Effect of intra-membrane C60 fullerenes on the modulus of elasticity and the mechanical resistance of gel and fluid lipid bilayers

Abstract

Penetration and partition of C₆₀ to the lipid bilayer core are both relevant to C₆₀ toxicity, and useful to realise C₆₀ biomedical potential. A key aspect is the effect of C₆₀ on bilayer mechanical properties. Here, we present an experimental study on the mechanical effect of the incorporation of C₆₀ into the hydrophobic core of fluid and gel phase zwitterionic phosphatidylcholine (PC) lipid bilayers. We demonstrate its incorporation inside the hydrophobic lipid core and the effect on the packing of the lipids and the vesicle size using a combination of infrared (IR) spectroscopy, atomic force microscopy (AFM) and laser light scattering. Using AFM we measured the Young's modulus of elasticity (E) of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) in the absence (presence) of intra-membranous C₆₀ at 24.5 °C. E of fluid phase supported bilayers is not altered by C₆₀, but E increases with incorporation of C₆₀ in gel phase bilayers. The increase is higher for longer hydrocarbon chains: 1.6 times for DPPC and 2 times for DSPC. However the mechanical resistance of gel phase bilayers of curved bilayered structures decreases with the incorporation of C₆₀. Our combined results indicate that C₆₀ causes a decrease in gel phase lipid mobility, i.e. an increase in membrane viscosity.