Spider Silk-production and Biomedical Applications - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 152

mouse fibroblasts (Kuhbier et al., 2010). Recombinant spider silk has several benefits
over the native silk, not only the better supply, but also the greater possibility to pro-
cess it into scaffolds of different formats, for example film, foam and porous scaffolds.
Such scaffolds offer a three dimensional (3D) structure and mechanical properties that
differ substantially from the plastic surfaces traditionally used for cell culture. Since,
substrate stiffness has been suggested to play a major role in cell responses (Nemir
and West, 2010), softer substrates than cell culture plates are probably beneficial, mak-
ing recombinant spider silk an interesting material. Recombinant spider silk scaffolds
prepared from 4RepCT have been shown to support the growth of human primary
fibroblasts (Widhe et al., 2010). These scaffolds, in formats of film, foam, fiber and
fiber mesh, differ substantially in 3D structure and surface topography, but all provide
a suitable in vitro environment for these cells. Another recombinant spider silk pro-
tein, IF9, can be used to form porous 3D scaffolds with good interconnectivity by salt
leaching, allowing for proliferation of mouse fibroblast (Agapov et al., 2009). Cells
attach to the scaffolds, proliferate and migrate into the deeper layers of the scaffolds
within one week. Both these types of recombinant spider silk originate from dragline
silk, and scaffolds prepared from them are apparently stable, cytocompatible and can
offer a 3D microenvironment. To further improve the cell supporting capacity, recom-
binant spider silk has been genetically engineered by the introduction of cell binding
domains or motifs originating from proteins of the extracellular matrix (see Table 1) .
Most studied is the introduction of the cell binding motif RGD (Arg-Gly-Asp) into re-
combinant spider silk derived sequences. The effects of this motif have been evaluated
regarding cellular growth or differentiation using mesenchymal stem cells (Bini et al.,
2006), murine osteoblastic cell line (Morgan et al., 2008) and mouse embryonic fibro-
blasts (Wang et al., 2009). Also, two larger peptides have been tried, that is an elastin
like peptide (ELP) (Scheller et al., 2004) and a silaffin-derived peptide from a silica
producing diatom (Mieszawska et al., 2010). The ELP was combined with the drag-
line silk derived from recombinant spider silk protein SO1, and was shown to support
growth and prevent dedifferentiation of human chondrocytes (Scheller et al., 2004).
The silaffin-derived peptide R5 was introduced in order to increase osteogenesis of
mesenchymal stem cells growing on recombinant spider silk films (Mieszawska et al.,
2010). Generally, it seems possible to prepare scaffolds from functionalized recombi-
nant spidroins, and they are apparently cytocompatible.
Though, so far relatively sparsely explored, functionalized recombinant spider silk
scaffolds for cell culture might provide a broad range of solutions for in vitro cell
culture and possibly also for tissue engineering applications.
spider silk for in vivo applications
There are only a few studies available on native spider silk implanted in living tissue.
In one of these, spider dragline silk from Nephila clavipes was used as a component
in artificial nerve constructs. The grafts were used to replace a 2 cm deficit of the
sciatic nerve in rats, and shown to promote regeneration of peripheral nerves with
high functionality, while the controls that received similar grafts without spider silk
gained nearly no myelinated nerve fibers and showed distinctive muscle degeneration
(Allmeling et al., 2008). Furthermore, no signs of inflammatory response or foreign