Integrating Theoretical and Experimental Methods for Multi-Scale Tissue Engineering of the Annulus Fibrosus of the Intervertebral Disc

There is a critical need for tissue engineered replacements for diseased and degenerated intervertebral discs in order to assuage low back pain while restoring function to the spine. Despite progress by many research groups, it remains a challenge to engineer a replacement tissue that can withstand the complex, demanding loading environment of the spine. Due to the hierarchical organization of the intervertebral disc, successful recapitulation of its functional behavior requires replication of anatomic form and physiologic function over a wide range of length scales. In this work, the technology of electrospinning has been employed for tissue engineering of the annulus fibrosus (AF) of the intervertebral disc using a multi-scale approach. The mechanics of electrospun nanofibrous assemblies was first characterized, focusing on how microscopic organization translates to macroscopic mechanical function. Next, engineered tissues were formed by culturing cells on nanofibrous scaffolds, generating aligned, dense collagenous tissues that replicate the single lamellar organization of the AF. This technology was then expanded to engineer angle-ply laminates that replicated both the anatomic form and mechanical function of the native AF. Finally, these results were further extended to engineer an angle-ply fiber-reinforced hydrogel composite that parallels the macroscopic structural organization of the intervertebral disc. Throughout, mechanical testing and mathematical modeling was used to understand material behavior, quantify functional growth, and guide comparison between engineered AF constructs and native tissue benchmarks. Emphasis has been placed on reconciling compositional and structural observations with their macroscopic mechanical implications, utilizing theoretical models to understand these relationships, and using engineered tissues to improve our understanding of structure-function relations within native fiber-reinforced soft tissues