Lipid vesicle fusion on mu CP patterned self-assembled monolayers: Effect of pattern geometry on bilayer formation

Microcontact printing (muCP) of lipophilic self-assembled monolayers (SAMs) has been used to fabricate micron dimensioned patterned surfaces that can be used as a means of attaching lipid bilayers to solid surfaces. This communication addresses how variation in the patterned SAM geometry affects vesicle adsorption. The substrates consisted of circular hydrophilic regions functionalized with mercaptoethanol surrounded by octadecanethiol (ODT). Three geometries were studied in which the diameter of the hydrophilic portion was varied between 4 and 16 mum and the center-to-center separation was varied between 10 and 40 mum. Thus, it was possible to study lipid adsorption on SAM systems with the same total hydrophilic surface area, but with different sized hydrophilic patches. Impedance spectroscopy showed that for the films of the same total hydrophilic area greater lipid coverage was obtained for SAMs with smaller diameter hydrophilic patches. To understand this observation, tapping mode AFM and surface plasmon microscopy were used to study lipid vesicles adsorption on such surfaces, A new mode of vesicle adsorption on micropatterned hydrophobic/hydrophilic surfaces is presented which shows that the simple picture of a bilayer spanning the hydrophilic patches is overly simplistic and that the real situation is considerably more complex and that the hydrophobic-hydrophilic edge plays an important role.