Abstract
Whilst much is known about the properties of silks, the means by which native silk feedstocks are spun still represent a gap in our knowledge. Rheology of the native silk feedstocks is germane to an understanding of the natural spinning process. Yet, an overview of the literature reveals subtle limitations and inconsistencies between studies, which has been largely attributed to sample-to-sample variation when testing these exquisitely flow-sensitive materials. This ambiguity has prevented reliable, consistent inferences from standard polymer rheology and constitutes an obstacle to further development.To address this challenge, we present the largest study to date into the rheological properties of native silk feedstocks from Bombyx mori larvae. A combination of shear and oscillatory measurements were used to examine in detail the relationships between concentration, low shear viscosity, relaxation times, complex modulus and estimates of the molecular weights between entanglements. The results from this highly detailed survey will provide a sound basis for further experimental or theoretical work and lay the foundations for future bio-inspired processing of proteins.
Highlights
Silks are natural protein fibres spun by many types of arthropods in the classes Arachnida, Insecta and Myriapoda [1e11]
In order to confirm the composition of the silk protein feedstocks used, FTIR spectra of the native silk protein solution and dried films are presented in Fig. 2, along with assignments of the main bands
The small peak at 3062 cmÀ1 may be ascribed to the aromatic CeH stretching band of tyrosine [95], which constitutes around 5% of the amino acids in B. mori silk proteins [16,34,35]
Summary
Silks are natural protein fibres spun by many types of arthropods in the classes Arachnida, Insecta and Myriapoda [1e11]. This may be a significant example of convergent evolution, as the ability to produce silk appears to have arisen independently at least 23 times [8]. The larvae of various lepidoptera (i.e. caterpillars) appear to produce only one type of silk at any time, the quantities and compositions vary between species [5] and developmental stage [12]. A large (up to 500 kDa) highly repetitive core section accounts for the high degree of order and partial crystallinity that can be observed in silk fibres [16e25]. The core is flanked by short non-repetitive globular terminal domains (typically 10e15 kDa), which appear to promote association with other chains in solution, through physical interactions initiated by a decrease in pH and changes in ion content [26e31]
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