Clinical efflux of cryoprotective agents from vitrified human articular cartilage

In previous research, we successfully cryopreserved intact human articular cartilage on its bone base with high chondrocyte viability using a vitrification protocol that entailed sequential exposure to several cryopreserving agents (CPAs) at lowering temperatures resulting in a high final concentration of CPA. The CPA must be removed from the cartilage at warming due to its toxicity to cells in the cryopreserved tissue and the post-transplant adjacent tissues. The current experiment explores the relationship between removal solution volume and time required for complete removal of CPA from bone-cartilage samples. Osteochondral dowels of 10mm diameter from five patients undergoing total knee arthroplasty were vitrified using our protocol resulting in 6.5M CPA within the matrix. In the primary experiment, the warmed dowels were immersed in 10 mL of X-VIVO for 30 min and this was repeated 5 times (the last wash being 5 min only). Removal solution osmolality was recorded at various times and compared to controls of pure X-VIVO. Changes in removal solution osmolality over time were normalized to tissue volume. In a secondary experiment, the procedure was repeated using double the volume of removal solution (20 mL X-VIVO). Results showed a rapid change in the osmolality of the removal solution indicating a rapid efflux of CPA from cartilage. The efflux rate decreased with time and during subsequent immersions until equilibrium was reached during the 4th immersion indicating effectively complete removal of CPA. Doubling the amount of removal solution demonstrated the effective removal of CPAs by the third immersion. The results of this study yield a practical relationship between the amount of removal solution and the time and number of immersions required to remove CPA from the transplantable tissue.