| Articular cartilage (AC) injury is a leading cause of human activity disability. Osteochondral allografting is an effective therapeutic strategy to treat diseased and traumatic areas of joint surfaces, but its application is limited by the inability to store AC for long periods of time. The recent developed liquidus-tracking method (LTM) achieved successful vitrification of AC. The LTM is a promising preservation method, but further improvement of the survival rate of post-warming chondrocytes is hampered by the lack of knowledge about the inherent mechanisms of the method. Based on a comprehensive review of the history and status of the studies on cryopreservation of AC, this dissertation, taking ovine AC as research object, aimed at reducing the step number and duration of cryoprotectant (CPA) treatment through investigation of the heat and mass transfer problems related to the LTM. Theoretical and experimental studies were carried out as follows:1) The optimal concentration of dimethyl sulfoxide (Me2SO) that should be achieved in AC sample was determined experimentally. Firstly, the critical cooling and warming rates for solutions of Me2SO in CPTes2[43%(w/w) to50%(w/w)] were obtained using the differential scanning calorimetric (DSC) technique, and then, the achievable cooling and warming rates for4mL solutions of Me2SO in CPTes2were measured. Based on the two experimental results above,47.5%(w/w) was determined as the final concentration loaded in AC sample.2) The permeation of Me2S0into AC was investigated. Quantification of Me2SO UV-visible absorption spectra was proposed, and validated experimentally. This method was then employed to obtain the time course of Me2SO uptakes by AC disks for various exposure concentrations [10%(w/w) to64.5%(w/w)] and at different exposure temperatures (37℃to-30℃). It was found that the equilibrium concentration of Me2SO reached in AC disks stabilized at about90%of the concentration of the surrounding exposure solution.3) A new model to describe the permeation of Me2SO into AC was developed. The effective diffusion coefficient of Me2SO in AC was estimated directly instead of being determined by fitting to the experimental permeation data. The model was validated by excellent congruence of the model predictions and the experimental measurements in the temperature and concentration ranges of the present study.4) The LTM procedure of AC was modeled and numerically studied. Using the new Me2SO permeation model and the cell membrane transport model, the spatial Me2SO concentration histories in the cartilage matrix and chondrocytes were determined, and possible injuries to the cell were reckoned according to biophysical properties of chondrocytes for the stepwise and continuous LTM, respectively. Based on this, A route to improve the stepwise LTM was proposed, which could lead to a reduction of treatment step by two and a cutting of treatment duration by35%with comparison to the existing protocol in the literature. Decrease of treatment step and duration is beneficial not only to the saving of manpower and material resources, but also to the lowering of the risk of the chondrocytes subjected to cytotoxicity and chilling injuries.5) The LTM protocol for osteochondral dowels (OCD) was proposed with the premise of avoiding ice formation inside AC. The treatment durations of OCD for stepwise and continuous LTM were respectively3.7and3.3times as long as that of AC disks with the same thickness. |
PDF Full Text Request