Effect of biomaterial surface properties on fibronectin–α5β1 integrin interaction and cellular attachment

The ability of fibronectin (Fn) to mediate cell adhesion through binding to α5β1 integrins is dependent on the conditions of its adsorption to the surface. Using a model system of alkylsilane SAMs with different functional groups (X=OH, COOH, NH2 and CH3) and an erythroleukemia cell line expressing a single integrin (α5β1), the effect of surface properties on the cellular adhesion with adsorbed Fn layers was investigated. 125I-labeled Fn, a modified biochemical cross-linking/extraction technique and a spinning disc apparatus were combined to quantify the Fn adsorption, integrin binding and adhesion strength, respectively. This methodology allows for a binding equilibrium analysis that more closely reflects cellular adhesion found in stable tissue constructs in vivo. Differences in detachment strength and integrin binding were explained in terms of changes in the adhesion constant (ψ, related to affinity) and binding efficiency of the adsorbed Fn for the α5β1 integrins (CH3≈NH2integrins when adsorbed on COOH vs. OH surfaces suggesting that negative charge may be a critical component of inducing efficient cellular adhesion. As evident by the low ψ values, Fn adsorbed on NH2 and CH3 surfaces interacted inefficiently with α5β1 integrins and also possessed significant non-specific components to adhesion. Lastly, comparison of cellular adhesion to Fn adsorbed onto smooth and rough surfaces showed that nano-scale roughness altered cellular adhesion by increasing the surface density of adsorbed Fn.