Advances in Annulus Fibrosus Repair: Hybrid Scaffolds and Fabrication Techniques for Regeneration

Intervertebral disc (IVD) herniation is a leading cause of lower back pain, with symptoms ranging from tingling to disability. Discectomy, as the most common treatment, relieves pain and reduces inflammation, but the unrevealed defect in annulus fibrosus (AF) inevitably increases the risk of herniation as high as 21%. Repair and regeneration of AF are crucial to prevent herniation and recreate healthy IVD. Mechanical repair strategies, including suture, annulus closure device, and AF patch, often fall short in material-tissue integration and tissue regeneration. Recent developments in tissue engineering integrate biological science and material engineering, mainly through hybrid hydrogels and synthetic polymer scaffolds, showing promising effects on AF repair and regeneration. This review outlines various repair strategies and their limitations. It emphasizes the need for a holistic approach considering material selection, scaffold design, and incorporating cytokines or stem cells to improve AF repair outcomes. First, advancements in electrospinning, 3D printing, and porosity engineering will be discussed to enhance the integration of scaffolds with surrounding tissue to mimic a natural AF environment. Second, the benefits of adding cells or biofactors will be reviewed to strengthen cellular interactions, migration, and differentiation of stem cells. Finally, future research will be proposed to develop innovative, multifunctional scaffolds that complement personalized medicine while also considering the impact of mechanical stimulation and scaffold porosity on cell behavior and drug delivery for more efficient repair effects.