Bottom-up engineering of the nucleus pulposus using a photocrosslinkable decellularized matrix hydrogel attenuates inflammaging and enhances microtissue-mediated regeneration

Degenerative disc disease (DDD), characterized by the pathological deterioration of nucleus pulposus (NP) tissue, affects millions globally. Tissue engineering strategies offer potential to create tissue-engineered NP (TE-NP) analogs to address DDD. However, traditional "top-down' approaches face challenges in achieving uniform cell distribution and replicating the intradiscal extracellular matrix (ECM) environment. In contrast, a "bottom-up' strategy utilizing microscale seed units represents a promising alternative. This study introduces an innovative "bottom-up' approach for constructing TE-NP, leveraging bioreactor-cultivated NP microtissues (NP-MTs) as seed units and a novel methacrylate-modified decellularized nucleus pulposus matrix (DNPM-MA) hydrogel as a supporting biomaterial. NP-MTs cultivated under low-magnitude hydrostatic pressure exhibit nascent ECM surroundings adapting well to the intradiscal microenvironment. The DNPM-MA hydrogel, with its compositional and mechanical attributes, supports the growth, migration, proliferation, and ECM synthesis of NP-MTs, making it an ideal biomaterial for long-term cultivation. The combination of NP-MTs and the DNPM-MA hydrogel yielded superior tissue regeneration outcomes both in vitro and in vivo. Transcriptome and molecular assessments revealed a correlation between the biological properties of the DNPM-MA hydrogel and the attenuation of inflammaging within encapsulated NP-MTs. Overall, this innovative "bottom-up' constructed TE-NP exhibits superior regenerative potential and is a promising tissue engineering strategy for treating DDD.