Osteoarthritis is the second leading cause of disabilities in the USA. Although total joint replacement remains the common treatment for severe cases of osteoarthritis, total joint resurfacing using tissue-engineered cartilage is proposed as a better alternative. However, to be a viable alternative, tissue engineered cartilage must have the integrity to withstand the mechanical and biological environment in a joint. This investigation focuses on tribological properties that are a key aspect of a tissue’s mechanical integrity.
A test setup, in which a cartilage sample is subjected to compression and slides over a glass counter face, was built to measure friction and stimulate wear. Wear and damage of the cartilage surface were of particular interest as they are thought to be more accurate indicators of the mechanical integrity of the cartilage than friction. The effect of phosphate buffered saline and two formulations of hyaluronic acid (HA1 and HA2) on the tribology of cartilage were also studied. The friction behavior of the cartilage before and after the wear tests were compared .The amount of Glycosaminoglycan dissolved in the lubricant was used as a measure of wear. Scanning Electron Microscopy and histology were employed to visualize microscopic damage to the cartilage.
Tests under intermittent sliding demonstrate that tissue engineered cartilage is capable of biphasic lubrication. Under continuous sliding, visually evident peeling of the cartilage surface was observed with PBS (7 of 12 samples) and HA1 (5 of 6 samples) as lubricant, but not with HA2. Cracks parallel to the surface of cartilage samples subjected to shear, was the predominant mode of damage observed in histology. With HA2 as lubricant, cracks were observed in all 4 of the available histology images (6 were tested), although no macroscopic damage was seen. Scanning electron microscopy showed wear tracks on samples subjected to shear.
For native cartilage, assays used to quantify wear and damage did not result in any discernable effects of shear.
In conclusion, although ex vivo tests are not a direct indicator of in vivo performance, these results suggest that the tribological characteristics of tissue engineered cartilage are inferior to those of native cartilage.