Highly Stretchable and Tough Physical Silk Fibroin–Based Double Network Hydrogels

Abstract

a facile way to construct strong RSF hydrogels simply by adding sodium dodecyl sulfate (SDS) into high molecular weight RSF solutions. The resulting hydrogels demonstrated high tensile strength of ≈0.74 MPa and fair extensibility of 140%. [6] Shao et al. also found that ionic liquid (IL)/water mixtures could generate RSF-based gels, whose tensile strength and breaking elongation reached up to 0.4 MPa and 147%, respectively. [11] Okay et al. reported a novel strategy to design mechanically robust and stretchable silk fibroin/hyaluronic acid hydrogels with chemical cross-links and physical cross-links (β-sheet domains). [7] The hybrid hydrogels exhibited a high extensibility up to around 400% and tensile strength of 65 kPa after equilibrium swelling. Okay also described a directional freezing/cryogelation method to produce high-strength silk fibroin cryogels with a degree of mechanical anisotropy. The compressive modulus of cryogels formed at 16.7 wt% RSF concentration was 45 MPa, but the tensile properties were not shown. [12] Consequently, achieving highly stretchable RSF hydrogels for wide-range applications [13] is still in its infancy.An alternative strategy to prepare strong and tough hydrogels is the double network (DN) hydrogel, which introduces a flexible and stretchable second network. These DN hydrogels demonstrated high fracture strength (0.1-10 MPa) and high water content (60-90%). [14][15][16][17][18][19] A series of DN gels using biomacromolecules (agar, cellulose) had been developed. [20,21] Chen et al. developed RSF-based DN hydrogels via introducing a hydrophobically associated gel of polyacrylamide (HPAAm) as the second network. [10] The DN hydrogels were conveniently synthesized by the one-pot method coupled with photo-polymerization, and the resultant RSF/HPAAm DN gels showed a tensile strength of ≈1.17 MPa, and breaking elongation of ≈1900%, but non-equilibrium RSF/HPAAm DN gels contained excessive residual monomers. It is notable that although the RSF gels could be rapidly achieved via introducing SDS, the gelation that takes only a few minutes is difficult to control. It is quite difficult to achieve uniform mixing between SDS micelles and the hydrophobic monomers via the one-step method, which often resulted in poor homogeneity of the gels. In addition, the swelling of as-prepared hydrogels in water destroys the RSF/SDS network so that equilibrium hydrogels cannot be obtained. In contrast, if the first RSF/SDS network can be stabilized first during the swelling of hydrogels, the Regenerated silk fibroin (RSF) is a promising biomedical material, but the poor mechanical properties of RSF hydrogels may hinder the use as structural components. Herein, an equilibrium RSF hydrogel is prepared and optimized based on the double network (DN) concept. After sufficient soaking in water and removal of small molecules, the equilibrium RSF DN hydrogels prove stable in water, strong, highly extensible, and tough with 0.26-0.44 MPa tensile strength, 500-900% elongation, and 2 MJ m −3 work of extension. The...

Functional silk fibroin hydrogels: preparation, properties and applications

“…Therefore, the improvement of the mechanical characteristics of the silk fibroin hydrogels has become a crucial research topic in the field of silk fibroin biomaterials. The preparation of the high strength silk protein hydrogels is currently achieved by strategies, such as double network structure 54,55 , nanomaterial composites, interpenetrating network structure, low temperature cross-linking/cryogelation, etc.…”

“…On the other hand, the double network structure is an effective alternative to improve the strength of the silk fibroin hydrogels. In a related study, due to the strong hydrophobicity and electrostatic interaction of the regenerated silk fibroin, Yu Zhao et al 55 first induced its self-assembly into a stable β-sheet structure through physical cross-linking. Strong and rigid RSF/sodium dodecyl sulfate (SDS) first network was, thus, formed.…”

Mechanically Robust Elastomers Enabled by a Facile Interfacial Interactions‐Driven Sacrificial Network

“…Based on these results, our group concludes that A aggregate network ruptures preferentially upon deformation to dissipate energy, which exhibits a characteristic feature of sacrificial network, as illustrated in Figure 4d. [ 34–37 ]…”

High-Strength Hydrogel Adhesive Formed via Multiple Interactions for Persistent Adhesion under Saline

“…Thus, they did not release toxic molecules, which is similar to other hydrogels by SDS micelles. 49 At the same time, the live/dead stain assay was performed to check the survival state of cells more intuitively after cell culture. Living cells were stained green by fluorescein diacetate, and dead cells were stained red by propidium iodide.…”