Role of magnesium-doped polylactic acid microspheres in surgical repair of rat rotator cuffinjuries
Objective This study aimed to determine the effects of magnesium-doped polylactic acid microspheres(PLLAMgs)in promoting bone-tendon healing in a rotator cuffinjury rat model.Methods Polylactic acid microspheres(PLLAms)were prepared and doped with magnesium oxide and magnesium carbonate to create the study material.Rat tendon-derived stem cells(TDSCs)were extracted and subjected to in vitro viability and proliferation assays using live/dead staining and CCK-8 experiments to verify the biocompatibility of PLLAMgs.Thirty-six SD rats weighing 200-300 g were used to establish an acute rotator cuffinjury model.The rats were randomly divided into three groups(PLLAMg;PLLAm;and control)that underwent simple surgical repair.PLLAMgs and PLLAms were injected into the bone tunnel and tendon-bone interface,while the control group received an equivalent volume of saline.After 4 and 8 weeks postoperatively the rats were euthanized and the supraspinatus tendon-humerus complex was dissected for gross examination.Histologic staining was performed on decalcified paraffin sections.The biomechanical testing involved subjecting the supraspinatus tendon-humerus complex to tensile tests.Failure load and displacement were recorded.Results In vitro cell viability and CCK-8 assays demonstrated that PLLAMgs had no cytotoxicity and promoted cell proliferation.At 4 weeks and 8 weeks postoperatively the PLLAMg group had reduced bone defects at the attachment site and better tendon-bone interface healing compared to the control group.HE staining revealed significantly reduced inflammatory cell infiltration in the PLLAMg group at 4 and 8 weeks postoperatively.Bone marrow cells aggregated within the bone marrow cavity and trabecular bone structure remained intact.Masson trichrome staining showed well-organized collagen fibers at 4 and 8 weeks postoperatively with an increased collagen transition zone at the tendon-bone interface,which indicated enhanced mineralized fibrocartilage.COL-1 immunohistochemistry demonstrated a significantly increased staining area and depth in the PLLAMg group at 4 and 8 weeks postoperatively compared to the control group.The PLLAMg group exhibited a significantly increased failure load compared to the control group at 4 and 8 weeks postoperatively.Stiffness was also increased at 8 weeks postoperatively with no statistical difference at 4 weeks postoperatively.Conclusion PLLAMgs had excellent biocompatibility and promoted tendon-bone interface healing in rats.The combined surgical approach using PLLAMgs holds great potential for improving scar healing and reducing re-tear risk after rotator cuffrepair.
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