Thermal and structural properties of 3D printed silk fibroin*

Silk fibroin, the protein in cocoon fibers of the Bombyx mori silkworm, is used across many fields due to its tensile strength and flexibility [1]. Because it is biocompatible and biodegradable, it is the ideal material for many biomedical applications [1]. We study the use of 3D printing to create printed parts of silk fibroin. The process involves extraction of fibroin from cocoon fibers, enrichment to obtain a printable solution, printing into a coagulation bath, and characterization of the secondary structures of the resulting parts. We focus on the salt-water coagulation bath, which crystallizes printed parts through the formation of beta pleated sheets [1]. Two factors must be considered during the coagulation process. First, silk fibroin takes up bound water during the printing process, which lowers its glass transition temperature (T_g), making it weaker [2]. Second, the presence of beta sheet crystals strengthens the material and increases T_g [3]. We examine the relationship between bound water content and degree of crystallinity, and the salinity of the coagulation bath. Building more resilient and stronger silk leads to better 3D printed parts, beneficial in biomedical applications.

References

[1] Mu, X. et al., Advanced Healthcare Materials, 19(5), e1900191 (2020).

[2] Hu, X. et al., Thermochimica Acta, 461(1-2), 137 (2006).

[3] Hu, X. et al., Macromolecules, 39(18), 6161 (2006).