Curcumin-loaded chitosan/sodium β-glycerophosphate thermosensitive hydrogel promotes tendon healing in rats

Abstract

BACKGROUND: Tendon injury repair is often compromised by inflammatory cascades and disordered collagen metabolism, leading to scar formation and mechanical deterioration. Curcumin exhibits anti-inflammatory, antioxidant, and pro-repair potential, but its rapid metabolism and low bioavailability limit clinical application. OBJECTIVE: To construct a thermosensitive injectable curcumin-loaded chitosan/sodium β-glycerophosphate hydrogel and evaluate its efficacy in tendon repair. METHODS: (1) Rat tendon stem cells were cultured with different concentrations of curcumin for 24 hours. Cell viability was assessed using the CCK-8 assay, and the 20 µmol/L concentration was selected for subsequent experiments. Rat tendon stem cells were cultured with 0 (control) and 20 µmol/L curcumin, and cell migration was assessed using a wound healing assay. Rat tendon stem cells were cultured in three groups: a control group received no treatment; a model group received tert-butyl hydroperoxide to induce oxidative stress; a curcumin group received tert-butyl hydroperoxide plus 20 µmol/L curcumin. qRT-PCR and western blot were used to detect the expression of matrix metalloproteinase 3, matrix metalloproteinase 13, collagen type I alpha 1 chain, collagen type III alpha 1 chain, Bcl-2, and Bax. (2) Chitosan/sodium β-glycerophosphate thermosensitive injectable hydrogels with or without curcumin (final concentration 20 µmol/L) were prepared. The microstructure and drug release were characterized. Rat tendon stem cells were co-cultured with the hydrogels, and cell compatibility was evaluated by live/dead staining and cytoskeletal staining. (3) Sixty SD rats were randomly divided into five groups: sham surgery (n=12), model (n=12), hydrogel only (n=12), curcumin solution (n=12), and curcumin-loaded hydrogel (n=12). The Achilles tendon rupture model was established, and treatments were injected at the tendon stump, with a second injection after 4 days. At 8 weeks post-surgery, peritendinous adhesion, hematoxylin-eosin staining, Masson staining, immunohistochemistry for cyclooxygenase-2 and collagen type I alpha 1 chain, and biomechanical analysis were performed. RESULTS AND CONCLUSION: (1) Curcumin promoted the migration of rat tendon stem cells. Compared with the model group, the curcumin group showed decreased mRNA and protein expression of matrix metalloproteinase 3, matrix metalloproteinase 13, collagen type III alpha 1 chain, and Bax protein (P < 0.05), and increased expression of collagen type I alpha 1 chain and Bcl-2 protein (P < 0.05). (2) Scanning electron microscopy revealed a typical three-dimensional porous network structure of the hydrogel with uniform pore size and interconnected pores. The curcumin-loaded hydrogel exhibited good sustained release. Live/dead and cytoskeletal staining showed good cytocompatibility. (3) The curcumin-loaded hydrogel group had lower peritendinous adhesion than the model, hydrogel only, and curcumin solution groups. Hematoxylin-eosin and Masson staining showed reduced inflammatory cell infiltration and orderly collagen deposition in the curcumin-loaded hydrogel group. Immunohistochemistry showed lower cyclooxygenase-2 expression and higher collagen type I alpha 1 chain expression in the curcumin-loaded hydrogel group compared with the model and hydrogel only groups (P < 0.05). The maximum tensile stress and elastic modulus were higher in the curcumin-loaded hydrogel group than in the model, hydrogel only, and curcumin solution groups (P < 0.05). In conclusion, the curcumin-loaded chitosan/sodium β-glycerophosphate thermosensitive hydrogel synergistically exerts anti-inflammatory effects and promotes orderly collagen deposition, significantly improving the quality of tendon repair.

1. Introduction

Musculoskeletal trauma frequently involves tendon injuries, which pose significant clinical challenges due to their high incidence and complex repair processes. Traditional surgical repair can restore anatomical continuity, but postoperative complications such as local inflammatory storms, oxidative damage, and aberrant extracellular matrix remodeling often lead to reduced mechanical properties and peritendinous adhesions, severely impairing functional recovery. This structure-function mismatch highlights the limitations of conventional treatments and underscores the need for advanced regenerative strategies.

Following tendon injury, a complex repair cascade is initiated, involving the release of inflammatory mediators and infiltration of inflammatory cells to clear damaged tissue. Concurrently, tendon stem cells, a resident undifferentiated cell population, are activated and migrate to the injury site. These cells proliferate and differentiate into tenocytes and fibroblasts, which synthesize extracellular matrix components including collagen and elastin, gradually restoring tissue integrity and mechanical strength. However, clinical observations indicate that the repair process often results in scar formation and suboptimal functional outcomes, necessitating innovative approaches to modulate the healing environment.