Design, synthesis, imaging, and biomechanics of a softness‐gradient hydrogel nucleus pulposus prosthesis in a canine lumbar spine model

Abstract

A hydrogel nucleus pulposus prosthesis (NPP) was designed to swell in situ, have intrinsic radiopacity, and restore intervertebral disc height and biomechanical functionality. These features were examined using an ex vivo canine lumbar model. Nine NPPs were implanted in five spines and their visibility was assessed on radiography, computed tomography (CT), and magnetic resonance imaging (MRI). The NPPs were visible on all imaging modalities and 8/9 NPPs stayed intact and in situ. Six other NPPs were tested biomechanically in six canine lumbar spines. Removal of the nucleus pulposus (nuclectomy) caused significant changes in biomechanical parameters. After implantation and swelling of the NPP, values were not significantly different from the native state for range of motion (ROM) of flexion-extension (FE) and lateral bending (LB), the neutral zone (NZ) of all motion directions, and the NZ stiffness (NZS) of FE. Biomechanical restoration by the NPP compared with the nuclectomized state was significant for the ROM of FE and axial rotation, the NZ of FE and LB, and the NZS of FE and LB. Disc height was significantly restored and 6/6 NPPs stayed intact and in situ. In conclusion, the NPPs swell in situ, have intrinsic radiopacity and restored disc height and aforementioned biomechanical properties.

Quantitative Analysis of the Nonlinear Displacement–Load Behavior of the Lumbar Spine

“…These results agree with the previous work on nucleus augmentation, although more significant differences were found when the nu cleus was pressurized [24,25]. These results indicate that RoM may not be a fully descriptive tool for studying the effects of motion preservation devices.…”

Safety of intradiscal injection and biocompatibility of polyester amide microspheres in a canine model predisposed to intervertebral disc degeneration

“…As the outer diameter of a 27G needle is 0.41 mm and of a 26G needle 0.47 mm, the ratios of needle diameter to disc height were calculated at 11% and 12%, respectively. The volume injected in this study consisted of 20% of the total NP volume (that is, 40 µL of 200 mm 3 ) . Postmortem, all IVDs were scored a Thompson grade II, in accordance with early IVD degeneration.…”

A review of gradient stiffness hydrogels used in tissue engineering and regenerative medicine

“…(c,d)]. This can restore intervertebral disc height and biomechanical functionality . Hydrogel grafts have also been applied to segmental bone loss repair .…”

“…(b) Schematic transverse overview of an IVD and the insertion of a nucleus pulposis prosthesis (NPP) and the annular closure technique: (b1) annular ring surrounding the nucleus pulposus, (b2) annulotomy to perform the nuclectomy, (b3) insertion of the xerogel prosthesis through the annular canal, (b4, b5) a rectangular piece of muscle fascia is sutured inside out with three single sutures on top, and (b6) swollen NPP in situ . (c, d) Radiographic evaluation of an NPP (white arrow) in the canine lumbar L2‐L3 IVD space (c) lateral view and (d) dorsoventral view …”