Macromolecular diffusion in intact, degraded and crosslinking-augmented intervertebral discs

Abstract

Injection of macromolecular anabolic enzymes is a promising treatment for disc degeneration. However, macromolecular diffusion within the degraded or crosslinking-augmented discs remains unclear. In this study, healthy porcine anular fibrosus (AF) and nucleus pulposus (NP) were prepared. After a 24 hr trypsin-induced matrix degradation and a following 24 hr genipin-induced crosslinking augmentation, the diffusion of 0.37 kDa fluorescein sodium, 4.4 kDa dextran and 40 kDa dextran in the AF and NP were evaluated. Regardless of molecular weight, macromolecular diffusion was highest along the circumferential AF followed by the radial AF and NP. Matrix degradation and the crosslinking-augmentation decreased macromolecular diffusion. Scanning electric microscopic (SEM) images revealed that the intact circumferential AF contained oval-shaped pores, while the intact radial AF included long and narrow cavities. These porous diffusion paths collapsed after matrix degradation. The following crosslinking augmentation recovered matrix hydration and the area encircled by pore contour. Nevertheless, the diffusion paths were still occluded by detached collagen fibrils. In conclusion, pore shapes regulate macromolecular diffusion in discs. The decrease of macromolecular diffusion after matrix degradation is due to pore deformation. The following crosslinking augmentation makes the macromolecules more easily trapped within the diffusion paths.