Zonal separation of articular cartilage

Articular cartilage is composed of three layers: superficial, middle, and deep. In small animal models, it is difficult to separate the layers by dissection, as done in large animal models. Zonal digestion is a method of harvesting cells from a tissue to produce highly purified samples in a quick, simple process. By immersing the tissue in collagenase, the superficial layer of bovine articular cartilage can be separated from the middle and deep layers. The combination of needle thickness measurements and histological staining shows that the superficial zone, 20% of the tissue, is completely digested after 2.5 hours in collagenase (200 U/ml). In the course of this experiment, the needle thickness measurement method was verified to within 10% variation through histological analysis of the same sample. Zonal cellularities were found to be 25×10⁶ cells/g and 19×10⁶ cells/g for the superficial and middle/deep zones, respectively. RT-PCR was used to detect the expression of superficial zone protein, type II collagen, and aggrecan in the different chondrocytes. Zonal digestion is shown to be a possible method to separate cartilage layers in small or large animal models.