Nano-scale mechanical probing of supported lipid bilayers with atomic force microscopy

TL;DR

This paper develops a theoretical model and conducts experiments using atomic force microscopy to measure the force-distance relationship of lipid bilayers, revealing insights into their mechanical properties and phase behaviors.

Contribution

It introduces a new theoretical framework for interpreting AFM force curves on supported lipid bilayers and validates it with experimental data, providing accurate measurements of the area compressibility modulus.

Findings

Force dominated by bilayer's area compressibility modulus

Model accurately describes AFM force curves in lipid phases

Liquid ordered phase exhibits yield-like response modeled by hydrogen bond breaking

Abstract

We present theory and experiments for the force-distance curve $F(z_0)$ of an atomic force microscope (AFM) tip (radius $R$) indenting a supported fluid bilayer (thickness $2d$). For realistic conditions the force is dominated by the area compressibility modulus $\kappa_A$ of the bilayer, and, to an excellent approximation, given by $F= \pi \kappa_A R z_0^2/(2d-z_0)^2$. The experimental AFM force curves from coexisting liquid ordered and liquid disordered domains in 3-component lipid bilayers are well-described by our model, and provides $\kappa_A$ in agreement with literature values. The liquid ordered phase has a yield like response that we model by hydrogen bond breaking.