Wetting films of lipids in the development of sensitive interfaces. An electrochemical approach

Electrochemical Investigation of the Stability of Poly-Phosphocholinated Liposomes

Poly[2-(methacryloyloxy)ethyl phosphorylcholine] liposomes (pMPC liposomes) gained attention during the last few years because of their potential use in treating osteoarthritis. pMPC liposomes that serve as boundary lubricants are intended to restore the natural lubrication properties of articular cartilage. For this purpose, it is important that the liposomes remain intact and do not fuse and spread as a lipid film on the cartilage surface. Here, we investigate the stability of the liposomes and their interaction with two types of solid surfaces, gold and carbon, by using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). With the aid of a hydrophilic species used as an electroactive probe in the solution, the charge transfer characteristics of the electrode surfaces are obtained. Additionally, from EIS, the capacitance characteristics of the surfaces are derived. No decrease of the peak currents and no displacement of the peak potentials to greater overpotentials are observed in the CV experiments. No decrease in the apparent capacitance and increase in the charge transfer resistance is observed in the EIS experiments. On the contrary, all parameters in both CV and EIS do change in the opposite direction. The obtained results confirm that there is only physical adsorption without fusion and spreading of the pMPC liposomes and without the formation of lipid films on the surfaces of both gold and carbon electrodes.

Action of Chicory Fructooligosaccharides on Biomimetic Membranes

Fructooligosaccharides from chicory (FOSC) are functional prebiotic foods recognized to exert several well-being effects in human health and animal production, as decreasing blood lipids, modulating the gut immune system, enhancing mineral bioavailability, and inhibiting microbial growth, among others. Mechanisms of actions directly on cell metabolism and structure are however little known. In this sense this work was targeted to investigate the interaction of FOSC with biomimetic membranes (liposomes and supported bilayer membrane; s-BLM) through cyclic voltammetry, impedance spectroscopy, spectrofluorimetry, and microscopy. FOSC was able to disrupt the membrane structure of liposomes and s-BLM from the onset of molecular pores induced on it. The mechanism of interaction of fructans with biomimetic membranes suggests hydrogen bonding between the polyhydroxylated structure of the oligosaccharides and the negative polar group of L-α-phosphatidylcholine (PC) present in both liposomes and s-BLM.

Functionalized lipid nanoparticles-cellophane hybrid films for molecular delivery: preparation, physicochemical characterization, and stability

Lipid nanoparticles functionalized with the sunscreen 2,4-dihydroxybenzophenone (FLNPs) have been prepared by the ultrasound method and embedded in highly hydrophilic cellophane supports (regenerated cellulose, RC), creating biocompatible hybrid films (RC-FLNPs samples). The morphology of the FLNPs was studied with transmission microscopy, whereas the surface and interior chemical composition was analyzed by micro-Raman spectroscopy. RC-FLNPs hybrid films were prepared from the immersion of two cellophane supports with different thicknesses and water uptake properties (RC-3 and RC-6) in an aqueous dispersion of FLNPs. The structure of this hybrid material was visualized with bright-field microscopy, which clearly showed the inclusion of the FLNPs in the cellophane matrix. The stability of the RC-FLNPs films with respect to both aqueous environments and time was demonstrated by NaCl diffusion measurements. The reduction in the diffusion coefficient through the nanoparticle-modified films compared with the original supports confirms the presence of nanoparticles for concentration gradients of up to 0.4 M (osmotic pressure around 10 bar), indicating the stability of the hybrid hydrophilic material, even in aqueous environments and under matter flow conditions for a period of 21 days.

Effects of divalent cations on the formation and structure of solid supported lipid films

The interaction of glassy carbon-supported thin wetting films of lecithin with some divalent cations is investigated by impedimetry and voltammetry. The influence of Ca2+, Mg2+, and Mn2+ on the film structure is explored in two different cases--the divalent cations are added to the electrolyte either before or after the formation of the film. When the film has been previously formed, the addition of divalent cations in millimolar concentrations leads to changes in the passive electrical parameters and the blocking properties of the films. On the one hand the dielectric properties of the film measured in 0.1 M KCl seem to improve after the interaction with divalent cations--the film capacitance decreases, the resistance and resistivity of the film increase. On the other hand the increase of the redox current in the presence of 1 mM Fe(CN)6(3-/4-) in the electrolyte suggests the formation of some defects in the lipid structure of the film after the action of divalent cations. It is shown that the amount of these defects could be significantly decreased when the divalent cations are present in the electrolyte solution before the film formation. The effect of divalent cations on the film stability is tested by applying negative potential to the film. In 0.1 M KCl the films are not stable at potential of - 0.8 V (vs. Ag/AgCl) and are destroyed. The addition of divalent cations stabilizes the films and at certain millimolar concentrations the films remain intact after the action of the negative potential. The effect of Mn2+ is more pronounced, the Ca2+ and Mg2+ have smaller commensurate effect. It is proposed that the changes in the films' properties could be related with more tight packing of the lipid molecules with the divalent cations inserted in the film and that some defects could be opened during the rearrangement of the lipids when the film has been previously formed.