Cryopreservation of artificial cartilage: viability and functional examination after thawing

In biomedical research and in reconstructive surgery, preservation of intact tissue has been an unsolved problem. In this study, we investigated the viability of cryopreserved artificial cartilage and its synthetic activity of cartilage-specific matrix proteins after thawing for in vitro use. A polymer fleece cylinder (diameter = 3 mm; height = 3 mm) was loaded with a suspension of bovine chondrocytes (25 x 10(6)/ml) and encapsulated with fibrin glue. After a culture period of 1 week, the artificial cartilage units were frozen in a cryoprotection solution containing 10% basal medium (RPMI 1640), 10% DMSO and 80% FCS. The freezing procedure consisted of three steps: a 30-min period at +4 degrees C followed by a 24-hour storage at -80 degrees C. After that, the tissue units were transferred into liquid nitrogen (-196 degrees C) for final storage. Using histochemical staining techniques of cryogenic slices, we investigated the ability of cryopreserved artificial cartilage to produce its specific matrix after thawing. A modified MTT assay was used to determine the viability of frozen tissue units in comparison with unpreserved samples at different moments after thawing. Depending on the chondrocytes used for the formation of artificial cartilage, the viability of cryopreserved tissue varied between 65 and 85%. Both the intensity of alcian blue staining for proteoglycans and the azan staining for collagens increased proportionally with incubation time after thawing. These findings indicate that cryopreservation of small artificial cartilage units is possible with a minor loss of cell viability. Secondly, its synthetic activity of cartilage-specific matrix did not decline after the freezing process.