2023 AIChE Annual Meeting

Dynamics of Chemical and Physical Crosslinking of Methacrylated Silk Fibroin Hydrogels for Applications in 3D Printing

Silk fibroin (SF) derived from Bombyx mori silk is a useful material in the biomedical field. Its biocompatible and tunable characteristics allow for applications in drug delivery, tissue engineering, and regenerative medicine (1). SF on its own is inert, therefore the addition of photocrosslinkable active sites via methacrylation (SilkMA) allows for interactions with Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), a photoinitiator. Using ultraviolet (UV) light (405 nm), SilkMA can be crosslinked to form a hydrogel (2). SF hydrogels created via chemical crosslinking can be tuned to increase their load bearing capacity to mimic the mechanical properties of tendons or ligaments (3). However, a significant challenge lies in maintaining these properties for extended periods, as silk hydrogels tend to lose elasticity due to the formation of beta sheet crystals (4). This physical crosslinking is irreversible as the hydrogel has reached its thermal equilibrium. Therefore, to mitigate the formation of these physical crosslinks, which are formed by hydrogen bonding leading to beta sheet formation and a more crystalline polymer network. We investigate variables that contribute to the chemical crosslinking of SF hydrogels to hopefully interfere with beta sheet formation. Namely, we hypothesize that decreasing SF molecular weight and increasing chemical crosslinking density will slow crystalline growth. Beta sheet formation is characterized by FTIR spectra and optical transparency, while mechanical properties are assessed with shear rheology, thermal gravimetric analysis, and differential scanning calorimetry. Thus, these results explore the factors of chemical crosslinking that play a role in reducing or increasing physical crosslinking in SF hydrogels.

References

  1. Rockwood DN, Preda RC, Yücel T, Wang X, Lovett ML, Kaplan DL. Materials fabrication from Bombyx mori silk fibroin. Nature Protocols. 2011;6(10):1612-31. doi: 10.1038/nprot.2011.379.
  2. Kim SH, Yeon YK, Lee JM, Chao JR, Lee YJ, Seo YB, Sultan MT, Lee OJ, Lee JS, Yoon SI, Hong IS, Khang G, Lee SJ, Yoo JJ, Park CH. Precisely printable and biocompatible silk fibroin bioink for digital light processing 3D printing. Nat Commun. 2018;9(1):1620. Epub 2018/04/26. doi: 10.1038/s41467-018-03759-y. PubMed PMID: 29693652; PMCID: PMC5915392.
  3. Zheng H, Zuo B. Functional silk fibroin hydrogels: preparation, properties and applications. Journal of Materials Chemistry B. 2021;9(5):1238-58. doi: 10.1039/D0TB02099K.
  4. Su D, Yao M, Liu J, Zhong Y, Chen X, Shao Z. Enhancing Mechanical Properties of Silk Fibroin Hydrogel through Restricting the Growth of β-Sheet Domains. ACS Applied Materials & Interfaces. 2017;9(20):17489-98. doi: 10.1021/acsami.7b04623.