An injectable hydrogel for nucleus pulposus regeneration

Abstract

Intervertebral discs within the human spine act as shock absorbers between each of the vertebrae in the spinal column. As people age, disc cells are constantly subjugated to degenerating stress by various mechanical and environmental factors leading to musculoskeletal impairment and lower back pain. Nucleus pulposus cells (NP cells), jelly-like avascular tissue within the middle of the intervertebral disc, are crucial component of the disc Disc degeneration starts here in these cells. Research into regenerating the NP cells in degenerating intervertebral discs may provide a breakthrough in treating spine disorders. This project is designed to fabricate and characterize hydrogel composites to investigate the growth and viability of human nucleus pulposus (HNP) cells and the extracellular matrix gene expression by the HNP cells in the hydrogel. Specifically, we fabricated type II collagen and hyaluronic acid hydrogels that were cross-linked with the ethyl-3(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide crosslinker (NHS). The hydrogels were cross-linked using varying concentrations of the crosslinkers. HNP were seeded into crosslinked and non-crosslinked hydrogels. Results from cell viability assays such as live/dead assay and AlamarBlue assay showed cell growth and proliferation in both non-crosslinked and crosslinked hydrogels. Quantitative PCR assay demonstrated the extracellular matrix gene expression by the cells cultured in these gels. The results of gene expression studies indicated the formation of extracellular matrix by the cells and adaption of cells to the environment after long-term cell culture in these hydrogels. This study suggests that the type II collagen-HA hydrogel and crosslinked hydrogel with EDC at low concentration are a permissive matrix for the growth of HNP cells and can potentially be applied to NP repair.