Three-Dimensional-Printed Flexible Scaffolds Have Tunable Biomimetic Mechanical Properties for Intervertebral Disc Tissue Engineering.

The intervertebral disc (IVD) exhibits complex structure and biomechanical function, which supports the weight of the body and permits motion. Surgical treatments for IVD degeneration (e.g., lumbar fusion, disc replacement) often disrupt the mechanical environment of the spine which lead to adjacent segment disease. Alternatively, disc tissue engineering strategies, where cell-seeded hydrogels or fibrous biomaterials are cultured in vitro to promote matrix deposition, do not recapitulate the complex IVD mechanical properties. In this study, we use 3D printing of flexible polylactic acid (FPLA) to fabricate a viscoelastic scaffold with tunable biomimetic mechanics for whole spine motion segment applications. We optimized the mechanical properties of the scaffolds for equilibrium and dynamic moduli in compression and tension by varying fiber spacing or porosity, generating scaffolds with de novo mechanical properties within the physiological range of spine motion segments. The biodegradation analysis of the 3D printed scaffolds showed that FPLA exhibits lower degradation rate and thus has longer mechanical stability than standard PLA. FPLA scaffolds were biocompatible, supporting viability of nucleus pulposus (NP) cells in 2D and in FPLA+hydrogel composites. Composite scaffolds cultured with NP cells maintained baseline physiological mechanical properties and promoted matrix deposition up to 8 weeks in culture. Mesenchymal stromal cells (MSCs) cultured on FPLA adhered to the scaffold and exhibited fibrocartilaginous differentiation. These results demonstrate for the first time that 3D printed FPLA scaffolds have de novo viscoelastic mechanical properties that match the native IVD motion segment in both tension and compression and have the potential to be used as a mechanically stable and biocompatible biomaterial for engineered disc replacement.