Introduction
Low back pain affects millions of people world-wide and is the number one cause for long-term disability. One major source for it is the degeneration of the intervertebral disc (IVD). IVDs connect adjacent vertebrae and enable the movement of the spine. Injections of cells have been suggested to repair degenerated IVDs to alleviate low back pain (Fig.1A). One cell source investigated are cells from the bone-marrow, the so-called mesenchymal stromal cells (MSC). Despite their huge potential, these cells often die shortly after injection due to the low nutrient and high-pressure environment of the IVD. In this project, we try to improve current cell therapies by 1) using cell-agglomerates instead of single-cell preparations (spheroids), 2) using a carrier (microscaffold) for additional mechanical support, and 3) preparing the cells for the harsh environment they later encounter in the IVD. In bovine disc disease models, we investigate whether these modifications improve the survivability and therapeutic efficacy of our novel therapy, which we call S-SPH (scaffolded spheroids).
Methods
Porous microscaffolds (⌀200µm) were fabricated using a two-photon polymerization 3D printer. S-SPH were generated by seeding human bone marrow MSCs onto microscaffolds (2k cells/scaffold, from 9 human donors) and cultured for 14 days under priming conditions (growth factor, low nutrient and oxygen), non-priming negative conditions (no growth factors, high nutrient and oxygen), or a basal medium. We then analysed S-SPH size, morphology, mechanical properties and IVD-like properties. The ability to survive after injection was investigated using a bovine whole-organ IVD degeneration model one day after injection and after three additional physiological loadings in a bioreactor. In addition, histology was performed to also get insights on structural parameters.
Results
S-SPH were formed successfully (Fig.1B). Primed S-SPH had a 37.2 % and 32.3 % larger area than negative and basal S-SPH respectively and formed a denser cell–matrix construct. The combination of microscaffold and priming conditions improved the mechanical properties. Primed cells also showed enhanced IVD-specific regeneration potential. Survival after injection was substantially improved in the primed S-SPH: while only 31 % of S-SPH remained viable in the negative group, 82 % were viable in the primed S-SPH group (Fig.1C). This effect remained stable after three additional days of culture and loading cycles with viabilities of 28 % and 89 %, respectively.
Discussion & Conclusion
S-SPH priming was consistently achieved and priming increased size and mechanical properties indicating increased matrix production and regenerative potential. Priming markedly improved intradiscal survival and interestingly, the observed cell death happened shortly after injection. This identifies the early phase post injection as the most decisive for intradiscal survival. This improved survival achieved by differentiation may give injected cells longer to be therapeutically active. Ongoing studies now assess anabolic and anti-inflammatory potential of this new cell therapy.
Acknowledgements
Funded by SNSF and FWF with grant 310030L_212196.
References
[1] ACS Appl. Mater. Interfaces 2026, 18, 10994−11007