The average roughness and fractal dimension of articular cartilage during drying

Cartilage is a unique material in part because of it biphasic properties. The structure of cartilage is a porous matrix of collagen fibers, permeated with synovial fluid which creates a gliding and near frictionless motion in articulating joints. However, during in vitro testing or surgery, there exists potential for cartilage to dehydrate, or dry out. The effects of this drying can influence experimental results. It is likely that drying also changes joint performance in vivo. In in vitro testing of equine cartilage explants exposed to open air, the average roughness of cartilage changes from 1.85 ± 0.78 to 3.66 ± 1.41 µm SD in a 5-h period. Significant changes in roughness in individual samples are seen within 10 min of exposure to open air. However, the multi-scale nature of cartilage, characterized by the fractal dimension, does not significantly change during the same period. The current study attempts to quantify the magnitude of error that is introduced when cartilage is removed from its native environment.