PDMS as a Substrate for Lipid Bilayers

PDMS (polydimethylsiloxane) is a cheap, optically clearpolymerthat is elastic and can be easily and quickly fabricated into a widearray of microscale and nanoscale architectures, making it a versatilesubstrate for biophysical experiments on cell membranes. It is easyto imagine many new experiments will be devised that require a bilayerto be placed upon a substrate that is flexible or easily cast intoa desired geometry, such as in lab-on-a-chip, organ-on-chip, and microfluidicapplications, or for building accurate membrane models that replicatethe surface structure and elasticity of the cytoskeleton. However,PDMS has its limitations, and the extent to which the behavior ofmembranes is affected on PDMS has not been fully explored. We useAFM and fluorescence optical microscopy to investigate the use ofPDMS as a substrate for the formation and study of supported lipidbilayers (SLBs). Lipid bilayers form on plasma-treated PDMS and showfree diffusion and normal phase transitions, confirming its suitabilityas a model bilayer substrate. However, lipid-phase separation on PDMSis severely restricted due to the pinning of domains to surface roughness,resulting in the cessation of lateral hydrodynamic flow. We show thehigh-resolution porous structure of PDMS and the extreme smoothingeffect of oxygen plasma treatment used to hydrophilize the surface,but this is not flat enough to allow domain formation. We also observebilayer degradation over hour timescales, which correlates with theknown hydrophobic recovery of PDMS, and establish a critical watercontact angle of 30 & DEG;, above which bilayers degrade or not format all. Care must be taken as incomplete surface oxidation and hydrophobicrecovery result in optically invisible membrane disruption, whichwill also be transparent to fluorescence microscopy and lipid diffusionmeasurements in the early stages.

Automated summary

PDMS is a versatile substrate for biophysical experiments on cell membranes, but it has its limitations and the extent to which it affects membrane behavior has not been fully explored.