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Supported planar lipid bilayers based on alkanethiol-tethering chemistry are becoming increasingly important biomimetic materials. Hybrid bilayers containing thiol-derivatized alkane moieties plus natural lipids provide a biomimetic matrix that permits the successful reconstitution of membrane protein activity. The hybrid membrane is self-assembled and sufficiently rugged to be of practical use in research and in commercial sensing applications. The coupling of the bilayer to a metal support allows a wide range of analytical techniques to be applied to this model membrane. This article reviews some of the fundamental studies of the formation, structure, and response of hybrid bilayer membranes.

A novel model lipid bilayer membrane is prepared by the addition of phospholipid vesicles to alkanethiol monolayers on gold. This supported hybrid bilayer membrane is rugged, easily and reproducibly prepared in the absence of organic solvent, and is stable for very long periods of time. We have characterized the insulating characteristics of this membrane by examining the rate of electron transfer and by impedance spectroscopy. Supported hybrid bilayers formed from phospholipids and alkanethiols are pinhole-free and demonstrate measured values of conductivity and resistivity which are within an order of magnitude of that reported for black lipid membranes. Capacitance values suggest a dielectric constant of 2.7 for phospholipid membranes in the absence of organic solvent. The protein toxin, melittin, destroys the insulating capability of the phospholipid layer without significantly altering the bilayer structure. This model membrane will allow the assessment of the effect of lipid membrane perturbants on the insulating properties of natural lipid membranes.

Thin films of the extracellular matrix protein, collagen, were prepared by adsorbing native or heatdenatured type I collagen onto hexadecanethiol self-assembled monolayers. The resulting films were characterized by atomic force microscopy, ellipsometry, and light microscopy. Denatured collagen formed a topographically smooth ∼3.6 nm thick film, consistent with an adsorbed protein monolayer. In contrast, the native collagen thin film consisted of supramolecular collagen fibrils. The density of the large fibrils could be varied by changing the native collagen concentration in the solution from which the films were prepared. The biomimetic nature of the thin collagen films was partially assessed by examining their effects on vascular smooth muscle cells. Automated quantitative analysis indicated that the morphology of smooth muscle cells on the thin films was dependent on whether the collagen was heat-denatured or was in its native fibrillar form. The area of cells on denatured collagen films was significantly larger than that of cells on thin films of native fibrillar collagen. This response closely mimicked the response of these cells to thick collagen gels. Examination of the relationship between collagen fibril density and cell area indicated that large fibrils play a role in determining how cells respond to collagen. Cells assumed a larger morphology on native collagen films with a lower density of large fibrils. In this study, it is clear that cell morphology on these films is determined by micron-scale interactions between cells and the matrix molecules and is not dependent on the bulk materials properties of collagen gels.