3D Printing of Dense and Anisotropic Collagen/Hyaluronan Hydrogels for Biofabrication of Layered Annulus Fibrosus Tissue.

Intervertebral disc degeneration is responsible for approximately 40% of low back pain cases and begins in the Nucleus Pulposus before compromising the integrity of the Annulus Fibrosus (AF), ultimately leading to disc herniation. Despite its clinical relevance, the pathophysiology remains poorly understood, due to inadequate animal models. In this study, a 3D-printed layered construct was developed to replicate key structural features of the native AF using type I collagen and tyramine-substituted hyaluronic acid (THA). A homogeneous bioink was obtained without polyionic complexation and used to fabricate anisotropic hydrogel layers via 3D printing. Photo-cross-linking of THA enhanced the mechanical properties of the construct. Human fibroblasts were seeded between hydrogel layers and remained viable, proliferated, and aligned along the anisotropic architecture of the construct. These results demonstrate that combining dense collagen with THA through 3D printing provides a promising biopolymer-based strategy for reproducing some essential physical characteristics of the human Annulus Fibrosus.