Search

The critical role of water in spider silk and its consequence for protein mechanics Cameron P. Brown, Jennifer MacLeod, Heinz Amenitsch, Fernando Cacho-Nerin, Harinderjit S. Gill, Andrew J. Price, Enrico Traversa, Silvia Licoccia and Federico Rosei Nanoscale , 2011, 3 , (DOI: 10.1039/c1nr10502g). Amendment published 18 th August 2011. The list of authors and affiliations should read as follows: Cameron P. Brown,* abcd Jennifer MacLeod, c Heinz Amenitsch, e Fernando Cacho-Nerin , e Harinderjit S. Gill, a Andrew J. Price, a Enrico Traversa, df Silvia Licoccia, bd and Federico Rosei, cd a Botnar Research Centre, University of Oxford, Oxford, UK. E-mail: cameron.brown@ndorms.ox.ac.uk b Centro NAST, Dipartimento di Scienze e Tecnologie Chimiche, Universita ` di Roma Tor Vergata, via Della Ricerca Scientifica, 000133, Roma, Italy c Institut National de la Recherche Scientifique, Universite ́ du Que ́ bec, 1650 boulevard Lionel-Boulet, Varennes, QC, Canada. E-mail: rosei@emt.inrs.ca d Italy-Quebec Joint Laboratory in Nanostructured Materials for Energy, Catalysis and Biomedical Applications e Institute for Biophysics and Nanosystems Research, Schmiedlstr. 6, 8042, Graz, Austria f International Research Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan

Due to its remarkable mechanical and biological properties, there is considerable interest in understanding, and replicating, spider silk's stress-processing mechanisms and structure-function relationships. Here, we investigate the role of water in the nanoscale mechanics of the different regions in the spider silk fibre, and their relative contributions to stress processing. We propose that the inner core region, rich in spidroin II, retains water due to its inherent disorder, thereby providing a mechanism to dissipate energy as it breaks a sacrificial amide-water bond and gains order under strain, forming a stronger amide-amide bond. The spidroin I-rich outer core is more ordered under ambient conditions and is inherently stiffer and stronger, yet does not on its own provide high toughness. The markedly different interactions of the two proteins with water, and their distribution across the fibre, produce a stiffness differential and provide a balance between stiffness, strength and toughness under ambient conditions. Under wet conditions, this balance is destroyed as the stiff outer core material reverts to the behaviour of the inner core.

We present the design, fabrication process, and the first test results of a high aspect ratio micromixer combined with a free jet for under 100 µs time resolved studies of chemical reactions. The whole system has been optimized for synchrotron small angle X-ray scattering (SAXS) experiments. These studies are of particular interest to understand the early stages of chemical reactions, such as the kinetics of nanoparticle formation. The mixer is based on hydrodynamic focusing and works in the laminar regime. The use of a free jet overcomes the fouling of the channels and simultaneously circumvents background scattering from the walls. The geometrical parameters of the device have been optimized using finite element simulations, resulting in smallest features with radius <1 µm, and a channel depth of 60 µm, thus leading to an aspect ratio >60. To achieve the desired dimensions deep X-ray lithography (DXRL) has been employed. The device has been tested. First the focusing effect has been visualized using fluorescein. Then the evolution and stability of the jet, which exits the mixer nozzle at 13 m s−1, have been characterized. Finally SAXS measurements have been conducted of the formation of calcium carbonate from calcium chloride and sodium carbonate. The fastest measurement is 75 µs after the beginning of the mixing of the reagents. The nanostructural evolution of chemical reactions is clearly discernible.