Enzymatically crosslinked and mechanically tunable silk fibroin/pullulan hydrogels for mesenchymal stem cells delivery

Hydrogels with good biocompatibility, proper degradation rates, and tissue-matched elasticity are widely used in tissue engineering, regenerative medicine, and drug delivery. In this study, enzymatically crosslinked biocompatible hydrogels were successfully developed using silk fibroin (SF) and pullulan (PL) under physiological conditions in the presence of both horseradish peroxidase and hydrogen peroxide. A series of properties of the hydrogels including gelation time, equilibrium swelling, enzyme degradation, morphology, rheological property, and compression modulus of SF/PL hydrogels were studied by varying the concentration of PL. The results showed that the SF/PL hydrogels had applicable gel-forming rate (ranging from 12 to 60 min), tunable compressive strength (ranging from 7 to 71 kPa) and shear mechanical properties (ranging from 200 to 1470 Pa). The properties of the SF/PL hydrogels were easily modulated by changing the concentration of PL. The compressive modulus of the SF + 20%PL hydrogels was 71.4 ± 9.3 kPa, which was in the range of that of musculoskeletal system. In addition, the rabbit bone marrow-derived mesenchymal stem cells were encapsulated in SF/PL hydrogels for 7 days, and cell viability and morphology were observed. Live/dead staining assay demonstrated that the hydrogel system possessed good cytocompatibility. These features support that SF/PL hydrogels have a potential as cell delivery scaffold in musculoskeletal tissue engineering.