Abstract
Natural silk spinning has undergone strong selection for resource efficiency and thus presents a biomimetic ideal for fiber production. Industrial replication of natural silk fibers would enable access to low energy, cost-efficient processing, but is hampered by a lack of understanding surrounding the conversion of liquid feedstock into a solid fiber as a result of flow. Previously, shear stress, shear rate, or time have been presented as criteria for silk fiber formation, but here it is proposed that spinning requires carefully balancing all three, and is a result of controlled energy accumulation in the feedstock. To support this hypothesis, rheology is used to probe the energy required for conversion, compare differences between amorphous solid and ordered fiber production and explain the energetic penalty the latter demands. New definitions of what constitutes an artificial silk fiber are discussed, along with methods to ensure that each spinning criterion is met during biomimetic spinning.
Highlights
Emulating the process of natural silk spinning is a long held aim in the field of biomaterials, as unfettered access to silk’s attractive properties would provide huge commercial benefits arising from efficient continuous fibre production, without the hindrances associated with traditional production methods.[1]
B. mori spin, via pultrusion,[2] a dual filament fibre composed primarily of the protein fibroin,[3] coated in layers of a secondary protein known as sericin, which acts as a lubricant in the duct[4] and a binder[5,6] in the cocoon, a non-woven composite structure.[7]
3.1 Oscillatory and low rate steady shear response The initial set of rheological tests confirmed that the fibroin samples tested were representative of a typical B. mori feedstock and suitable for characterisation of their work to gelation (Figure 1)
Summary
Emulating the process of natural silk spinning is a long held aim in the field of biomaterials, as unfettered access to silk’s attractive properties would provide huge commercial benefits arising from efficient continuous fibre production, without the hindrances associated with traditional production methods.[1]. While spider silk is perhaps the most well-known, or at least promoted, super material, the vast majority of everyday silk products are woven from fibres produced from cocoons spun as a protective layer by the Chinese silkworm Bombyx mori In their native environment, B. mori spin, via pultrusion,[2] a dual filament fibre composed primarily of the protein fibroin,[3] coated in layers of a secondary protein known as sericin, which acts as a lubricant in the duct[4] and a binder[5,6] in the cocoon, a non-woven composite structure.[7] Whilst B. mori’s natural fibre mechanical properties[8] are less desirable than those of, say the dragline filaments of Nephila edulis,[9] there is abundant evidence to suggest that they can be further processed to comparable performance levels[10,11,12] and their generally more abundant, accessible nature makes them currently a more practical technology platform.[13,14,15,16,17,18,19]. We consider these results within the wider context of understanding the fundamental mechanisms behind shear induced denaturation alongside the implications for industrialists wishing to mimic silk fibre spinning, as it allows for much less stringent conditions in feedstock production
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