Nanomechanical Properties of Artificial Lipid Bilayers Composed of Fluid and Polymerizable Lipids

Abstract

Polymerization enhances the stability of a planar supported lipid bilayer (PSLB) but it also changes its chemical and mechanical properties, attenuates lipid diffusion, and may affect the activity of integral membrane proteins. Mixed bilayers composed of fluid lipids and poly­(lipids) may provide an appropriate combination of polymeric stability coupled with the fluidity and elasticity needed to maintain the bioactivity of reconstituted receptors. Previously (Langmuir, 2019, 35, 12483–12491) we showed that binary mixtures of the polymerizable lipid bis-SorbPC and the fluid lipid DPhPC form phase-segregated PSLBs composed of nanoscale fluid and poly­(lipid) domains. Here we used atomic force microscopy (AFM) to compare the nanoscale mechanical properties of these binary PSLBs with single-component PSLBs. The elastic (Young’s) modulus, area compressibility modulus, and bending modulus of bis-SorbPC PSLBs increased upon polymerization. Before polymerization, breakthrough events at forces below 5 nN were observed, but after polymerization, the AFM tip could not penetrate the PSLB up to an applied force of 20 nN. These results are attributed to the polymeric network in poly­(bis-SorbPC), which increases the bilayer stiffness and resists compression and bending. In binary DPhPC/poly­(bis-SorbPC) PSLBs, the DPhPC domains are less stiff, more compressible, and are less resistant to rupture and bending compared to pure DPhPC bilayers. These differences are attributed to bis-SorbPC monomers and oligomers present in DPhPC domains that disrupt the packing of DPhPC molecules. In contrast, the poly­(bis-SorbPC) domains are stiffer and less compressible relative to pure PSLBs; this difference is attributed to DPhPC filling the nm-scale pores in the polymerized domains that are created during bis-SorbPC polymerization. Thus, incomplete phase segregation increases the stability of poly­(bis-SorbPC) but has the opposite, detrimental effect for DPhPC. Overall, these results provide guidance for the design of partially polymerized bilayers for technological uses.

Molecular dynamics analysis of axonal membrane during traumatic brain injury

“…Other studies applying compression to lipid bilayers using atomistic force microscopy calculate a Young’s modulus of 19.3 to 28.1 MPa for a bilayer of DOPC/DPPC lipids 58 , 27 to 31 MPa for POPC and PDPC bilayers 59 and 50 MPa for artificial lipid bilayers of DPhPC lipids 60 . The calculated Young’s modulus in the presented study are in the corridor of the data derived for other membranes and lipid bilayers.…”

Interaction of imidazolium-based ionic liquids with supported phospholipid bilayers as model biomembranes

“…Considering a vertical approach on the phospholipid bilayer, the FC presents specific and recognizable features. [75][76][77] Upon contacting the surface at the contact point, the tip exerts a compressive stress on it, which first induces an elastic deformation of the bilayer, and then the rupture and penetration of the bilayer when a force threshold is reached (breakthrough event, corresponding to a breakthrough force F bt ). The nonlinear force vs. distance dependence in the compressive part of the FC accounts for the elastic resistance of the bilayer (d max is the maximum compression, or indentation).…”

Interaction of imidazolium-based ionic liquids with supported phospholipid bilayers as model biomembranes

“…Considering the vertical approach on phospholipid bilayer, the FC presents specific and recognizable features. [75][76][77] Upon contacting the surface at the contact point, the tip exerts a compressive stress on it, which first induces an elastic deformation of the bilayer, and then the rupture and penetration of the bilayer when a force threshold is reached (breakthrough event, corresponding to a breakthrough force Fbt). The nonlinear force vs distance dependence in the compressive part of the FC accounts for the elastic resistance of the bilayer (max is the maximum compression, or indentation).…”