Nose to Spine: Spheroids Generated by Human Nasal Chondrocytes for Scaffold-Free Nucleus Pulposus Augmentation

Cell-based strategies for nucleus pulposus (NP) regeneration that adequately support the engraftment and functionality of therapeutic cells are still lacking. This study explores a novel scaffold-free approach for NP repair, which is based on spheroids derived from human nasal chondrocytes (NC), a resilient cell type with robust cartilage-regenerative capacity. We generated NC spheroids (NCS) in two types of medium (growth or chondrogenic) and analyzed their applicability for NP repair by investigating injectability, biomechanical and biochemical attributes, and integration potential in conditions simulating degenerative disc disease (DDD). NCS engineered in both media were compatible with a spinal needle in terms of size (lower than 600mm), shape (roundness greater than 0.8), and injectability (no changes in catabolic gene expression after passing through the needle). While growth medium ensured stable elastic modulus (E) at 5 kPa, chondrogenic medium time-dependently increased E of NCS, in correlation with gene/protein expression of collagen. Notably, DDD-mimicking conditions did not impair NCS viability nor NCS fusion with NP spheroids mimicking degenerated NP in vitro. After being injected via a spinal needle in ex vivo-cultured bovine intervertebral discs (IVD), NCS were maintained in the NP region. In conclusion, NC cultured as spheroids are compatible with strategies for minimally invasive NP repair. Future studies will need to address the capacity of NCS to integrate within degenerated NP under loading conditions.