Nanostructured layers of adsorbed collagen: conditions, mechanisms and applications

Abstract

The nanometer-scale organization of collagen (type I) adsorbed on polystyrene (PS) and plasma-oxidized PS (PSox) was investigated using atomic force microscopy (AFM) as well as radioassays and X-ray photoelectron spectroscopy. The surface properties induced by plasma treatment of PS were examined: PSox was more hydrophilic than PS, owing to oxygen incorporation, and was covered by a layer of polyelectrolyte which could be swollen by water. Collagen adsorbed on PS formed elongated structures, the density and the height of which increased with the adsorption duration. On PSox, a smooth and homogeneous collagen layer was formed after up to 2 h of adsorption, but elongated structures appeared after 24 h. A similar contrast was found between CH₃- and OH-terminated self-assembled monolayers, indicating the role of surface hydrophilicity. The adsorption duration affected the nanostructure of adsorbed collagen layers, not only through the adsorbed amount but also owing to reorganizations of the adsorbed phase. Compared with collagen adsorbed on PSox, collagen adsorbed on PS was more easily picked up for attachment to the AFM probe and more easily displaced along the surface plane by scanning with the atomic force microscope or by drying. This suggests that collagen molecules adsorbed on PS leave segments protruding into the solution, while they form a felt of lying molecules on PSox. The observed elongated structures may be due to association of collagen segments, and/or to particular interactions with the atomic force microscope probe. The respective importance of these two mechanisms may depend on the chemical nature of the substratum. Nanostructured collagen layers offer attractive perspectives to control mammalian cell response or as a template to create nanostructured polymer surfaces.

Acknowledgements: The authors wish to thank V. De Cupere for the radiolabeling and for helpful discussions, I. Jacquemart for the adhesion map, as well as late Prof. P. Grange and P. Bertrand for the use of the atomic force microscope and of the spin-coater, respectively. C.D.-G. is a postdoctoral researcher of the Belgian National Foundation for Scientific Research (F.N.R.S.). The support of the F.N.R.S., of the Foundation for Training in Industrial and Agricultural Research (F.R.I.A.), of the Federal Office for Scientific, Technical and Cultural Affairs (Interuniversity Poles of Attraction Program) and of the Research Department of the Communauté Française de Belgique (Concerted Research Action) is gratefully acknowledged.