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Highlights • Biomimetic membranes are prepared using the natural myriad of each lipid structures that constitute the bacterial membrane. • The biomimetic membranes are very elastic due to the presence of several unsaturations in the lipids structures. • The model membranes present the same physical state and minor rigidity differences regardless the PE:PG or PE:CL ratio. • The similar rigidity suggests that the changes in the lipid composition may influence the membrane proteins function. Abstract Novel antimicrobial agents are focused to interact with the bacterial membrane whose lipid composition (number and position of unsaturations and lipid headgroup) is adapted according to environmental signals. The anticipation of the adapted membrane properties is of high relevance to increase the targetability of such drugs. Herein, natural lipids extracted from Escherichia coli -phosphatidylethanolamine (PE), phosphatidylglycerol (PG) and cardiolipin (CL)- are used to form biomimetic membranes constituted by several PE:lipid ratios using the Langmuir and Langmuir-Blodgett techniques. The use of these techniques and the natural myriad of each lipid structures that constitute the biological E.coli membrane establishes a simple and reproducible model to evaluate the lipid-lipid interactions. PE and PG present similar shape and size, thus establish ideal and fluid -liquid expanded (LE) state - mixtures, whereas the differences between PE and CL motivate the formation of non-ideal and fluid (LE state) mixtures. The same physical state and the minor differences in elasticity (differences in the inverse of the compressibility modulus < 15 mN·m−1) between both systems regardless the PE content in the (PE:lipid) mixture suggest that the changes in the lipid composition influence the membrane proteins function rather than affecting the rigidity of the bacterial membrane. [ABSTRACT FROM AUTHOR]

• Lipid-containing artificial tears can be studied with the Langmuir technique. • Interactions between natural tear components and lipid tears can be investigated. • Albumin and lysozyme proteins interact strongly with lipid tear products. • The influence of albumin and lysozyme on lipid π-A isotherms, at pH of 7.4, is opposite. • The natural tear components affects the fluidity of the lipid layer. We studied the behaviour of three lipid tear products, commercialised by the same brand, as Langmuir films at the air/liquid interface to simulate the ocular environment. No significant differences were observed in the surface behaviour of two of them disclosing the same composition, but commercialised for different applications. The interaction of several subphases, namely sodium chloride, glucose, albumin and lysozyme present in the natural tear, with the lipid films was assessed at room temperature and the temperature of human tear using surface pressure-area isotherms and elastic modulus plots. There is a notable influence of sodium chloride and the proteins albumin and lysozyme on the surface pressure-area isotherm of the lipid Langmuir films. Albumin shifted this isotherm to lower areas while an opposite shift was caused by lysozyme. These studies could be useful for the formulation of new lipid-containing artificial tears, and for increasing the confidence of the customers in commercial eye care formulations. [ABSTRACT FROM AUTHOR]

• DMSO expands the area per lipid for DPPC, but causes compression for POPC, highlighting species dependent effects. • Ethylene glycol and glycerol expand monolayers regardless of lipid species, implying they insert into the headgroup region. • Dimethylformamide compresses the monolayer for all lipid species, implying it dehydrates the lipid head groups. • Under physiological conditions, the penetrating action of cryoprotectants may only occur for unsaturated phospholipids. The influence of four common cryoprotectants (dimethyl sulfoxide, glycerol, ethylene glycol and dimethylformamide) on monolayers of four common phospholipids (DPPC, DOPC, POPC and POPE) have been studied using Langmuir isotherms and monolayer insertion experiments. The cryoprotectant concentrations were chosen to be directly relevant to cryoprotection. We show that DMSO causes an expansion of the DPPC area per lipid (in contrast to previous work at higher concentrations). However, it caused compression for POPC, and had little effect for POPE or DOPC. As most previous studies have involved only DPPC, this highlights the importance of studying different lipid types as these may have a significant effect on the interactions. We show that both ethylene glycol and glycerol cause a small expansion of the monolayer at fixed pressure, implying that they insert into the headgroup regions, regardless of lipid species, and consistent with their ability to penetrate membranes. By contrast, dimethylformamide causes monolayer compression for all lipid species, implying it dehydrates the lipid head groups. Membrane insertion experiments at physiological values of lateral pressure highlight that DPPC is the most difficult lipid to penetrate, implying that the penetrating action of cryoprotectants may only occur for unsaturated phospholipids. Thus, extrapolations of results based solely on the DPPC need to be made with care. [ABSTRACT FROM AUTHOR]