Spider silks possess a range of qualities that are rarely found simultaneously in one material, and it is no surprise that an enormous effort has been made to replicate or learn from them.1,2 Toughness, extensibility and strength are only a few of the desirable traits that make spider silk of such interest. Silk is biodegradable and, unlike synthetic high-performance fibres such as Kevlar, it is extremely lightweight.3,4 A further advantage lies in its processing conditions and requirements. Whereas production of Kevlar and other such synthetics comes at a high monetary and environmental cost, spiders spin recyclable fibres on demand, under ambient conditions using water as a solvent, all at the energetic cost of an insect dinner.5,6
Spider silks are produced in vivo through a combination of chemistry to produce a liquid crystalline ‘aquamelt’ spinning dope,7 and a series of predominantly mechanical steps to induce restructuring, alignment and phase separation processes during spinning.8 Duct architecture is particularly important. The major ampullate duct, for example, is folded three times in a gradually tapering structure, making it five times longer than would be necessary to simply attach the sac to the spinneret. The underlying mechanisms of restructuring and assembly within the duct are still being investigated,9-11however the processing of silk proteins is known to include a decrease in pH, ion exchange, dehydration, elongation and alignment.12-14 We suggest that the low, constant stresses in the long, hyperbolic duct, and the resultant maximisation of chain ordering,15,16 allows efficient formation of the complex, defect-supressed structural organisation of spider silk during spinning.8,17 The resulting interactions within and between the major proteins in spider silk,18,19 and their variation across the diameter of the fibre,20 may have potential to be translated to synthetic fibres, particularly those produced with similar approaches such as dry or gel spinning.
1 Brown, C. P., Whaite, A. D., MacLeod, J. M., Macdonald, J. & Rosei, F. With great structure comes great functionality: Understanding and emulating spider silk. Journal of Materials Research 30, 108-120 (2015).
2 Brown, C. P., Rosei, F., Traversa, E. & Licoccia, S. Spider silk as a load bearing biomaterial: tailoring mechanical properties via structural modifications. Nanoscale 3, 870-876 (2011).
3 Widhe, M., Johansson, J., Hedhammar, M. & Rising, A. Invited review: Current progress and limitations of spider silk for biomedical applications. Biopolymers 97, 468-478 (2012).
4 Bittencourt, D., Oliveira, P. F., Prosdocimi, F. & Rech, E. L. Protein families, natural history and biotechnological aspects of spider silk. Genet. Mol. Res. 11, 2360-2380 (2012).
5 Vollrath, F. & Porter, D. Silks as ancient models for modern polymers. Polymer 50, 5623-5632 (2009).
6 Rising, A. Controlled assembly: A prerequisite for the use of recombinant spider silk in regenerative medicine? Acta Biomaterialia 10, 1627-1631 (2014).
7 Holland, C., Vollrath, F., Ryan, A. J. & Mykhaylyk, O. O. Silk and Synthetic Polymers: Reconciling 100 Degrees of Separation. Advanced Materials 24, 105-109 (2012).
8 Vollrath, F. & Knight, D. P. Liquid crystalline spinning of spider silk. Nature 410, 541-548 (2001).
9 Hijirida, D. H., Do, K. G., Michal, C., Wong, S., Zax, D. & Jelinski, L. W. 13C NMR of Nephila clavipes major ampullate silk gland. Biophys. J. 71, 3442-3447 (1996).
10 Jin, H. J. & Kaplan, D. L. Mechanism of silk processing in insects and spiders. Nature 424, 1057-1061 (2003).
11 Rammensee, S., Slotta, U., Scheibel, T. & Bausch, A. R. Assembly mechanism of recombinant spider silk proteins. Proc. Natl. Acad. Sci. U.S.A. 105, 6590-6595 (2008).
12 Hardy, J. G., Römer, L. M. & Scheibel, T. R. Polymeric materials based on silk proteins. Polymer 49, 4309-4327 (2008).
13 Vollrath, F. & Knight, D. P. Structure and function of the silk production pathway in the Spider Nephila edulis. International Journal of Biological Macromolecules 24, 243-249 (1999).
14 Leclerc, J., Lefèvre, T., Gauthier, M., Gagné, S. M. & Auger, M. Hydrodynamical properties of recombinant spider silk proteins: Effects of pH, salts and shear, and implications for the spinning process. Biopolymers 99, 582-593 (2013).
15 Ihm, D. W. & Cuculo, J. A. A visualization study of polyethylene terephthalate flow using a pseudohyperbolic die geometry. Journal of Polymer Science Part B: Polymer Physics 25, 619-640 (1987).
16 Chen, G.-Y., Cuculo, J. A. & Tucker, P. A. Characteristics and design procedure of hyperbolic dies. Journal of Polymer Science Part B: Polymer Physics 30, 557-561 (1992).
17 Knight, D. P. & Vollrath, F. Liquid crystals and flow elongation in a spider's silk production line. Proc. Roy. Soc. B 266, 519-523 (1999).
18 Xu, M. & Lewis, R. V. Structure of a protein superfiber: spider dragline silk. PNAS 87, 7120-7124 (1990).
19 Heim, M., Romer, L. & Scheibel, T. Hierarchical structures made of proteins. The complex architecture of spider webs and their constituent silk proteins. Chemical Society Reviews 39, 156-164 (2010).
20 Brown, C. P., MacLeod, J., Amenitsch, H., Cacho-Nerin, F., Gill, H. S., Price, A. J., Traversa, E., Licoccia, S. & Rosei, F. The critical role of water in spider silk and its consequence for protein mechanics. Nanoscale 3, 3805-3811 (2011).
Projects are available in the characterisation of silk properties, specifically the relationship between structure and the impressive mechanical properties of the material. Projects are also available to explore and reproduce the processing that creates these phenomenal materials.
This work will advance the understanding of spider silk mechanics, and provide a path to reproducing the production and performance of the material. Some projects can expect translational outcomes with health impacts.
Skills and experience
Students with a physics, materials, mechanical or electrical engineering background are encouraged to apply.
Contact the supervisor for more information.