3D Bioprinting of Self‐Standing Silk‐Based Bioink

Abstract

Silk/polyethylene glycol (PEG) hydrogels are studied as self‐standing bioinks for 3D printing for tissue engineering. The two components of the bioink, silk fibroin protein (silk) and PEG, are both Food and Drug Administration approved materials in drug and medical device products. Mixing PEG with silk induces silk β‐sheet structure formation and thus gelation and water insolubility due to physical crosslinking. A variety of constructs with high resolution, high shape fidelity, and homogeneous gel matrices are printed. When human bone marrow mesenchymal stem cells are premixed with the silk solution prior to printing and the constructs are cultured in this medium, the cell‐loaded constructs maintain their shape over at least 12 weeks. Interestingly, the cells grow faster in the higher silk concentration (10%, w/v) gel than in lower ones (7.5 and 5%, w/v), likely due to the difference in material stiffness and the amount of residual PEG remaining in the gel related to material hydrophobicity. Subcutaneous implantation of 7.5% (w/v) bioink gels with and without printed fibroblast cells in mice reveals that the cells survive and proliferate in the gel matrix for at least 6 week postimplantation. The results suggest that these silk/PEG bioink gels may provide suitable scaffold environments for cell printing and function.

Rapid Photocrosslinking of Silk Hydrogels with High Cell Density and Enhanced Shape Fidelity

“…One key example demonstrated in this current study is the rapid stabilization of the silk bioink mediated by visible light exposure, permitting the creation of complex porous architectures via extrusion printing within a sacrificial template. It is to be highlighted that the silk bioink in this study has not undergone any lengthy modification process to graft photolabile groups onto the protein, nor require addition of rheological modifiers as per the literature . By tuning the resolution and design of the sacrificial Pluronic F‐127 sacrificial template, silk fibroin filaments of high resolution (40 µm) were printed, superior to previously reported studies using this sacrificial approach and gelatin‐based inks .…”

“…3D extrusion printing of silk fibroin has to date required addition of other compounds at high concentrations, including, e.g., gelatin (10–15 wt%), glycerol (25 wt%), or poly(ethylene glycol) (PEG, 40 wt%), to achieve the necessary rheological properties for fiber extrusion. The crosslinking mechanisms utilized in these methods are not compatible with cell encapsulation at high densities required for most regenerative medicine applications.…”

Combining Stem Cells and Biomaterial Scaffolds for Constructing Tissues and Cell Delivery

“…This study opens intriguing areas for future work. Silk has also recently been evaluated as a potential bioink [103], making the 3D printing stem cell-derived tissues possible.…”

Water‐insoluble amorphous silk fibroin scaffolds from aqueous solutions

“…Besides the inherent virtues of silk fibroin, such as biocompatibility, a green formation process, and tunable biodegradability, another feature is its diversity of conformations, hierarchical microstructures and various material states, endowing the possibility of designing biomaterials with selective and useful performance (Gorenkova et al, ; Hu et al, ; Kumar, Nandi, Kaplan, & Mandal, ; Qi et al, ; Rockwood et al, ). However, it is difficult to fabricate soft, insoluble RSF scaffolds in the absence of chemical crosslink reagent such as glutaraldehyde or horseradish peroxide, since enough beta‐sheet structure is considered a prerequisite for water‐insolubility, but in turn results in a higher stiffness for the material (Cao et al, ; Kim, Park, Kim, Wada, & Kaplan, ; Zheng et al, ).…”