Combined Verapamil-Polydopamine Nanoformulation Inhibits Adhesion Formation in Achilles Tendon Injury Using Rat Model

INTRODUCTION: Topical verapamil has been demonstrated to reduce the fibroproliferative scar. Therefore, it was hypothesized that topical verapamil could reduce adhesion formation after tendon repair. The current study aimed to examine the effects of verapamil-loaded polydopamine nanoparticles (VP-PDA NPs) on the adhesion formation of Achilles tendon laceration and repair in a rat model. METHODS: We randomly assigned 72 male Sprague-Dawley rats to the control, the PDA NPs, and the VP-PDA NPs groups (n = 24 per group). The quality of tendon healing was evaluated by the maximal tensile strength four and six weeks after surgery. The degree of tendon adhesion was scored on days 4, 15, 29, and 43 after surgery. The expressions of transforming growth factor-beta 1 (TGF-β1), vimentin, α-smooth muscle actin (α-SMA), and collagens type I and III were detected through Western blotting or immunohistochemistry at four weeks after surgery. RESULTS: In vitro release tests revealed that 61.3% of verapamil was released from VP-PDA NPs in four weeks. There was a significant increase in average failure to load in the VP-PDA NPs group (89.27 ± 5.09 N) compared with the PDA NPs group (65.52 ± 2.04 N) (p = 0.003) and the control group (74.52 ± 4.24 N) (p = 0.029). Adhesion scores were significantly reduced in the VP-PDA NPs group at six weeks (3.175 ± 0.08) and four weeks (3.35 ± 0.25) compared with the other groups. Moreover, VP-PDA NPs significantly reduced the expression of vimentin, α-SMA, TGF-β1, and collagens type I and III. CONCLUSION: These data suggest that VP-PDA NPs reduced adhesion formation and enhanced tendon healing during rat tendon injury. Since topical verapamil has been used in clinics without side effects, VP-PDA NPs would have direct translation implications. However, its anti-adhesive effects on intrasynovial tendon injury must be examined.