Injectable, Moderately Adhesive, and Thermoresponsive Hydrogel for Preventing Disc Reherniation by Obstructing the Annulus Fibrosus.

Up to 25% of patients who have undergone disc microdiscectomy experience lumbar herniation recurrence due to the limited self-healing capability of the annulus fibrosus, with the potential for the continuous herniation of nucleolus pulposus under strain. Despite their potential, injectable hydrogels have primarily been suggested for nucleus pulposus replacement or regeneration. Herein, we introduce the concept of using an injectable and moderately adhesive hydrogel (TX) to physically obstruct the annulus fibrosus following disc microdiscectomy to prevent disc reherniation. The physico-mechanical characteristics of TX hydrogel were investigated within the context of lumbar disc application, and its injection volume for the intended application under a clinically relevant load, i.e., 0.5-1 kN, was optimized through an ex vivo bovine coccygeal spine model. Finally, the usability, efficacy, and safety of the hydrogel device were evaluated through an in vivo ovine study for disc microdiscectomy (five lumbar levels between lumbar (L) 1-2, L2-3, L3-4, L4-5, L5-6 in six animals). Overall, the sites treated with TX exhibited a reduced percentage of defect area and a greater degree of newly formed, organized tissue compared with untreated sites, suggesting the favorable application of TX to obstruct annulus fibrosus. The supporting role of the hydrogel is achieved as it withstands the mechanical forces and stabilizes the site to minimize the protrusion of nucleolus pulposus while providing an environment for sealing annulus fibrosus defects.