[Development of an improved cryopreservation vial for cryopreservation of donor corneas]

To date, corneal cryopreservation has been performed in vials made of glass or plastic, where the cornea is placed in a large volume of culture medium. For improved cell survival, an attempt was made to define freezing curves, which are induced by variations in the temperature in the freezing chamber. Depending on the mass of the specimen to be frozen and on the material conducting the heat, the freezing vials used so far cannot be regarded as optimum. As glass and plastic do not conduct heat very well, we developed a new freezing vial that is especially suitable for corneal cyropreservation. In our experiments, the interaction of the chamber temperature and the temperature near the corneal endothelium were monitored. Additionally, endothelial cell survival was studied by postculturing the tissue and by vital staining. As a result, a cylindrical vial made of aluminum 2-4 mm thick was designed, which enables even heat transfer from the freezing chamber to the cornea. In this vial, the amount of freezing medium could be reduced to 400 microliters, so that the heat from the crystallization process was very low. In a small series the conditions that had been optimal with porcine tissue were tested on ten human donor corneas. The endothelial cell density before (2365 cells/mm2, range 1675-2800) and after cryopreservation (2199 cells/mm2, range 1600-2720) did not differ significantly.