Exploring the Gelation Mechanisms and Cytocompatibility of Gold (III)-Mediated Regenerated and Thiolated Silk Fibroin Hydrogels

Abstract

Accelerating the gelation of silk fibroin (SF) solution from several days or weeks to minutes or few hours is critical for several applications (e.g., cell encapsulation, bio-ink for 3D printing, and injectable controlled release). In this study, the rapid gelation of SF induced by a gold salt (Au3+) as well as the cytocompatibility of Au3+-mediated SF hydrogels are reported. The gelation behaviors and mechanisms of regenerated SF and thiolated SF (tSF) were compared. Hydrogels can be obtained immediately after mixing or within three days depending on the types of silk proteins used and amount of Au3+. Au3+-mediated SF and tSF hydrogels showed different color appearances. The color of Au-SF hydrogels was purple-red, whereas the Au-tSF hydrogels maintained their initial solution color, indicating different gelation mechanisms. The reduction of Au3+ by amino groups and further reduction to Au by tyrosine present in SF, resulting in a dityrosine bonding and Au nanoparticles (NPs) production, are proposed as underlying mechanisms of Au-SF gel formation. Thiol groups of the tSF reduced Au3+ to Au+ and formed a disulfide bond, before a formation of Au+-S bonds. Protons generated during the reactions between Au3+ and SF or tSF led to a decrease of the local pH, which affected the chain aggregation of the SF, and induced the conformational transition of SF protein to beta sheet. The cytocompatibility of the Au-SF and tSF hydrogels was demonstrated by culturing with a L929 cell line, indicating that the developed hydrogels can be promising 3D matrices for different biomedical applications.

Impacts of Blended Bombyx mori Silk Fibroin and Recombinant Spider Silk Fibroin Hydrogels on Cell Growth

“…Blended SF:eADF4(C16) hydrogels were fabricated in order to combine the advantages of eADF4(C16) in facilitating rapid gelation and enhanced interactions with cells provided by SF. As shown in Figure 1 , it can be clearly seen that the addition of eADF4(C16) can induce faster gelation of SF, i.e., the gelation of 5:5 and 3:7 hydrogels occurred within 48 h. The gelation of pure 2% and 3% SF solutions were not observed after one week, which was in agreement with a previous study [ 20 ]. As expected, an increase of protein concentration from 2% to 3% led to a shorter gelation time, due to a higher opportunity in chain-chain interactions [ 5 , 10 ].…”

Surface Functionalization and Reversible Disassembly of DNA-Assembly Nanoparticles for Sensitive and Multiplexed Detection of DNA Targets Without Enzymatic and Catalytic Amplification

“…26,27,32−34 Direct evidence of the Au−S binding was obtained from the S 2p XPS spectra of the pDNA-bcDNA NPs, which showed only the binding energy corresponding to Au-bound S at 162.2 eV (Figure 3E). 27,35 In contrast, the control, free 11-mercaptoundecanoic acid (11-MUA), shows the binding energy not only at 162.8 eV but also at 165.8 eV that indicates the presence of unbound thiol groups. Without Au 3+ coating, the bcDNA NPs exhibited a much lower intensity at 162.2 eV after the addition of HS-pDNA, strongly supporting the successful DNA functionalization of the bcDNA NP@Au 3+ s via Au−S binding chemistry.…”

“…Following the binding of HS-pDNA on the bcDNA NP@Au 3+ s, however, the binding energies were 87.8 and 83.9 eV, indicating an additional reduction of Au 3+ to Au + and Au 0 . 20,27,28,31 The additional reduction of Au 3+ upon addition of HS-pDNA implies that the thiol groups of the excess HS-pDNA strands were partially oxidized to disulfide bonds. Despite the oxidation and reduction occurring on the surface of the bcDNA NP@Au 3+ s, the DNA functionalization of the bcDNA NP@Au 3+ s is well understood because both HS-pDNA and its disulfide derivatives are capable of binding to both Au + and Au 0 .…”

Silk Fibroin-Induced Gadolinium-Functionalized Gold Nanoparticles for MR/CT Dual-Modal Imaging-Guided Photothermal Therapy

“…Because of the intense affinity of carboxyl groups to metal ions, Gd 3+ and Au 3+ species were absorbed on SF. Au 3+ was reduced to Au + by the amino group, which was further reduced to Au by tyrosine’s cresol groups due to their strong electron-donating ability [ 34 , 35 ]. During the synthesis, the mixture solution of SF, HAuCl 4 ·4H 2 O, and GdCl 3 ·6H 2 O gradually turned from pale yellow to dark red when the NaOH solution was added to adjust the pH to 9–10, suggesting that the tyrosine of SF exhibited reducing properties under alkaline conditions and thereby reduced Au ions into AuNPs ( Figure 1 A).…”