Silk enhances the ligamentization of the polyethylene terephthalate artificial ligament in a canine anterior cruciate ligament reconstruction model

Anterior cruciate ligament (ACL) reconstruction is the leading treatment for ACL rupture. Ligament Advanced Reinforcement System (LARS), which is made of polyethylene terephthalate (PET), is the most frequently used artificial ligament for ACL reconstruction. However, PET is hydrophobic, so it is difficult to induce the ingrowth of the autologous tissue. The aim of this study is to explore the effects of silk hybrid on the ligamentization of the PET artificial ligament in a canine ACL reconstruction model. Silk/PET hybrid suspensory ligament was fabricated with silk in the weft yarn and PET in the warp yarn, while PET suspensory ligament was fabricated with PET in both the weft and warp yarns. After fabrication, the micromorphology of the ligaments was observed and mechanical testing was performed. Though the failure loads of the degummed silk/PET hybrid suspensory ligaments were significantly lower than those of the PET suspensory ligaments (P < 0.001), both of them were enough for ACL reconstructions of beagle dogs. In the animal study, 14 beagle dogs were divided into PET suspensory ligament group and silk/PET hybrid suspensory ligament group randomly, with 7 dogs in each. The dogs underwent ACL reconstructions in their right knees. At postoperative 6 months, the dogs were sacrificed, and the specimens were evaluated with gross observation, histology, immunohistochemistry, and mechanical testing. The histological and immunohistochemical results showed that the native ACL of the beagle dog held abundant fibroblasts and collagen. The PET-regenerated ligament was loose, and there was a small amount of autologous tissue and collagen. Compared to the PET-regenerated ligament, the silk/PET hybrid-regenerated ligament had a compact structure, and there was more regenerated autologous tissue and collagen. In conclusion, compared to the PET ligament, the silk/PET hybrid ligament kept greater ability to induce the ingrowth of the autologous tissue, indicating that the silk hybrid had enhanced the ligamentization of the PET artificial ligament.