Biomimetic method for combining the nucleus pulposus and annulus fibrosus for intervertebral disc tissue engineering

Tissue engineering strategies for the intervertebral disc (IVD) have traditionally focused either on the annulus fibrosus (AF) or the nucleus pulposus (NP) in isolation, or have simply compared AF cells and NP cells in identical culture conditions. Recently, others in the field have become aware of the advantage of combining the AF and NP into a more comprehensive strategy to address IVD tissue engineering, and have introduced biomimetic approaches to either AF or NP tissue engineering. Here, we introduced a new method for developing a biomimetic, cell-seeded IVD by electrospinning circumferentially-orientated polycaprolactone fibres (AF analogue), seeding them with cells (porcine chondrocytes) and then gelling a cell-agarose solution in the centre (NP analogue). Scanning electron microscopy images demonstrated a high degree of fibre alignment and, along with fluorescent actin staining, confirmed a preferred orientation of cells in the direction of the fibres. Viability assays and histology collectively demonstrated that cells were viable and well-distributed around the interface between the NP and AF regions. In addition, mechanical testing confirmed that the composite IVD scaffolds had higher moduli than the agarose hydrogels alone. As we enter the new decade and the fields of AF and NP tissue engineering begin to merge into a new interfacial and functional IVD tissue-engineering field, approaches such as the method presented here will serve as the foundation for continuously advancing technology that we ultimately endeavour to bring to the clinic for the treatment of patients severely afflicted by degenerative disc disease.