the black foam film method. Pulmonary surfactant is modeled by a commercially available lung surfactant preparation (LSP). The effect of rhamnolipid concentration on the formation and stability of films formed from mixtures of LSP and rhamnolipids is experimentally studied by measurements of the probability W of formation of black foam films as a function of both LSP and rhamnolipid concentrations at the physiologically relevant electrolyte concentration C(el) = 0.15 mol dm(-3) NaCl. The obtained curves show that addition of rhamnolipid at a concentration C(RhL) = C(c) (critical concentration of black foam film formation) to LSP suspensions causes destabilization of the foam films. In this case, additional quantities of lung surfactant preparation are needed to obtain black films with probability W = 100%. Rhamnolipid adsorption and formation of mixed adsorbed layers at the solution/air interfaces of foam films formed from mixtures of lung surfactant and rhamnolipids are experimentally studied by monitoring the effect of electrolyte and rhamnolipid concentrations on the thickness h of the foam films. The incorporation of rhamnolipid ions in the adsorbed layers at the film interfaces is evidenced also by direct measurements of the disjoining pressure Pi in the films. The Pi(h) isotherms demonstrate that the added rhamnolipids change the surface electric parameters of the films and their thickness and stability at higher pressures. The obtained results show that the different molecular components in the mixture and the increased surface charge at the film interfaces originating from the rhamnolipid ions have a significant effect on the surface forces operative in the studied films.

Influence of surfactant protein C on the interfacial behavior of phosphatidylethanolamine monolayers

In the current work we study with monolayer tensiometry and Brewster angle microscopy (BAM) the surface properties of Dipalmitoleoylphosphatidylethanolamine (DPoPE) films at the air/water interface in presence and absence of specific surfactant protein C (SP-C). DPoPE is used, as it readily forms both lamellar (Lα) and non-lamellar inverted hexagonal (HII) phases and appears as a suitable model phospholipid for probing the interfacial properties of distinct lipid phases. At pure air/water interface Lα shows faster adsorption and better surface disintegration than HII phase. The interaction of DPoPE molecules with SP-C (predeposited at the interface) results in equalizing of the interfacial disintegration of the both phases (reaching approximately the same equilibrium surface tension) although the adsorption kinetics of the lamellar phase remains much faster. Monolayer compression/decompression cycling revealed that the effect of SP-C on dynamic surface tensions (γmax and γmin) of mixed films is remarkably different for the two phases. If γmax for Lα decreased from the first to the third cycle, the opposite effect is registered for HII where γmax increases during cycling. Also the significant decrease of γmin for Lα in SP-C presence is not observed for HII phase. BAM studies reveal the formation of more uniform and homogeneously packed DPoPE monolayers in the presence of SP-C.

Evaluation of therapeutic pulmonary surfactants by thin liquid film methods

An example of the application of the Black Foam Film (BFF) Method and the Wetting Film Method, using the Microinterferomertric and the Pressure Balance Techniques, for characterization interfacial properties of the animal derived therapeutic pulmonary surfactant preparations (TSP), is presented. BFF thickness, probability of black film formation, and disjoining pressure for foam films from TSP aqueous solutions are measured as well as the wetting properties of TSP solutions on solid surfaces with different hydrophobicity have been studied. Interfacial characteristics such as minimal surfactant concentration to obtain black film (critical concentration) and concentration at which a black film is 100% obtained (threshold concentration) are determined. An evaluation of the four widely used TSP – Curosurf, Infasurf, Survanta, and Alveofact – by these methods has been carried out. Thus the methods of the thin liquid films are useful tools for studying the interfacial properties of TSP solutions, as well as for their improvement.

Interfacial properties of therapeutic pulmonary surfactants studied by thin liquid films

Abstract The pulmonary surfactants are considered predominantly from the perspective of surfactant insufficiency in preterm newborns developing respiratory distress syndrome (RDS). Currently, lung extracts of animal origin, known as therapeutic pulmonary surfactants, are largely used in RDS treatment. We introduced a new in vitro method for the study of therapeutic pulmonary surfactants based on the model black foam film, including bilayer film. Microscopic foam films from aqueous surfactant solutions are explored by means of interferometric technique which provides for introducing new parameters and measuring new dependences characterising interfacial properties of therapeutic pulmonary surfactants. Film thickness, probability of black film formation and disjoining pressure are measured. The wetting properties of surfactant solutions are studied. Interfacial characteristics such as minimal surfactant concentration to obtain black film and concentration at which a black film is 100% obtained are determined. The following therapeutic pulmonary surfactants are studied: Curosurf, Infasurf, Survanta, Alveofac and Exosurf.

Inactivation of Pulmonary Surfactant by Lysophosphatidylcholine

ABSTRACT The aim of the study is to examine the influence of the lysophosphatidylcholine (lysoPC) to surface properties of INFASURF, a replacement lung surfactant, using the methods of thin foam films and Wilhelmy method. By the latter it is shown the change of surface tension (γ, mN/m) during time of the pure INFASURF and their mixture with lysoPC. Foam films are an efficient and useful model for the study of many surface phenomena especially for investigating the surface properties of pulmonary surfactant. Formation and stability of common black foam films (CBF) of pure INFASURF and of mixtures with various concentrations of lysoPC indicate the influence of low concentrations of lysoPC for the stability of CBF from INFASURF. It is proved that the curve W/C (where W is probability and C—concentration) is shifted to the lower concentrations.

Electric light scattering from single-stranded DNA in linear polyacrylamide solutions.

The electric light scattering (ELS) of ssDNA (calf thymus, 10 kbp, 55 μg/mL) in denaturing polyacrylamide (PAA) solutions was studied as a function of applied sinusoidal electric field and polymer concentration. Electric fields of strengths up to 300 V/cm and of frequencies between 100 and 5000 Hz were applied. It was found that the ELS effect increases with the field strength and decreases at high frequencies. The dependence of the ELS effect of ssDNA on polymer concentration passes through a maximum at 1% PAA. The relaxation times of decay of the ELS effect increase with increasing polymer concentrations. It was demonstrated that ELS is a useful method for investigation of ssDNA behavior in the course of pulse‐field electrophoresis in polymer solutions.