No technique has been consistently successful in the repair of large focal defects in cartilage, particularly in older patients. Tissue-engineered cartilage grown on synthetic scaffolds with appropriate mechanical properties will provide an implant, which could be used to treat this problem. A means of monitoring loads and pressures acting on cartilage, at the defect site, will provide information needed to understand integration and survival of engineered tissues. It will also provide a means of evaluating rehabilitation protocols. A "sensate" scaffold with calibrated strain sensors attached to its surface, combined with a subminiature radio transmitter, was developed and utilized to measure loads and pressures during gait. In an animal study utilizing six dogs, peak loads of 120N and peak pressures of 11 MPa were measured during relaxed gait. Ingrowth into the scaffold characterized after 6 months in vivo indicated that it was well anchored and bone formation was continuing. Cartilage tissue formation was noted at the edges of the defect at the joint-scaffold interfaces. This suggested that native cartilage integration in future formulations of this scaffold configured with engineered cartilage will be a possibility.

Treatment of cartilage defects is essential to the prevention of osteoarthritis. Scaffold-based cartilage tissue engineering shows promise as a viable technique to treat focal defects. Added functionality can be achieved by incorporating strain gauges into scaffolds, thereby providing a real-time diagnostic measurement of joint loading. Strain-gauged scaffolds were placed into the medial femoral condyles of 14 adult canine knees and benchtop tested. Loads between 75 and 130 N were applied to the stifle joints at 30°, 50°, and 70° of flexion. Strain-gauged scaffolds were able to reliably assess joint loading at all applied flexion angles and loads. Pressure sensitive films were used to determine joint surface pressures during loading and to assess the effect of scaffold placement on joint pressures. A comparison of peak pressures in control knees and joints with implanted scaffolds, as well as a comparison of pressures before and after scaffold placement, showed that strain-gauged scaffold implantation did not significantly alter joint pressures. Future studies could possibly use straingauged scaffolds to clinically establish normal joint loads and to determine loads that are damaging to both healthy and tissue-engineered cartilage. Strain-gauged scaffolds may significantly aid the development of a functional engineered cartilage tissue substitute as well as provide insight into the native environment of cartilage.

To develop implantable, engineered, cartilage constructs supported by a scaffold, techniques to encourage rapid tissue growth into, and on the scaffold are essential. Preliminary studies indicated that human endothelial cells proliferated at different rates on different calcium phosphate ceramic (CPC) particles. Judicious selection of particles may encourage specific cell proliferation, leading to an ordered growth of tissues for angiogenesis, osteogenesis, and chondrogenesis. The goal of this study was to identify CPC surfaces that encourage bone and vascular cell growth, and other surfaces that support chondrocyte growth while inhibiting proliferation of vascular cells. Differences in bone and vascular cell proliferation were observed when using epoxy without embedded CPCs to encourage bone cells, and when three CPCs were tested, which encouraged vascular cell proliferation. One of these (CPC 7) also substantially depressed cartilage cell proliferation. Only one small-diameter crystalline CPC (CPC 2) supported rapid chondrocyte proliferation, and maintained the cartilage cell phenotype.