Localized Delivery of a Small Molecule Hedgehog Agonist via Poly(ε-caprolactone) Scaffolds Enhances Tendon-to-Bone Integration.

Abstract

Tendon and ligament injuries often require surgery, with successful recovery, whether direct repair of a torn tendon to bone or reconstruction of ligaments, requiring effective tendon-to-bone integration. Unfortunately, re-tear rates can be high, demonstrating the need for improved treatment strategies. The Hedgehog (Hh) pathway is critical to fibrocartilage formation at tendon and ligament insertion sites during development, and recent studies indicate that it promotes tendon-to-bone integration post-surgery. However, systemic delivery of Hh signaling agonists can result in off-target effects. In this study, we developed a scaffold system for local delivery of a Hh signaling agonist (SAG) to promote tendon-to-bone integration. We fabricated aligned electrospun scaffolds loaded with four concentrations of SAG and quantified the fiber alignment and diameter, which were not different between the different concentrations. We then measured the in vitro release profile and found a dose-dependent release of SAG from the scaffolds, as measured by expression of the downstream Hh target gene, Gli1, in bone marrow stromal cell cultures that received conditioned media. Finally, we combined the scaffolds with tendon grafts and inserted them into bone tunnels created in the proximal tibiae of mice. SAG released from the scaffolds did not affect cell infiltration in the graft or scaffold, but increased expression of Gli1 by cells in the bone tunnels while also increasing mineralized fibrocartilage formation in a dose-dependent manner. These findings indicate that scaffold-mediated local delivery of SAG can effectively enhance tendon-to-bone integration, offering a promising strategy for treating tendon and ligament injuries.