A biomimetic artificial intervertebral disc system composed of a cubic three-dimensional fabric

Abstract Background context In the quest for clinically functional artificial intervertebral discs (AIDs), multidisciplinary technologies have been employed. Existing solid mobile AIDs essentially consist of the superposition of solid plates and core materials; however, it is thought that an ideal surgical AID technology has not yet been developed. To overcome the limitation of these existing AIDs, we developed a unique flexible AID disc system on the basis of our original biomimetic concept. The AID is composed of a cubic three-dimensional fabric (3DF) with a triaxial fiber alignment, which offers biomimetic long-term dynamic mechanical behavior along with durability. Purpose This article substantiates the potential clinical use of the 3DF disc system that quite differs from existing ones. Study design We designed the lumbar and cervical 3DF discs that improved the structural weaknesses caused by the collagenous fiber alignment of biological intervertebral disc. Bioresorbable hydroxyapatite particles were deposited on the surface layer of the 3DF disc to promote new bony ingrowth and to ensure secure binding at the interface of the contacting vertebral bodies. A stand-alone system was devised for surgical reliability in terms of both positioning and fixation, allowing tight press fitting with the vertebral bodies. Bioactive and bioresorbable pins were penetrated through the 3DF disc body and projected from the surface to allow ideal insertion and fixation to the disc space, preserving the precise position during dynamical movement. In vitro endurance of the 3DF disc was examined under long-term alternating stresses, and the in vivo animal tests were conducted in the intervertebral lumbar discs at L5–L6 excised from baboons and replaced with the lumbar 3DF disc. Methods The static mechanical endurance was assessed through a creep test. In vitro endurance of the 3DF disc under repetitive stresses including axial compressing, flexion-extension, torsional twisting, and lateral bending were applied to the 3DF disc for a long-term for up to 105 million stresses, which is roughly equivalent to exposure of natural biological movement for more than 50 years. In the animal test, eight baboons were euthanized 6 months postoperatively. To their extracted spines, six pure moments (flexion and extension, left and right lateral bending, and left and right torsion) were applied vertically to the superior end of the specimen and then values of range of motions (ROMs) were