Interaction of hydrophobic polymers with model lipid bilayers

D Bochicchio,E Panizon,G Rossi,L Monticelli

doi:10.1038/s41598-017-06668-0

Abstract

The interaction of nanoscale synthetic materials with cell membranes is one of the key steps determining nanomaterials’ toxicity. Here we use molecular simulations, with atomistic and coarse-grained resolution, to investigate the interaction of three hydrophobic polymers with model lipid membranes. Polymer nanoparticles made of polyethylene (PE), polypropylene (PP) and polystyrene with size up to 7 nm enter easily POPC lipid membranes, localizing to the membrane hydrophobic core. For all three materials, solid polymeric nanoparticles become essentially liquid within the membrane at room temperature. Still, their behavior in the membrane core is not the same: PP and PS disperse in the core of the bilayer, while PE shows a tendency to aggregate. We also examined the interaction of the polymers with heterogeneous membranes, consisting of a ternary lipid mixture exhibiting liquid-ordered/liquid-disordered phase separation. The behavior of the three polymers is markedly different: PP disfavors lipid phase separation, PS stabilizes it, and PE modifies the topology of the phase boundaries and causes cholesterol depletion from the liquid ordered phase. Our results show that different hydrophobic polymers have major effects on the properties of lipid membranes, calling for further investigations on model systems and cell membranes.

Highlights

The interaction of nanoscale synthetic materials with cell membranes is one of the key steps determining nanomaterials’ toxicity
The favorable association between nanoplastics and lipids has been suggested to play a role in driving plastic nanoparticles to the brain[12], via penetration of the blood-brain barrier, but no molecular study has so far explored the physical mechanisms at the basis of such an interaction
We recently developed MARTINI CG models of PS, PP, and PE that reproduce the free energy of transfer of small oligomers from water to membranes obtained in atomistic simulations[19,20,21]

Summary

Introduction

The interaction of nanoscale synthetic materials with cell membranes is one of the key steps determining nanomaterials’ toxicity. We use molecular simulations, with atomistic and coarsegrained resolution, to investigate the interaction of three hydrophobic polymers with model lipid membranes. Polymer nanoparticles made of polyethylene (PE), polypropylene (PP) and polystyrene with size up to 7 nm enter POPC lipid membranes, localizing to the membrane hydrophobic core. Most every-day use plastic materials (for instance, polystyrene (PS), polyethylene (PE), polypropylene (PP)) have a strong hydrophobic character, which might drive a favorable, passive interaction of the smallest nanoparticles (below 10 nm in diameter) with lipid membranes. The favorable association between nanoplastics and lipids has been suggested to play a role in driving plastic nanoparticles to the brain[12], via penetration of the blood-brain barrier, but no molecular study has so far explored the physical mechanisms at the basis of such an interaction. System composition POPC POPC + 8 PP107 POPC + 23 PP107 POPC + 38 PP107 POPC + 8 PE80 POPC + 23 PE80 POPC + 38 PE80 Ternary mixture Ternary mixture + 6 PP107 Ternary mixture + 44 PP107 Ternary mixture + 6 PE80 Ternary mixture + 44 PE80 Ternary mixture + 3 PS100 Ternary mixture + 19 PS100

Methods

Results

Conclusion