Delivering cells via ECM mimetic hydrogel microspheres for promoting the reconstruction of rat lumbar nucleus pulposus

Nucleus pulposus (NP) discectomy is a clinical procedure for the treatment of late-stage intervertebral disc (IVD) degeneration; however, it is associated with the potential for serious complications. The reconstruction of the NP tissue presents challenges due to its avascular structure and prolonged compression within the IVD. In this study, we have developed a novel biomimetic hydrogel microsphere composed of gelatin methacryloyl (GelMA) and fucoidan, a polysaccharide derived from marine brown seaweed, to mimic the extracellular matrix (ECM) of the native NP. The GelMA and fucoidan (GelMA@FD) hydrogel microspheres demonstrate favorable cytocompatibility and significantly enhance the synthesis of matrix components in nucleus pulposus cells (NPCs), including aggrecan and type II collagen. Transcriptome sequencing analysis demonstrates a correlation between the augmentation of matrix synthesis and the enrichment of genes and pathways related to mitochondrial function. Subsequent molecular investigations provide evidence that NPCs cultured on GelMA@FD exhibit enhanced mitochondrial functions, including elevated adenosine triphosphate production and respiratory chain factor expression, alongside a reduction in mitochondrial reactive oxygen species. When implantated into rat lumbar IVDs that have undergone discectomy, the incorporation of NPCs within GelMA@FD hydrogel microspheres facilitates the regeneration of the NP and reinstates its structural and biomechanical properties. This is substantiated by the observed augmentation in IVD disc height and water content within the NP compartment. Collectively, these results demonstrate the potential of employing cell-laden GelMA@FD hydrogel microspheres as a promising strategy for NP regeneration in degenerated IVDs.