Fig. 6: Man-made protein-based fibers used to mimic the extracellular matrix (ECM) for tissue engineering applications.

The ECM has several properties important for the attachment and proliferation of cells, like fiber diameter, pore size, topography, as well as stiffness. The SEM image in the top lane is representative for the ECM, in this case showing the myocardium of a rat heart. Adapted with permission from ref. ²¹⁶, licensed under CC BY 4.0. Electrospun fibrous proteins are able to mimic the properties of the natural ECM. Exemplarily, electrospun non-woven meshes derived from (a) recombinant spider silk (seeded with mouse fibroblasts) is used as scaffold for different cell types. Adapted and modified with permission from ref. ¹⁴⁶, copyright John Wiley and Sons, 2011. b Cell adhesion was evaluated after 4 h on electrospun meshes made of recombinant spider silk proteins with different fiber diameters (150, 250, 480 and 680 nm). As control, a treated cell culture plate was used. The adhesion test showed that meshes with a larger fiber diameter are better suited for fibroblast adhesion than smaller fiber diameters. Adapted and modified with permission from ref. ¹⁴⁶, copyright John Wiley and Sons, 2011. c Regenerated B. mori fibers are used as scaffold for human oral keratinocytes (NHOK). Adapted and modified with permission from ref. ²¹⁷, copyright Elsevier, 2004. d The spreading behavior of the set-up of (c) was investigated. Polystyrene (used as control) as well as the pure B. mori silk fibers showed less cell spreading, whereas collagen I coated silk fibroin fibers were showing a good cell spreading behavior. Adapted and modified with permission from ref. ²¹⁷, copyright Elsevier, 2011. e Electrospun collagen fibers were seeded with human osteoblasts. Adapted with permission from ref. ²¹⁸, copyright John Wiley and Sons, 2009. f In the set-up of (e) F-actin was stained in red using phalloidin, and the nuclei were stained in blue by using DAPI. The collagen fibers enhanced cell growth regardless of the fiber diameter. Adapted with permission from ref. ²¹⁸, copyright John Wiley and Sons, 2009. g Human mesenchymal stem cells were seeded on extracted keratin fibers. Adapted and modified with permission from ref. ¹⁶⁰, copyright Elsevier, 2015. h Cell viability of human mesenchymal stem cells on different keratin scaffolds of the set-up in (g), as well as different calcium phosphate (CaP) coated fibers was determined by using a PicoGreen assay, measuring the amount of double-stranded DNA after 4 days of culturing. Keratin containing scaffolds (cKeratin-PCL (crosslinked Keratin-PCL; poly-ε-caprolactone) and sCaP-cKeratin-PCL (CaP surface coated PCL–cKeratin scaffold) showed increased cell proliferation in comparison to the controls (PCL and CaP surface coated PCL scaffolds). Adapted and modified with permission from ref. ¹⁶⁰ copyright Elsevier, 2015.