Micromanipulation of phospholipid bilayers by atomic force microscopy

Abstract

The molecular details of adhesion mechanics in phospholipid bilayers have been studied using atomic force microscopy (AFM). Under tension fused bilayers of dipalmitoylphosphatidylcholine (DPPC) yield to give non-distance dependent and discrete force plateaux of 45.4, 81.6 and 113+/-3.5 pN. This behaviour may persist over distances as great as 400 nm and suggests the stable formation of a cylindrical tube which bridges the bilayers on the two surfaces. The stability of this connective structure may have implications for the formation of pili and hence for the initial stage of bacterial conjugation. Dimyristoylphosphatidylcholine (DMPC) bilayers also exhibit force plateaux but with a much less pronounced quantization. Bilayers composed of egg PC, sterylamine and cholesterol stressed in a similar way show complex behaviour which can in part be explained using the models demonstrated in the pure lipids.

Fusion of biomimetic stealth probes into lipid bilayer cores

“…Unfunctionalized tips (Fig. 4A) show lipid-tether formation as typically observed with hydrophilic probes, characterized by the multiple step-like failure events with zero-withdrawal force plateaus on withdrawal (25,26). These thin membrane tubules nonspecifically bind to the probe and are extruded from the main bilayer with low resistance, often extending tens of microns in length (27).…”

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…A possible mechanism leading to the weak long-range attraction is the formation of a bilayer tether between the tip and planar surface (Fig. 37) [738,788]. Such membrane tethers have also been observed on various whole cells by different methods (e.g.…”

“…It is at least 10 times lower then the breakthrough force and certainly below 1 nN. It does not depend strongly on distance and is sometimes relatively constant until it drops to zero at distances of up to 20 nm [770,788]. Such weak long-range attraction indicates that some kind of contact is maintained over distances exceeding the thickness of the two bilayers.…”

“…37. Schematic of tether formation and experimental force curves interpreted as tether formation (adapted with kind permission from [788]). The curves are acquired on mica whit silicon nitride cantilevers and tips, which were rendered hydrophilic by a water plasma treatment prior to use.…”

Experimental and Computational Methods Pertaining to Surface Tension of Pharmaceuticals

“…Atomic force microscopy allows imaging and measurement of biological and biomaterial samples, ligand-receptor interaction, protein adsorption and folding (Alonso and Goldmann, 2003;Edwardson and Henderson, 2004). This device is fast becoming a valuable tool in the pharmaceutical industry and is used in formulation and surface characterization of liposome vesicles (Maeda et al, 2002), microparticle preparation and biomaterials (Méndez-Vilas et al, 2006), surface characterization of parenteral nutrition bags (Realdon et al, 2003), wetting properties of human hair (Dupres et al, 2004) and other applications are discussed elsewhere (Santos and Castanho, 2004).…”