Generic Role of Polymer Supports in the Fine Adjustment of Interfacial Interactions between Solid Substrates and Model Cell Membranes

Abstract

To understand the generic role of soft, hydrated biopolymers in adjusting interfacial interactions at biological interfaces, we designed a defined model of the cell-extracellular matrix contacts based on planar lipid membranes deposited on polymer supports (polymer-supported membranes). Highly uniform polymer supports made out of regenerated cellulose allow for the control of film thickness without changing the surface roughness and without osmotic dehydration. The complementary combination of specular neutron reflectivity and high-energy specular X-ray reflectivity yields the equilibrium membrane-substrate distances, which can quantitatively be modeled by computing the interplay of van der Waals interaction, hydration repulsion, and repulsion caused by the thermal undulation of membranes. The obtained results help to understand the role of a biopolymer in the interfacial interactions of cell membranes from a physical point of view and also open a large potential to generally bridge soft, biological matter and hard inorganic materials.

Interplays of Interfacial Forces Modulate Structure and Function of Soft and Biological Matters in Aquatic Environments

“…(D) Calculated van der Waals, hydration repulsion, and membrane undulation forces. Equilibrium membrane-substrate distance coincides with the point of zero force at which the sum of three forces (red) crosses = 0 (Rossetti et al, 2015). The results culculated for thin (dry thickness ≈ 40 Å) and thick (dry thickness ≈ 160 Å) films are presented, showing good agreements with the values determined by specular neutron and X-ray reflectivity experiments.…”

“…κ is the bending modulus of the membrane, which is in the order of 10 k B T, while the pre-factor confirmed later by Monte Carlo simulations (Bachmann et al, 2001). Rossetti et al (2015) showed that the equilibrium membranesubstrate distance determined by specular neutron and Xray reflectivity experiments could be reproduced quantitatively from the point of zero force determined by the summation of hydration repulsion, van der Waals interaction, and undulation force (Figure 3D). Intriguingly, we found that the disjoining pressure is dominated by the interplay of attractive van der Waals force and hydration repulsion, while the undulation force had a smaller contribution due to its shallower slope.…”

“…roughness becomes comparable to or larger than the layer thickness. The density profile of highly swollen polymer films in contact with water can be characterized by using a parabolic function (Milner et al, 1988;Kuhl et al, 1998) or an exponential function with decay length Λ and stretching factor h (Schneck et al, 2009;Rossetti et al, 2015),…”

“…However, it is experimentally very difficult to quantify individual forces acting in complex, stratified systems under water. Therefore, it is better to start from a relatively simple case: a membrane of zwitterionic phospholipids on a uncharged polymer supports deposited on a silicon wafer (Figure 3B) (Rossetti et al, 2015). The electrostatic interaction between SiO 2 and the membrane is screened by using a buffer close to the physiological condition (e.g., 10 mM phosphate buffer with 100 mM NaCl) and a 10-100 nm thick neutral polymer film, because the Debye screening length (<10 Å) is more than one order of magnitude smaller than the polymer thickness.…”

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research

“…In many cases, membranes are formed on a polymer cushion in order to shield the lipids and proteins from detrimental interactions with the solid support. Adsorption of a model cell membrane on to hydrated biopolymers located at the solid-liquid interface (the cushion layer mentioned above) allowed adjusting the interfacial interactions and creating more biologically relevant membranes [170]. High energy XRR is mandatory for studies of buried interfaces, yielding the equilibrium membrane-substrate distances, which can quantitatively be modeled by computing the interplay of van der Waals interaction, hydration repulsion, and repulsion caused by the thermal undulations of the membrane.…”