Interaction Profiles and Stability of Rigid and Polymer-Tethered Lipid Bilayer Models at Highly Charged and Highly Adhesive Contacts

Abstract

Understanding interaction force versus distance profiles of supported lipid bilayers (SLBs) is relevant to a number of areas, which rely on these model systems, including, e.g., characterization of ligand/receptor interactions or bacterial adhesion. Here, the stability of 4 different SLB architectures was compared using the surface forces apparatus (SFA) and atomic force microscopy (AFM). Specifically, the outer envelope of the bilayer systems remained constant as 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). The inner layer was varied between DPPC and 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP) both on mica, and self-assembled monolayers (SAMs) of hexadecanethiol and the polymer-tethered diphytanylglycerol-tetraethylene glycol-lipoid acid (DPhyTL) on smooth gold surfaces. In that same order these gave an increasing strength of interaction between the inner layer and the supporting substrate and hence improved stability under highly adhesive conditions. Detachment profiles from highly charged and highly adhesive contacts were characterized, and approach characteristics were fitted to DLVO models. We find increasing stability under highly adhesive loads, approaching the hydrophobic limit of the adhesive energy between the inner and outer layers for the SAM-based systems. For all four SLBs we further compare AFM surface topographies, which strongly depend on preparation conditions, and the DLVO fitting of the SFA approach curves finds a strong charge regulation behavior during interaction, dependent on the particular model system. In addition, we find undulation characteristics during approach and separation. The increased stability of the complex architectures on a gold support makes these model systems an ideal starting point for studying more complex strongly adhesive/interacting systems, including, for example, ligand/receptor interactions, biosensing interactions, or cell/surface interactions.