Optimization of engineered endplates to improve in vivo integration of atissue engineered intervertebral disc

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Low back pain, most commonly caused by degeneration of the intervertebral disc, places a significant social and economic burden on the general public, active duty military and veterans alike. Current clinical treatments for disc degeneration are limited in that they do not restore disc structure or function. To address this, our group has developed a whole, tissue engineered intervertebral disc composite (eDAPS) composed of engineered annulus fibrosus, nucleus pulposus and endplate regions. The endplate component, composed of an acellular porous polymer foam, is a critical aspect of the design that forms the interface between the engineered disc and native vertebral bone, but has yet to be optimized to promote the accelerated development of a vascularized, boney interface. The purpose of this study is to generate design modifications to the endplate region of the eDAPS that will accelerate integration following in vivo implantation. We will achieve this translational goal through two Aims: Aim 1: Modify the composition and geometry of the endplate region of the eDAPS to enhance osteogenesis and neovascularization. In this Aim, poly(ε-caprolactone) (PCL) endplates will be fabricated via a salt-leaching procedure with various design modifications to promote osteogenesis and neovascularization. PDMS molds will first be used to create macroscopic channel geometries within the endplates. Endplates will be further modified via hydroxyapatite deposition, and the incorporation of microspheres containing vascular endothelial growth factor (VEGF). The potential for mesenchymal stem cell osteogenesis on the hydroxyapatite modified scaffolds will be established in vitro, via the alkaline phosphatase assay, qPCR analysis of osteogenic genes, and histology. The bioactivity of the VEGF released from the microsphere containing scaffolds will also be assessed in vitro using the tube formation assay. Aim 2: Determine the effect of optimized endplate design on the in vivo integration and nutrition of a whole tissue engineered disc construct. In this Aim, optimized endplates will be utilized in eDAPS to be implanted in vivo in the rabbit lumbar spine for 10 or 20 weeks. New bone and vascular formation in the endplates following in vivo implantation will be assessed via calcein and alizarin labelling and microFil enhanced µCT, respectively. Small molecule trans-endplate diffusion into the engineered disc implants will be assessed via post-contrast enhanced MRI. Integration strength of the eDAPS with the native vertebral bodies will be assessed via tension, compression and torsional mechanical testing at physiologic loads. Animal functional rehabilitation following eDAPS implantation will be assessed via activity monitoring using the Motionwatch-8R, and ground reaction force mapping during ambulation using a Tekscan system. The proposed work will advance the state-of-the art in the field of intervertebral disc tissue-engineering, and provide insights that will speed translation of the eDAPS technology towards clinical use.