Minimal invasive treatments for troubling lower back discs
The vertebrae in the spinal column are separated from each other by intervertebral discs (IVDs) that allow a smooth bending movement. The discs consist of an elastic gelatinous core, the nucleus pulposus (NP), surrounded by annulus fibrosus, a tough outer layer of fibrocartilage. As NP loses water and intradiscal pressure with age, more mechanical stress affects the annulus, causing cracking, inflammation and nerve root impingement. As DD disease (DDD) does not self-repair, treatments range from anti-inflammatory medication and physiotherapy to spinal fusion surgery. The EU-funded project NPMIMETIC (Biomimetic nano-fiber-based nucleus pulposus regeneration for the treatment of degenerative disc disease) has developed biomimetic nano-polymer–based gels for minimally invasive disc regeneration. Initial assessment of healthy and diseased IVDs showed that the crucial factor determining the mechanical behaviour of disc was the intradiscal pressure and not just the liquid flow properties in the NP. For mildly degenerated IVDs, the researchers developed and validated innovative fibrinogen-hyaluronic acid (FBG-HA) nanobiopolymer conjugates functionalised with chondrogenic growth factors (GFs). Another gel showed stronger biological activity. Tests of both in vitro and in vivo found them safe and feasible. Further studies are recommended to explain in vivo and in vitro differences in results and to investigate GF dosage and the controlled release system. A ‘ravioli’, a load resistant NP, was developed to tackle more severe cases of disc degeneration. The NP-mimicking implant consists of a hydration-triggered swelling film, wrapped in a polymer envelope mesh. The implant possesses mechanical strength, wettability and lack of toxicity. Furthermore, there was cell adhesion and proliferation on the envelope material, proof of concept for drug containment potential and its controlled release and resistance to forces well above physiological and peak loading without rupturing. In an in vivo pilot study, the raviolis showed insufficient swelling pressure and implant retention and also invaded the drill holes in the goat vertebral bodies. Further studies are still required but NPMIMETIC deliverables promise to bridge the gap between more conservative treatment and radical interbody spinal fusion. The new therapies are offering a potential minimally invasive solution to DDD. Once validated through clinical trials, an injectable scaffold allowing tissue regeneration will provide a much-needed minimally invasive treatment option for low back pain.
Keywords
Minimal invasive treatment, DDD, gel, NP implant, ravioli