Knitted silk mesh-like scaffold incorporated with sponge-like regenerated silk fibroin/collagen I and seeded with mesenchymal stem cells for repairing Achilles tendon in rabbits

A scaffold knit with natural sericin-free silk fibroin fiber possesses desirable mechanical properties, biocompatibility, ease of fabrication, and slow degradability. However, regenerated silk fibroin degrades faster than natural silk. In this study, natural silk fibroin fiber mesh-like scaffolds were prepared by a weft-knitting method and the pores were filled with sponge-like regenerated silk fibroin-collagen I. The microporous sponge and mesh-like scaffolds were fused to achieve gradient degradation of the scaffolds, and rabbit bone marrow mesenchymal stem cells (BMSCs) were seeded onto the scaffolds to form scaffold–BMSCs composites. The composites were implanted into gap defects made in the rabbit Achilles tendon. Twenty weeks after implantation, histological observation showed that tendon-like tissue had formed, collagen I mRNA was expressed, abundant collagen was generated, and that there was no obvious degradation of silk. The maximum load of the neo-Achilles tendon was 62.14% that of the natural Achilles tendon. These outcomes were superior to those obtained in the group implanted with a scaffold without BMSCs. These findings suggest the feasibility of constructing tissue-engineered tendons using weft-knitted silk scaffolds incorporated with sponge-like regenerated silk fibroin/collagen I and seeded with BMSCs, and show potential of the scaffold–BMSCs composites to repair Achilles tendon defects.