Atomic Force Microscopy Force Mapping in the Study of Supported Lipid Bilayers

Abstract

Investigating the structural and mechanical properties of lipid bilayer membrane systems is vital in elucidating their biological function. One route to directly correlate the morphology of phase-segregated membranes with their indentation and rupture mechanics is the collection of atomic force microscopy (AFM) force maps. These force maps, while containing rich mechanical information, require lengthy processing time due to the large number of force curves needed to attain a high spatial resolution. A force curve analysis toolset was created to perform data extraction, calculation and reporting specifically in studying lipid membrane morphology and mechanical stability. The procedure was automated to allow for high-throughput processing of force maps with greatly reduced processing time. The resulting program was successfully used in systematically analyzing a number of supported lipid membrane systems in the investigation of their structure and nanomechanics.

The temperature-dependent physical state of polar lipids and their miscibility impact the topography and mechanical properties of bilayer models of the milk fat globule membrane

“…Measurement of F B maps on multiple-phase lipid membranes therefore sets a link between local molecular interactions and the microscopic phase structure [21]. The increase in F B values of both the continuous and dispersed phases with decreasing temperature is consistent with other reports.…”

“…Previous reports have shown that this approach successfully scales high features of ordered lipid domains as significantly more rigid than the l d phase at ambient temperature [17,21,40,56]. To the authors' knowledge, except for the DPPC/cholesterol study by Redondo-Morata et al [42] no previous AFM investigation of the temperature-dependence of the mechanical properties had been reported so far on multiple-component lipid bilayers.…”

“…Rupture is considered as an activated process where the applied load (or force) decreases the energy barrier for splitting adjacent molecules apart. Thus, rupture becomes more likely as the applied force increases, resulting in a speed-dependent Gaussian frequency of the yield force, or "breakthrough" force, F B [21,[26][27][28], assuming the frequency factor to be near the resonance frequency of the cantilever [29].…”

“…Recently, AFM investigation of binary MSM/dioleylphosphatidylcholine (DOPC) model membranes of the MFGM showed the formation of MSM domains, for temperatures below 35°C[16]. Moreover, AFM provides force spectroscopy ability that allows association of mechanical information on the nanometer lateral scale with structural information corresponding to phases of the lipid bilayer[17][18][19][20][21]. Due to this, a correlation between thermodynamics and mechanics can be established.…”

Characterization of Repulsive Forces and Surface Deformation in Thin Micellar Films via AFM

“…6 The study of how surfaces deform when probed with an AFM tip is a thoroughly researched field, and several well established theories exist which can relate the surface deformation to the load force and the Young's modulus of a substrate. [7][8][9][10] In the case of thin biological films, it has been shown that these theories can be adapted to determine elastic moduli if information about how the deformation of the film changes with load is known. [9][10][11] Assuming that the micelles at the surface behave elastically at measurable load forces, it might then be possible to apply adapted versions of these theories to micellar surfaces.…”