Atomic force microscopy (AFM) study of thick lamellar stacks of phospholipid bilayers

TL;DR

This study uses AFM to analyze the mechanical properties and ripple structures of thick multilamellar DMPC lipid stacks, revealing phase-dependent behaviors and effects of osmotic pressure.

Contribution

It provides the first detailed AFM-based measurements of compressional modulus and rupture force in thick lipid stacks across different phases and conditions.

Findings

Measured compressional modulus B aligns with literature values.

Observed ripple period Lambda_r increases near phase transition and with osmotic pressure.

Detected metastable ripples with doubled wavelength Lambda_r.

Abstract

We report an Atomic Force Microscopy (AFM) study on thick multi lamellar stacks of approx. 10 mum thickness (about 1500 stacked membranes) of DMPC (1,2-dimyristoyl-sn-glycero-3-phoshatidylcholine) deposited on silicon wafers. These thick stacks could be stabilized for measurements under excess water or solution. From force curves we determine the compressional modulus B and the rupture force F_r of the bilayers in the gel (ripple), the fluid phase and in the range of critical swelling close to the main transition. AFM allows to measure the compressional modulus of stacked membrane systems and values for B compare well to values reported in the literature. We observe pronounced ripples on the top layer in the Pbeta' (ripple) phase and find an increasing ripple period Lambda_r when approaching the temperature of the main phase transition into the fluid Lalpha phase at about 24 C. Metastable ripples with 2Lambda_r are observed. Lambda_r also increases with increasing osmotic pressure, i.e., for different concentrations of polyethylene glycol (PEG).