Crystallinity and Stiffness of Spider Silk Govern the Migration of Schwann Cells

Abstract

Introduction: Nerve guidance conduits are a promising alternative to autologous nerve transplantation and conduits filled with fibrous materials have shown great potential in bridging nerve gaps. The application of spider silk as a filament material has led to results comparable to nerve autograft.1 However, the use of spider silk has been phenomenological so far and the reasons for its success are still not identified. The aim of this study is to elucidate the material properties of spider silk leading to its unique medical performance. This knowledge enables a targeted production of synthetic alternatives such as recombinant silk. Materials and Methods: In this work, various silk types were investigated.2 Schwann cells were seeded on the spider silks and monitored by live cell imaging and immunofluorescent staining. In addition, the silk fibers were inspected with an electron microscopy, Raman spectroscopy wide angle X-ray scattering, and tensile tests to determine morphology, secondary protein structure, crystallinity and stiffness, respectively. Results: It was found that the secondary protein structure and specifically the high content of β-sheets in the direction of silk’s axis gives the fiber its ability to act as a guiding element for Schwann cells. In addition, the results show that the crystallinity of the silk does not affect the proliferation of Schwann cells, while the directed movement of cells is affected by this material property. Conclusion: This direct comparison demonstrated the crucial role of the secondary protein structures and crystallinity of spider silk for the guidance properties of fibers during nerve regeneration. The crystalline structure of silk affects its stiffness, which in turn influences the directed migration of Schwann cells. These results should be considered during the targeted production of synthetic fibrous materials for nerve regeneration. 1. Kornfeld T, Nessler J, Helmer C, et al. Spider silk nerve graft promotes axonal regeneration on long distance nerve defect in a sheep model. Biomaterials 2021;271:120692. 2. Naghilou A, Pöttschacher L, Millesi F, et al. Correlating the secondary protein structure of natural spider silk with its guiding properties for Schwann cells. Mater Sci Eng C. 2020;116:111219.