Silk-Based Scaffold for Ligament Tissue Engineering

Abstract

In recent years, silk has been increasingly studied as the scaffold for ligament tissue engineering due to the biocompatibility, slow degradability, and remarkable mechanical properties. Braided silk scaffold modified with short polypeptide also significantly increases collagen synthesis on it. To increase cell attachment and tissue infiltration, the braided scaffold can be incorporated with silk-gelatin microsponges. A novel silk cable-reinforced gelatin/silk fibroin hybrid scaffold was fabricated, which, apart from providing proper mechanical strength and enlarged surface area, also supported the proliferation and differentiation of MSCs on it. The knitted silk mesh is another important silk-based scaffold for its excellent mechanical properties and good nutrients transport. To prevent cells from leaking out of scaffold after seeding, freeze-dried silk microsponges were incorporated into the macro pores of knitted scaffold. In vitro culture demonstrated that MSCs on scaffolds proliferated vigorously and produced abundant collagen. The transcription levels of ligament-specific genes (collagen I, collagen III, and tenascin-C) also increased significantly with time. The comparison of MSCs and fibroblasts as cell sources for ligament tissue engineering demonstrated that MSC was the most suitable candidate for its vigorous proliferation and ECM production. The MSCs/knitted scaffolds were implanted into rabbits to regenerate ACL in vivo. After 24 weeks, histology observation showed that MSCs were distributed throughout the regenerated ligament and exhibited fibroblast morphology. The key ligament ECM components including collagen I, collagen III, and tenascin-C were produced prominently. Furthermore, direct ligament-bone insertion with typical four zones (bone, mineralized fibrocartilage, fibrocartilage, ligament) was reconstructed, which resembled the native structures of ACL-bone insertion. The tensile strength of regenerated ligament also met the mechanical requirements of daily activities. In conclusion, the results imply that silk scaffold has great potentials in future clinical applications.