Silk fibroin/ZnSr-ß-TCP composite scaffolds as bone tunnel fillers for anterior cruciate ligament reconstruction

The development of bioinspired implants capable of filling the bone tunnel and simultaneously promote osteointegration in anterior cruciate ligament (ACL) replacement surgeries is still a big challenge in orthopedics¹. In this study, we propose biomimetic composite tubular grafts (CTGs) made of horseradish peroxidase (HRP)-cross-linked silk fibroin (SF) hydrogels containing ZnSr-doped β-tricalcium phosphate (ZnSr-β-TCP) particles, as promising bone tunnel fillers to be used in ACL grafts (ACLGs) implantation². Plain HRP-cross-linked SF hydrogels (PTGs) were fabricated and used for comparative purposes. Sonication and freeze-drying methodologies were applied for producing CTGs and PTGs with a stable and constant crystalline β-sheet conformation. A homogeneous microstructure was achieved from microporous to nanoporous scales. The mechanical properties were dependent on the inorganic powder’s incorporation, with a superior tensile modulus observed on the CTGs (12.05 ± 1.03 MPa) as compared to the PTGs (5.30 ± 0.93 MPa). The CTGs presented adequate swelling properties to fill the space in the bone structure after bone tunnel enlargement and provide a stable degradation profile under low concentration of protease XIV. The preliminary in vitro studies revealed that SaOs-2 cells adhered, proliferated and remained viable when cultured into the CTGs. In addition, the bioactive CTGs supported the osteogenic activity of cells in terms of alkaline phosphatase (ALP) production, activity, and relative gene expression of osteogenic-related markers. This study is the first evidence that the developed CTGs hold adequate structural, chemical, and biological properties to be used as bone tunnel fillers capable of connecting to the ACL tissue while stimulating bone tissue regeneration for a faster osteointegration.