Significant progress has been made in the tissue engineering of intervertebral discs in recent years. Researchers here report on an initial study in larger animals, demonstrating that the implanted intervertebral discs exhibit the correct behavior and otherwise hold up well for at least a few months. Degeneration of intervertebral discs is universal to at least some degree in older people, with a sizable portion of the population suffering pain and loss of function, and the consequences of disc injury at any stage of life can also be lasting and severe. Thus approaches that can meaningfully address this issue are most welcome, whether they involve engineered replacement discs, or act through forms of regenerative therapy that can spur existing tissues to restore themselves.
The soft tissues in the spinal column, the intervertebral discs, are essential for the motions of daily life, such as turning your head to tying your shoes. At any given time, however, about half the adult population in the United States is suffering from back or neck pain, for which treatment and care place a significant economic burden on society - an estimated $195 billion a year. While spinal disc degeneration is often associated with that pain, the underlying causes of disc degeneration remain less understood. Today's approaches, which include spinal fusion surgery and mechanical replacement devices, provide symptomatic relief, but they do not restore native disc structure, function, and range of motion, and they often have limited long-term efficacy. Thus, there is a need for new therapies.
Tissue engineering holds great promise. It involves combining the patients' or animals' own stem cells with biomaterial scaffolds in the lab to generate a composite structure that is then implanted into the spine to act as a replacement disc. For the last 15 years, a team has been developing a tissue engineered replacement disc, moving from in vitro basic science endeavors to small animal models to larger animal models with an eye towards human trials. Past studies from the team successfully demonstrated the integration of their engineered discs, known as disc-like angle ply structures (DAPS), in rat tails for five weeks. This latest research extended that time period in the rat model - up to 20 weeks - but with revamped engineered discs, known as endplate-modified DAPS, or eDAPS, to mimic the structure of the native spinal segment. The addition of the endplates helped to retain the composition of the engineered structure and promote its integration into the native tissue.
MRI, along with histological, mechanical, and biochemical analyses, showed that the eDAPS restored native disc structure, biology, and mechanical function in the rat model. Building off that success, the researchers then implanted the eDAPS into the cervical spine of goats. They chose the goat because its cervical spinal disc dimensions are similar to humans' and goats have the benefit of semi-upright stature. Researchers demonstrated successful total disc replacement in the goat cervical spine. After four weeks, matrix distribution was either retained or improved within the large-scale eDAPS. MRI results also suggest that disc composition at eight weeks was maintained or improved, and that the mechanical properties either matched or exceeded those of the native goat cervical disc.