A novel 3D-printed silk fibroin/hydroxypropyl methyl cellulose scaffold with good biocompatibility and controllable degradation in vivo

Abstract

In this study, novel silk (SF)-fibroin based scaffolds were fabricated via 3D printing of a thixotropic SF/hydroxypropyl methyl cellulose (HPMC) hydrogel. Two different concentrations of 3D printed SF/HPMC scaffolds (20 wt% and 30 wt%) were implanted subcutaneously in SD rats for 24 weeks to investigate in vivo degradation and biocompatibility. Scaffold morphology, tissue ingrowth (collagen fibers, blood vessels), and local inflammatory responses were assessed using SEM, histology (HE, Masson staining), immunohistochemistry (CD31, CD68), and RT-qPCR (IL-6, IL-1β, IL-10, TGF-β1 mRNA). Results showed that no purulent secretions were found around the two scaffolds during implantation. Collagen fibers, blood vessels and other tissues could grow into the scaffolds after implantation. The number of collagen fibers and CD31-positive vascular endothelial cells in the 20 wt% SF/HPMC scaffolds were greater than that in the 30 wt% SF/HPMC scaffolds. SEM detection showed the pore structure in the cross section of 20 wt% SF/HPMC scaffolds began to collapse at 12 weeks; No obvious collapse of the pore structure was found in the cross section of the 30 wt% SF/HPMC scaffolds during the period of implantation. Mechanical properties test showed that the compressive modulus of 20 wt% SF/HPMC scaffolds decreased significantly at 12 weeks and was lower than that at the pre-implantation. The mechanical properties of the 30 wt% SF/HPMC scaffolds remained relatively stable, and the mechanical properties were slightly higher at 24 weeks than that before implantation. Both scaffolds did not cause severe inflammatory reactions during the degradation process, and their structures could allow the growth of blood vessels, collagen fibers and other tissues. The degradability was correlated to the concentrations of SF/HPMC and insights gained in this study can serve as a guide to match desired degradation behavior with specific applications for the 3D printed SF/HPMC scaffold.