Influence of a superficial tangential zone over repairing cartilage defects: implications for tissue engineering.

The superficial tangential zone (STZ) plays a critical role in normal cartilage function but is not yet a focus for designing tissue-engineered constructs for cartilage repair. Without material properties of sufficient quality in this zone, transplanted constructs in vivo may have little chance of survival. This finite element study investigates the impact of the superficial tangential zone on the mechanical function of normal articular surfaces as well as those with transplanted constructs. The zone is modeled as a thin transversely isotropic material with strain dependent permeability. The analyses predict that a normal transversely isotropic STZ placed over a repair region reduces the axial compression (55-68%) of, and the rate of fluid loss (45-82%) from the articular surface. A reduction was also found in von Mises stress (26-57%), axial strain (22-56%), and radial strain (69-73%), and an increase in fluid pressure (19-45%) in repair tissue under the STZ. Incorporating a quality superficial tangential zone in tissue-engineered constructs may be a critical factor in achieving mechanical environments conducive for successful cartilage repairs.