Hyaluronan-Coated Aligned Collagen Hydrogel Promotes Stabilization of the Intervertebral Disc by Inducing Fibrosis in Annulus Fibrosus

Intervertebral disc degeneration is a primary cause of chronic low back pain (LBP), which affects people worldwide and leads to disability. Intervertebral discs (IVDs) are a mechanically dynamic tissue where the annulus fibrosus (AF) absorbs axial load, supports spinal motions, and resists disc deformation and degeneration. Axial stress applied to the disc translates into interlamellar radial stress, potentially leading to AF tears and nucleus pulposus (NP) extrusion, especially in the lumbar region. We developed a hyaluronan-coated type-I collagen (Col-I HA) hydrogel scaffold to promote AF tissue repair and mechanically stabilize IVD. These scaffolds exhibit high tensile strength (∼5 MPa), comparable to that of the annulus fibrosus, which is attributed to the alignment of collagen fibrils with preserved secondary structures. The developed scaffolds demonstrated high cell viability and alignment of isolated primary AF cells and rat bone marrow stem cells (RBMSCs) along the collagen fibrils. Notably, primary AF cells and RBMSCs cultured on the Col-I HA hydrogel scaffold showed high expression of native ECM markers, such as collagen-I and aggrecan, reflecting the regenerative potential of the developed scaffold. Elevated levels of CD146 and Acta2 indicated a shift toward a contractile phenotype in both cell types. Ex vivo and in vivo studies using annulotomy-induced rat coccygeal disc model following Col-I HA implantation demonstrated mechanical restoration of IVD when investigated for uniaxial compressive strength. Histological and immunohistochemical analyses revealed significant collagen and glycosaminoglycan (GAG) deposition in Col-I HA-treated discs compared with the untreated AF-defective disc. Interestingly, fibrotic changes were observed in the Col-I HA-treated groups, as confirmed by the upregulation of profibrotic markers, including fibronectin, transforming growth factor, and α-smooth muscle actin, in the in vivo model. Thus, the Col-I HA hydrogel scaffold exhibited fibrotic changes in the AF and contributed to IVD stabilization.