Self-assembled multilayers based on native or denatured collagen: mechanism and synthesis of size-controlled nanotubes

Abstract

The mechanism of layer-by-layer (LbL) assembly using collagen, the major protein of the extracellular matrix, was investigated on flat substrates and in nanoporous templates, with a view to synthesize collagen-containing nanotubes. The effect of parameters related to geometrical constraints (flat substrate vs. nanoporous template with different pore diameters) and to protein conformation (native vs. denatured collagen) were examined. Protein conformation was shown to play a major role in the mechanism of LbL assembly. The combination of ellipsometry and quartz crystal microbalance data revealed a linear and a saw-toothed growth for multilayers based on native and denatured (d-COL) collagen, respectively. This can be attributed to the stronger interaction of poly(styrene sulfonate) (PSS), the polyanion used in LbL assembly, with denatured compared to native collagen, as evidenced by force spectroscopy. This leads, on the one hand, to the formation of soluble d-COL/PSS complexes upon addition of PSS to the multilayer, and on the other hand, to a strong adsorption of d-COL on the remaining PSS outermost layer. Incorporation of either native or denatured collagen into LbL assemblies within porous templates led to the successful synthesis of collagen-based nanotubes with highly controlled dimensions (diameter of about 200 and 500 nm). Monitoring of the multilayers build-up kinetics showed that denatured collagen is more suitable for nanotube fabrication in pores with diameters smaller than the length of the native collagen molecule (∼300 nm), because it may diffuse more easily within the pores.