Thermoplastic Molding of Regenerated Silk
Historically, early insights into the unique structure and properties of native silk indicate that thermal processing was not a good option for this material due to the stability of β-sheet nanocrystallites, resulting in thermal degradation prior to melting. Thus, canonical approaches developed over the past 65 years to fabricate silk-based materials for biomedical applications involve solution-derived processing methods that have advantages and limitations with regard to silk protein solubility, stability in solution, and time and cost efficiency. Here we report the first successful solid-state thermal processing of regenerated silk, resulting in the molding of solid silk directly into bulk ‘parts’ or devices with tunable mechanical properties, while retaining machinability, biocompatibility and degradability. At elevated temperature and pressure,regenerated amorphous silk nanomaterials (ASN) with ultralow β-sheet content undergo thermal fusion via molecular rearrangement and self-assembly assisted by bound waterto form a robust bulk material. This transformativethermal processing technique with silk reverses presumptions about the limitations of direct thermal processing of silk into functional devices, demonstrating new options in molding silk into a wide range of new material formats that align with more traditional thermal processing options for synthetic polymer. Furthermore, a variety of silk-based functional composite materials can be made for tailoring the properties of the devices.