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 di-phytanylglycerol-tetraethyleneglycollipoid 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 find a strong charge regulation behaviour 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 make these model systems an ideal starting point for studying more complex strongly adhesive/interacting systems, including for example ligand/receptor interactions, bio-sensing interactions or cell/surface interactions.

Control of Polymer Brush Morphology, Rheology, and Protein Repulsion by Hydrogen Bond Complexation

“…A new prototype SFA including a semiconductor strain gauge was used for simultaneous measurements of interaction forces and absolute distance. 22 Experiments were conducted in a clean room environment within laminar flow hoods (ISO class 1). Physical vapor deposition was used to deposit 2 nm of Cr and 30 nm of Au on the substrate for the polymer brush (glass disk with 2 cm radius of curvature).…”

Visualization of Ion|Surface Binding and In Situ Evaluation of Surface Interaction Free Energies via Competitive Adsorption Isotherms

“…During the approach of one surface to the other (black markers), a mechanical instability ( jumps-in to contact) is observed at a distance D ∼ 15 nm close to the fully extended contour length of the polymer tether ( L c = 12.5 nm), plus the thickness of the inner monolayer of C 16 and the outer lipid layer. 11 The jump into contact is mediated by the specific intermolecular interaction between the positively charged amines and the negatively charged mica binding sites, which indicate a shorter range at higher ion concentrations due to the expected screening effect. This jump in brings the surfaces into a strong adhesive contact, with the brush compressed to about 60–70% of its contour length at D ∼ 7–8 nm as expected for a brush with 5–10% coverage.…”

“… 40 Our fit presents σ mica = −0.26 ± 0.01 and σ LMS = 0.016 ± 0.002 C/m 2 , for the couple of regulator parameters p 1 = 0.3 and p 2 = 0.95 at C = 0.01 M for a van der Waals plane of origin located at D VdW = 5.6 nm. 11 …”

“…In the last decades, the surface forces apparatus (SFA) and atomic force microscope (AFM) have been extensively used to probe a variety of interactions to establish their nanomechanical and dynamic properties. This includes studies on biofouling of marine fauna, 6 − 8 receptor–ligand interactions, 9 , 10 engineered lipid bilayer membranes, 11 , 12 and polymers investigated for different density, electrolyte, or pH conditions. 13 , 14 Further, many studies on specific binding systems have been performed in order to establish an understanding of interfacial interactions across the full range of length and energy scales, thus bridging the gaps between molecular scale interactions and macroscopic properties.…”

Structural Evidence for a Reinforcing Response and Retention of Hydration During Confinement of Cartilage Lipids

“…Investigations into the force response of individual lipids under confinement is well established using the surface force apparatus (SFA) [14][15][16][17]. In particular, Orozco-Alcaraz and Kuhl [14] applied the technique to lipids while using silica as the substrate, to study symmetric DPPC-DPPC interactions and understand the influence of substrate charge on the bilayer interactions in confinement.…”