PROJECT SUMMARY Minor injuries to articular cartilage can initiate a catabolic cascade, causing small defects to progress into larger, more symptomatic defects. Pain, lesion progression, and accelerated joint deterioration may be avoided with strategies that repair small defects with hyaline-like cartilage. The repair of chondral defects using arthroscopic techniques, performed in a minimally invasive manner, has advantages over traditional open approaches due to enhanced access and visualization in the joint, lower risk of infection, and quicker recovery. For the hip and ankle, arthroscopic cartilage repair is particularly attractive because these joints are difficult to access with open approaches. To address the need for an effective arthroscopic cartilage repair treatment, Cartilage Inc. has developed Chondrofluid™, an injectable, biologically active, off-the-shelf cartilage repair product that can be easily applied arthroscopically to any chondral defect on the femoral and tibial surfaces. Chondrofluid™ is derived from active, juvenile, allogeneic, costal (rib) chondrocytes using Cartilage Inc.’s patent-pending platform technologies. At 4ºC, Chondrofluid’s™ liquid form allows it to flow into every crevice of cartilage defects. Arthroscopic delivery into the body raises Chondrofluid™ past the critical micellization temperature of its components, causing the self-assembly of cubic lyotropic liquid crystal structures that turn Chondrofluid™ into a gel, allowing it to attach and lock itself into defects. Ex vivo application of Chondrofluid™ to partial-thickness defects showed excellent repair tissue fill that integrated into the native cartilage. In vivo, preliminary data show that Chondrofluid™ fills gouge defects with neocartilage and integrates tissue engineered implants to native cartilage when applied using open arthrotomy onto defects on the femoral trochlea. The Chondrofluid™ formulation has been modified for arthroscopic approaches, and, toward the regulatory approval of Chondrofluid™ for arthroscopic use, in vivo validation is needed. Using a preclinical minipig model, this proposal investigates the arthroscopic treatment of two types of clinically relevant chondral lesions in the knee using Chondrofluid-MP (minipig cellular product analogous to Chondrofluid). First, a partial thickness, linear, gouge defect of the medial femoral condyle will be arthroscopically created and treated with injectable Chondrofluid- MP, or microfracture (positive control), or left empty (negative control) arthroscopically. Second, full-thickness, small (8x4 mm, which is equivalent to a critical size 1 cm2 defect in the human knee) tibial defects will be arthroscopically created on the medial tibial plateau and treated with Chondrofluid-MP, or microfracture (positive control), or left empty (negative control) arthroscopically.