Intervertebral disc (IVD) degeneration is associated with chronic low back pain, a leading cause of disability worldwide. Current back pain treatment options are unable to fully address symptoms and have limited long-term efficacy. In addition, IVD regeneration strategies have shown promise in preclinical studies; however, despite such potential, no such therapies have been broadly adopted clinically. Understanding the mechanisms of IVD degeneration to stop or reverse this process is a challenge at the intersection of biomaterials, biomechanics, and cell biology which would benefit from having a reproducible and adaptable 3D model able to recapitulate the relevant complexity of the IVD. The IVD models available at present are standard in vitro cultures in 2D and 3D, ex vivo systems employing human or animal IVDs and bioreactors (Fig 1). Unfortunately, none of the current models can truly represent the IVD structure and function or resemble the microenvironment of the degenerated IVD.
We have pioneered and developed a unique technique (simultaneous sonication and alkali digestion) to selectively eliminate extracellular matrix and cells to reveal the collagen and elastic fibers of the IVD (Fig 1), which has identified its novel structural features not reported previously [1-8]. These new insights have significantly enhanced knowledge about the IVD structure-function relationship over multiple scales. Building on these, we successfully employed additive manufacturing techniques to develop the first reproducible and adaptable 3D IVD-on-a-chip organ model that recapitulates the relevant IVD function and its structural complexity (Fig 1). Our organ model allows real-time monitoring in a controlled microenvironment, precise tuning of material, mechanical and biological properties, and IVD research that targets precise questions. We have so far successfully employed our organ model to evaluate cell viability and to understand the impact of IVD microstructure on cell behavior.