In nature most cells are surrounded by an extracellular matrix (ECM), which contains protein nanofibers. The most abundant human ECM proteins are collagen and fibrinogen, which can be found in many tissues. The distinct structural and mechanical properties of different tissues are determined by the architecture, interaction and orientation of the protein nanofibres in the ECM with the embedded cells.
Recently, a novel extrusion approach to prepare nanofibres under physiological conditions was established. In this process a nanoporous alumina membrane is used as template material. Thus, either aligned fibre bundles or nanofibrous meshes were obtained. (1) It was previously shown that the concentration of the protein feed solution and the pore diameter control the diameter of the extruded fibers. At the same time, these parameters tune the mechanical strain in extruded protein fibers. (2)
Following up on these results we studied the influence of different biochemical modifications on the assembly of extruded nanofibers from different ECM proteins. We adjusted the pH and ionic strength of different aqueous buffers to influence the fibrillogenesis. Further on, the nanoporous membranes were functionalized, for instance using silanization or polymer coatings, to change the pore properties by adding different functional groups on the alumina surface. We used the same modifications to functionalize glass surfaces, on which the nanofibres were collected for further analysis. Using scanning electron microscopy to study the morphology of the nanofibre assemblies we found out that the salt concentration of the extrusion buffer is a key parameter in the extrusion approach as it influences which hierarchical fibre assembly is achieved.
The results of this study will enable us to prepare well-controlled nanofibrous protein scaffolds, which mimic the nanofiber assembly in the ECM of native tissue and can be used for versatile tissue engineering applications.
1. M. Raoufi et al., Template-Assisted Extrusion of Biopolymer Nanofibers under Physiological Conditions. Integrative Biology. 8, 1059–1066 (2016).
2. M. Raoufi et al., Nanopore Diameters Tune Strain in Extruded Fibronectin Fibers. Nano Lett. 15, 6357–6364 (2015).