The energetic and topography changes of mixed lipid bilayers deposited on glass

Characterization of the changes in wetting, energetic and topography of mixed phospholipid/sterol bilayer (BL) deposited on solid support was undertaken in these studies. Synthetic phospholipid (1,2-dipalmitoyl-sn-glycero-3-phosphocholine – DPPC) and sterol (cholesterol – Chol) were used. The lipid and mixed phospholipid/sterol bilayers were deposited on glass surface from chloroform solutions by spontaneous spreading or using Langmuir–Schaefer technique. The studied bilayers prepared by solution spreading were additionally incubated in water and then analyzed. Wettability of the films was investigated via contact angle measurements performed for three probe liquids (water, formamide and diiodomethane). The contact angles allowed evaluation of the total surface free energy and its components for particular systems applying two theoretical approaches, the one proposed by van Oss et al. (LWAB) and the other one of Chibowski (CAH). In order to visualize the changes of structure and properties of studied films their topography images were taken employing atomic force microscopy (AFM). The performed studies showed, that incorporation of cholesterol into the DPPC bilayers influenced their energetic and wetting properties, what reflected in the changes of contact angle and consequently the surface free energy of these films. The increasing sterol concentration fosters creation of rafts and organization of DPPC hydrocarbon chains on the layer surface. This causes changes in the surface free energy of mixed DPPC/Chol layers depending on the cholesterol concentration. The changes in topography of the studied layers observed with a help of AFM correlate well with the changes of their energetic properties.

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► Cholesterol in DPPC bilayers deposited on glass affects their surface properties.
► The way of bilayer deposition influences its organization and surface free energy.
► Surface free energy and topography of the bilayer changes after contact with water.
► Topography of the bilayers correlate well with the changes of their free energy.