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Thermoplastic moulding of regenerated silk

Abstract

Early insights into the unique structure and properties of native silk suggested that β-sheet nanocrystallites in silk would degrade prior to melting when subjected to thermal processing. Since then, canonical approaches for fabricating silk-based materials typically involve solution-derived processing methods, which have inherent limitations with respect to silk protein solubility and stability in solution, and time and cost efficiency. Here we report a thermal processing method for the direct solid-state moulding of regenerated silk into bulk ‘parts’ or devices with tunable mechanical properties. At elevated temperature and pressure, regenerated amorphous silk nanomaterials with ultralow β-sheet content undergo thermal fusion via molecular rearrangement and self-assembly assisted by bound water to form a robust bulk material that retains biocompatibility, degradability and machinability. This technique reverses presumptions about the limitations of direct thermal processing of silk into a wide range of new material formats and composite materials with tailored properties and functionalities.

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Fig. 1: Process to generate silk-based bulk materials from native silk.
Fig. 2: Comparison of degummed natural silk fibre and ASN.
Fig. 3: Thermal processing of ASN.
Fig. 4: Physical properties of fabricated silk-based bulk materials.
Fig. 5: In vitro and in vivo testing of functional silk-based medical devices.

Data availability

The authors declare that all data supporting the findings of this study are available within the paper and its Supplementary Information files and from the corresponding author upon reasonable request.

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Acknowledgements

This work was supported by grants from the National Institutes of Health (R01AR068048, R01DE016525), the Air Force Office of Scientific Research (FA9550-17-1-0333) and the Stepping Strong Foundation, Brigham and Women’s Hospital (A. Nazarian and G. Dyer). We thank J. Yarger, B. Cherry and N. Sisco at Arizona State University for help with NMR instrumentation and data collection. We thank G. Dyer for clinical relevance discussions. We also thank S. Maccorkle and D. Dupuis at the Tufts University Machine Shop for materials machining.

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C.G., C.L and D.L.K. conceived and designed the project and experiments; C.G., C.L., H.V.V. and Y.Q. performed the materials fabrication and characterizations; P.H., A.L. and A.N. performed animal studies; C.G., C.L., X.M., S.L. and S.J.L. performed the data analysis and results discussion; D.L.K. supervised the entire project; and C.G. and C.L. wrote the manuscript. All authors discussed the results and commented on the manuscript.

Corresponding authors

Correspondence to Chunmei Li or David L. Kaplan.

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Supplementary Figures 1–27, Tables 1–8, a note and refs. 1–7.

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Guo, C., Li, C., Vu, H.V. et al. Thermoplastic moulding of regenerated silk. Nat. Mater. 19, 102–108 (2020). https://doi.org/10.1038/s41563-019-0560-8

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