Coarse-grain simulations of mechanically induced transformations in supported lipid bilayers and micelles at heterointerfaces

Supported lipid bilayers (SLBs) mimicking biological membranes are synthetic surface biosystems with a great potential for fundamental biophysical studies and applied biomedical research. One of the most important parameters among those influencing the behaviour of biological and biomimetic SLBs is their lipid composition, in turn determining their mechanical characteristics. Atomic Force Microscopy (AFM)-based Force Spectroscopy performed in liquid is an ideal tool for the nanoscale mechanical investigation of SLBs. Force-displacement curves clearly show the sequential compression of each of the two lipid layer. Finer details suggest that the lipid layer can undergo to a phase transition under the influence of the tip-induced local pressure. Nevertheless, lack of atomic resolution in AFM measurements hinders the full understanding of this phenomenon. Quasi-atomistic coarse-grain (CG) computational simulations have been proven to be an essential tool for the study of the mechanical properties of complex lipid assemblies[1]. Allowing to span much larger time and size domains when compared to normal atomistic simulations, CG simulations enable the investigation of complex bio-inspired systems. In particular, the well-established CG MARTINI[2] force field has been extensively employed to model the mechanical properties of lipid membranes. In this work, we perform large scale CG simulations of SLBs of different composition deposited on prototypical supporting surfaces. We show that computational simulations are able to discriminate between mechanical response of SLBs composed of lipids with different degree of saturation in the lipophilic tails and to reproduce the behaviour of mixed structures. Lastly, we show how these results are easily ported to more complex systems in which the bilayer is topologically closed such as synthetic nano-micelles. The results achieved for these prototypical structures, pave the way for simulating more realistic biological systems like extracellular vesicles. References: [1] H. I. Ingólfsson, C. Arnarez, X. Periole, S. J. Marrink, Journal of Cell Science, (2016), 0, 1-12. [2] D. H. de Jong, G. Singh, W. F. D. Bennett et al., Journal of Chemical Theory and Computation, (2013), 9, 687-697.