Polymer-tethered membranes as quantitative models for the study of integrin-mediated cell adhesion

Here we report a remarkable enhancement in the adhesion strength of transmembrane cell receptors, human platelet integrin, in a new class of supported lipid membranes, which are separated from the solid substrates by linear polymer spacers. The amphiphilic polymer tether consists of linear hydrophilic poly(2-oxazoline) chains of defined length (degree of polymerization n = 104, M_W/M_n = 1.30), whose chain termini are functionalized with the tri-functional silane surface coupling group and hydrophobic n-alkyl chains as membrane anchors (lipopolymers). As a model of test cells, giant lipid vesicles were functionalized with synthetic ligand molecules containing the RGD sequence, and the free energy of adhesion Δg_ad between the integrin-doped tethered membrane and the vesicle was measured using a micro-interferometry technique. It has been demonstrated that the adhesion function of integrin receptors in these polymer-tethered membranes is 30 times stronger than those incorporated into membranes directly deposited onto solid substrates (solid-supported membranes). The obtained results demonstrate that linear lipopolymer spacers provide a fluid and non-denaturing environment for the incorporated cell receptors and allow quantitative modelling of cell adhesion processes.