Simulation results for stress–strain in the cartilage matrix during a hypothetical CPA-loading protocol have shown that the middle and deep cartilage may experience a significant mechanical stress due to outward osmotic water flow, which would also influence the interstitial ionic environment, resulting in an hyperosmotic environment for chondrocytes [4].

Such modeling results can provide an explanation for some unexpected outcomes seen in other studies, where in transplantation follow-up studies, only chondrocytes in the superficial layer survived while the middle and deep layers were observed to be acellular [72] and [74]. Both the cellular system and the ultrastructure of the cartilage matrix are required to be efficiently preserved PD-166866 nmr for any cryopreserved-cartilage transplant to be successful Fluorouracil clinical trial in the long term. To achieve this, vitrification is the approach that has been successful. For vitrification of cartilage, where no vascular system exists to facilitate the CPA transport into deep

cartilage, the major hurdle is CPA permeation into thick cartilage, during which the chondrocytes are exposed to potential CPA cytotoxic effects. The eventual answer to the thickness problem requires a combination of the following approaches: (1) stepwise loading-cooling, whereby decreasing the cartilage-bath system temperature to reduce the cytotoxic effects is in concert with the increase in CPA concentration as the CPA is gradually introduced, and (2) use of multiple-CPA solutions instead of single-CPA solutions. It must be noted that an adverse effect of the liquidus-tracking method is that, since the CPA diffusion rate has an Arrhenius temperature dependence, lowering the temperature also Benzatropine slows down the rate of CPA transport within the tissue. For example, the Fickian diffusion coefficient for Me2SO decreases by 25% going from 0 °C to −10 °C [51]. This temperature dependence is even more significant for some other common CPAs

such as glycerol and propylene glycol, which decrease about 50% within the same temperature range [51]. This means that longer diffusion times are needed to reach the same desired concentration, which also means longer exposure of the chondrocytes to the CPA, hence higher toxicity. Additional information that is important to improve the success of vitrification protocols includes: (3) dose-dependence of CPA cytotoxicity, which is required to be clearly defined as a function of temperature, concentration and exposure time, and (4) modeling, which will facilitate the design of loading protocols and will greatly reduce the number of trial and error experiments. Recently, successful vitrification of intact human articular cartilage on its bone base has been achieved by Jomha et al. [52] by incorporation of all the aforementioned elements. Early work with single-solution high concentrations of Me2SO (Jomha et al.