Superior Tendon Repair and Healing Ability of PLGA Sutures Are Related to the Weaker Regulatory T-cell and Macrophage Responses Compared With PGA Sutures in a Rat Model

Background: Absorbable sutures (such as Vicryl sutures) support tendon rupture repair, but the immune response triggered by the sutures affects tendon healing. A rat Achilles tendon model was used in this study to explore the role of sutures in tendon healing. Purpose: To evaluate the physicochemical properties, biomechanical properties, cytotoxicity, heat-induced pain sensitivity, histological alterations, and the responses of regulatory T (Treg) cells and macrophages to polyamide (PA), polyglycolic acid (PGA), and poly(lactic-co-glycolic acid) (PLGA) sutures in Achilles tendon healing. Study Design: Controlled laboratory study. Methods: A rat Achilles tendon rupture model was established, followed by modified Kessler repair with size 5-0 PA, PGA, and PLGA sutures. The repaired tendons were tested at 2 weeks and 4 weeks after surgery. The ultimate load and failure stress of the repaired tendons were evaluated using a uniaxial loading device. The samples were stained with hematoxylin and eosin (H&E) as well as Sirius red for histological evaluation. Immunohistochemical analysis was conducted to investigate alterations in macrophages and Treg cells. Results: All 3 sutures (PA, PGA, and PLGA) maintained structural integrity after repair. However, compared with nonabsorbable PA, absorbable sutures (PGA and PLGA) demonstrated higher failure loads. At 4 weeks after suture, the postsutured tendons in the 3 groups were thicker, and the PGA (78.64 ± 4.69 N) and PLGA (71.19 ± 3.81 N) groups demonstrated significantly greater ultimate loads than the PA (54.76 ± 5.79 N) group; compared with the PLGA group, the PGA group exhibited more adhesion. Histologically, the Bonar scores for the PGA (9.60 ± 0.89) and PLGA (9.80 ± 0.83) groups were significantly lower than that for the PA group (11.20 ± 0.83) at 4 weeks postsuture. Collagen type III predominated in the PA and PLGA groups, whereas collagen type I was predominant in the PGA group at 2 weeks postsuture. Immunohistochemical analysis demonstrated that the proportions of CD86 + (M1, proinflammatory) macrophages, CD206 + (M2, anti-inflammatory) macrophages, and CD25 and Foxp3 (Treg cell markers) were significantly greater in the PGA group than in the PLGA and PA groups at 2 weeks after surgery. Conclusion: The PGA and PLGA groups demonstrated comparable biomechanical properties, whereas compared with the PGA group, the PLGA group exhibited superior healing outcomes (fewer adhesions and more balanced collagen remodeling) and milder Treg cell and macrophage responses. Clinical Relevance: These results can help clinicians choose suture materials.