Tubular Silk Fibroin/Gelatin-Tyramine Hydrogel with Controllable Layer Structure and Its Potential Application for Tissue Engineering.

In recent years, biomimetic tubular scaffolds have been widely used to repair various human tissue defects, due to their hollow structure similar to the native tissues such as blood vessel, trachea, ureter, and bone marrow cavity. However, there are still many challenges in manufacturing a tubular hydrogel scaffold with suitable mechanical properties, specific microstructure, and good biocompatibility. In this study, we exploited an enzymatic cross-linking method using horseradish peroxidase (HRP) as an enzyme and hydrogen peroxide (HO) as a substrate, and combining with gelatin's thermal sensitivity to produce an enzymatically cross-linked silk fibroin/gelatin-tyramine (E-SF/GT) tubular hydrogel. Through further treatment with methanol, we fabricated an EM-SF/GT tubular hydrogel with fine-wall architecture that consists of two different layers (inner and outer, dense and porous). Mechanical measurement showed that the compressive moduli values were up to 4.82 MPa and the tensile moduli values were up to 4.79 kPa under the static loading conditions. Also, degradation test showed that the hydrogel's degradation time was prolonged. Finally, the bioactivity was tested by seeding mouse bone marrow mesenchymal stem cells (mBMSCs) in the lumen of a small-diameter (2 mm) EM-SF/GT tubular hydrogel. Cell morphology and immunofluorescence test indicated that mBMSCs differentiated into endothelial cells and lined the inner surface of the tubular hydrogel under induction. This work provided a feasible strategy for developing tubular hydrogels, which could be potentially used as scaffolds for hollow multilayer tissue engineering, such as blood vessels.