Polymorphic regenerated silk fibers assembled through bioinspired spinning

Shengjie Ling,Zhao Qin,David L Kaplan,Chunmei Li,Wenwen Huang,Markus J Buehler

doi:10.1038/s41467-017-00613-5

Shengjie Ling, Zhao Qin + Show 4 more

Open Access

https://doi.org/10.1038/s41467-017-00613-5

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Abstract

A variety of artificial spinning methods have been applied to produce regenerated silk fibers; however, how to spin regenerated silk fibers that retain the advantages of natural silks in terms of structural hierarchy and mechanical properties remains challenging. Here, we show a bioinspired approach to spin regenerated silk fibers. First, we develop a nematic silk microfibril solution, highly viscous and stable, by partially dissolving silk fibers into microfibrils. This solution maintains the hierarchical structures in natural silks and serves as spinning dope. It is then spun into regenerated silk fibers by direct extrusion in the air, offering a useful route to generate polymorphic and hierarchical regenerated silk fibers with physical properties beyond natural fiber construction. The materials maintain the structural hierarchy and mechanical properties of natural silks, including a modulus of 11 ± 4 GPa, even higher than natural spider silk. It can further be functionalized with a conductive silk/carbon nanotube coating, responsive to changes in humidity and temperature.

Highlights

A variety of artificial spinning methods have been applied to produce regenerated silk fibers; how to spin regenerated silk fibers that retain the advantages of natural silks in terms of structural hierarchy and mechanical properties remains challenging
We found that HFIP can partially dissolve B. mori silkworm cocoon silk fibers to microfibrils with diameters of 5–50 μm and contour lengths of 50–500 μm after incubating silk fiber/HFIP mixtures at 60 °C44, 45
After 15 days, the silk fibers are partially dissolved to form the microfibrils, but in this case the silk microfibril (SMF) present in smaller diameters (5–10 μm) and longer contour lengths (Fig. 2c)

Summary

Introduction

A variety of artificial spinning methods have been applied to produce regenerated silk fibers; how to spin regenerated silk fibers that retain the advantages of natural silks in terms of structural hierarchy and mechanical properties remains challenging. Spiders and silkworms construct webs and cocoons by directly spinning a pre-assembled nematic silk protein dope, which is solidified immediately to a fiber once it leaves the spinneret[5, 10, 11] All of these processes are conducted under physiological and ambient conditions without any additional immobilization and post-processing steps[5, 9,10,11]. They still require complex post-processing treatments (e.g., dehydration and crystallization processes7) to generate useful fibers This drawback deeply hinders the application of these methods, and, more importantly, all of these attempts (including wet and dry spinning) only focus on reproducing the mechanical properties of natural silks, and pay less focus on retaining the hierarchical structures of silks, a key feature in the properties of the natural protein fibers[22,23,24,25,26,27]. We show how the scope of these RSFs can be amplified by adding conductive silk/ carbon nanotube coatings, which are suitable for generating humidity and temperature sensors with potential in wearable device/biosensor applications due to the robust silk fibers as a foundation

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