Tissue Engineered Total Disc Replacement in a Large Animal Model

Low back pain, which is most commonly caused by intervertebral disc degeneration, is the most common source of chronic pain in veterans. Current clinical treatments for disc degeneration, including spinal fusion, are limited in that they do not restore healthy disc structure or function. To overcome this limitation, our group has developed a whole, tissue engineered endplate-modified disc-like angle ply structure (eDAPS) composed of engineered annulus fibrosus, nucleus pulposus and endplate regions. To date, we have completed the long-term evaluation of the eDAPS in a small animal model, in addition to short-term evaluation in a large animal, goat cervical disc replacement model. The overarching goal of the current proposal is to generate in vitro and in vivo data to motivate the first in man trials of this technology. We will achieve this translational goal via the following specific aims: Specific Aim 1: Evaluate the long-term function of a tissue-engineered intervertebral disc replacement that is subjected to physiologic loading in our large animal model. In this Aim, we will first establish the duration of immobilization necessary for optimal long-term performance of the tissue engineered disc in vivo. We will then develop and test a resorbable provisional fixation system to be utilized in conjunction with the engineered disc implant, which will eliminate the need for a second surgery and increase the clinical translatability of our technology. Specific Aim 2: Determine the ability of a tissue-engineered disc replacement to restore healthy motion segment structure and function when implanted in a degenerative environment. In this Aim, we will induce degeneration of the goat cervical intervertebral disc using our established model of chondroitinase ABC injection. After degeneration has progressed for 12 weeks, a second surgery will be performed to implant the eDAPS with the resorbable fixation system developed in Aim 1. Animals will be euthanized after 1 year of eDAPS implantation. During this time, implant status will be tracked with serial radiographs and in vivo MRI. A custom EMG and kinematic tracking system will be implemented to assess cervical spine muscle activation and range of motion as objective measures of pain and function. At the 1 year study endpoint, eDAPS implants will be compared to untreated, degenerative controls by analyzing the structural and function properties across the whole motion segment (disc/implant, facet joints, neural structures) using a multiscale and multimodal approach. Aim 3: Fabricate anatomical tissue-engineered discs from human cell sources. In Aim 3, we will evaluate the use of different human mesenchymal cell sources for the seeding of the eDAPS constructs. Human bone marrow derived stem cells will be utilized, in addition to AF-like and NP-like cells derived from human induced pluripotent stem cells and compared to native disc tissue cells. The cell source yielding constructs with structure-function properties nearest to the native human disc will be utilized to generate eDAPS sized for the human lumbar and cervical spine. Overall, the proposed work will significantly drive the translation of the eDAPS implant towards clinical use and advance the state of the art in spine therapeutics.