Spider Silk-production and Biomedical Applications - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 147

Chapter 13
spider silk-production and Biomedical
applications
Anna Rising, Mona Widhe, and My Hedhammar
iNtroduCtioN
Spider silk is Nature's high performance fiber with an unprecedented ability to ab-
sorb energy, due to a combination of strength and extensibility. Also, spider silk has
been ascribed abilities to stop bleedings and promote wound healing (Bon, 1710-1712;
Newman and Newman, 1995). These traits have made spider silk an attractive mate-
rial for biomedical applications. While the outstanding mechanical properties of spi-
der silk have been well documented (see e.g., Gosline et al., 1999; Hu et al., 2006),
the suggested utility of spider silk has been hampered by lack of large scale produc-
tion. Spiders are territorial and produce low amounts of silk and can therefore not be
employed as such for industrial silk production. An alternative then is recombinant
expression of spider silk proteins (spidroins), or designed proteins with sequences
inspired by the overall properties of spidroins. The nature of spidroins (i.e. they are
large, repetitive, and aggregation prone) pose significant challenges to their produc-
tion. Several quite different production strategies have been described, the most com-
mon being prokaryote expression systems (e.g., Echerichia coli ) and processes that
involve use of precipitation and resolubilization procedures, cf below and (Rising et
al.) potential applications of recombinant spider silk include implants to restore the
function of damaged tissue (e.g., tendon repair) as well as matrices for cell culture and
tissue engineering. In line with this, some recombinant spider silks have been used
in cell culture studies and also there are a few reports on the in vivo tolerance of this
material.
spider silk
Some spiders have up to seven different types of silk glands (Candelas and Cintron,
1981), each producing a silk with a specific purpose and unique mechanical proper-
ties. The dragline silk is the most studied silk, it is a strong and extendible fiber used to
make the framework of the webs and as a lifeline (Gosline et al., 1999). The dragline
silk is composed mainly of two similar proteins, major ampullate spidroin (MaSp) 1
and 2 (Hinman and Lewis, 1992). These proteins are large, approximately 3500 amino
acid residues long and can be encoded by several gene loci (Ayoub et al., 2007; Rising
et al., 2007). The MaSps have a tripartite composition of a non repetitive N-terminal
domain (~130 amino acid residues) (Rising et al., 2006), an extensive repetitive region
(Ayoub et al., 2007), and a non repetitive folded C-terminal domain of ~110 residues
(Hagn et al., 2010). In the repetitive region, tandem repeat units of a glycine rich