A Refinement to the Liquidus-Tracking Method for Vitreous Preservation of Articular Cartilage

The recent liquidus-tracking method developed by Pegg et al. (2006a), as an alternative pathway to vitrification, achieved reasonable survival of post-thawing chondrocytes in situ. One of the main drawbacks of this method is the long duration of the cryoprotectant addition/removal process. This study was conducted to investigate the possibility of reducing the time by rationalizing the final dimethyl sulfoxide (Me₂SO) concentration loaded in tissue before being plunged into liquid nitrogen. Using the differential scanning calorimetric technique, the critical cooling and warming rates for solutions of Me₂SO in CPTes2 (a potassium-rich medium, modified slightly from Taylor's original formulation by Pegg et al.) were obtained. The critical cooling and warming rates for 47.5%(w/w) solution are < 2.5°C/min and < 10°C/min, respectively, which could be readily realized for 4 ml solution samples held in polypropylene cryovials as demonstrated by experiments. For articular cartilage, 47.5%(w/w) may be recommended as the final concentration of Me₂SO loaded in the tissue, which will lead to a time cut of about one-third compared with the original protocol of Pegg et al. (2006a).