Project Summary This proposal seeks to engineer an allogeneic zygapophyseal (facet joint) articular resurfacing (AZAR) system by following a rational experimental approach in three specific aims: the AZAR system will consist of a cartilage component (chondro-portion) robustly integrated with a bone-like scaffold component (osteo-portion); the replacement will be secured in situ in the recipient bone bed of the facet joint. In Aim 1, three levels of human and minipig facet joints from both sexes will be fully characterized to define design criteria for the AZAR system. The AZAR system will be designed and fabricated through three phases in Aim 2. First, cytochalasin-D and hyaluronidase will be applied to minipig passaged chondrocytes to engineer the chondro-portion of the implant with compressive properties mimetic to native tissue values. In the same phase, methods for using lysyl oxidase like protein-2 (LOXL2) and tensile stimulation (CoTenS) will be identified to improve the tensile properties of the chondro-portion to native tissue levels. In Aim 2, Phase II, the pore size of the osteo-portion (i.e., the bone portion) directly beneath the engineered cartilage will be fine-tuned for optimum cartilage integration. In Aim 3, minimally invasive surgical methods will be developed for implanting a total facet replacement in the minipig, analogous to the ones currently employed in human patients. Finally, the AZAR system will be implanted into both male and female minipigs to examine its efficacy prior to moving to bipedal models in future studies. Successful completion of this proposal will allow, for the first time, resurfacing of an entire articular surface in a diarthrodial joint using a tissue engineered construct. It will also shed light on as-of-yet unexplored structure- function relationships in the poorly studied facet joint. Last, but not least, it will contribute toward new therapies for facet-related ailments.