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Engineering properties of spider silk 213

45
40 MaSp1 + 1% CNT nanofibers
35
30
Stress (MPa) 25

20
15
10 MaSp1 nanofibers
5
0
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14
Strain
Figure 6.17 Effect of CNT on the tensile properties of aligned MaSp1 nanofiber. (Ko and
Gandhi, 2007).

and appeared to have a structure consistent with that of denatured proteins. This lack of
crystallinity does explain the poor mechanical properties of electrospun spider silk.
To address the issue of low strength of the regenerated transgenic spider silk, a
hybrid nanocomposite approach is proposed by taking advantage of the superior prop-
erties of carbon nanotube (CNT) and the electrospinning process (Ayutsede et al.,
2006). With a Young’s modulus of 1 TPa and a strength of 30e60 GPa at breaking
elongation ranging from 6% to 30%, CNT is an ideal reinforcing material to
strengthen the regenerated spider silk (Witt et al., 2012). On the basis of elongation
balance (29, 30) spider silk (20%e30% elongation at break) and CNT (6%e30%
elongation at break) are the most compatible material systems amongst the strong in-
dustrial fibers known to date. Incorporation of 1% CNT in MaSp1 significantly
increased the mechanical properties of spider silk (Ko and Gandhi, 2007; Ko et al.,
2004b). There was w a 10-time increase in the modulus and a 5-time increase in
the tensile strength, as shown in Fig. 6.17. MaSp1 with 1% CNT was found to
have modulus, strength, and elasticity of 1004.36 53.41 MPa, 40.74 6.32 MPa,
and 7.39 1.45%, respectively.

6.6 Summary and conclusions

Spider MA silks demonstrate a unique combination of strength and toughness charac-
terized by a sigmoidal, balanced stress-strain relationship, which is quite essential for
withstanding foreign object bombardment and absorbing the impact energy generated
by insects colliding with and becoming ensnared in the web. Another outstanding char-
acteristic of spider silk is its high level of shear rigidity compared to industrial fibers.
Torsional stability is essential in order for the spider’s dragline to serve as a lifeline for
the spider in thin air.