3D-printed auxetic-structured intervertebral disc implant for potential treatment of lumbar herniated disc.

In this study, a novel artificial intervertebral disc implant with modified "Bucklicrystal" structure was designed and 3D printed using thermoplastic polyurethane. The new implant has a unique auxetic structure with building blocks joined "face-to-face". The accompanied negative Poisson's ratio enables its excellent energy absorption and stability under compression. The deformation and load distribution behavior of the implant under various loading conditions (bending, torsion, extension and flexion) has been thoroughly evaluated through finite element method. Results show that, compared to natural intervertebral disc and conventional 3D implant, our new implant exhibits more effective stress transfer and attenuation under practical loading conditions. The implant's ability to contract laterally under compression can be potentially used to alleviate the symptoms of lumbar disc herniation. Finally, the biocompatibility of the implant was assessed and its ability to restore the physiological function of the disc segment was validated using an animal model.