Silk Fibroin Aqueous-Based Adhesives Inspired by Mussel Adhesive Proteins

Abstract

Silk fibroin from the domesticated silkworm Bombyx mori is a naturally occurring biopolymer with charged hydrophilic terminal regions that end-cap a hydrophobic core consisting of repeating sequences of glycine, alanine, and serine residues. Taking inspiration from mussels that produce proteins rich in L-3,4-dihydroxyphenylalanine (DOPA) to adhere to a variety of organic and inorganic surfaces, the silk fibroin was functionalized with catechol groups. Silk fibroin was selected for its high molecular weight, tunable mechanical and degradation properties, aqueous processability, and wide availability. The synthesis of catechol-functionalized silk fibroin polymers containing varying amounts of hydrophilic polyethylene glycol (PEG, 5000 g/mol) side chains was carried out to balance silk hydrophobicity with PEG hydrophilicity. The efficiency of the catechol functionalization reaction did not vary with PEG conjugation over the range studied, although tuning the amount of PEG conjugated was essential for aqueous solubility. Adhesive bonding and cell compatibility of the resulting materials were investigated, where it was found that incorporating as little as 6 wt % PEG prior to catechol functionalization resulted in complete aqueous solubility of the catechol conjugates and increased adhesive strength compared with silk lacking catechol functionalization. Furthermore, PEG-silk fibroin conjugates maintained their ability to form β-sheet secondary structures, which can be exploited to reduce swelling. Human mesenchymal stem cells (hMSCs) proliferated on the silks, regardless of PEG and catechol conjugation. These materials represent a protein-based approach to catechol-based adhesives, which we envision may find applicability as biodegradable adhesives and sealants.

Recent approaches in designing bioadhesive materials inspired by mussel adhesive protein

“…Naturally occurring biopolymers such as silk fibroin, HA, and chitosan functionalized with catechol have also been investigated 240, 241, 242, 243, 244. Silk fibroin is a hydrophobic biopolymer with repeated amino acid sequence of glycine, alanine, and serine residues,245 and has recently attracted attentions as a biomaterial platform 246, 247.…”

Temperature‐dependent structure and compressive mechanical behavior of alginate/polyethylene oxide–poly(propylene oxide)–poly(ethylene oxide) hydrogels

“…It is also feasible to create hydrogels that have a both high fracture stress and high fracture strain by fabricating multicomponent gels with both a high alginate and F127 concentration. Similar strategies have been used previously with double‐network, IPN, and composite hydrogels that contain both stiff and soft components (Birch, Barney, Pandres, Peyton, & Schiffman, ; Burke, Roberts, & Kaplan, ; Dragan, Lazar, Dinu, & Doroftei, ; Higuchi, Saito, Sakai, Gong, & Kubo, ; Mai, Matsuda, Nakajima, Gong, & Urayama, ; Matricardi, Di Meo, Coviello, Hennink, & Alhaique, ; Stoppel et al, ; Stoppel, Ghezzi, McNamara, Black III, & Kaplan, ; Stoppel, Hu, Domian, Kaplan, & Black III, ; Williams et al, ; Zhang et al, ). We have achieved similar results here, but through the use of relatively straightforward individual polymer components, alginate and F127.…”

Evaluation of the Spectral Response of Functionalized Silk Inverse Opals as Colorimetric Immunosensors

“…Figure 2a shows that there was no statistically significant difference between covalent and noncovalent attachment, and this is thought to be due the small amount of glutamic acid and aspartic acid residues that are available in silk for conjugation, though this may be increased in the future through modification of serine residues. 46,47 Despite this, covalent attachment of avidin was continued because immobilization by covalent bonding was anticipated to enhance stability of avidin on the silk surface, though this would need to be confirmed with additional studies. Finally, increasing the avidin concentration from 2.5 to 5.2 mg/mL did not result in statistically larger amounts of avidin attached to silk, thus all subsequent experiments used a 2.5 mg/mL solution of avidin with the covalent coupling route to prepare the sensing surfaces.…”