Challenges involving tendon and ligament repair have motivated the investigation of new strategies to improve clinical outcomes. These have been mainly based on polymer constructs, which may be non-biodegradable or biodegradable. The former typically fails due to lack of device integration and the latter demands a complex balance between biodegradability and tissue ingrowth, often failing due to insufficient mechanical properties. This work presents the development of hybrid braids based on polyethylene terephthalate (PET) and polylactic acid (PLA) yarns. A textile technique was used to fabricate braids based on 16 multifilament yarns of varying PLA/PET composition. The composition was varied to maximize biodegradability while ensuring mechanical performance. The braids' morphology, physical and mechanical properties were characterized. As production parameters and architecture were maintained, the braids exhibited similar porosity and wicking ability. The breaking force and stiffness decreased significantly as the number of PLA yarns increased, although strain levels remained constant. Braids containing 10 and 12 PET yarns (out of the total 16 yarns) demonstrated good creep and force-relaxation behavior, as well as resistance to cyclic loading. These compositions were selected for future work, to be assembled into more elaborate structures to mimic the fibrous organization and tensile properties of different tendons/ ligaments.
Anterior cruciate ligament (ACL) replacement is still a big challenge in orthopedics due to the need to develop bioinspired implants that can mimic the complexity of bone-ligament interface. 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) implantation. For comparative purposes, plain HRP-cross-linked SF hydrogels (PTGs) were fabricated. Sonication and freeze-drying methodologies capable of inducing crystalline β-sheet conformation were carried out to produce both the CTGs and PTGs. 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 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. Therefore, 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.
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