Hydrogel adhesives with a hydrodynamically induced liquid–solid transition for annular fissure sealing and inflammation modulation following microdiscectomy

Background Intervertebral disc (IVD) herniation is a major cause of low back pain and disability, with microdiscectomy being the standard surgical treatment. However, microdiscectomy fails to address annulus fibrosus (AF) defects, increasing the risk of recurrent herniation. Current therapeutic strategies for this condition remain limited in efficacy. The lack of repair following injury and unresolved inflammation can further damage the IVD function, ultimately leading to irreversible IVD degeneration. Therefore, the development of an AF adhesive capable of both mechanically stabilizing annular fissures and enabling localized anti-inflammatory drug delivery emerges as a promising strategy to address this clinical challenge. Methods The developed AF adhesive system, designated as STIG, is formulated from silk fibroin, tannic acid, ibuprofen, and guanidine hydrochloride (GuCl). A comprehensive evaluation is conducted on STIG, encompassing its microstructure, composition, injectability, tissue adhesion, rheological properties, and biocompatibility. To assess anti-inflammatory efficacy, an in vitro inflammatory microenvironment is established via lipopolysaccharide (LPS)-stimulated AF cells. For in vivo validation, a rat model of IVD degeneration is surgically induced through puncturing the AF to simulate nucleus pulposus (NP) herniation. This experimental framework enables evaluation of STIG's ability to prevent NP protrusion, modulate inflammatory responses, and delay IVD degeneration. Results In the STIG system, GuCl serves the role of a hydrogen bond disruptor, facilitating its release into bodily fluids, which in turn allows for the reformation of hydrogen bonds. This property endows STIG with the ability to transition from an injectable, low-stiffness state to a high-stiffness adhesive gel upon contact with water. The inclusion of ibuprofen in the adhesive effectively curbs the production of inflammatory mediators and the breakdown of extracellular matrix constituents. In a rat tail model, STIG effectively preserves the NP water content, maintains the disc height index, and safeguards the structural integrity of the IVD post-surgery. Conclusion These findings highlight STIG's potential as a promising therapeutic solution for sealing AF fissures and preventing IVD degeneration. The translational potential of this article STIG shows significant clinical potential in spinal surgery. It offers a novel approach to reduce the recurrence rate post-microdiscectomy and improving long-term patient outcomes.