Viscoelastic Silk Fibroin Hydrogels with Tunable Strength

Abstract

Hydrogels are often used as synthetic\nextracellular matrices (ECMs)\nfor biomedical applications. Natural ECMs are viscoelastic and exhibit\npartial stress relaxation. However, commonly used hydrogels are typically\nelastic. Hydrogels developed from ECM-based proteins are viscoelastic,\nbut they often have weak mechanical properties. Here, biocompatible\nviscoelastic hydrogels with excellent mechanical performance are fabricated\nby an all aqueous process at body or room temperature. These hydrogels\noffer obvious stress relaxation and tunable mechanical properties\nand gelation kinetics. Their compressive modulus can be controlled\nbetween 2 kPa and 1.2 MPa, covering a significant portion of the properties\nof native tissues. Investigation of the gelation mechanism revealed\nthat silk fibroin gelation is caused by the synergistic effects of\nhydrophobic interaction and hydrogen bonding between silk fibroin\nmolecules. Newly formed crystals serve as the cross-link sites and\nform a network endowing the hydrogel with stable structure, and the\nflexible noncrystalline silk nanofibers connect disparate silk fibroin\ncrystals, endowing hydrogels with viscoelastic properties. The all\naqueous gelation process avoids complex chemical and physical treatments\nand is beneficial for encapsulating cells or biomolecules. Encapsulation\nof chondrocytes results in high initial survival rate (95% ±\n1%). These silk fibroin-based viscoelastic hydrogels, combined with\nsuperior biocompatible and tunable mechanical properties, represent\nan exciting option for tissue engineering and regenerative medicine.